ASME SECTION IV: RULES FOR THE CONSTRUCTION OF HEATING BOILERS

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CHAPTER

18 ASME SECTION IV: RULES FOR THE CONSTRUCTION OF HEATING BOILERS Geoffrey M. Halley and Edwin A. Nordstrom1 18.1

INTRODUCTION

To help the reader understand and use the ASME Boiler and Pressure Vessel (B&PV) Code, this chapter for ASME Code Section IV2 (2007 edition) is presented in a simplified manner with the understanding that it is not a Codebook and was not written to replace the Codebook published by the American Society of Mechanical Engineers (ASME). Although the rules of the ASME B&PV Code, Section IV constitute the minimum requirements for the safe design, construction, installation, and inspection of low-pressure-steam boilers and hotwater boilers (which are directly fired with oil, gas, electricity, or other solid or liquid fuels), they do not cover the operation, repair, alteration, rerating, and maintenance of such boilers. By definition, a low-pressure-steam boiler is a steam boiler in which the operating pressure does not exceed 15 psi (103 kPa), whereas a hot-water boiler is defined as a boiler used for an operating pressure not exceeding 160 psi (1,100 kPa) and/or for a temperature not exceeding 250F (121C). Hot-water boilers include hot-waterheating boilers and hot-water-supply boilers. Also covered by the rules of Section IV are potable-water heaters and water-storage tanks for operation at pressures not exceeding 160 psi (1,100 kPa) and water temperatures not exceeding 210F (99C).

18.1.1

History of ASME Section IV

On September 15, 1911, the ASME appointed a seven-member Boiler Code Committee to formulate standard specifications for the construction of steam boilers and other pressure vessels.3 The first chairperson was J. A. Stevens, a consulting engineer. In November 1914, an eighteen-member Advisory Committee was appointed, with C. W. Obert as secretary. In its progress report during the sixth and final session on December 4, 1914, the Boiler Code Committee discussed the necessity of cooperation from users, industries, and states. Finally, on December 15, 1914, both the Boiler Code Committee and the Advisory Committee began to prepare the final draft of the Code. 1

The first ASME Code, Rules for the Construction of Stationary Boilers and Allowable Working Pressures, was finally adopted in the spring of 1915. Known as the 1914 edition, it consisted of 114 pages and a complete index of 28 additional pages. It was divided into the following parts: • • • • •

Part I, New Installation (87 pages) Section I, Power Boilers (80 pages) Section 2, Heating Boilers (7 pages) Part II, Existing Installation (5 pages) Appendix (20 pages)

The 1914 Code edition was revised in 1918; the Committee adopted the 1918 Code edition on December 3 of that year. At that time, revision of Part I, Section 2 was incomplete. A fourteen- member Subcommittee on Heating Boilers was appointed on September 26, 1919, with S. F. Jeter as the chairperson, to revise the section of the Code that discussed heating boilers. The subcommittee presented its final report to the Boiler Code Committee after holding a series of meetings and public hearings. The 1923 edition of the Code for Low Pressure Heating Boilers, also known as the ASME Code Section IV, was approved by the ASME Council on May 23, 1923. It contained 113 pages and consisted of the following parts: • Part I, Steel Plate Boilers (paragraphs H-1 to H-83) • Part II, Cast Iron Boilers (paragraphs H-84 to H-120) In Part I, paragraph H-1, the Code was limited to steam boilers with pressures of 15 psi and hot-water boilers to 160 psi and 250F. The method of computing the maximum allowable working pressure was stated in paragraph H-4, and the specifications of the materials to be used followed the rules for power boilers. Paragraphs H-15 to H-26 addressed the requirements for joints, braces, and stayed surfaces. Paragraphs H-27 to H-64 addressed the requirements for boiler openings, supports, settings, installations,

M. A. Malek and John I. Woodworth were the authors of this chapter for the first edition. Copies of the ASME B&PV Code, Section IV may be obtained by writing to the American Society of Mechanical Engineers, 3 Park Avenue, New York, NY 10016. Copies may also be obtained via the Society’s web site:www.asme.org. 3 History of the ASME Boiler Code, by Dr. A. M. Greene, Jr., is a collection of articles published in the journal Mechanical Engineering in July, August, September, November, and December of 1952, and also in February, March, July, and August of 1953 (two chapters previously unpublished are also included). Dr. Greene was a member of the Boiler Code Committee from 1915 to 1943. 2

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and fittings and appliances (including safety valves). Paragraphs H-65 to H-68 addressed hydrostatic tests with shop inspection, stamping, and marking. The remaining paragraphs, H-76 to H-83, addressed welded boilers. In Part II, paragraphs H-84 to H-86, the pressures and temperatures to be used with cast-iron boilers were specified. Paragraphs H-87 to H-89 contained the requirements for boiler openings, flanged connections, and threaded openings. Six paragraphs addressed boiler installation, and twelve paragraphs addressed both safety valves and water-relief valves. The 1927 edition of Section IV (Low Pressure Heating Boilers) incorporated a number of revisions to the 1923 edition. The important changes were the following: • The inclusion of specifications for flange-quality steel plates used for forged welding • The inclusion of specifications for base metal used in autogenous welding • The basing of safety valve–relieving capacity on the grate area rather than the radiating surface • The inclusion of formulas for copper-tube thickness • The inclusion of an index of seven pages. The 1931 edition of Section IV was prepared from addenda to clarify statements of the 1927 edition. Minor changes were made to paragraphs H-40, H-44, H-55, H-56, H-64, H-93, H-108, H-117, and H-120, and the portion of the Code entitled “Autogenous Welded Boilers” was changed to “Fusion Welded Boilers.” The 1932 edition of Section IV contained only minor changes and rewordings, including some made to paragraphs H-35 and H-66. The Material Specifications that appeared in the 1931 edition were transferred to Section II (Material Specifications). The 1935 edition of Section IV had few important changes. Paragraphs H-64 and H-117, both entitled “Automatic Low-Water Fuel Cut-Off and/or Waterfeeding Device,” were expanded to cover construction, location, attachment, operation, flushing, and training. Changes were also made to paragraphs H-1 to H-83, and H-84 to H-118. The 1937 edition of Section IV was produced under the direction of the same committee that produced the 1935 edition. In this edition, the minimum allowable thickness of the tubesheet or heads 1 given in Table H-1 was increased by 16 in.; for shells or other areas, 1 the thickness was reduced by 16 in. Changes were made to paragraphs H-12, H-21, H-38, H-40, H-44, H-64, H-65, H-70, H-93, H-117, and H-118. An index of slightly more than four pages was included in the Code. The 1940 edition of Section IV had major changes to paragraphs H-43 to H-54 of Part I and paragraphs H-96 to H-107 of Part 2. These paragraphs on both safety valves and water-relief valves addressed the markings of such valves with data and a symbol. Other major changes were made to Tables H-6 and H-7 and to paragraphs H-12, H-65, and H-118. A new Form No. H-1 (Manufacturer’s Test Report of Safety Valves) was added before the appendix. The 1941 edition of Section IV was a revision of safety-valve and water relief-valve requirements. These changes expanded the first section on safety valves (paragraphs H-43 and H-96) and water-relief valves (paragraphs H-44 and H-97) describing the features of the valve. New methods for determining the required capacity of safety valves and water-relief valves, such as by dividing by 1,000 the maximum output at the boiler nozzle (Btu/hr) obtained from the fuel and also by multiplying the boiler heating surface by 5, simplified the computation and deleted paragraphs

H-52 and H-105 and the former Tables H-6, H-7, H-9 and H-10 from the 1940 edition. The 1943 edition of Section IV was broadened by the addition of new paragraphs in the preamble, by the revision of paragraph H-43 (Safety Valves) as well as paragraph H-44 (Water Relief Valves), the revision of paragraphs H-46, H-47, H-48, H-49, H-51, H-52, H-53, H-61, H-68, and H-96 to H-117, and the revision of Tables H-6 and H-7. This edition made a book of forty-five pages, with an index of slightly more than four pages. Since 1953, the ASME B&PV Code, Section IV has been revised every three years, and the latest edition always includes all previous addenda. The Code edition was published in the following years: 1946, 1949, 1952, 1953, 1956, 1959, 1962, 1965, 1968, 1971, 1974, 1977, 1980, 1983, 1986, 1989, 1992, 1995, and 1998. Colored-sheet addenda, which include additions and revisions to individual sections of the Code, are published annually. Code Interpretations, that is, written replies to inquiries, are published separately from the Code edition; they are issued semiannually (in July and December). The B&PV Committee also issues Code Cases to clarify the intent of existing requirements or to provide (when the need is urgent) rules for material or construction not covered by the existing Code rules. The Code Cases, when adopted, appear in the Code Casebook for Boiler and Pressure Vessels; later, they are incorporated into the Code itself.

18.1.2

Organization of this Chapter

This chapter is divided into five parts and two subparts, in a similar manner to the format of Section IV of the ASME Boiler and Pressure Vessel Code. Necessary figures and tables are included in each part, or subpart. For easy identification paragraph numbers, figures, and tables from the Code book are used in the running text. This chapter also includes several appendices, one of which—Appendix 18.D—provides a glossary of boiler, design and welding-related terms. The other appendices—all reproductions from the Code book—are: • Appendix B—Methods of checking safety valve and safetyrelief valve capacity—Shown in this chapter as Appendix 18.A • Appendix C—Methods of calculating welded ring reinforced furnaces—Shown in this chapter as Appendix 18.B • Appendix D—Examples of computation methods for boiler shell openings—Shown in this chapter as Appendix 18.C • Appendix L—Examples of Manufacturers’ Data Report Forms—Shown in this chapter as Appendix 18.E.1 and 18.E.2 A brief outline of the contents of each part and subpart is given in the following paragraphs. Part HG: General Requirements for all Materials of Construction Part HG addresses material requirements, design, pressure-relieving devices, tests, inspection, stamping, instruments, fittings and controls, and the installation of low-pressuresteam-heating boilers, hot-water-heating boilers, hot-water-supply boilers, and the boilers’ appurtenances, but it does not cover the requirements of potable-water heaters. The requirements of Part HG are used together with the specific requirements in Part HF and Part HC, whichever is applicable. Part HF: Requirements for Boilers Constructed of Wrought Materials There are special requirements for heating boilers constructed primarily of wrought materials. The requirements of this

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part are applicable to steam-heating boilers, hot-water-heating boilers, hot-water-supply boilers, and the boiler parts constructed of wrought materials. Part HF has two subparts: HW and HB. Part HF, Subpart HW: Requirements for Boilers Fabricated by Welding The requirements of this subpart are applicable to heating boilers and their parts fabricated by welding. Because the construction method of the boiler is welding, all the applicable rules of ASME Code Section IX are followed as well. Part HF, Subpart HB: Requirements for Boilers Fabricated by Brazing This subpart addresses the requirements for steamheating boilers, hot-water-heating boilers, hot-water-supply boilers, and the boilers’ fabrication by brazing. The applicable rules of ASME Code Section IX are also used. Part HC: Requirements of Boilers Constructed of Cast Iron The requirements of Part HC apply to steam-heating boilers, hotwater-heating boilers, and hot-water-supply boilers and their parts, which are fabricated primarily of cast iron. In addition to these requirements, those of Part HG are used. Part HA: Requirements for Boilers Constructed of Cast Aluminum The requirements of Part HA apply to hot water boilers constructed primarily of cast aluminum. Part HLW: Requirements for Potable-Water Heaters Part HLW apply to water heaters in commercial or industrial settings for supplying potable water at pressures not exceeding 160 psig (1,100 kPa) and temperatures not exceeding 210F (99C). It is not applicable to residential water heaters. All details of design and construction are not covered by the foregoing rules. The Manufacturer, responsible for the safe design and construction of boilers, provides details of the design and construction that are subject to acceptance by the Authorized Inspector. The Authorized Inspector is the person responsible for reviewing the boiler designs and inspecting of the boilers during their construction to ensure that all requirements are met. Moreover, the repair, alteration, rerating, and inservice inspection of the heating boilers are done in accordance with the National Board Inspection Code (NBIC),3 published by the National Board of Boiler and Pressure Vessel Inspectors, a nonprofit organization composed of chief boiler inspectors of various U.S. states and cities as well as various Canadian provinces and cities. It is the NBIC’s purpose to maintain the integrity of pressure-retaining items after they have been placed into service by providing rules for inspection, repair, and alteration. The NBIC provides guidance to jurisdictional authorities, Inspectors, Users, and organizations performing repairs and alterations.

18.1.3

Adoption of Section IV

Section IV is composed of a set of rules for the construction of heating boilers. These rules are extracted from neither design

4

manuals nor textbooks. The objective of the Code is to establish safety rules for providing reasonable protection of life and property. The rules of the Code encompass requirements, prohibitions, and guidance for the design, fabrication, inspection, testing, and certification of heating boilers. The Code rules are nonmandatory unless they are adopted into the laws of a governmental jurisdiction—a state, province, county, or city or in the absence of a jurisdiction, by contract. A jurisdiction may adopt these rules either partly or completely. Once adopted, the jurisdiction enforces these now-mandatory rules by using Authorized Inspectors under the supervision of a Chief Inspector. Currently, most states, provinces, large cities, and some counties have adopted Section IV. A Synopsis of Boiler and Pressure Vessel Laws for the United States and Canada is published by the National Board of Boiler and Pressure Vessel Inspectors.4

18.1.4

Design Considerations Beyond Section IV of the ASME Boiler and Pressure Vessel Code (Authors’ Opinion)

It should be noted that this Code, and typically many Codes, provide a minimum set of design requirements that must be adhered to. However provided that these requirements are followed, there is nothing wrong with the designer going beyond the scope of the Code in order to circumvent potential problems, caused by specific operating or environmental conditions, which may affect the longevity of the boiler. The following are offered for consideration: • In situations where the boiler is swing loaded rather than base loaded and could experience a cyclic operating condition, consideration should be given to an evaluation of the fatigue effects of thermally induced operating stresses caused either by the fuel burning equipment being cycled on and off, the pressure and/or bulk water temperature swinging in response to load excursions, or the effects of electric load shedding in hot water boiler systems whereby large quantities of cold water may return to the boiler, as heating zones are brought back on line. It has been shown that under certain types of system operating conditions, fatigue failures in the high strain-low cycle regime have been experienced5. While these failures are seldom catastrophic in nature, they can be both troublesome and expensive. • The current trend to smaller footprint boilers for a given capacity and high furnace heat releases coupled with the desire for low NOx emissions has produced a generation of fuel burning equipment that while environmentally friendly, is more sensitive to setup conditions and local environmental changes. This may result in more episodes of unstable combustion than previously experienced. Incidents have been noted in which unstable combustion (pulsations) has affected such things as tube joint integrity, particularly in designs that have long tube bundles. Thus a vibration analysis of the boiler structure may become necessary for certain types and sizes of boiler, in order to avoid costly repairs.

Copies of the NBIC and the Synopsis of Boiler and Pressure Vessel Laws may be obtained by writing to the National Board of Boiler and Pressure Vessel Inspectors, 1055 Crupper Avenue, Columbus, OH 43229. Copies may also be obtained via the National Board’s web site: www.nationalboard.org. 5 Halley, G. M., “Thermally Induced Stress Cycling,” National Board of Boiler and Pressure Vessel Inspectors Bulletin, Winter 1998.

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18.2

PART HG: GENERAL REQUIREMENTS FOR ALL MATERIALS OF CONSTRUCTION

18.2.1

Article 1

18.2.1.1 Scope The scope of Part HG addresses material requirements, design, pressure-relieving devices, tests, inspection, stamping, instruments, fittings and controls, and installation requirements of low-pressure-steam-heating boilers, hot-water-heating boilers, hotwater-supply boilers, and the boilers’ appurtenances, but it does not cover potable-water heaters. The rules of Part HG are required to be used with the specific requirements of Part HF (Boilers of Wrought Materials) and Part HC (Cast-Iron Boilers), whichever is applicable. Provisions are made in Part HG for mandatory requirements, specific prohibitions, and nonmandatory guidance for minimum construction requirements for the design, fabrication, installation, and inspection of steam-heating, hot-water-heating, and hot-watersupply boilers. Enforcement or regulatory authorities having jurisdiction at the location of an installation may establish applicability of these rules in whole or in part. Therefore, the rules become mandatory only if they are adopted by a jurisdiction. 18.2.1.2 Service Restrictions Section IV, Part HG rules are restricted to steam-heating boilers for operation at pressures not exceeding 15 psi (Saturation temperature 250F) (103 kPa) and to hot-water-heating and hot-water-supply boilers at pressures not exceeding 160 psi (1,100 kPa) and/or temperatures not exceeding 250F (121C).6 If the service requirements exceed these limits, the rules of Section I will be applicable.

18.2.2

Article 2

18.2.2.1 Material Specifications and Properties are found in Section II Parts A, B, and C. Material requirements in terms of maximum allowable design stress levels are found in Section IV while other material requirements are found in Section II D of the Code. 18.2.2.2 General Requirements Material subject to stress from pressure shall be selected from the Material Specifications of Section II (Materials), Parts A, B, C, and D. If the material is not listed in Section II, it can be used only after approval is obtained from the ASME Boiler and Pressure Vessel Committee.7 Section II, Part D, Appendix 5 (Guideline on the Approval of New Materials under the ASME Boiler and Pressure Vessel Code) is to be followed for adoption of new materials. Material Specifications in Section II are not limited by the production method if the product complies with the requirements of the specification. If it complies with the other

FIG. 18.1 6

requirements of the specification and with the thickness requirements of this Code, materials exceeding the thickness limit of Section II may be used. Materials not identified by mill test reports may be used for nonpressure parts, provided failure of such parts do not affect the pressure parts to which they are attached. 18.2.2.3 Specific Materials In addition to the wrought materials described previously, Sections HF (wrought materials) and HC (cast iron) provide specific material requirements beyond the general requirements of HG-200. Wrought materials are those that have been “worked” by such manufacturing processes as rolling.

18.2.3

Article 3: Design

The design of a heating boiler involves calculations, drawings, and specifications to satisfy the service conditions of the plants or facilities. During the process of designing a boiler, two terms are used frequently: design pressure, used for calculating the minimum thickness requirement for the boiler parts, and maximum allowable working pressure, which is the maximum gage pressure or the pressure above atmospheric that is permitted in the boiler and which is based on the lowest design pressure of any boiler part. 18.2.3.1 Design Pressure A heating boiler is designed for a minimum pressure of 30 psi (kPa). The required thickness or design pressure is calculated by formulas provided in paragraphs HG-301 to HG-345. The maximum allowable working pressure (MAWP) is stamped on a boiler as specified in paragraph HG-530 (Stamping of Boilers) and must not exceed the design pressure of any parts. No boiler shall be operated at a pressure exceeding the MAWP except when the safety devices are discharging, at which time the MAWP shall not be exceeded by more than the amount provided in paragraph HG-400 and Table HG-400.1 18.2.3.1.1 Vacuum Boilers A vacuum boiler is a factory-sealed steam boiler that is operated below atmospheric pressure. It is designed for a MAWP of 15 psi vacuum (103 kPa vacuum) and a maximum temperature of 210F (99C). Rules for vacuum boilers are given in Appendix 5 (Mandatory Vacuum Boilers). Example What is the Design Code for a vacuum boiler with an MAWP of 15 psi and a temperature of 200F? The vacuum boiler must be designed in accordance with ASME Section IV, Appendix 5 (Mandatory Vacuum Boilers). (See paragraph 5-200 of that appendix for details.)

CYLINDER UNDER INTERANAL PRESSURE

Similar international boiler codes are the British Standard BS 2790, Specifications for Design and Manufacture of Shell Boilers of Welded Construction, and the Canadian Standard CSA B51, Part 1, Boiler, Pressure Vessel, and Pressure Piping Code. 7 Technical inquiries may be submitted to the Secretary, the ASME Boiler and Pressure Vessel Committee, 3 Park Avenue, New York, NY 10016.

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thickness of tubes and of pipes used as tubes, neither one of which is strength-welded to the tubesheet, header, or drum. t =

PR + 0.4 SE - 0.6P

where the rolling and structural stability allowance 0.04 in. (1 mm). This factor is based on Section I’s use of 0.04 in the factor e in paragraph PG-27.2, Note 4. Rolling and structural stability allowance  0 for tubes strength-welded to tubesheets, headers, or drums. Sealedwelded tubes would still require the addition of 0.4 in. The minimum thickness of a tube or of a pipe used as a tube shall not be less than 0.061 in. (1.5 mm), although there is no minimum thickness requirement for nonferrous tubes installed by brazing. FIG. 18.2

BALANCE OF FORCES

18.2.3.2 Cylindrical Parts under Internal Pressure Consider a cylinder of radius, R, under internal pressure, P. For the balancing of forces, it is easy to understand that PR  F. The stress in the wall is F/A, or, for a cylinder of unit length, F/t. Thus S  Ft PRt. The equation S  PRt is the simplest form of the circumferential stress in a cylinder, commonly known as the hoop stress. It assumes a uniform stress distribution across the thickness. In reality, the stress varies from a maximum at the inside surface to a minimum at the outside. (See Fig. 18.1.) In 1852, Gabriel Lamé published a complex set of equations describing the actual variation of stress in the cylinder wall. Primarily because of the complexity and difficulty of use, Lamé equations have been replaced with an approximate simplified formula that accurately represents the maximum circumferential stress at the inside surface. This formula [1], known as the modified Lamé formula, was used in the preceding paragraph. This formula is identical to the equation for circumferential stress given in paragraph UG-27(C)(1)8 of Section VIII, Division 1, and although it is also similar to the equation in paragraph PG-27.2.2 of Section I, it lacks the y factor that accounts for creep relaxation and stress redistribution. Elevated temperatures do not occur with Section IV construction.

Example What is the required thickness of a cylinder, welded by a full-penetration double-butt joint, if the plates are of SA-285, Grade B; the inside diameter is 42 in.; and the working pressure is 150 lb? Find the drum thickness, given the following: P  150 psi S  10,000 psi for SA-285, Grade B (Table HF-300.1) R  21 in. (half the inside diameter of 42 in.) E  0.85 (paragraph HW-702) t =

PR SE0.6P

t =

150 * 21 10,000 * 0.85 - 0.6 * 150

t =

3,150 8,410

t = 0.37 in. 18.2.3.3 Formed Heads In a manner similar to the derivation of the simple hoop stress formula, the underlying basis for Section IV head formulas can be derived. By considering the balance of forces, the following equations can be obtained (see also Fig. 18.2). PpR2 = 2pRS

18.2.3.2.1 Cylindical Parts The following formula is used to calculate the required thickness and design pressure of any cylindrical part under internal pressure: PR SE - 0.6P SEt P = R + 0.6t

t =

Where P  the design pressure, psi (not less than 30 psi or 207 kPa) S  the maximum allowable stress value from Tables HF300.1 and HF-300.2, psi t  the required wall thickness, in. R  the inside radius of cylinder, in. E the efficiency of the longitudinal joint or ligament between tube holes, whichever is less. For seamless shells, E  1, but for welded joints, the efficiency in paragraph HW-702 should be used. 18.2.3.2.2 Tubes The foregoing formula, modified as shown in the following equation, is used when determining the required

or S = Pr/2t or t = PR/2S Again, as with the hoop stress, this relationship assumes that the stress is uniformly distributed across the cross section. The actual maximum stress accurately represented by the approximate formula in paragraph HG-305.4 is stated as t =

PL SE - 0.2P

18.2.3.3.1 Heads The three types of heads used for construction of a boiler are ellipsoidal, torispherical, and hemispherical. The pressure may be on either the concave or convex side. The design pressure on the convex side shall be equal to 60% of that for heads of the same dimensions having pressure on the concave side. The following symbols are used in the formulas to calculate required thickness of different types of heads under pressure on the concave side:

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t  the required wall thickness after forming, in. P  the design pressure, psi (not less than 30 psi or 207 kPa) D  the inside diameter of the head skirt, or the inside length of the major axis of an ellipsoidal head, or the inside diameter of a cone head at the point under consideration and measured perpendicular to the longitudinal axis, in. S  the maximum allowable stress value from Tables HF-300.1 and HF-300.2, psi. L  the inside spherical or crown radius, in. E  the lowest efficiency of any joint in the head (for seamless head, E  1; for welded joints, the efficiency provided in paragraph HW-702 should be used) 18.2.3.3.2 Ellipsoidal Heads Formulas for ellipsoidal heads are basically modifications of the equation for spherical heads to account for greater stress as the head becomes shallow. For a dished head with a depth of half the radius (2:1 elliptical head), the maximum stress is twice that for a spherical head (consult ref. [2] for a discussion of dished and flanged heads); for the spherical head, 2L  D. The 2:1 elliptical head formula of paragraph HG-305.2 is the same as the spherical head formula except that D is substituted for L. The following formulas shall be used for calculating the required thickness and design pressure of a dished head of ellip-forging, in. soidal form. Use of this formula is limited to 2:1 elliptical heads. PD 2SE - 0.2P

t = or

P =

2SEt D + 02t

18.2.3.3.3 Torispherical Heads Tests by Hohn and others [3] were used to establish the empirical formula used by Section VIII, Division 1 in equation (3) of Appendix I-4. With the proportions specified in paragraph HG-305.3, M becomes 0.885 and provides the equation for a torispherical head. The following formulas shall be used for calculating the required thickness and the design pressure of a dished head of torispherical form. Use of this formula is limited to heads that meet dimensional requirements of paragraph HG-305. t =

0.885PL SE - 0.1P

18.2.3.4 Flat Heads Flat heads and covers are used for the construction of boilers. The thickness of such unstayed heads, cover plates, and blind flanges shall be calculated in accordance with the formulas specified in paragraph HG-307. The following symbols are used for acceptable types of unstayed flat heads and covers shown in the Fig. HG-307 (given here as Fig. 18.3.) C  the factor depending on the method of attachment (values may be found in paragraph HG-307.4) D  the long span of noncircular heads or covers measured perpendicular to short span, in. d  the diameter or short span, in. HG  the gasket moment arm, in. L  perimeter of the noncircular bolted head, measured along the centers of the bolt holes, in. l  the length of flange or flanged heads, measured from tangent line of knuckle, in. m  the ratio tr/ts P  the design pressure, psi r  the inside corner radius on the head firmed by flanging or forging, in. S  the maximum allowable working stress value, psi (from Tables HF-300.1 and HF-300.2) t  the minimum required thickness of the head or cover, in. te  the minimum distance from the beveled end of drum, pipe, or header (before welding) to the outer face of the head, in. tf  the actual thickness of the flange on the forged head (at the large end), in. th  the actual thickness of the flat head or cover, in. tr  the required thickness of the seamless shell, pipe, or header for pressure, in. ts  the actual thickness of the shell, pipe or header, in. tw  the thickness through the weld joining the edge of the head to the inside of the drum, pipe, or header, in t1  the throat dimension of the closure weld, in. W  the total bolt load, 1b Z  the factor or noncircular heads and covers that depends on the ratio of short span to long span. 18.2.3.4.1 Circular Flat Plates The maximum stress in flatcircular plates with fixed and simply supported edge [4] is shown by the following equations: Smax =

or P =

SEt 0.885L + 0.1t

18.2.3.3.4 Hemispherical Heads The following formulas shall be used for calculating the required thickness and the design pressure of a dished head of hemispherical form: PL t = 2SE - 0.2P or P =

2SEt L + 0.2t

A formed head of a thickness less than that of the required thickness calculated by the foregoing formulas may be used if it is stayed as a flat surface in accordance with paragraph HG-340.

Smax =

3 PR2 * 2 4 t

3(3 + p) PR2 * 2 t 8

These equation take the following general form: S =

CPR 2 t2

where C varies with the degree of edge restraint. (See Fig. 18.4.) Solving for t, the equation takes the following form: CP A S

t = d

except when the head, cover, or blind flange is attached by bolts.

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FIG. 18.3 SOME ACCEPTABLE TYPES OF UNSTAYED FLAT HEADS AND COVERS (THESE ILLUSTRATIONS ARE DIAGRAMMATIC ONLY; OTHER DESIGNS THAT MEET THE REQUIREMENTS OF HG-307 ARE ACCEPTABLE)

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r  the inside knuckle radius, in. P  the design pressure, psi S  the maximum allowable stress value, psi (from Tables HF-300.1 and HF-300.2) T  the flange thickness, in. Mo  the total moment, in./lb determined as in Section VIII, Division 1, Appendix 2 The following formulas shall be used for calculating the minimum thickness requirement of heads conforming to Fig. HG-309(a). PD t = 2SE - 0.2P or

FIG. 18.4 FLATE CICULAR PLATE WITH FIXED EDGES

This equation is the same as paragraph PG-31.2.2(1) of Section I and paragraph UG-34(c)(2)(1) of Section VIII, Division 1 with the various c factors, depending on the method of attachment of the head to the shell. For the head, cover, or blind flange attached by bolts: t = d 2CP/S + 1.9WHG/Sd 3 The thickness shall be determined for both operating conditions and gasket setting; the value greater of these two shall be applicable. Note: The terms Wand HG are not well-defined in Section IV; they are the same as in the flanged design rules of Section VIII, Division 1, Appendix 2, where a complete definition can be found. 18.2.3.4.2 Noncircular Flat Heads The following formula shall be used to calculate the required thickness for noncircular, flat, unstayed heads, covers, or blind flanges: t = d2ZCP/S where Z = 3.4 or

2.4d (Z should not exceed 2.5) D

18.2.3.5 Spherically Dished Covers (Bolted Heads) Circular, spherically dished heads with bolting flanges are used for the construction of boilers and are shown in Fig. HG-309. The following symbols are used in the formulas for thickness calculations: A  the outside diameter of flange, in. B  the inside diameter of flange, in. C  the bolt circle diameter, in. t  the minimum required thickness of head plate after forming, in. L  the inside spherical or crown radius, in.

0.88PL SE - 0.1P

t =

PL 2SE - 0.2P

or

The following formula shall be used for calculating the minimum thickness requirement of heads conforming Fig. HG-309(b). For head thickness: 5PL t = 6S For flange thickness of the ring gasket: T =

Mo A + B c d A SB A - B

For flange thickness of the full-face gasket:

P B(A + B)(C - B) c d AS A - B

T = 0.6

The following formula shall be used for calculating the minimum thickness requirement of heads shown in Fig. HG-309(c). For head thickness: 5PL t = 6S Flange thickness of the ring gasket shall be calculated as follows for heads with round bolting holes: T = Q +

t = d 2ZCP/S + 6WHG/SLd 2

when the noncircular heads, covers, or blind flanges are attached by bolts causing a bolt-edge moment. The thickness shall be determined for both the operating conditions and the gasket seating, from which the value greater of these two shall be applicable.

t =

1.875M o (C + B) A SB(7C - 5B)

where Q =

PL C + B c d 4S 7C - 5B

The required flange thickness shall be calculated as above, but the value shall not be less than that of the head thickness calculated above. The following formulas shall be used for calculating the minimum thickness requirement of heads shown in Fig. HG-309(d). For head thickness: 5PL t = 6S For flange thickness [5]: T = F + 2F 2 + J

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FIG. 18.5

where F =

STREES-STRAIN CURVE

PB24L2 - B 2 8S(A - B)

and J = a

Mo A + B ba b SB A - B

18.2.3.6 Cylindrical Parts under External Pressure Cylindrical pressure parts—furnaces, tubes, and so on—are subjected to external pressure. Section II, Part D, Appendix 3 (Basis for Establishing External Pressure Charts) is used as the basis of these rules. The external pressure is equal to the compressive stresses, and buckling can occur below the elastic limit. (See Fig. 18.5.) Equations developed for this activity are similar to those developed for column theory, where different relationships exist for the critical load depending on the length of the column. In the ASME approach, the two equations for critical buckling pressure [6] are the following:

Pc =

2E t 3 a b 1 - p2 d

and Pc =

t 2.6Ea b2.5 d L a b d

For generalizing and simplifying the design methodology, graphical charts were developed by the Pressure Vessel Research Council (PVRC)8; they appear in Section II, Part D. Figure G, given here as Fig. 18.6, represents the geometric properties of the cylinder, and Figs. CS-1 to CS-6 represent material properties for carbon steels. 18.2.3.6.1 Furnaces Plain-type furnaces, tubes, ring reinforced-type furnaces, corrugated-type furnaces, combination-type furnaces, and semicircular-type furnaces are all examples of items having cylindrical parts used for their construction. Formulas and procedures for the calculation of wall thickness for the cylindrical parts of these items can be found in paragraph HG-312. The following symbols shown in Fig. HG-312.3 are used in the formulas: 8

A  the factor determined from Fig. G in Subpart 3 of Section II, Part D B  the factor determined from the applicable material in Subpart 3 of Section II, Part D for maximum design and metal temperature, psi. Do  the outside diameter of the furnace, in. L  the design length of the plain furnace taken as the distance from center to center of weld attachment, in. P  the design pressure, psi t  the minimum required wall thickness of furnaces, in. (a) Plain-Type Furnaces These furnaces are the most commonly used because of their simplicity and low cost. The design temperature of the furnace is specified to be 500F (260C), but no design temperature is specified for other components, as this task is left to the designer. Furnace thickness shall not be less than 14 in. (6 mm). The following procedures shall be followed to determine the required minimum wall thickness of the furnace: (1) Assume a value for t; then determine the ratios L/Do and Do /t. (2) Enter Fig. G (Subpart 3 of Section II, Part D) at the value of L/Do. If L/Do is less than 0.05, enter the chart at a value of L/Do  0.05; if L/Do is more than 50, enter the chart at a value of L/Do  50. (3) Move horizontally to the line for the value of Do /t, as determined is step (2). From this point of intersection, move vertically downward to determine the value A. (4) With value A, move vertically to an intersection with the material-temperature line for the design temperature. From this point of intersection, move horizontally to read the value B. (5) Calculate the value of the maximum allowable external working pressure, Pa, by using the following formula: Pa =

B Do >t

(6) Compare Pa with P. If it is less than P, then a different value of t, a different value of L, or a combination of both must be selected for Pa to be equal to or greater than P. (b) Tubes The procedure outlined in the preceding list shall be used to calculate the wall thickness of ferrous tubes under external pressure. Additional thickness allowance of 0.04 in. (1 mm) shall be added as additional allowance for rolling and structural

Publications on pressure vessel research may be obtained by contacting the Pressure Vessel Research Council, 3 Park Avenue, New York, NY 10016.

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FIG. 18.6

GEOMETRIC CHART FOR COMPONENTS UNDER EXTERNAL OR COMPRESSIVE LOADINGS (FOR ALL MATERIALS) (Source: Fig. G, Section II, Part D of the ASME B&PV Code)

stability. This additional thickness is not required for tubes that are strength-welded to tubesheets, headers, or drums. (c) Ring Reinforced–Type Furnaces Ring-reinforced furnaces are not typically used for Section IV construction because of the low pressure involved and the cost of fabrication. The ring-reinforced furnace is a plain furnace with a circular stiffening ring welded to it. This stiffening ring is cross-sectionally rectangular, and its 5 thickness shall not be less than 18 in. (8 mm) or more than 13 16 in. 1 (21 mm)—in no case 14 times thicker than the furnace wall. The ratio of ring height to its thickness (Hr /Ht) shall be neither less than 3n nor more than 8. Both the furnace- and tube-wall thickness and the stiffening-ring design are determined by the procedures that are applied to the plain furnace. The moment of inertia of the stiffening ring shall be calculated by the following formula: D 2oLat + Is =

As bA L

14

where Is  the required moment of inertia about its neutral axis parallel to the axis of the furnace, in.4 As  the cross-sectional area of the stiffening ring, in.2 The procedure for determining the moment of inertia is as follows: (1) Assume that Do, L, and t are known. Select a rectangular ring and determine its area, As.

(2) Calculate moment of inertia I by using preceding the formula. Use the following formula to calculate B: B =

PDo As t + L

(3) Enter the righthand side of the chart in Fig. G (Subpart 3 of Section II, Part D) for the material at the value B, calculated in the preceding formula. (4) Follow horizontally to the material line; then move down vertically to read A. (5) With the value of all the symbols now known, calculate Is. If it is greater than I, select a new section and calculate a new Is. The ring section is satisfactory if Is is smaller than I. (d) Corrugated-Type Furnaces The rules, developed in the late 1800s, are based on tests performed at the Leeds Foundry in England. Corrugated furnaces welded to plain furnaces are sometimes used in construction for easy expansion and cleaning. As with ring-reinforced furnaces, corrugated furnaces are not typically used because of their low pressure and high cost of fabrication. Different types of corrugated furnaces exist, depending on the type of construction used: for example, Leeds suspension bulb, Morison, Fox, Purves, and Brown. The design pressure of a corrugated furnace with plain portions at the ends not exceeding 9 in. (229 mm) long shall be determined by the following formula: P = Ct/D

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FIG. 18.6

Where P  the design pressure, psi 5 t  the thickness, in.-minimum 16 in. (8 mm) for Leeds suspension bulb, Morrison, Fox, and Brown types and mini7 mum 16 in. (11 mm) for Purves and other furnace types corrugated by sections not exceeding 18 in. (45 mm) long D  the mean diameter, in.—take the inside diameter plus 2 in. as the mean diameter for the Morison furnace C  17,300 for Leeds suspension bulb furnaces; 15,600 for Morison furnaces; and 14,000 for Fox, Purves, and Brown furnaces Example A corrugated furnace (Brown type, 42 in. mean diameter) is found in a boiler. The plain ends of the furnace are 812 in. long, the desired working pressure is 125 psi, and the corrugations are 834 in. from center to center and 158 in. deep, with sections 1712 in. long. Given the following, what is the required thickness? P  125 D  42 C  14, 000 Ct P = D PD t = C

(CONTINUED)

125 * 42 14,000 3 t = 0.375 or in. 8 (e) Combination-Type Furnaces Combination furnaces are widely used. They are designed so that each type of furnace used in combination is self-supporting—that is, not requiring support from other furnaces at the connecting points. For plain-section furnaces, the formulas in paragraphs HG-312.1 and HG-312.3 shall be used; for corrugated-section furnaces, the formula of paragraph HG-312.6 shall be used. Full-penetration welding must be used to connect a plain self-supporting section to a corrugated self-supporting section, as shown in Fig. HG-312.6. (f) Semicircular-Type Furnaces or Crown Sheets The thickness of the semicircular furnace or crown sheet shall be a minimum of 5 16 in. (8 mm); the allowable working pressure shall not exceed 70% of Pa, as calculated by the formula as outlined in Paragraph 18.2.3.6.1(a) and by using the applicable chart. t =

18.2.3.7 Openings in Boilers 18.2.3.7.1 Shape of Openings The shape of the openings shall be circular, elliptical, or obround for cylindrical, spherical, and conical portions of boilers or in formed heads. An obround opening denotes one that is formed by two parallel sides and semicircular ends.

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12 • Chapter 18

FIG. 18.7 CHART SHOWING LIMITS OF SIZES OF OPENINGS WITH INHERENT COMPENSATION IN CYLINDRICL SHELLS (MAXIMUM PERMISSIBLE DIAMETER OF OPENING IS 8 IN.) (Source: Fig. HG-320, Section IV of the ASME D&PV Code)

18.2.3.7.2 Size of Openings With adequate reinforcement, openings in cylindrical and spherical shells are not limited to any size. The rules are intended to apply to the openings of the following dimensions: (1) Half of the boiler diameter, but not exceeding 20 in. (508 mm) for boilers up to 60 in. (1,520 mm) in diameter.

(2) One-third of the boiler diameter, but not exceeding 40 in. (1,000 mm) for boilers over 60 in. (1,520 mm) in diameter. 18.2.3.7.3 Design of Finished Openings Finished openings shall be designed as specified in paragraph HG-320.3 The following symbols are used in Fig. HG-320 (given here as Fig. 18.7): P  design pressure, psi

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d  maximum allowable diameter of opening, in. D  outer diameter of the shell, in. t  nominal thickness of the shell, in. S  maximum allowable stress value, psi (from Table HF-300) K  PD/2St (K represents the ration of hoop stress to allowable stress) For any K value  50%, the opening will be inherently compensated by the excess thickness in the shell (i.e., A1  Ar). Calculate K from the formula; then calculate Dt. Locate the intersecting point of K and Dt, go left horizontally from this intersecting point, and determine the maximum diameter of the opening. 18.2.3.8 Reinforcement Requirement for Openings 18.2.3.8.1 Theory of Reinforced Openings When a hole for a nozzle is cut in a shell, the vessel is weakened. Extra metal is provided to compensate for this weakness and strengthen the vessel. A certain amount of metal in the shell and in the nozzle wall is required to support the internal pressure. Any metal in excess of that required to support the internal pressure in the shell and nozzle is available as compensation for the nozzle opening. Figures 6.17 and 6.20, given here as Figs. 18.8 and 18.9, respectively, explain the basic theory of reinforced openings. The general principle is one of direct area replacement. The common rules are as follows: (1) Add enough reinforcement to compensate for weakening yet preserve the general dilation or strain pattern. (2) Place material adjacent to the opening for optimum distribution. 18.2.3.8.2 Reinforcement This is required for all openings except those in definite patterns and those that are small. This

FIG. 18.8

reinforcement shall be provided in such amount and distribution that the requirements are satisfied for all planes through the center of the opening and normal to the boiler surface. The total crosssectional area of reinforcement A required shall be determined by the following formula by using the symbols as shown in Figs HG-326.1 and HG-326.2, the latter given here as Fig. 18.10. A = dt rF + 2t nt rF(1 - fr1) where d  the diameter in the given plane of the finished opening, in. 1 F = cos2u + 0.75 4 For the correction factor, a value 1.00 may be used. The F factor is based on Mohr’s circle for principal stress. tr  the required thickness of a seamless shell or head, in. A1  the area in excess of thickness in the boiler shell available for reinforcement, in.2 A2  the area in excess of thickness in the nozzle wall available for reinforcement, in.2 E1  1.0 when an opening is in the solid plate or when the opening passes through a circumferential joint in a shell or cone  the joint efficiency obtained when any part of the opening passes through any other welded joint Dp  the outside diameter of the reinforcing element, in. Rn  the inside radius of the nozzle under consideration, in. S  the maximum allowable stress value, psi (from Table HF-300) Sn  the allowable stress in nozzle, psi

VARIATION IN STRESS IN REGION OF A CIRCULAR HOLE IN: (A) CYLINDER; (B) SPHERE SUBJECTED TO INTERNAL PRESSURE (Source: Ref. [6])

FIG. 18.9 DIAGRAMMATIC LOCATION OF NOZZLE OPENING REINFORCEMENT: (A) UNBALANCED INSIDE; (B) UNBALANCED OUTSIDE; (C) BALANCED (Source: Ref. [6])

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14 • Chapter 18

FIG. 18.10 NOMENCLATURE AND FORMULAS FOR REINFORCED OPENINGS (THIS FIGURE ILLUSTRATES A COMMON NOZZLE CONFIGURATION AND IS NOT INTENDED TO PROHIBIT OHER CONFIGURATIONS PERMITTED BY THE CODE) (Source: Fig. HG-326.2, Section IV of the ASME B&PV Code)

Sv  the allowable stress in vessel, psi Sp  the allowable stress in reinforcing element (plate) fr  the strength-reduction factor (not more than 1.0) fr1  Sn /Sv for nozzle inserted through the vessel wall 1.0 for nozzle wall abutting the vessel wall fr2  Sn /Sv fr3  (lesser of Sn or Sp)/Sv

fr4  Sp / Sv h  the distance that the nozzle projects beyond the inner surface of the vessel wall, in. te  the thickness of attached reinforcing pad, in. t  the nominal thickness of the boiler shell, in. tr  the required thickness of the seamless shell or head, in. tn  the nominal thickness of the nozzle wall, in.

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trn  the required thickness of the seamless nozzle wall, in. d  the diameter in the plane of the finished opening, in. 18.2.3.9 Inspection and Access Openings A boiler is equipped with a manhole or a combination of handholes, inspection openings, and washout plug openings to allow for the inspection and removal of accumulated deposits. An electric boiler with an internal gross volume of more than 5 ft3 (exclusive of casing and insulation) shall have an opening for inspection. Also, an electric boiler equipped with immersion-type resistance elements that lacks a manhole shall have an inspection opening not less than 3 in. pipe size (DN 75) located in the lower portion of the shell or head; an electric boiler for steam service shall have an inspection opening or manhole at or near the normal waterline. In addition, access doors shall be provided for the furnaces of internally fired boilers. 18.2.3.9.1 Manholes A manhole is required in the front head below the tubes of a horizontal-return-tubular boiler that is at least 60 in. (1,520 mm) in diameter. Except in a vertical-firetube boiler, a manhole shall be provided in the upper part of the shell or in the head of a firetube boiler that is at least 60 in. (1,520 mm) in diameter. An elliptical manhole size shall be a minimum of 12 in.  16 in. (305 mm  406 mm); a circular manhole size shall be a minimum of 15 in. (381 mm) in diameter. Moreover, the width of the bearing surface for a gasket of a manhole shall not be less than 11 16 in. (18 mm). 18.2.3.9.2 Handholes, Inspection Openings, and Washout Plug Openings In the absence of a manhole, each boiler shall be provided with a combination of handholes, inspection openings, and washout plug openings. The locations of these openings are given in paragraph HG-330.4. Locomotive- or firebox-type boilers must have one handhole or washout plug opening in the lower part of the waterleg and at least one opening near the line of crown sheet. In addition, the boilers for steam service shall have at least one inspection opening above the top row of tubes. The minimum size of the inspection opening shall be NPS 3 (DN 75); of the washout plug opening, 112 in. pipe size (DN 40); and of the handhole opening, 234 in.  312 in. (70 mm  89 mm). 18.2.3.9.3 Fire or Access Doors A fire door or access door shall be provided for a furnace that has at least a 28 in. diameter within an internally fired boiler. The size of the door shall be a minimum of 11 in.  15 in. (280 mm  381 mm), 10 in.  16 in. (254 mm  406 mm), or 15 in. (381 mm) in diameter; the access door for use in a boiler setting shall be 12 in.  16 in. (305 mm  406 mm) or an equivalent size. 18.2.3.10 Stayed Surfaces Flat plates with cross-sectionally uniform stays or staybolts are used for boiler construction. Figures HG-340.1 and HG-340.2 show acceptable methods of staying. The equation for flat-stayed surfaces is an adoption of the flat-head equation, with the diameter replaced with the distance stays or pitch. In this case, the C factor represents the degree of restraint to rotation that the stay attachment provides. The thickness and design pressure for the stayed plates are calculated by the following formulas: t = p2P/SC P = t 2SC/P 2 Where t  the required thickness of plate, in. P  the design pressure, psi

S  the maximum allowable stress value from Tables HF300.1 and HF-300.2 P  the maximum pitch measured between straight lines passing through the centers of the stays in the different rows, in. C  a factor that depends on the type of stays given in paragraph HG-340.1 While connecting two plates by staying and one of them requires staying, the value of C shall be governed by the thickness requiring staying. C  2.7 for stays welded to plates C  3.1 for stays screwed through plates r  the radius of the firebox corner, in. Two considerations in the design stays are the loading on the plate and the loading on the stay. The plate loading is addressed by the foregoing formula, and the stay load is addressed by the following: stay load  the pressure (the full pitch area – the area occupied by the stay) Stay load/allowable stress  the required area of the stay The SCI requires the stay area to be increased by an additional 10%. Two flat-stayed surfaces may intersect at an angle as shown in Fig. HG-340.1, in which case the pitch shall be calculated by the following formula: P =

90t CS bA p

The maximum pitch shall not exceed 812 in. (216 mm) except for welded-in stays, in which case it shall not exceed 15 times the stay diameter. 18.2.3.11 Staybolts 18.2.3.11.1 Threaded Staybolts The ends of the threaded staybolts should extend to a minimum of two threads beyond the plate, after which point they are riveted over or fitted with extended nuts. The outside ends of solid staybolts up to 8 in. (203 mm) 3 long should be drilled with telltale holes at least 16 in. (4.8 mm) in 1 diameter to a depth extending at least 2 in. (13 mm) beyond the inside of the plate. However, solid staybolts over 8 in. (203 mm) long should not be drilled, for hollow staybolts may be used instead of solid staybolts with drilled ends. Moreover, telltale holes are not required for staybolts attached by welding. Annealing should also be done after upsetting on the ends of the threaded stays upset for threading. It is important to not expose the ends of the nut-fitted staybolts to radiant heat. 18.2.3.11.2 Welded-In Staybolts Installation requirements of welded in staybolts are given in paragraph HW-710. 18.2.3.12 Dimensions of Stays 18.2.3.12.1 Area of Stays The required area of a stay is determined by the minimum cross section at the root of the thread. Corrosion allowance is not considered. This required area is calculated by dividing the load on the stay by the allowable stress value for the material. 18.2.3.12.2 Load Carried by Stays The area supported by a stay is based on the full pitch dimensions minus the area occupied by the stay. The load carried by a stay is calculated by multiplying the area supported by the design pressure.

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TABLE 18.1

COPPER PLATES AND COPPER STAYBOLTS

Copper Plate Thickness (In.)

Minimum Staybolt Diameter (In.)

 81 3  16 3  16

1 2 5 8 3 4

 18 but not

18.2.3.12.3 Stays Fabricated by Welding Normally, stays of one-piece construction are used; indeed, those made of individual parts may be attached by welding. A joint efficiency of 60% is used for calculating the strength. Also, ferrous stays welded in by fusion have a minimum cross–sectional area of 0.44 in.2 (284 mm2). 18.2.3.12.4 Nonferrous Stays There are minimum diameter requirements for nonferrous stays such as those composed of copper and coppernickel stays. Tables 18.1 and 18.2 show these minimum diameters. 18.2.3.13 Diagonal Stays 18.2.3.13.1 Area of Diagonal Stays Diagonal stays are used to support the tubesheet and shell diagonally. All details of the installation of diagonal stays are shown in the Fig. HG-343. The required area of a diagonal stay is calculated by the following formula: A =

aL l

surface of a flanged head welded to the shell should be p (as calculated in paragraph HG-340) plus the inside radius of the supporting flange, in which the value of C is given for the thickness of the plate and the type of stay. Also, the greatest distance between the edges of the tube holes and the center of the first row of stays is calculated in paragraph HG-340, in which the value of C is given for the thickness of the plate and the type of stay. Horizontal-firetube boilers with manholes on the heads are shown in Fig. HG-345.1(a) and Fig. HG-345.1(b). The area to be stayed may be reduced by 100 in.2 (645 cm2) if an unflanged manhole ring that meets the requirements of paragraph HG-321 is present in a flat-stayed head under the following conditions: (1) The distance between the manhole and the inner surface of the supporting flange does not exceed half the maximum allowable allowable pitch for an unflanged manhole or half the maximum allowable pitch plus the inside radius of the supporting flange for a flanged-in manhole in a flanged head. (2) The distance between the centers of the first row of stays or the edges of the tube holes and the manhole does not exceed half the maximum allowable pitch as determined in paragraph HG-340. 18.2.3.15 Tubesheets Firetubes in a firetube boiler may be used as stays. The required thickness, maximum pitch, and design pressure for tubesheets with firetubes used as stays may be calculated by using the following formulas: t =

where A  the sectional area of the diagonal stay, in.2 a  the sectional area of the direct stay, in.2 L  the length of the diagonal stay, in. l  the length of the line (drawn perpendicular to the supported boiler head or surface) to the center of the palm of the diagonal stay, in. 18.2.3.14 Staying of Heads Any portions of the heads that require staying are stayed as flat heads. In boilers with equal to or less than 30 psi (207 kPa) pressure that contain unflanged heads, staying is not required if the greatest distance measured along a radial line from the inner surface of the shell to a point does not exceed 1.25p. In boilers with over 30 psi (207 kPa) pressure that contain unflanged heads or in boilers of any pressure that contain flanged heads, staying is not required when the greatest distance measured does not exceed 1.5p. The maximum distance between the inner surface of the shell and the centers for unflanged heads should not be more than the allowable pitch as calculated in paragraph HG-340, in which the value of C is given for thickness of the plate and the type of stay. The greatest distance between the inner surface of the supporting flange and the lines parallel to the shell TABLE 18.2 COPPER–NICKEL PLATE AND COPPER–NICKEL STAYBOLTS

Copper–Nickel Plate Thickness (In.)  81 3  18 but not  16 3  16

Minimum Staybolt Diameter (In.) 3 8 7 16 1 2

pD 2 P b b + ap 2 4 A CS

P =

a

CSt 2 pD 2 b + a b A P 4 a

P =

CSt 2 P-a

pD2

4

b

where t  the required plate thickness in. p  the maximum pitch measured between the centers of tubes in different rows, in. 7 C  2.7 for firetubes welded to plates not over 16 in. (11 mm) thick 7 C  2.8 for firetubes welded to plates over 16 in. (11 mm) thick S  the maximum allowable stress values given in Tables HF-300.1 and HF-300.2 P  the design pressure, psi D  the outside diameter of the tubes, in. The pitch of firetubes used as stays does not exceed 15 times the diameter of the tubes. Firetubes welded to tubesheets and used as stays meet the requirements of HW-713. 18.2.3.16 Ligaments A ligament—sometimes referred to as a webbing—is the area of metal between the holes in a tubesheet. The three types of ligaments are as follows: (1) longitudinal, which are located between the front and lengthwise holes along the drum. (2) circumferential, which are located between the holes and which encircle the drum.

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(3) diagonal, which constitute a special case because they are located between the holes and are offset at an angle to each other. The rules of ligaments are applicable to groups of openings in cylindrical-pressure parts that form a definite pattern. These rules also apply to openings not spaced to exceed two diameters center to center. The following symbols are used in the formulas for calculation of ligament efficiency: P  the longitudinal pitch of adjacent openings, in. P¿  the diagonal pitch of adjacent openings, in. P–  the transverse pitch of adjacent openings, in. P1  the pitch between corresponding openings in a series of symmetrical groups of openings, in. d  the diameter of openings, in. n  the number of openings in length, p1 E  the ligament efficiency 18.2.3.16.1 Openings Parallel to Shell Axis These openings may have equal pitch in every row or unequal pitch in symmetrical groups. The ligament efficiency is determined by the following formulas. For equal pitch of openings in every row (see Fig. HG-350.1, given here as Fig. 18.11): p - d E = P

(18.1)

For unequal pitch in symmetrical groups of openings (see Figs. HG-350.2 and HG-350.3): E =

p1 - nd p1

(18.2)

If the openings are not in symmetrical groups, the efficiency is determined as follows for the group of openings that gives the lowest efficiency: (1) efficiency as calculated by equation (18.2), using p1 equal to the inside diameter of the shell or 60 in. (1,520 mm), whichever is less; or (2) .25 times the efficiency calculated by equation (18.2), using P1 equal to the inside radius of the shell or 30 in.(760 mm), whichever is less. 18.2.3.16.2 Opening Transverse to Shell Axis The ligament efficiency of openings spaced at right angles to the axis is equal to two times the efficiency of similarly spaced holes parallel to the shell axis, as calculated by equations (18.1) and (18.2).

FIG. 18.11 EXAMPLE OF TUBE SPACING WITH PITCH OF HOLES EQUAL IN EVERY ROW (Source: Fig. HG-350.1, Section IV of the ASME B&PV Code)

FIG. 18.12 EXAMPLE OF TUBE SPACING WITH TUBE HOLES ON DIAGONAL LINES (Source: Fig. HG-350.4, Section IV of the ASME B&PV Code)

18.2.3.16.3 Holes Along a Diagonal The ligament efficiency of openings that are equally spaced diagonally (see Fig. HG-350.4, given here as Fig. 18.12) is calculated by the following formula: P¿ - d E = p¿F where F is the factor shown in Fig. HG-321 (given here as Fig. 18.13) for the angle of the longitudinal axis through which the diagonal makes a plane. Using the F factor for diagonal ligaments is an approach that differs from that of Section I and Section VIII, Division 1, as it gives slightly higher efficiencies. 1 Example The shell of a vessel is drilled for tube holes of 332 in.

diameter spaced longitudinally in groups of two tubes pitched 478 in. with 6 in. of spacing between the groups. Circumferentially, the tube holes are symmetrical. Given the following equations, what is the efficiency of the longitudinal tube ligaments? P1  10.875 in. n2 d  3.03125 P1 - nd E = p1 10.875 - (2)(3.03125) 10.875 4.813 E = 10.875 E  0.4425 or 44.25% E =

18.2.3.17 Tube Holes and Tube Attachments 18.2.3.17.1 Tube Holes Tube holes are drilled to full size from the solid plate. They may also be punched 12 in. (13 mm) smaller in diameter than full size if the plate thickness exceeds 83 in. (10 mm) or punched 21 in. (3.2 mm) smaller in diameter than full size when the plate thickness is 38 in. (10 mm) or less. After punching, the holes are drilled, reamed, or finished full size with rotating cutters; then, the sharp edges of the tube holes are removed with a file or other suitable tool. 18.2.3.17.2 Tube Attachments The ends of firetubes may be attached to tubesheets by expanding and flaring, by expanding and beading, by expanding and welding, or simply by expanding

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TABLE 18.3 MINIMUM THICKNESS OF MATERIAL FOR THREADED CONNECTIONS TO BOILERS

18.2.3.18 External Piping 18.2.3.18.1 Threaded Connections Threaded pipe connections should be tapped into material with a minimum thickness as shown in Table HG-370, given here as Table 18.3. The minimum thickness of a tapped, curved surface should be sufficient to permit at least four full threads. 18.2.3.18.2 Flanged Connections Flanged connections to external piping should meet the requirements of ANSI B16.5 (Steel Pipe Flanges and Flanged Fitttings). Steel flanges, which do not meet the requirements of ANSI B16.5, should be designed in accordance with Appendix II of Section VIII, Division 1.

18.2.4 Article 4: Pressure-Relieving Devices

FIG. 18.13 CHART FOR DETERMINING VALUES OF F (Source: Fig. HG-321, Section IV of the ASME B&PV Code)

or welding alone. Firetubes attached by expanding and welding or by welding only should comply with the requirements of paragraph HW-713. However, those that are attached by flaring and expanding or by expanding only should comply with the following requirements: (1) If the fire tube ends are in contact with primary furnace gases, they should extend not less than the tube thickness or 1 8 in. (3.2 mm), whichever is greater, nor should they extend more than 14 in. (6 mm) or the tube thickness, whichever is greater. (2) If the firetube ends are not in contact with primary gases, they should extend not less than the tube thickness or 81 in. (3.2 mm), whichever is greater, nor should they extend more than 38 in. (10 mm) or the tube thickness, whichever is greater. Watertubes may be attached to the drums by expanding and flaring, by expanding and beading, by expanding and welding, or by expanding or welding only. Watertubes attached by other than expanding and beading should extend neither less than 114 in. (6 mm) nor more than 12 in. (13 mm). Nevertheless, watertubes in hot-water boilers may be installed into headers by using O-ring seals instead of expanding, welding, or brazing under the conditions of paragraph HG-360.2(e) of the Code.

18.2.4.1 Pressure Relieving–Valve Requirements 18.2.4.1.1 Safety–Valve Requirements for Steam Boilers The safety valve shall relieve all the steam generated by a steam-heating boiler. Each boiler shall have at least one spring pop–type safety valve to discharge all the steam at a pressure not exceeding 15 psi (103 kPa). In addition, the size of the safety valve shall be a minimum of NPS 12 (DN 15) and a maximum of NPS 421 (DN 115). The minimum capacity required by the safety valve can be determined by either of the following methods: (1) Determine the maximum Btu output at the boiler nozzle and divide that output by 1,000. (Doing so is applicable for a boiler that uses any type of fuel.) (2) Determine the minimum amount of steam generated per hour per square foot of boiler heating surface as shown in Table HG-400.1, given here as Table 18.4. 18.2.4.1.2 Safety Relief–Valve Requirements for Hot-Water Boilers For each water-heating or -supply boiler, there shall be at least one safety-relief valve of the automatic-reseating type. This valve shall be identified with the ASME Code Symbol V or HV and shall be set at or below the maximum allowable working pressure. The size of the safety-relief valve shall not be less than NPS 34 (DN 20) nor more than NPS 421 (DN 115). A safety-relief valve of NPS 12 (DN 15) size may be used for a boiler with a heat input of not more than 15,000 Btu /hr (4.4 kW). The relieving capacity of the pressure-relieving device on a hot water boiler shall be determined by the same methods used for a steam boiler. For a cast-iron boiler, the minimum relieving capacity shall be determined by the maximum output method. Example 1 A 72 in.-diameter stoker-fired horizontal-returntubular (HRT) boiler has 1,450 ft2 of heating surface and a MAWP of 15 psi. What safety valve–relieving capacity is required?

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TABLE 18.4 MINIMUM POUNDS OF STEAM PER HOUR PER SQUARE FOOT OF HEATING SURFACE

(3) In case of capacity or performance failure, the test shall be repeated at the rate of two replacement valves for each valve that failed. (4) If any of the replacement valves fails, the Manufacturer’s Code Symbol HV on the type of valve that failed shall berevoked. 18.2.4.2.4 Manufacturer’s Testing The Manufacturer shall have a well-established program for testing both safety valves and safety-relief valves. Under the Code, safety valves are tested on steam or air. Every safety valve is tested to demonstrate its popping point, blowdown, and tightness. Similarly, safety-relief valves are tested on water, steam, or air. Very important for the safety-relief valve is a tightness test, which is conducted at the maximum operating pressure not exceeding the reseating pressure. 18.2.4.2.5 Design Requirements The Manufacturer is required to submit valves for capacity certification or testing by a test laboratory, at which time an ASME designee is authorized to review the valve design to ensure that it conforms to Code requirements.

1,450  7  10,150 lb/hr safety valve–relieving capacity required. (See Table HG-400.1.) Example 2 Given an electric boiler with a 50 kW electric element, what is the relieving capacity of the safety valve in Btu/hr? 50  3.5  175 lb/hr  1,000  175,000 Btu/hr safety valverelieving capacity required. [See Table HG-400.1, Note (a).] 18.2.4.2 Minimum Requirements for Safety and SafetyRelief Valves 18.2.4.2.1 Mechanical Requirements All safety valves shall be designed to have a control blowdown of 2–4 psi (13.8–28 kPa). The safety valves shall be spring-loaded, and the full-lift-spring compression shall not exceed 80% of the solid deflection. In addition, the set-pressure tolerance shall not exceed 2 psi (13.8 kPa) for the safety valve and 3 psi (20.6 kPa) for the safety-relief valve when the boiler pressure does not exceed 60 psig. For pressures over 60 psig, the tolerance is 5%. 18.2.4.2.2 Material Selection Materials of construction for valve bodies and bonnets or pressure parts shall conform to Section II. The Manufacturer can use materials other than those listed in Section II if the specifications that require equivalent chemical and physical properties are maintained. Materials used for seats and disks should withstand heat and provide resistance to steam cutting. 18.2.4.2.3 Manufacturing and Inspection An ASME designee is required to inspect the manufacturing, inspection, and testing operations, including capacity. The facilities for manufacturing, production, and testing and the quality control procedures must all be accepted by an ASME designee. The Manufacturer may obtain permission from the ASME to produce pressure-relief valves with the ASME Code Symbol HV. This permission is issued for five years. To obtain permission, the Manufacturer shall successfully demonstrate the following conditions: (1) Two relief valves shall be selected by an ASME designee from sample production. (2) Operational and capacity tests will be conducted by an ASME-accepted laboratory in the presence of an ASME designee.

18.2.4.3 Discharge Capacities of Safety and Safety-Relief Valves 18.2.4.3.1 Valve Markings The Manufacturer and/or Assembler shall possess a valid Certificate of Authorization from the ASME to apply the Code Symbol Stamp to each safety valve. As specified in paragraph HG-402.1, each safety valve is required to be marked with the following data: (1) the name or acceptable abbreviation of the Manufacturer; (2) the Manufacturer’s design and type number; (3) the NPS size ——— in. (i.e., the nominal pipe size of the valve inlet); (4) the set pressure ——— psi; (5) the capacity ——— lb/hr or Btu/hr; (6) the year built; and (7) the ASME Code Symbol. See Fig. HG-402, given here as Fig. 18.14, for an example of an ASME Code Symbol. 18.2.4.3.2 Calculation of Capacity to Be Stamped on Valves The valve capacity test shall be conducted in the presence of and certified by an ASME Authorized Observer. One of the following test methods is required: (a) Coefficient Method This method, based on coefficient calculation, is used for safety valves. Three valves of each of the three sizes (for a total of nine valves) are tested. A coefficient of discharge is determined by the following formula:

FIG. 18.14 OFFICIAL SYMBOL FOR STAMP TO DENOTE THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS’ STANDARD (Source: Fig. HG-402, Section IV of the ASME B&PV Code)

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KD =

actual steam flow theoretical steam flow K  average KD  0.90

where K  the coefficient of discharge for the design KD  the average coefficient of nine tests The stamped capacity is determined by the following formulas: For a 45 deg. seat: W = 51.5pDLP * 0.707K For a flat seat: W = 51.5pDLPK For a nozzle: W = 51.5APK where W  the weight of steam/hr, lb D  the seat diameter, in. L  the lift, in. P  (1.10  set pressure  14.7 psia for hot-water application)  (5.0 psi  15 psi set  14.7 psia for steam boilers) A  nozzle–throat area, in.2 (b) Slope Method This method, based on slope calculation, is used for pressure-relief valves. Four valves of each combination of pipe and orifice are used for the test. The slope is calculated by the following formula: measured capacity Slope = w/p = absolute flow pressure, psia

18.2.4.3.3 Capacity Testing This testing is conducted at a testing facility9 and must conform to the requirements of ASME PTC 25, an ASME Performance Test Code for pressure-relief devices. An ASME Authorized Observer is required to witness the testing. Data reports on the tests shall be signed by both the Manufacturer and the Authorized Observer. All testing facilities are subject to review by the ASME every five years. Safety valves are tested at 5 psi (35 kPa) over the set pressure; safety-relief valves, at 110% of the set pressure. The testing medium should be dry-saturated steam at a minimum quality of 98% and a maximum temperature of 20F (11C). Safety relief—valve capacity in terms of Btu can be calculated by multiplying the capacity in pounds per hour (W) by 1,000. 18.2.4.3.4 Test Record Data Sheet The Test Record Data Sheet is prepared and signed by the ASME Authorized Observer. The Manufacturer uses this Data Sheet for the construction and stamping of valves of corresponding design and construction. If the design affecting the flow path, lift, or performance characteristics is changed, new tests shall be conducted. 18.2.4.4 The Heating Surface The heating surface is defined as the surface in which one side comprises water and the other side comprises combustion products. The heating surface is measured on the side that receives heat; this measurement is used to calculate the steam-generation capacity of the boiler. The heating surface outside of the furnace, however, is measured circumferentially. The waterwall-heating surface within the furnace is measured as the projected area (diameter  length). The heating surface of the tubes, fireboxes, shells, and tubesheets, as well as the projected area of headers, are all considered for this purpose. The boiler heating surface is calculated by using the followingformulas: For the heating surface of the sell: H(shell) =

The slope shall be calculated for each test point and the average slope shall be determined. The testing values should be between the minimum and maximum slope value range. An ASME Authorized Observer may require additional valves to be tested if the values are not within this range. The relieving capacity to be stamped is determined by the following method: stamped capacity  rated slope  (1.10  set pressure  14.7 psia for hot-water applications) where the rated slope  0.90  the average slope (c) Three-Valve Method When one or more sizes of a design are set at one pressure, the Manufacturer may submit three valves of each size of each design set at one pressure for testing. In that case, the stamped capacity should not exceed 90% of the average capacity of the three valves tested. 9

pDL

For the heating surface of the tube: HS(tube) = Np(ID)L

where the minimum slope  0.95  average slope the maximum slope  1.05  average slope

1 2

For the heating surface of the heads: D * D(0.7854) HS(head) = 144 The total heating surface: HS(total)  HS(shell)  HS(tube)  HS(heads) where N  the number of tubes D  the diameter of the shell, in. ID  the inside diameter of the tubes, in. L  the length of the tubes, in. Example Calculate the total heating surface of an HRT boiler 78 in. in diameter and 20 ft long that contains 100 tubes 4 in. ID, given the following: D  78 in. ID  4 in.

The National Board of Boiler and Pressure Vessel Inspectors’ testing laboratory, located at 7437 Pingue Drive, Worthington, OH 43085, is an ASMEapproved safety valve–testing facility.

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L  20  12  240 in. N  100 1 * pDL 2 * 144 1 * 3.14 * 78 * 240 = 2 * 144

HS(shell) =

= 204.1 ft 2 HS(tubes) = Np(ID)L =

100 * 3.1416 * 4 * 240 144

= 2,094.4 ft 2 HS(head) = HS(heads) - HS(tube holes) D 2 * 0.7854 * 2 144 78 * 78 * 0.7854 = * 2 144

steps of one-tenth the design pressure until the final test pressure is reached. Strain gage and hydrostatic pressure readings are taken for each pressure increment, and the permanent strain at each gage is recorded. Two curves are plotted: one strain versus test pressure and one permanent strain after removing pressure. The test pressure is the maximum hydrostatic pressure and does not exceed the pressure at which the plotted points of the strained gage line reaches the value of • 0.2% permanent strain for carbon, low-alloy, and high-alloy steels • 0.5% strain under pressure for copper-base alloys The design pressure, P, shall be determined by one of the following formulas: If the average yield strength is not known: P  0.4H Ys P = 0.5H Ya

=

= 84.50 ft 2 D2 * p * N HS(tube holes) = * 2 144 =

4 * 4 * 0.7854 * 100 * 2 144

= 17.45 ft 2 HS(head) = 84.50 - 17.45 = 67.5 ft 2 For the total heating surface: HS = 204.1 + 2,094.40 + 67.05 = 2,365.55 ft 2

18.2.5

Article 5: Tests, Inspection, and Stamping

Sometimes, the design pressure of pressure parts cannot be determined by the foregoing formulas because the necessary information is unavailable. In such cases, proof tests may be used to establish the design pressure of different boiler pressure parts. An Authorized Inspector is requires to witness and accept these tests. The two types of tests used for determining the internal design pressure are as follows: (1) The yield test, in which the materials may be accepted for Code Stamping if a proof test shows no permanent yielding in accordance with paragraphs HG-502.1 and HG-502.2. This test is applicable for materials with a ratio of minimum yield to ultimate strength of maximum 0.625. (2) The burst test, in which the materials are not accepted for Code Stamping if they are proof-tested under the provisions of this test. 18.2.5.1 Proof Test Procedures 18.2.5.1.1 Strain Measurement Test In this test, which may be applied to any material permitted for use by ASME Section IV, strain is measured by a strain gage in the direction of the maximum stress at the most stressed parts. The strain gage should be capable of indicating strains to 0.00005 in. /in. (0.005%). The hydrostatic pressure is increased gradually until it is one and a half times the design pressure, after which the pressure is increased in

where H  the hydrostatic test pressure, psi at which the test was stopped Ys  the specified minimum yield strength Ya  the actual average yield strength 18.2.5.1.2 Displacement Measurement Test In this test, which may be applied to the pressure parts for which the yield point can be determined, displacement is measured at the highly stressed parts. Any type of measuring device capable of measuring up to 0.001 in. (0.02 mm) can be used. The hydrostatic test pressure may be increased gradually until it is one and a half times the design pressure, after which the pressure is increased in steps of one-tenth the design pressure until the final test pressure is reached. Displacement and hydrostatic pressure readings are taken for each pressure increment, and the permanent displacement at each gage is recorded. Two curves are plotted: one displacement versus test pressure and one permanent displacement after removing pressure. The test pressure is stopped when the displacement curve deviates from a straight line. The design pressure, P, shall be determined by one of the following formulas. If the average yield strength is known, for carbon steel: Ys P = 0.5H Ya For carbon steel with a specified tensile strength not exceeding 70,000 psi (481 MPa): P = 0.5H a

S b S + 5,000

or P  0.4 H where H  the hydrostatic test pressure, psi Ys  the specified minimum yield strength, psi Ya  the actual average yield strength, psi S  the specified minimum tensile strength, psi

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18.2.5.1.3 Bursting Test In this test, which may be applied to any material permitted for use under ASME Section IV, the design pressure is established by a hydrostatic test to failure by rupture. The hydrostatic test may be stopped when the test pressure reaches the value calculated by the following formula. This value constitutes the design pressure. P =

S B * 5 Sa or Sm

where B  the bursting test pressure, psi S  the specified minimum tensile strength, psi Sa  the average actual tensile strength, psi Sm  the maximum tensile strength of the range of specifications, psi 18.2.5.1.4 Brittle Coating Test Procedure In this test, which may be applied to the pressure parts for which the yield point can be determined, the parts are coated with a limewash or other brittle coating. Pressure is applied gradually while the parts are examined at each pressure increment for any yielding, the first sign of which makes stopping the pressure necessary. The design pressure is computed by the formulas used for the displacement measurement test. 18.2.5.2 Collapse Test Section IV has no specific rules for the collapse test in which the parts should, without deformation, with stand a hydrostatic test that has a minimum of three times the design pressure. 18.2.5.3 Hydrostatic Test The requirements of the hydrostatic test are determined by the Code part under which the boiler is designed and constructed. Cast-iron boilers are tested in accordance with the requirements of paragraph HC-410; wrought-iron boilers are tested in accordance with paragraph HF-204.1. The general requirements of the hydrostatic test are as follows: (1) For boilers with a 160 psi design pressure, a minimum 240 psi hydrostatic test pressure is applied and held for a minimum of 5 minutes at the same pressure, then reduced to the MAWP. A thorough inspection follows. (2) For all other boilers, a minimum 60 psi (414 kPa) (or 112 times the MAWP) hydrostatic test pressure is applied, and the pressure is controlled to prevent it from exceeding 10 psi (69 kPa). 18.2.5.4 Safety-Valve Accumulation Tests Sometimes the capacity of the safety valve or safety-relief valve is not known. In that case, one of the following methods may be used to verify the capacity: (1) The accumulation test, in which all the discharge outletsfrom the boiler are shut off and the fires are forced to the maximum. The safety device should not exceed the pressure in accordance with paragraphs HG-400.1(f) and HG400.2(f). (2) The fuel-measuring method, in which the maximum amount of fuel burned is measured. The evaporative capacity is calculated on the basis of the heating value of the fuel by using

the following formula: W =

C * H * 75 1,000

where W  the weight of steam/hr, lb C  the total weight or volume of fuel burned/hr at the time of maximum forcing, lb or ft3 H  the heat of combustion of fuel, Btu/lb or Btu/ft3 The total capacities marked on the safety valves are required to be at least equal to W. The heating values of various fuels are given in Appendix 18.A. 18.2.5.5 Inspection and Testing During its construction, a boiler is inspected and tested in the shop in accordance with paragraph HG-515. The Manufacturer is responsible for design, construction, and quality control in accordance with the Code requirements. An Authorized Inspector is responsible for inspection and testing of a boiler for Code compliance (except cast iron). A boiler can be marked with ASME Code Symbol H only if the requirements of paragraph HG-515 and the specific requirements of inspection and testing given in Parts HF and HC are all met. 18.2.5.5.1 The Manufacturer’s Responsibility The Manufacturer is required to manufacture a boiler in accordance with all Code requirements, follow the quality control system of the shop, and cooperate with the Authorized Inspector at various stages of construction to make significant product under the Code. The Manufacturer shall provide the following documents and information to the Authorized Inspector: (1) the Certificate of Authorization from the ASME for manufacturing the type of boiler; (2) the design calculations and drawings for the boiler or part; (3) the identification of the materials used for construction; (4) the Data Reports; (5) the material identification, dimension check, and material test reports; (6) the qualification of the welding and/or brazing procedures; (7) the qualification of welders, welding operators, or brazers used in production; (8) the records of examination of parts before they are joined by welding or brazing; (9) the records of examination of parts for marking, surface defects, and dimensions; (10) the records of hydrostatic testing, if applicable; and (11) the application of the required stamping and/or nameplate to the boiler. In addition, the Manufacturer shall do the following: (1) allow the Authorized Inspector access to various areas of the shop; (2) keep the Authorized Inspector informed of the work’s progress; (3) receive permission from the Authorized Inspector to correct nonconformities; and (4) prepare and retain the Data Reports. In case of multiple, duplicate boiler fabrications, the Manufacturer will specify detailed procedures in the quality control manual that are accepted by the inspection agency, jurisdiction, and

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ASME designee. The Authorized Inspector employed by the inspection agency will carry out the inspection procedures. 18.2.5.5.2 Authorized Inspector’s Responsibility The Authorized Inspector, commissioned by the National Board of Boiler and Pressure Vessel Inspectors,10 is employed by an Authorized Inspection Agency (AIA) accredited by the ASME. The AIA may be either a jurisdiction or an insurance company licensed to write boiler and pressure vessel insurance. The Authorized Inspector is assigned the following responsibilities: (1) checking the validity of the Manufacturer’s Certificate of Authorization; (2) ensuring that the Manufacturer follows the quality control system accepted by the ASME; (3) reviewing the design calculations, drawings, specifications, procedures, records, and test results; (4) checking the material to ensure that it complies with the Code requirements; (5) checking all of the welding and brazing procedures to ensure that these are qualified; (6) checking the qualification of welders, welding operators, brazers, and brazer operators; (7) checking for the proper joint factors for brazed joints; (8) visually inspecting the transfer of material identification; (9) witnessing the proof tests; (10) inspecting each boiler and water heater during and after construction; (11) verifying the stamping and/or nameplate information and attachment; and (12) signing the Manufacturer’s Data Reports. The Authorized Inspector ensures that all necessary inspections enable him or her to certify that the boilers have been designed and constructed in accordance with Section IV and that Code Symbol Stamp can be applied. 18.2.5.6 Data Reports When a boiler or parts of a boiler is completed, data reports are prepared by the manufacturer and signed by the Authorized Inspector. The three types of data reports are as follows: 18.2.5.6.1 Manufacturer’s Master Data Report The Manufacturer of heating boilers to which the ASME Code Symbol H Stamp is applied is required to prepare the Master Data Report, which may include serial numbers of more than one identical boiler that is completed, inspected, and stamped in a continuous eighthour period. The following are two ASME Data Report forms: • H-2 (Manufacturer’s Data Report for All Types of Boilers Except Watertube and those Made of Cast Iron) • H-3 (Manufacturer’s Data Report for Watertube Boilers) The Manufacturer distributes a copy of the Data Report to the Owner, the insurance agency, and the jurisdiction. The Manufacturer must keep a file copy of the Data Report for at least five years; otherwise, he or she may have the boiler registered and the original Data Report filed with the National Board of Boiler and Pressure Vessel Inspectors. 18.2.5.6.2 The Partial Data Report The Manufacturer may be required to buy parts from another Manufacturer to complete the 10

FIG. 18.15 OFFICIAL SYMBOL FOR STAMP TO DENOTE THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS’ STANDARD (source: Fig. HG-530.1, Section IV of the ASME B&PV Coode)

boiler, in which case the Parts’ Manufacturer will submit a Partial Data Report completed on Form H-4 (Manufacturer’s Partial Data Report), in duplicate, to the Manufacturer of the finished boiler. 18.2.5.6.3 The Supplementary Data Report A supplementary sheet is used to record additional data when the Data Report form is insufficient. Additional data is recorded on Form H-6 (Manufacturer’s Data Report Supplementary Sheet) and attached to the Manufacturer’s Data Report. 18.2.5.7 Stamping of Non-Cast-Iron Boilers Each boiler that is designed, constructed, and inspected in accordance to the rules of Part HG shall be stamped with the Code Symbol H Stamp as shown in Fig. HG-530.1, given here as Fig. 18.15. The following data, as shown in Figs. HG-530.2 and HG- 530.3 (given here as Figs. 18.16 and 18.17, respectively), shall be 5 stamped with letters (at a minimum height of 16 in. on the boiler 3 proper or on the nameplate and with a minimum thickness of 64 in.) that are permanently fastened to the boiler. (1) The Boiler Manufacturer’s name—to be inserted after thewords “Certified by”; (2) the MAWP; (3) the safety- or safety relief-valve capacity, lb/hr or MBH (i.e., thousands Btu/hr) (4) the heating surface, ft2 (for electric boilers, kilowatt power input); (5) the Manufacturer’s serial number (optional) (6) the year built; and (7) the maximum water temperature. The stamping should be in a conspicuous, easily visible location. Such locations for different types of boilers are found in paragraph HG-530. 18.2.5.8 Cast-Iron Boilers Each boiler section designed and constructed of cast iron and inspected in accordance with the rules of Part HC shall be casted with the Code Symbol H Stamp as shown in Fig. 18.15. The following data, as shown in Figs. HG530.4 and HG-530.5, shall be casted onto each boiler section at a 5 minimum height of 16 in.: (1) the Boiler or Parts’ Manufacturer’s name or acceptable abbre-viation—to be inserted following the words “Certified by”; (2) the MAWP; (3) the pattern number; (4) the casting date; and (5) the shop assembler’s name or acceptable abbreviation (optional).

The National Board of Boiler and Pressure Vessel Inspectors also offers a training course for Authorized Inspectors.

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NOTE: Acceptable abbreviations to any of the stamp wording may be used. (1) Kilowatt power input for electric boilers. (2) May be omitted when year built is prefix to serial number (see HG-530.1). (3) For steam only boilers, MAWP Water and Maximum Water Temperature markings are optional. FIG. 18.16 STEAM AND WATER BOILERS (Source: Fig. HG530.2, Section IV of the ASME B&PV Code)

FIG. 18.17 BOILERS SUITABLE FOR WATER ONLY (Source: Fig. HG-530.3, Section IV of the ASME B&PV Code)

The following data, as shown in Figs. HG-530.6 and HG-530.7 (given here as Figs. 18.18 and 18.19, respectively), may be used to mark a completed cast-iron boiler by means of the Code Symbol H Stamp.

boiler is assembled by another party, in which case it is the Authorized Assembler who completes the Data Report, using the terms “Assembler” or “Assembly Organization” instead of “Manufacturer.” If welding on an assembly or subassembly is required, it is a heating-boiler Stampholder who performs the work, for which the Authorized Inspector performs the inspections needed to certify the boiler as having been constructed in accordance with Code requirements. The Assembler’s H Symbol Stamp is applied in the field and the Unit Manufacturer’s H Symbol Stamp is applied in the field only if the Certificate of Authorization reveals the use of the H Stamp in the field. The Authorized Inspector then signs the fieldinspection-certificate portion of the Data Report.

(1) The shop assembler’s name—to be inserted following the words “Certified by”; (2) the MAWP; (3) the safety- or safety relief-valve capacity, lb/hr or MBH; and (4) the maximum water temperature. 18.2.5.9 Stamping of Parts and Accessories Stamping is required for the parts and accessories for which Partial Data Reports have been furnished. The following markings are required on such parts and accessories: (1) the official Code Symbol, above the word “Part,” shown in Fig. 18.18; (2) the Parts’ Manufacturer’s name; and (3) the Parts’ Manufacturer’s serial number.

18.2.5.11 Field-Assembled Cast-Iron Boilers The Manufacturer shall complete the hydrostatic testing on each individual section or boiler part in accordance with paragraph HC-410 before their shipment for assembly in the field. He or she shall also provide the installer with printed instructions for the boiler’s mechanical assembly, including instructions for attaching the nameplate.

18.2.5.10 Field-Assembled Boilers and Boiler Parts There is more than one party involved in the completion of the unit in the field. For example, it is the Boiler Unit Manufacturer who completes the Manufacturer’s Data Report Form H-2 or H-3 unless the

18.2.5.12 The Code Symbol Stamp The ASME uses three Code Symbol Stamps—H, HLW, and HV, either individually or in combination—for the design, construction, and assembly of boilers and

FIG. 18.18 STEAM AND WATER BOILERS (Source: Fig. HG530.6, Section IV of the ASME B&PV Code)

FIG. 18.19 BOILERS SUITABLE FOR WATER ONLY (Source: Fig. HG-530.7, Section IV of the ASME B&PV Code)

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boiler parts in accordance with Section IV. If an organization qualifies as specified in paragraph HG-540, the ASME will issue the Certificate of Authorization and grant the use of the Code Symbol Stamp. It is important to note that the Certificate of Authorization and the three Code Symbol Stamps are all properties of the ASME. 18.2.5.12.1 Application Any organization interested in obtaining a Certificate of Authorization for one or more of the ASME Code Symbols must apply to the Society on the required prescribed forms. It is essential that a separate application be submitted for each plant where Code items are to be built. In addition, the organization is required to sign an agreement with an AIA for Code Inspection at each location; if approved, an administrative fee must be paid, after which a Certificate of Authorization and Code Symbol Stamp are issued to the qualified organization.11 The Certificate of Authorization for the H, HLW, and HV Symbols remains valid for three years; however, for the H Symbol used for cast-iron boilers, it remains valid for one year. An organization may apply for a renewal six months before the expiration date of the certificate. 18.2.5.12.2 Inspection Agreement The Manufacturer must have an inspection agreement signed with an AIA for providing inspection services. This agreement specifies the mutual responsibilities of the Manufacturer and the Authorized Inspectors. If any change or cancellation to the inspection agreement is made, the Manufacturer must notify the ASME. A Manufacturer of pressure relief valves or castiron-heating boilers is not required to have an inspection agreement. 18.2.5.12.3 Quality Control System A quality control system is a written document that establishes the compliance of all Code requirements for production. It describes authority and responsibility, organization, drawings, design calculations, specification and material control, examination and inspection programs, correction of nonconformities, welding, calibration of measurement and test equipment, sample forms, and the responsibilities of the Authorized Inspector. An example of a mandatory quality control system is shown in Appendix F of the Code. 18.2.6 Article 6: Instruments, Fittings, and Controls All instruments, fittings, mountings, controls, and safety devices are installed in the Manufacturer’s factory before shipment. In a fielderected boiler, these instruments, fittings, and controls are installed before its operation. Many jurisdictions have adopted ASME Code CSD-1, Controls and Safety Devices for Automatically Fired Boilers. Boilers installed within these jurisdictions shall meet the requirements of the CSD-1 Code within any operating period.

permissible water level in the boiler is recommended by the Boiler Manufacturer. To avoid overheating, the lowest visible part of the gage glass should be a minimum of 1 in. (25 mm) above the lowest water level. During fabrication, a boiler is permanently marked to indicate the lowest permissible water level. The water-gage glass of a submerged-type electric boiler shall indicate water levels at both the start-up time and under the maximum steam load. For a resistance element–type electric boiler, the lowest visible part of the water gage shall be located at a minimum of 1 in. above the lowest permissible water level; then, an automatic low-water fuel cutoff shall be installed on this boiler type so that the power supply is automatically cut off before the water level falls below the visible part of the glass. 18.2.6.1.3 Water Column A water column has two connections: the steam connection, which is taken from the top of the shell, and the water connection, which is taken from a point below the centerline of the shell. The size of the pipe connecting a water column to the boiler should be a minimum of 1 in. (25 mm), and the water column drainpipe should be a minimum of NPS 43(DN 20). 18.2.6.1.4 Pressure Control Two pressure-operated controls are used to protect a steam boiler from overpressure. A safetylimit control is used to cut off the fuel supply by preventing the steam pressure from exceeding 15 psi (103 kPa) MAWP. A second control cuts off the fuel supply if pressure reaches the operating limit, which is less than the MAWP. The minimum connection size is NPS 14 (DN 10) except for steel, in which it is NPS 43 (DN 15). 18.2.6.1.5 Low-Water Fuel Cutoff An automatic low-water fuel cutoff is required to be installed on all boilers to cut off the fuel supply when the water level falls below its lowest permissible level. A waterfeeding device, if installed, should supply the required feedwater. A low-water fuel cutoff and a waterfeeding device may be attached to a boiler. 18.2.6.1.6 Modular Steam-Heating Boilers A steam-heating assembly consisting of a group of individual steam boilers called modules is intended to be installed as a unit with no intervening stop valves. Modules may be under one jacket or may be individually jacketed. The individual modules shall be limited to a maximum input of 400,000 Btu/hr (117, 228 W) for gas, 3 gph (11.4 L/h) for oil, and 115 kW for electric. A pressure control is required to be installed on an assembled modular steam-heating boiler. Each module of this boiler type has a steam gage, a water-gage glass, a pressure control, and a lowwater fuel cutoff.

18.2.6.1 Steam-Heating Boilers 18.2.6.1.1 Steam Gages A steam gage or a compound steam gage is required to be installed on all steam-heating boilers. The gage or piping to the gage contains a siphon to maintain a water seal by preventing steam to enter into the gage tube. This gage connection should be a minimum of NPS 21 (DN 15), and the scale on the dial of the gage shall be a minimum of 30 psi (207 kPa) and a maximum of 60 psi (414 kPa).

18.2.6.2 Hot-Water-Heating and Hot-Water-Supply Boilers 18.2.6.2.1 Pressure or Altitude Gage A pressure or altitude gage installed on a hot-water-heating or on a hot-water-supply boiler may be shut off by a cock with a tee or lever handle. The range on the gage dial shall be 112 312 times the safety-valve set pressure, and the connection size shall be less than NPS 1 (DN 25) if a nonferrous metal is used.

18.2.6.1.2 Water-Gage Glass One or more water-gage glasses are required to be installed to the water column or boiler by means of valve fittings of a minimum size of NPS 12 (DN 15). The lowest

18.2.6.2.2 Thermometer A thermometer for indicating the boiler water temperature is required to be installed on both a hotwater-heating and hot-water-supply boiler.

11

Application forms, as well as related information and instructions, may be obtained by writing to the Secretary, the ASME Boiler and Pressure Vessel Committee, 3 Park Avenue, New York, NY 10016.

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18.2.6.2.3 Temperature Control Two temperature-operated controls are used on a hot-water-heating or hot-water-supply boiler for protecting it from overtemperature: One is a high-temperature-limit control, which cuts off the fuel supply by preventing the water temperature from reaching its maximum temperature at the boiler outlet, whereas the other is a second temperature control, which cuts off the fuel supply when the temperature reaches its operating temperature (which is less than the maximum water temperature). 18.2.6.2.4 Low-Water Fuel Cutoff An automatic low-water fuel cutoff designed for hot-water service is required to be installed on a hot-water boiler with more than 400,000 Btu/hr heat input (117 kW) to cut off the fuel supply when the water level falls below its permissible level. The Manufacturer establishes a safe, permissible water level that could be at any location, as there is no normal waterline for a hot-water boiler. A flow-sensing device may be used for a coil-type boiler of a watertube-forcedcirculation-type boiler with more than 400,000 Btu/hr heat input. This sensing device cuts off the fuel supply when the circulating flow is interrupted. 18.2.6.2.5 Modular Hot-Water Boilers A hot-water-boiler assembly consisting of a group of individual hot-water boilers called modules is intended to be installed as a unit with no intervening stop valves. Modules may be under one jacket or may be individually jacketed. The individual modules shall be limited to a maximum input of 400,000 Btu/hr (117,228 W) for gas, 3 gph (11.4 L/h) for oil, and 115 kW for electric. A modular hot-waterheating boiler is required to be installed with a temperature control and a low-water fuel cutoff. Each module of this boiler type has a pressure-altitude gage, a thermometer, and a temperature control. 18.2.6.3 All Boilers 18.2.6.3.1 Instruments Mounted Inside Jackets Instruments, fittings, and controls may be mounted inside the boiler jackets if the water gage, pressure gage, and thermometer are all visible through openings. 18.2.6.3.2 Electrical All electrical wiring, controls, heat-generating apparatuses, and other boiler appurtenances shall be installed in accordance with the requirements of the National Electrical Code (NFPA) 70, published by the National Fire Protection Association, or with any nationally recognized standards and/or local jurisdictional electrical codes. Examples of nationally recognized standards are the following: • The American National Standards Institute (ANSI) Z21.13, Gas-Fired Low-Pressure Steam and Hot-Water Boilers • The Underwriters Laboratories (UL) 296, Standards for Safety, Oil Burners • The Underwriters Laboratories (UL) 726, Standards for Safety, Oil-Fired Boiler Assemblies • The Underwriters Laboratories (UL) 834, Electric Heating, Water Supply, and Power Boilers 18.2.6.3.3 Shutdown Switches The main shutdown switch or circuit breaker, which may be located outside the boiler room door, should be clearly marked for identification. 18.2.6.3.4 Safety Controls Primary safety (or flame-safeguard) controls, safety-limit switches, and burners or electric elements used on boilers should conform with nationally recognized standards.

18.2.7

Article 7: Installation Requirements

Heating boilers may be installed in accordance with the following Codes: • American National Standards Institute (ANSI) Z21.13, GasFired Low-Pressure Steam and Hot-Water Boilers • The National Fire Protection Association (NFPA) 31, Installation of Oil-Burning Equipment • The National Fire Protection Association (NFPA) 54, FuelGas Code • The Underwriters Laboratories (UL) 834, Electric Heating, Water Supply, and Power Boilers 18.2.7.1 Mounting Safety Valves Safety and safety-relief valves are required to be directly connected to an opening in the boiler or to a header connecting steam or water outlets on the boiler. They should be located on the highest practical part of the boiler. No shutoff valve is allowed to be installed between the safety or safety-relief valves and the boiler or on the discharge pipes between such valves and the atmosphere. 18.2.7.1.1 Discharge Piping A discharge pipe, which should be as short and straight as possible, is used at the outlet of the safety or safety-relief valve for discharging steam or water. The crosssectional area of the discharge pipe shall be not less than the full area of the valve outlet. In addition, the discharge from the safety or safety-relief valves should be piped away from the boiler to a safe point and drained properly. 18.2.7.1.2 Temperature-and-Pressure (T&P) Safety-Relief Valve A temperature-and-pressure (T&P) safety-relief valve is used on hot-water-heating or hot-water-supply boilers limited to a water temperature of 210F (99C). This valve should be mounted directly onto the boiler and may be installed in the horizontal position with the outlet (including the discharge pipe) pointed down. 18.2.7.2 Piping A pipe expands with the application of heat and contracts when in contact with cold fluid. Provisions should be made for enough expansion and contraction of steam and water piping connected to the boilers. The piping should be provided with sufficient anchorage at suitable points and swing joints to avoid the transmission of strain to the boilers. The return piping should form a loop so that water cannot be forced out below the safe water level. A provision should also be made for cleaning the interior of the return piping close to the boiler. A typical piping installation is shown in Fig. HG-703.2, given here as Fig. 18.20. 18.2.7.3 Feedwater Connections Feedwater for a steam boiler should be introduced through an independent connection or return piping. It should not be discharged directly onto any boiler parts exposed to heat from the furnace. A check valve shall be installed on the feed-water line near the boiler, and a stop valve shall be installed between the check valve and the boiler or between the check valve and the return pipe systems. Make-up water is normally added to hot-water boilers; it should be introduced through an independent connection or piping system and should not be discharged directly onto boiler parts exposed to direct heat. A check valve should be installed on the makeup-water line near the boiler, and a stop valve shall be installed between the check valve and the boiler or between the check valve and the piping system.

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FIG. 18.20 HOT-WATER BOILERS IN BATTERY—ACCEPTABLE PIPING INSTALLATION (Sorce: Fig. HG-703.2, Section IV of the ASME B&PV Code)

18.2.7.4 Oil Heaters An oil heater is used to preheat the oil before it enters the burner. It is important for a means to be installed to prevent the introduction of oil into the boiler feedwater system, as it is harmful for boiler operation. No oil heater should be installed in the steam or water space of a boiler. 18.2.7.5 Storage Tanks A water-storage tank is used when the capacity of a hot-water-supply system is more than 120 gal. It may be designed under Section VIII, Division 1, or under Section X. Figure HLW-809.1 shows a typical installation of water-storage tank. 18.2.7.6 Expansion Tanks An expansion tank, which may be of the open or closed type, is used to provide thermal expansion in hot-water systems. An indoor overflow from the upper part of the open-type expansion tank is provided and connected to a drain. A closed-type expansion tank of the proper size is installed to handle the system capacity. The minimum capacity of the closed-type expansion tank may be determined from Tables HG-709.1 and 12

HG-709.2. In addition, the minimum capacity may be determined by the following formula:12 Vt  [(0.00041T 0.0466)Vs] [(Pa Pf ) (Pa Po) where Vt  the minimum volume of the tank, gal Vs  the volume of the system, not including tank T  the average temperature, F Pa  the atmospheric pressure, psia Pf  the fill pressure, psia Po  the maximum operating pressure, psia For system pressure of more than 30 psi (207 kPa), an expansion tank is required to be constructed in accordance with Section VIII, Division 1, or with Section X. If the working pressure for the system is 30 psi (207 kPa) or less, the expansion tank should be designed for a hydrostatic test pressure of 75 psi (517 kPa). An

The same formula is referenced in Section 1009 of the International Mechanical Code, published by the International Code Council, 5203 Leesburg Pike, Suite 708, Falls Church, VA 22041.

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airtight expansion tank is installed if a hot-water-supply system is equipped with a check valve or pressure-reducing valve in the cold-water inlet line.

Part HF has two subparts: Subpart HW, applicable to heating boilers fabricated by welding, and Subpart HB, applicable to heating boilers fabricated by brazing.

Example A closed-expansion tank has to be constructed for a hotwater-heating system pressure of 50 psi. What would be the Construction Code for the expansion tank? (See paragraph HG-709.) For system pressure of more than 30 psi, an expansion tank is required to be constructed in accordance with Section VIII, Division 1, or to Section X.

18.3.2

18.2.7.7 Stop Valves A stop valve should be located on both the supply and return lines as near to the boiler as possible. If the boiler is located above the system and can be drained without also draining the system, a stop valve is not required. The minimum pressure rating of a stop valve should be at least equal to the pressure stamped on the boiler, and the temperature rating should not be less than 250F (121C). This stop valve is properly designated by a tag of metal or other material fastened to the valve. 18.2.7.8 Blowoff and Drain Valves A bottom-blowoff connection fitted with a valve is required to be installed on a steam boiler’s lowest water space. (Table HG-715 shows the size of bottomblowoff piping, valves, and cocks.) However, a blowoff valve is not required for a boiler with a capacity not exceeding 25 gal (95 L). One or more drain connections fitted with valves or cocks are required to be connected to the lowest water-containing spaces of a steam or hot-water boiler. The drain valve and piping size should be a minimum of 34 in. (19 mm).13 The minimum pressure rating for blowoff valves and cocks is required to be at least equal to the pressure stamped on the boiler or a minimum of 30 psi (207 kPa), and the minimum temperature rating for such valves and cocks should be 250F (121C). 18.2.7.9 Modular Boilers A modular boiler is assembled in the field and consists of individual modules manifolded together without any intervening valves. The capacity of each individual module should not exceed 400,000 Btu/hr for gas, 3 gal/hr (11 L/hr) for oil, and 115 kW for electricity. An assembled, modular steam-heating boiler should be fitted with a feedwater connection and a return pipe connection. Each module of a steam-heating boiler should also have a safety valve, blowoff valve, and drain connection. An assembled, modular hotwater-heating boiler should be fitted with a make-up water connection and should have provisions made for thermal expansion and stop valves. Each module of a hot-water-heating boiler should have a safety-relief valve

18.3

PART HF: REQUIREMENTS FOR BOILERS CONSTRUCTED OF WROUGHT MATERIALS

18.3.1

Article 1: General

There are special rules for heating boilers constructed primarily of wrought materials. These rules in Part HF are applicable to steamheating boilers, hot-water-heating boilers, and hot-water-supply boilers constructed of wrought materials. The general requirements of Section IV, Part HG may also be applied to these boilers. 13

Article 2: Material Requirements

Materials described in Article 2 are used for heating boilers constructed primarily of wrought materials. The use of new material requires the approval from the ASME B&PV Committee. 18.3.2.1 Plate If plate is used for the construction of pressure parts, a material test report is required to verify that the chemical and mechanical properties are within the range allowed in Section II. The stress values of plate material shall conform to the stress values shown in Tables HF-300.1 and HF-300.2. Stainless-steel plates, SA-240, may be used for the construction of hot-waterheating boilers if the material is fully annealed and the water temperature is at a maximum of 210F (99ºC). 18.3.2.2 Rods, Bars, and Shapes If rods, bars, and shapes are used for the construction of pressure parts, they must conform to the specifications in Section II and be limited to those listed in Tables HF-300.1 and HF-300.2. Rods, bars, and shapes may be used for nonpressure parts if their structural quality conforms to the specifications of Section II. 18.3.2.3 Prefabricated Parts The Manufacturer (other than the Boiler Manufacturer) may supply prefabricated or preformed parts. With these parts, the Manufacturer is required to conform to the Code requirements, including those for shop inspection and the furnishing of Partial Data Reports. 18.3.2.3.1 Standard Pressure Parts Standard pressure parts, such as valves, flanges, and nozzles, may be formed by casting, forging, or die-forming. They shall be made of materials permitted under Section II or under ANSI- or Code-accepted standards, and neither an inspection nor the submittal of a mill test report or Partial Data Report is required. The standard pressure parts are marked with the Manufacturer’s name and trademark, as well as other markings required by the standards. 18.3.2.3.2 Nonstandard Pressure Parts Nonstandard pressure parts, such as shells, heads, and removable cover plates, may be formed by casting, forging, rolling, or die-forming. They shall be made of materials permitted under Section II, and the Manufacturer must submit mill test reports. The nonstandard parts are marked with the Manufacturer’s name and trademark, as well as other markings, to identify the parts. 18.3.2.4 Pipes and Tubes Pipes and tubes used in boiler construction may be of seamless or welded construction. They are required to conform to the specifications given in Section II and to the stress values in Tables HF-300.1 and HF-300.2. 18.3.2.4.1 Integrally Finned Tubes Integrally finned tubes may be constructed from the tubes that conform to the specifications given in Section II. The maximum allowable stress values for this tube shall conform to the stress values given in Tables HF-300.1 and HF-300.2.

The National Board of Boiler and Pressure Vessel Inspectors’ Manual NB-27, Rules and Recommendations for the Design and Construction of Boiler Blowoff Systems, provides information about blowdown or blowoff equipment.

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18.3.2.4.2 Stainless-Steel Tubes Stainless-steel tubes may be used in the construction of hot-water-supply boilers. The degree of wall thickness of these tubes subject to any internal or external pressure may be determined by the formulas in Part HG. The minimum tube thickness shall be 0.035 in. (0.89 mm).

allowable thickness of nonferrous shell plates, tubesheets, and heads for various shell diameters is given in Table HF-301.2.

18.4

18.3.2.5 Unidentified Materials Unidentified materials may be used for construction if acceptance tests are performed on them and the results are satisfactory.

PART HF, SUBPART HW: REQUIREMENTS FOR BOILERS FABRICATED BY WELDING

18.4.1

Article 4: General Requirements

18.3.2.5.1 Acceptance by Test Record An authenticated test record and marking should be submitted for chemical and mechanical properties within the range permitted in Section II. The Authorized Inspector may ask for additional tests if the authenticcated test record is considered insufficient.

A boiler may be fabricated by welding or brazing. The rules in Part HF, Subpart HW are applicable for steam-heating, hot-waterheating, and hot-water-supply boilers in addition to their parts fabricated by welding. Because the construction method of the boiler is welding, all applicable rules of welding in the ASME Code are used during the fabrication of the boiler.

18.3.2.5.2 Acceptance by Testing Chemical analysis and mechanical tests are required for plates, as well as two tension tests and two bend tests. The Authorized Inspector will decide if the carbon and manganese contents obtained by analysis are acceptable. To meet the requirements of the permitted specifications, the chemical analysis and sufficient mechanical tests are done on each length of tube, pipe, rod, bar, and shape. However, sufficient tests are also performed to satisfy the requirements of the Authorized Inspector. 18.3.2.5.3 Marking and Test Reports Once the material’s identity is established, each piece of the material is marked to the satisfaction of the Authorized Inspector. A report called the “Report on Tests of Nonidentified Material” is completed and certified by the Manufacturer or testing agency. When it is accepted by the Authorized Inspector, this report will act as the authority to permit the use of the material. 18.3.2.6 Maintaining Material Identification Material used for pressure parts must carry identification markings at all times. When such material is divided into pieces, the original markings should be transferred to these pieces. At the same time, materials may be identified by any method acceptable to the Authorized Inspector.

18.3.3

Article 3: Design Stresses and Minimum Thickness

The maximum stress value for material is used for calculations of boiler design. The maximum allowable stress values for ferrous and nonferrous materials are given in Table HF-300.1 (given here as Table 18.5) and Table HF-300.2. 18.3.3.1 Minimum Thickness The minimum thickness is calculated on all pressure parts to ensure that the materials can withstand the pressure for which they are designed. 18.3.3.1.1 Ferrous Plates The minimum thickness of any ferrous plate used under pressure shall be 41 in. (6 mm). If any pipe is used instead of a plate, the pipe’s thickness shall also be 41 in. (6 mm). Exception to the minimum thickness is permitted in paragraphs HF-301.1(c) and (d). The minimum allowable thickness of ferrous shell plates, tubesheets, and heads for various shell diameters, is given in Table HF-301.1. 18.3.3.1.2 Nonferrous Plates For any nonferrous plate under pressure, the minimum thickness shall be 18 in. (3.2 mm) for cop3 per admiralty and 32 in. (2.4 mm) for copper-nickel. The minimum

18.4.1.1 Manufacturer’s Responsibility The Manufacturer or contractor is held responsible for the welding done on the boiler. The Manufacturer must also have welding procedures established that comply with the requirements of Section IX. In addition to qualifying the welding procedures required for boiler construction under Section IV, the Manufacturer is responsible for the performance tests of welders and welding operators who apply the welding procedures.

18.4.2

Article 5: Material Requirements

Materials used for pressure parts are required to conform to the specifications given in Section II. The stress values of such materials should conform to the values given in Tables HF-300.1 and HF 300.2. Materials for welding grouped as P-numbers can be seen in Tables HF-300.1 and HF-300.2, and the assigned P-numbers are found in Section IX. Other requirements are the following: • The carbon content in carbon or alloy steel should not be more than 0.35% • The plates should not be shaped by oxygen-cutting or other thermal-cutting process • The stud materials should not contain more than 0.27% carbon with a minimum tensile strength of 60,000 psi (410 MPa) 18.4.2.1 Different Specifications Requirements of Section IX are applicable when two materials for construction are welded. Two different materials of different specifications are welded in accordance with the requirements of paragraph QW-251.2 of Section IX. 18.4.2.2 Small Parts Small parts, such as pipe fittings and welding caps, may be used as standard pressure parts when they are formed by casting, forging or die-forming. Such parts should be of good weldable quality for construction use.

18.4.3

Article 6: Welding Processes and Qualifications

The welding processes described in Section IX are used for the construction of boilers. However, not all of these welding processes are permitted to be used on boiler fabrication. The following processes may be used for the welding of pressure and non-pressure parts: (1) Arc or Gas Welding, processes that are limited to shielded metal–arc, submerged-arc, gas metal–arc, gas tungsten-arc, plasma-arc, atomic hydrogen metal-arc, and oxyfuel-gas welding.

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TABLE 18.5

MAXIMUM ALLOWABLE STRESS VALUES FOR FERROUS MATERIALS, KSI (MULTIPLY BY 1,000 TO OBTAIN PSI) (Source: Table HF-300, 1, Section IV of the ASME B&PV Code)

(2) Pressure Welding, processes that are limited to flash, induction, resistance, pressure-thermit, pressure-gas, and inertia and continuous drive-friction welding. 18.4.3.1 Welding Qualifications The requirements of Section IX are applied to qualify the welding process, the welders, and the welding operators. Welding on pressure parts and the joining of nonpressure parts to pressure parts are done by Section

IX–qualified welders and welding operators using Section IX–qualified procedures. 18.4.3.2 Production Work Production work is undertaken if the welding procedures, the welders, and the welding operators have been qualified in accordance with the requirements of Section IX. Welding may be performed within the first 3 ft (0.9 m) of the first production weld if the welders are qualified as specified

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TABLE 18.5

in Section IX, paragraph QW-304, and the welding operators are qualified as specified in Section IX, paragraph QW-305. 18.4.3.3 Interchanging Qualifying Tests The Manufacturer or contractor is responsible for performance qualification tests of the welders and welding operators employed by his or her organization.

(CONTINUED)

However, the performance tests conducted by one Manufacturer or contractor do not qualify a welder or welding operator to work for any other Manufacturer or contractor. 18.4.3.4 Maintenance of Records A complete record of qualifications and identifying marks will be maintained by the

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TABLE 18.5

Manufacturer or contractor. This record includes the welding procedures and the welders and welding operators employed by the Manufacturer, the date and results of the test, and the identification marks assigned to each welder. The records are certified by the Manufacturer and made available to the designated Authorized

(CONTINUED)

Inspector. The welder or welding operator also stamps his or her identification mark on or adjacent to all welding joints. As an option, the Manufacturer may keep a record of all the welded joints and the names of the welders and welding operators whoperformed the welding of these joints.

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TABLE 18.5

(CONTINUED)

All welds shall be made to ensure satisfactory penetration and fusion into the base metal to the root of the weld. In addition, all members should be properly prepared, fitted, aligned, and retained in the position in accordance with the specifications of the welding procedures.

another pressure part. In a like manner, the butt joint should be double-welded, or filler-metal may be added from one side to make the weld penetration complete, with reinforcement on both sides of the joint. If the plates are of unequal thickness, butt welding may be performed as illustrated in Fig. HW-701.1. The welding joint may be in the tapered section or adjacent to it.

18.4.4.1 Butt Joints A butt joint—longitudinal, circumferential, or other type—used for welding plates of a drum, shell, or

18.4.4.2 Lap Joints If the welding joint is not in direct contact with the products of combustion, a lap joint may be used for

18.4.4 Article 7: Design of Weldments

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TABLE 18.5

longitudinal or circumferential joints for welding plates of a shell. The lap joint should be of full-fillet weld both inside and outside, with the throat a minimum of 0.7 times the thickness of the thinner plate and the length of the overlap a minimum of 4 times the thickness of the thinner plate. 18.4.4.3 Corner or Tee Joints A corner or tee joint with singlefull-fillet weld may be used for a boiler designed for a maximum of 30 psi (207 kPa). The throat of the fillet weld should be a minimum of 0.7 times the thickness of the thinner plate. Also, a corner or tee joint with double-full-fillet or full-penetration weld should be used for a hot-water boiler designed for more than 30 psi (207 kPa). Some forms of attachments of pressure parts to flat plates to form a corner (or tee) joint are shown in Fig. HW-701.3. 18.4.4.4 Joint Efficiencies The joint efficiency, E, is used in the formulas of paragraphs HG-301 and HG-305 to calculate the minimum thickness and design pressure of boiler parts under internal pressure. However, E is not required when the boiler parts are designed only under external pressure. The following joint efficiencies, E, are used for the welding of joints by arc- or gas-welding processes: (1) E  85% for full-penetration double-welded butt joints. (2) E  80% for full-penetration single-welded butt joints with backing strips. (3) E  60% for single-welded butt joints without backing strips. (4) E  65% for double-full-fillet lap joints for boilers designed for a minimum of 30 psi. (5) E  49% for double-full-fillet lap joints for boilers designed for a maximum of 30 psi.

(CONTINUED)

18.4.4.5 Welded Stays 18.4.4.5.1 Horizontal Stays The horizontal stays are inserted through holes; the clearance between these holes and the stays 1 should be a maximum of 16 in. (1.6 mm). Also, the ends of the stays should be clearly visible and not project more than 38 in. (10 mm) beyond the surfaces. 18.4.4.5.2 Diagonal Stays Diagonal stays are attached to the inner surfaces of the shell by fillet welds. Examples of diagonal stays for installations by welding are shown in Figs. HW-710.4(a) and (b). 18.4.4.6 Heads and Tubesheets 18.4.4.6.1 Flanged Heads or Tubesheets An outwardly or inwardly flanged head or tubesheet may be attached to the shell by fillet welding if the head or tubesheet is supported by tubes,braces, or a combination of both. While an outwardly flanged head or tubesheet is attached, the welding joint should be completely within the shell. However, inwardly flanged heads or tubesheets should be full fillet-welded both inside and outside. The throats of the full-fillet welds should be a minimum of 0.7 times the thick ness of the head or tubesheet. 18.4.4.6.2 Unflanged Heads or Tubesheets Unflanged heads or tubesheets may be attached to the shell by welding if they are supported by tubes, braces, or a combination of both. The weld for boilers of more than 30 psi (207 kPa) should be of the fullpenetration or double-full-fillet variety. 18.4.4.7 Furnace Attachments 18.4.4.7.1 For Boiler Pressure  30 Psi A furnace or crown sheet may be attached to the head or tubesheet with a full-fillet

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weld if the furnace does not extend beyond the outside face of the head or tubesheet for a distance that is greater than the head thickness. The throat of the full-fillet weld should be minimum of 0.7 times the head or tubesheet thickness.

requirements of paragraph HW-731. Some acceptable types of welds for fittings, nozzles, and other connections to shells, drums, and headers are shown in Fig. HW-731. The following symbols are used in Fig. HW-731 for describing such attachment welds:

18.4.4.7.2 For Boiler Pressure  30 Psi A furnace or crown sheet in a hot-water boiler may be attached to a head or tubesheet by a fullpenetration weld, provided the sheet extends through the minimum of the full thickness of the head or tubesheet. When exposed to primary gases, the furnace or crown sheet projections will not extend beyond the face of the plate by more than 38 in. (10 mm).

t  the nominal thickness of the boiler shell or head, in. tn  the nominal thickness of the nozzle wall, in. tw  the dimension of the partial-penetration attachment welds, in. tc  not less than the smaller of 14 in. (6 mm) or 0.7tmin tmin  the smaller of 43 in. (19 mm) or the thickness of the thinner of the parts joined by a fillet, single-bevel, or single-J-weld, in. t1  t2  not less than the smaller of 14 in. (6 mm) or 0.7tmin, and t1  t2 not less than 114 tmin

18.4.4.8 Tube Attachments Welding may attach the tubes to the tubesheet. However, the projection of the tubes beyond the tubesheet will not exceed a distance equal to the tube thickness. The firetube extension through the tubesheets for welded construction is shown in Table HW-713, and a maximum projection of 1 2 in. (13 mm) is allowed for the watertube extension. 18.4.4.9 Head-to-Shell Attachments The head forms— ellipsoidal, torispherical, and hemispherical—that are concave or convex to the pressure side may be welded to the shell in accordance with Fig. HW-715.1, given here as Fig. 18.21. A skirt is not required if the head thickness does not exceed 114 times the shell thickness; if it does exceed that amount, a skirt with a length of not less than 3 times the head thickness or 112 in. (38 mm)—whichever is less—must be provided. For formed heads of full hemispherical shape that are concave to the pressure side, an integral skirt is not required. The flanged ellipsoidal and torispherical heads that are convex to the pressure side may be welded to the shell with a full-fillet weld containing a throat not less than 0.7 times the head thickness. 18.4.4.10 Attachment Welds Nozzles, fittings, and other connections may be welded to shells, drums, and headers. The location and minimum size of attachment welds should conform to the

FIG. 18.21

18.4.4.11 Resistance Welding Resistance welding is applicable for carbon-steel joints (other than butt joints) and hydraulically formed panels. Two types of resistance welding are used for the construction of embossed or dimpled assemblies: resistance-spot welding and resistance-seam welding. The construction consists of joining two sheets of metals together by applying either of these welding types. Resistance welding may be used for carbon steels SA-285, SA-620, and SA-414, each with a carbon content of not more than 0.15%. The welding process, proof test, work-manship samples, machine settings and controls, pressure tests and inspections, and any recordkeeping must be done in accordance with paragraphs HW-740 and HW-745 and Figs. HW-740 and HW-745.

18.4.5

Article 8: Fabrication Requirements

18.4.5.1 Forming Plates The longitudinal joints of boiler shells are formed from plates, the ends of which are formed to the proper curvature by pressure, not by sledging.

HEADS ATTACHED TO SHELLS (Source: Fig. HW-715.1, Section IV of the ASME B&PV Code)

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18.4.5.2 Base-Metal Preparation Base metals must be prepared for joints by machining, thermal cutting, chipping, grinding, or a combination of these methods before welding. Mechanical and metallurgical properties of the base metal should not be destroyed if the thermal-cutting method is used. Before welding, cast surfaces should be machined, chipped, or ground properly and also be free from all scale, rust, oil, grease, and other foreign material. 18.4.5.3 Assembly Parts to be welded are properly fitted, aligned, and retained in position during the welding operation. Bars, jacks, clamps, or tack welds may be used to hold the edges of parts, and alignment tolerance should be maintained. 18.4.5.4 Alignment Tolerance The edges of the plates for a butt joint should not be offset from each other by more than the amounts noted in the following table, where t is the plate thickness: Direction of Joints in Cylindrical Vessels Plate Thickness (In.) … 7

1 2 1 2

-

3 4

Over 7

3 4

Longitudinal 1 4t 1 8 in. 1 8 in.

Circumferential 1 4t 1 4t 3 16 in.

Tack welds may be used to secure the alignment. To incorporate these into the final weld, tack welds should be removed completely or prepared properly by grinding or other suitable means. In addition, tack welds should be made by a fillet-weld or buttweld procedure qualified in accordance with Section IX. If the tack welds need to be left in place, they should be made by welders qualified in accordance with Section IX and be inspected visually for defects. 18.4.5.5 Distortion The cylinder of a drum or shell subjected to internal pressure should be circular at any section within a limit of 1% of the mean diameter. Suitable methods, such as reheating, rerolling, or reforming, may be used to make a distorted cylinder circular. Likewise, cylindrical parts subjected to external pressure should be circular with a maximum deviation of not more than 41 in. (6 mm) from a true circle. 18.4.5.6 Specific Welding Requirements 18.4.5.6.1 Longitudinal and Circumferential Joints Finished butt-welded joints should have complete penetration and fusion. The surface may be left as welded if the weld is free of ripples, grooves, overlaps, abrupt ridges, and valleys. The welding process should not reduce the thickness by more 1 than 32 in. (0.8 mm) or 10% of the nominal thickness of the adjoining surface, whichever is less. For double-welded butt joints, the root is prepared by suitable methods including chipping or grinding before the weld metal on the second side is applied for welding. 18.4.5.6.2 Fillet Welds Adequate penetration into the base metal at the root of the weld will be obtained while making fillet weld. The thickness of the base metal will not be reduced because of the welding process. 18.4.5.6.3 Stud Welding There are two types of stud-welding processes: arc-stud welding and resistance-stud welding. If stud

welding is used for attaching load-carrying studs, a productionstud-weld test of the procedure and the welding operator is performed on five studs, each welded and tested in accordance with the requirements of Section IX. Procedure and performance qualification tests are also made in accordance with Section IX. If stud welding is used for joining non–pressure-bearing attachments to pressure parts by an automatic welding process in accordance with a welding procedure specification complying with Section IX, procedure and performance qualification testing is not required. If stud welding is used to attach non-load-carrying studs, the Manufacturer will specify a production-weld test to be performed. 18.4.5.6.4 Welding by Noncertificate Holders The Manufacturer is the holder of the Certificate of Authorization. He or she may use welders (including brazers) and welding and brazing operators not employed by him or her if (1) the Manufacturer takes responsibility of all Code construction; (2) all welders are qualified by the Manufacturer in accordance with Section IX; (3) all welding is performed in accordance with the Manufacturer’s Section IX–qualified welding procedure specifications; (4) the Manufacturer’s quality control system includes the supervision of welders, the termination of welders, and the assigning of identification symbols to welders; and (5) the Manufacturer is responsible for Code Symbol Stamping and completing the Data Report Forms. 18.4.5.7 Welding-Defect Repairs Welding defects, such as cracks, pinholes, and incomplete fusion, shown during leakage tests should be repaired. They must be removed by mechanical means or by thermal-grooving processes. Once the defects are removed, the joint is re welded and reexamined. 18.4.5.8 Post–Hydrostatic Test Sometimes nonpressure parts are required to be welded to the pressure parts after the final hydrostatic test. If nonpressure parts other than insulation-attachment pins are welded to the pressure parts after the hydrostatic test, the following requirements shall apply: (1) the welding is limited to P-No. 1 materials; (2) the attachments are made by stud welding or fillet welds and the throat does not exceed the lesser of 1.5 times the thickness of the pressure part or 14 in. (6 mm); (3) the completed weld is inspected by the Authorized Inspector; and (4) the Manufacturer’s Data Report Form is signed after completion of the welding. An inspection by the Authorized Inspector is not required if insulation-attachment pins are stud-welded to pressure parts after the hydrostatic testing. A production-stud-weld test is also not required. Insulation-attachment pins should have a diameter of not more 3 than 50% of the plate thickness or 16 in. (4.8 mm), whichever is less. They must be installed before applying the Code Symbol Stamp and signing the Manufacturer’s Data Report.

18.4.6

Article 9: Inspection

The Authorized Inspector designates the stages of inspection during the fabrication of the boiler and other pressure parts. A hold point, known as the inspector’s inspection point, is recorded in a document called a Traveler or Process Sheet. The Manufacturer offers the boiler or pressure part for inspection at the hold

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point. Fabrication work cannot resume without the Authorized Inspector releasing the hold point.

18.5.3

18.4.6.1 Welding Procedure Qualifications The Authorized Inspector should be satisfied that the welding procedures used in fabrication have been qualified in accordance with Section IX. Documents complying with the requirements of the Code are submitted to the Authorized Inspector by the Manufacturer. The Authorized Inspector may call for and witness the test welding and testing at any time.

18.5.3.1 Brazing Processes Brazing processes are classified by the method of heating used. The following are permitted brazing processes:

18.4.6.2 Performance Qualifications The Authorized Inspector should be satisfied that welding performed by welders or welding operators is qualified in accordance with Section IX. As with welding procedure qualifications, the Manufacturer makes available to the Authorized Inspector the record of performance qualification testing as required by the Code, and the Authorized Inspector may call for and witness the test welding and testing at any time.

18.5

PART HF, SUBPART HB: REQUIREMENTS FOR BOILERS FABRICATED BY BRAZING

18.5.1

Article 10: General Requirements

The provisions of Subpart HB are applicable to steam-heating boilers, hot-water-heating boilers, hot-water-supply boilers, and the parts of these boilers that are fabricated by brazing. 18.5.1.1 Manufacturer’s Responsibility The Manufacturer or contractor is responsible for the brazing done on a boiler and pressure part. He or she establishes the procedures and conducts the tests to qualify the brazing procedures in accordance with Section IX. The Manufacturer also conducts performance tests of brazers and brazing operators to determine their ability to carry out brazing as required by the Code.

18.5.2

Article 11: Materials Requirements

The materials to be used for construction should be of brazing quality, have brazing-filler metal, and conform to the specifications in ASME Section II. Only materials with allowable stress values as noted in Table HF-300.1 and Table HF-300.2 are allowed. 18.5.2.1 Dissimilar Materials Combinations of brazing-quality dissimilar metals may be joined by brazing. Such brazing will meet the requirements of Section IX. 18.5.2.2 Filler Metals The brazing-filler metal is selected based on the suitability for the base metals. Filler metal is suitable if the brazing procedure qualification is satisfactory in accor dance with Section IX. Filler metals not listed in Section II, Part C, SFA-5.8 should be qualified separately for both procedures and performance qualification in accordance with Section IX. 18.5.2.3 Fluxes and Atmospheres Fluxes, atmospheres, or a combination of both may be used to prevent oxidation. The flux and/or atmosphere are considered suitable for use if the brazing procedure qualification is satisfactory in accordance with Section IX.

• • • • •

Article 12: Brazing Processes, Procedures, and Qualifications

Torch brazing Furnace brazing Induction brazing Electrical-resistance brazing Dip brazing (salt-and-flux bath)

18.5.3.2 Brazing Procedures A brazing procedure is required for each type of joint. The brazing sequence is recorded on the drawing if there is more than one joint in a brazed assembly. Form QB-480 of Section IX is recommended for recording brazing procedures. Welding and brazing may be done on the same assembly if required, in which case welding should precede brazing so that the welding heat does not affect the braze to be made. 18.5.3.3 Brazing Qualifications 18.5.3.3.1 Procedure Qualification Each procedure used for fabrication is required to be qualified in accordance with Section IX. The Manufacturer conducts the required tests for qualifying all brazing procedures. 18.5.3.3.2 Qualification of Brazers It is the Manufacturer’s or contractor’s responsibility to conduct tests for brazers and brazing operators. Brazers that use manual brazing are required to passthe tests as required by Section IX. Likewise, brazing operatorswho use automatic means or use furnace, induction, electrical-resistance, or dip brazing are required to pass the tests as required by Section IX. 18.5.3.3.3 Production Work Production work is undertaken after both the brazing procedure and the brazers or brazing operators have been qualified in accordance with Section IX. 18.5.3.3.4 Maintenance of Records The Manufacturer maintains a record of all the brazers and brazing operators employed by his or her organization. This record, which should be accessible to the Authorized Inspector, should reflect the date and results of any qualifying tests and the identifying number, letter, or symbol assigned to each test.

18.5.4

Article 13: Design

To produce a strong joint for the operating range of temperature, it is the responsibility of a designer to select the brazingfiller metal. The strength of the brazed joint should be not less than the strength of the base metal or the weaker of the two base metals of dissimilar metal joints. For a brazed joint, the joint efficiency factor is taken as 0.80 when brazing-filler metal penetrates the entire joint; however, it is 0.50 for the same joint when the brazing-filler metal does not entirely penetrate it. 18.5.4.1 Minimum Thickness The minimum allowable thickness of ferrous and nonferrous shell plates, heads, and tubesheets is shown in Table HF-301.1 and Table HF-301.2.

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18.5.4.2 Service Temperature Brazing procedures qualified in accordance with Section IX, Part QB are considered satisfactory for a maximum service temperature of 250F (121C). Also, the base materials, the brazing-filler metal, the flux and/or atmosphere, and other procedure variables can all be used up to the same temperature limit. 18.5.4.3 Filler-Metal Application As part of the joint design, the application of filler metal should flow into the joint or be distributed across the joint. A visual inspection should reveal that the penetrated filler metal may be applied either by manual or preplaced application. 18.5.4.3.1 Manual Application Manual application to a joint by face-feeding should be made from only one side of the joint. A visual inspection of the joint’s other side should expose the required full-penetration, but if the other side cannot be visually inspected, a joint efficiency factor of 0.50 is used in the joint design. 18.5.4.3.2 Preplace Application Filler metal, such as slugs, powder, rings, strips, cladding, and spraying, may be preplaced. After brazing, the filler metal should be visible on both sides of the joint. A joint efficiency factor of 0.80 is used for such a joint design. If the filler metal is preplaced on the outside of a blind joint, and the other side cannot be inspected, a joint efficiency factor of 0.50 is used. 18.5.4.4 Joint Clearances Joint clearances should be small enough to enable the filler-metal to be distributed by capillary attraction. Such clearances for the assembly of joints should be within the tolerances permitted by the joint design and as used for the qualification specimens made in accordance with Section IX. Brazing alloys reflect the maximum unit strength if the permitted clearances are maintained. The recommended joint clearances at brazing temperature for various types of filler metals are noted in the following table:

Brazing-Filler Metal Group B–AISi B–CuP B–Ag B–CuZn B–Cu

Clearance (In.) 0.006–0.010 (for laps  41 in.) 0.010–0.025 (for laps  14 in.) 0.001–0.005 0.002–0.005 0.002–0.005 0.000–0.002

18.5.4.5 Openings The openings for nozzles and connections maintain a distance from main brazing joint so that the joint and the reinforcement plates for opening do not interfere with each other. Equally important is for the openings of pipe connections to be made by inserting couplings not more than NPS 3 (DN 75) or similar devices and securing them by welding performed by qualified welders. 18.5.4.6 Connections Lap joints of brazed construction, not exceeding a size of NPS 3 (DN 75), may be used to attach connections, such as saddle-type fittings, inserted into openings formed by outward flanging of the vessel wall. Sufficient brazing

should be applied on each side of the line to develop the strength of the reinforcement.

18.5.5

Article 14: Fabrication Requirements

18.5.5.1 Cleaning of Surfaces The surface to be brazed should be clean and free from grease, paint, oxides, scale, and other foreign matter. A cleaned surface suitable for brazing is provided by any chemical or mechanical cleaning method. 18.5.5.2 Postbrazing After the brazing operation, joints should be thoroughly cleaned of flux residue by any suitable means. A visual inspection of brazed joints may be conducted only after a thorough cleaning. Postbrazing operation, as with thermal treatments, is performed in accordance with the qualified procedure. 18.5.5.3 Defect Repair Brazed joints may be rebrazed if they are found to be defective upon the visual inspection. Defective brazing must be thoroughly cleaned. Repetition of the same brazing procedure as the original is usually applied; a procedure different from the original may be applied if the procedure is established and qualified in accordance with Section IX. Once established, a repair-brazing procedure should control the filler-metal application to meet the requirements of paragraph HB-1301.

18.5.6

Article 15: Inspection and Stamping

All brazing procedures must be qualified in accordance with Section IX. The Authorized Inspector shall examine the procedure to ensure that the joint has been fabricated according to the qualified procedure. If at any time the Authorized Inspector is dissatisfied with the quality of the brazing procedures, he or she may request and witness these procedures. 18.5.6.1 Certification of Brazers The Manufacturer certifies that brazing operations are performed by brazers or brazing opera tors qualified in accordance with Section IX. Likewise, the Authorized Inspector ensures that only qualified brazers and brazing operators are used for brazing operations. The Manufacturer also makes a record of each brazer’s and brazing operator’s qualification tests for the Authorized Inspector, who at any time may request and witness these tests. 18.5.6.2 Visual Inspection The Authorized Inspector visually inspects both sides of each brazed joint after its flux residue removal. If the Authorized Inspector fails to inspect one side of the brazed joint (i.e., the blind joint), he or she checks the design and ensures that the proper joint efficiency factor has been applied. It is important that the Authorized Inspector looks for evidence that the brazing-filler metal has penetrated the joint. The butt braze may be repaired or redone if any concavity is revealed. Any of the following conditions may cause rejection: • • • •

The presence of a crack in the brazing-filler metal The presence of a crack in the base metal adjacent to the braze Visible pinholes or open defects in the braze Rough fillets, particularly those with a convex appearance

18.5.6.3 Stamping Boilers may be stamped according to the requirements of paragraph HG-530. Alternatively, a nonferrous plate may be stamped and attached to the boiler.

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18.6

18.6.1

PART HC: REQUIREMENTS FOR BOILERS CONSTRUCTED OF CAST IRON

Article 2: Material Requirements

Gray-iron castings are used to produce cast-iron parts for boiler construction. All materials used for cast-iron boilers should meet the requirements of Article 2. 18.6.2.1 Chemical Composition Although any procedure for melting may be used by the Manufacturer, the cast material should have the following composition: (1) The manganese should be controlled to meet Mn  (1.7  S)  0.2, where Mn  manganese % and S  sulfur %. (2) The phosphorous content should not be more than 1.00%. 18.6.2.2 Tensile Strength Casting is listed by class and the minimum tensile strength. The following table lists the casting classifications used for boiler construction:

Class (No.)

Tensile Strength (Minimum psi)

20 25 30 35 40

20,000 25,000 30,000 35,000 40,000

18.6.2.3 Tension Test The tension test is the primary test for qualification required by Article 2, the result of which determines the various classes of castings as shown in paragraph 18.6.2.2. 18.6.2.3.1 Test Bar Bars for testing are casted separately from the castings. However, the bars should be produced with the same sand conditions of castings. The tension specimen is machined from the castings to the dimensions as shown in Fig. HC-205.1 (given here as Fig. 18.22). The sizes of cast test bars are determined by the thickness of the controlling section of the casting, as shown in the following table. The dimensions of the test bars are shown in Fig. HC-206.1.

14

Cast Test Bar

 0.5 0.51–1.00 1.00

A B C

Article 1: General

Cast-iron boilers are used widely because their initial installation cost is low and because of their ease of operation and maintainability. These boilers are primarily used for steam-heating and hot-water heating; it is the requirements of Part HC that are applicable to steam-heating, hot-water-heating, and hot-watersupply boilers fabricated mostly of cast iron.14 In addition, the requirements of Part HG may be used.

18.6.2

Thickness of controlling Casting Section (In.)

18.6.2.3.2 Test Procedure Tension test specimens should fit the holders of the testing machine so that the load is axial. When the stress value reaches 15,000 psi (103 MPa), the speed of the moving head of the testing machine should not exceed 0.125 in./min (3.18 mm/min). Figure HC-205.1 shows the dimensions for a tensile test specimen. 18.6.2.4 Transverse Test The transverse test may be used instead of a tension test, except for the tensile test required by paragraph HC-402.2. The minimum breaking load for a transverse test should be as follows: Class No. Test Bar A (Lb) 20 25 30 35 40

900 1,025 1,150 1,275 1,400

Test Bar B (Lb) Test Bar C (Lb) 1,800 2,000 2,200 2,400 2,600

6,000 6,800 7,600 8,300 9,100

If the transverse test fails, the Manufacturer may perform the tension test. In fact, the tension test specimen may be taken from the broken end of the tested transverse bar. The requirements of the Code will be met if the result of the tension test is satisfactory, despite failure of the transverse test. 18.6.2.5 Transverse Test Procedure The transverse test is performed on the bar as cast with central loading between supports. Correction factors for transverse test bars are referenced in Table HC-210. It is important to note that the controlling dimensions represent the diameter of the bar at fracture. The load is applied so that the fracture for the 0.875 in. (22 mm) diameter bar is produced in a minimum of 15 sec, a 1.2 in. (30 mm) diameter bar is produced in a minimum of 20 sec, and a 2.0 in. (51 mm) diameter bar is produced in a minimum of 20 sec. 18.6.2.6 Number of Tests For a tension test of each iron class, two or more test bars are casted from each melt; for a transverse test, two or more test bars are casted. Nevertheless, one chemical composition test is made on each melt, and either a tensile or a transverse test is performed on each melt for each controlling section. 18.6.2.7 Retests A test specimen should be free from defective machining and lack of metal continuity. Any defective specimen should be replaced by a new specimen. However, a retest may be performed if the test bar fails to meet the specified strength within 90% of its value. If the result of the retest is unsatisfactory, the casting is rejected. When the transverse test fails, the tension test may be performed on the test specimen machined from the brokenends of the transverse test bar. The casting is accepted if tension specimens meet the requirements.

Ratings of cast-iron boilers are certified by the Hydronics Institute, Inc., 35 Russo Place, Berkeley Heights, NJ 07922. The Institute’s publication entitled I–B–R Ratings for Boilers, Baseboard Radiation, and Finned Tube (Commercial) includes ratings of cast-iron boilers manufactured by Institute-licensed Manufacturers.

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FIG. 18.22

DIMENSIONS OF TENSILE TEST SPECIMEN (Source: Fig. HC-205.1, Section IV of the ASME B&PV Code)

18.6.2.8 Examinations and Tests The Manufacturer is responsible for all examinations and tests. A purchaser’s representative may be present when the work under contract is performed. All examinations and tests are performed at the Manufacturer’s shop unless otherwise specified. The Manufacturer is required to record and retain all test results for a minimum period of one year.

18.6.3

Article 3: Design

For calculating design pressure, stress values are used in the formulas provided in Part HG. Table HC-300, given here as Table 18.6, illustrates the maximum allowable stress values in tension

TABLE 18.6 MAXIMUM ALLOWABLE STRESS VALUES IN TENSION FOR CAST IRON, KSI (MULTIPLY BY 100 TO OBTAIN PSI)

Class

Minimum Tensile Strength, ksi

Maximum Allowable Design Stress Values, in Tension, ksi

20 25 30 35 40

20.0 25.0 30.0 35.0 40.0

4.0 5.0 6.0 7.0 8.0

for cast iron. The maximum allowable stress value in bending is 112 times the value permitted in tension; in compression, on the other hand, it is 2 times the value. 18.6.3.1 Heads Heads with pressure on the concave side are designed according to the formula in paragraph HG-305. The maximum allowable stress values in tension are used as reflected in Table HC-300. In addition, cast-iron pipes, flanges, and flanged fittings of Classes 125 and 250 may be used for parts with pressures not exceeding the ANSI ratings and temperatures not exceeding 450F (232C). For heads with pressure on the convex side, however, the thickness should not be less than the thickness required for heads with pressure on the concave side. Under any circumstances, the thickness shall not be less than 0.01 times the inside diameter of the head skirt. 18.6.3.2 Spherically Shaped Covers Spherically shaped covers with bolting flanges are shown in Fig. HC-311, given here as Fig. 18.23. Such covers may be designed according to the formulas of this paragraph and also be subjected to proof testing. The following symbols are used in the formulas: A  the outside diameter of the flange, in. B  the inside diameter of the flange, in. C  the bolt circle diameter, in. t  the minimum required thickness of the head plate after forming, in. L  the inside spherical or crown radius, in.

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FIG. 18.23

SPHERICALLY SHAPED COVERS WITH BOLTING FLANGES (Source: Fig. HC-311, Section IV of the ASME B&PV Code)

r  the inside knuckle radius, in. P  the design pressure, psi S  the maximum allowable stress, in. T  the flange thickness, in. Mo  the total moment, in-lb, determined as in Section VIII, Division 1 Hr  the radial component of the membrane load in the spherical segment, lb.  HDcot 1 hr  the force H lever arm nearly centroid of the flange ring, in. HD  the axial component of the membrane load in the spherical segment, lb.  0.875B2P hD  the radial distance from the bolt circle to the inside of the flange ring, in. 1  the angle formed by the tangent to the centerline of the dished-cover thickness, at its point of intersection with the flange ring, and by a line perpendicular to the axis of the dished cover  arc sin [B/(2L  t)] 18.6.3.2.1 Head Concave to Pressure For heads of the type shown in Fig. HC-311(a), the following formulas apply. Head thickness:

Flange thickness, T, for the full-face gasket: P B(A + B)(C - B) c d AS A - B

T = 0.6

For heads of the type shown in Fig. HC-311(b), the following formulas apply. Head thickness: t =

Flange thickness for the ring gasket—heads with round bolting holes: T = Q +

5PL 6S

Flange thickness, T, for the ring gasket: T =

M0 A + B c d A SB A - B

1.875M o(C + B) A SB(7C - 5B)

where Q =

t =

5PL 6S

PL C + B c d 4S 7C - B

Flange thickness for the ring gasket—head edges through which bolting holes are slotted: T = Q +

A

1.875M o(C + B) SB(3C - B)

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where PL C + B c d 4S 3C - B

Q =

Flange thickness for the full-face gasket: T = Q +

A

Q2 +

3BQ(C - B) L

The value of Q is calculated by any of the foregoing formulas. For heads of the type shown in Fig. HC-311(c), the following formulas apply. Head thickness: t =

5PL 6S

Flange thickness: T = F + 2F 2 + J

where F =

PB24L2 - B 2 8S(A - B)

flanges, nozzles, and opening reinforcements required in the design calculations should be cast integrally with the boilers and parts. 18.6.3.4. Washout Openings All cast-iron boilers are required to have washout openings for removal of sediments. The minimum washout plug size is NPS 112 (DN 40) for boilers with a gross internal volume exceeding 5 ft3 (142 L). For boilers with gross internal volume less than 5 ft3 (142 L), the minimum washout plug size should be 1 in. (25 mm). 18.6.3.5. Assembly Method Cast-iron boilers are assembled using internal connections such as nipples or grommet seals. Also, external connections such as cast-iron headers or threaded headers are used to complete the assembly. The assembled boilers are tested hydrostatically for acceptance.

18.6.4

18.6.4.1 Bursting Test Procedure The design pressure of any part is established by a hydrostatic test to failure by rupture. The pressure is based on a testing of three representative parts to destruction. The lowest value of PB of the three tests is used to determine the design pressure in the following formula: PR =

and J = a

Mo A + B b a b SB A - B

Example A circular cast-iron spherically dished head that contains a bolting flange (pressure on the concave side) and is designed for 30 psi pressure, is of Material Class 25, and has an inside crown radius of 36 in. Find the thickness of the head, given the following: P  30 psi L  36 psi S  5,000 psi from Table HC-300 The thickness of the head is t =

5PL 6S

t =

5 * 30 * 36 6 * 5,000

t =

5,400 30,000

t = 0.18 in. 18.6.3.3. Openings and Reinforcements The design of openings and reinforcements in boilers and pressure parts should meet the requirements of paragraphs HG-320 through HG-328. Cast-iron

Article 4: Tests

The design pressure of boilers and boiler parts is calculated by the formulas in Part HG. Sometimes, however, they cannot be calculated by these formulas, for all the parameters are not known. A bursting test may be used to establish the design pressure of those parts or components for which thickness cannot be determined by the formulas and for which a retest is required for any change in design. A bursting test should be repeated every five years.

specified minimum tensile strength PB * c d 5 average tensile strength of associated test bar

where the specified tensile strength is the tensile strength for the class of iron set forth in Table HC-300, and PR  design pressure, psi PB  destruction test pressure, psi 18.6.4.1.1 Test Gages An indicating gage is connected directly to the boiler, and the pressure is controlled by an operator all the time during the test. A recording gage may be used in addition to an indicating gage, especially for large vessels. The dial on the indicating gage should be double the intended maximum test pressure, but not less than 112 or more than 4 times that pressure. Both the indicating gages and recording gages should be calibrated against a standard deadweight tester. 18.6.4.1.2 Associated Test Bar A test bar casted separately is produced, machined, and tested for requirements of the tensile bar test procedure for each of the three boiler sections to be tested to destruction. The average tensile strength of these three bars is calculated and used in the design formula of paragraph HC-402. Specifically, the actual tensile strength of any of these three bars should not be more than 10% under the minimum tensile strength shown in Table HC-300. In particular, the tensile strengths of the associated bars should be recorded in Form H-5 (Manufacturer’s Master Data Report for Boilers Constructed from Cast Iron). 18.6.4.2 Recording and Certifying Tests The Manufacturer’s designated person is responsible for witnessing the tests used to

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establish the design pressure of a boiler. Bursting tests are recorded on Form H-5 (Manufacturer’s Master Data Report for Boilers Constructed from Cast Iron); then the completed form is certified by the Manufacturer’s designated person and is kept on file by the Manufacturer. 18.6.4.3 Hydrostatic Test A hydrostatic test is required to be performed on all boilers and boiler parts. The test result should be satisfactory for acceptance the boilers or boiler parts. 18.6.4.3.1 Steam Boilers Each individual section and boiler part is tested under hydrostatic pressure of a minimum of 60 psig (414 kPa). The test is performed at the shop that fabricated the section or part. The complete boiler is required to be tested under hydrostatic pressure of a minimum of 45 psig (310 kPa), and the hydrostatic test pressure should be controlled so that it cannot be exceeded by more than 10 psi (69 kPa) during the test. 18.6.4.3.2 Hot-Water Boilers Each individual section and part of a hot-water-heating and a hot-water-supply boiler with a maximum working pressure of 30 psi (207 kPa) is tested under a minimum hydrostatic pressure of 60 psig (414 kPa). Similarly, each individual section or part of a hot-water-heating and a hot-watersupply boiler with a working pressure greater than 30 psi (207 kPa) is tested under a hydrostatic pressure of 212 times the MAWP. The hydrostatic test is performed at the shop that makes the section or part. The complete boiler is required to be tested at a minimum hydrostatic pressure of 112 times the MAWP.

18.6.5

Article 5: Quality Control and Inspection

A quality control system is a written system that is based on the Code requirements for material, design, testing, fabrication, examination, and inspection by the Manufacturer and shop assembler. Each Manufacturer must have a quality control system for the fabrication of ASME Code products in his or her shop. The Manufacturer’s quality control system may include provisions for both Code and non-Code work; yet, the systems Code work requirements may exceed the minimum Code requirements. The Manufacturer may at any time change parts of the system that do not affect the Code requirements and may write the quality control system based on individual circumstances; nonetheless, the scope of his or her system depends on the type of products, the technical complexity, and the size and type of organization. The Manufacturer’s written description of the system may contain information—brief or voluminous—of a confidential nature for technical processes. Distribution of the quality control system manual is not required except to the ASME designee, who reviews it. A Code item will be produced based on the manufacturer’s quality control system. If this system can be demonstrated satisfactorily to be capable of producing an item in accordance with Code requirements, the ASME Code Symbol Authorization will be granted. 18.6.5.1 Outline of Quality Control System The following items should be included in the Manufacturer’s written description of the quality control system for his or her shop: (a) Product or Work Description The Manufacturer will include a brief description of the products he or she wishes to fabricate under the Code. This description may contain the names of all such products as well as product mixes, and it may also contain any work that is intended to be accomplished under the Code. 15

(b) Authority and Responsibility The person responsible for quality control should be identified clearly in the Manufacturer’s description, as should the details of his or her authority and responsibility. This person should have sufficient authority to identify quality control problems and provide solutions to correct such problems. (c) Organization The position of the person responsible for quality control functions is very important. The Manufacturer will have an organization chart that shows the functional relationship between the management and the processes of quality control, inspection, engineering, purchasing, and manufacturing. This chart will identify the functions of various groups responsible for the production of Code work. (d) Drawings and Design Calculations The quality control system should include the use of the latest applicable design calculations, drawings, test results, and specifications required by the Code. These documents will be used for the manufacturing, assembly, examination, inspection, and testing processes. (e) Material Control The quality control system will require verification that the material meets the requirements of the Code and only the material permitted in the Code will be used for construction. (f) Examination Program Provisions should be made in the quality control system for the bursting test procedure, the fabrication operations, and the stages at which specific examinations will be performed. (g) Correction of Nonconformities The procedures for correcting nonconformities, defined situations not complying with the Code requirements, should be described in the quality control system. All nonconformities must be corrected before boiler parts can be used in Code construction. (h) Calibration of Equipment The quality control system will describe procedures for the calibration of all equipment used for examination, measuring, and testing requirements of the Code. (i) Sample Forms The forms used for the quality control system should be marked “sample” and be included in the quality control system manual. These forms will be used for the actual production and test procedures. (j) Retention of Records The Manufacturer will retain the Manufacturer’s Data Forms for a minimum of fifteen years. There should be provisions in the quality control system for the retention of these Data Forms. (k) ASME Designee The ASME will designate a person to review the Manufacturer’s quality control system for issuing the Certificate of Authorization and ASME Symbol Stamp.15 There will be a reference to the ASME designee in the quality control system manual. A controlled copy of the quality control system manual will be submitted by the Manufacturer to the ASME designee for review. Also, there should be provisions in the quality control system for the ASME designee to have access to all drawings, calculation, specifications, procedures, process sheets, repair procedures, records, test results, and any other documents necessary to perform a review in accordance with the Code. 18.6.5.2 Examination Each boiler or boiler part should be thoroughly examined in accordance with Article 2 of Part HC. After completion of assembly, a hydrostatic test (which is the Manufacturer’s responsibility) should be performed in accordance with paragraph HC-410.

The American Society of Mechanical Engineers may designate the National Board of Boiler and Pressure Vessel Authorized Inspectors to act as an ASME designee for the purpose of review.

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18.7

RULES OF PART HA: HOT WATER HEATING BOILERS CONSTRUCTED PRIMARILY OF CAST ALUMINUM

calculation should be integrally cast with the boiler or boiler part. Core holes in aluminum castings may be plugged with push-in sealing caps provided that the caps are made from an electrochemically compatible material.

18.7.1

Article 1: General

18.7.3.4 Corners and Fillets Abrupt changes in surface contour or in wall thickness should be avoided. In addition, liberal radii should be used at projecting edges, reentrant corners, and wherever heat conducting fins and pins connect to the casting. Fillets between main pressure containment walls should have radii at least as thin as the thinner of the two walls being joined.

The rules of Part HA apply to hot water heating boilers constructed primarily of cast aluminum. 18.7.2 Article 2: Material Requirements Materials in Article 2 are used for heating boilers constructed of cast aluminum. The use of materials, other than those listed in Part H, require approval from the ASME B&PV Committee. 18.7.2.1 General Material Requirements In addition to cast sections, external appurtenances such as cast or welded headers and other pressure parts should only be constructed of alloys listed in Part HF. Use the rules of Part HG whenever the design pressure for these parts cannot be calculated. 18.7.2.2 Workmanship, Finish, and Repair The surface of the casting should agree with the drawings or the dimensions predicated by the pattern. The surface should be free of injurious defects and burnt on sand, and it should be reasonably smooth. Projections used in the casting process should be removed. With an approved quality control system, minor leaks may be repaired by plugging, impregnation, or welding, but these are subject to limitations. Threaded pipe plugs may be aluminum, brass, or stainless steel, and they are limited in size and depth. (NPS 1; four threads) Impregnation requires an approved process, Class 1 materials from MIL-STD-17563C, and proper marking. In addition, impregnated repairs preclude welding on those parts and require additional hydrostatic testing. Welding also requires an approved process and certified welders. 18.7.2.3 Examinations and Tests The Manufacturer is responsible for all examinations and tests. These examinations and tests generally have to be made at the place where the castings are made and prior to shipment, but they are not to interfere unduly with the operation of the works. 18.7.2.4 Test Records The Manufacturer has to record and retain all test results for one year and in a manner that relates the test results to the casting tested.

18.7.3

Article 3: Design

18.7.3.1 Maximum Allowable Stress Values Tables in Part HF give the maximum allowable stress values for aluminum castings. Where the design pressure cannot be calculated using available formulas, the design pressure should be established using the rules in Article 4 of this Part. 18.7.3.2 Heads and Spherically Shaped Covers Heads that are circular, spherically dished, with bolting flanges and conforming to one of the types shown in Fig. 18.23 are to be made according to the requirements of Section 18.6.3.2 18.7.3.3 Openings and Reinforcements All of the dimensional requirements found in HG-320 through HG-328 apply here, and they are to be used here for design of openings and reinforcements. Any cast flanges, nozzles, or openings that enter into the design

18.7.3.5 Washout Openings All cast aluminum hot water boilers should have washout (cleanout) openings that will allow the end user to remove any sediment that might accumulate in use. Minimum sizes for these openings are designated based on the internal water content of the boiler. 18.7.3.6 Assembly Method Sections may be assembled using internal connections such as grommet seals or (electrochemically compatible) push nipples or using external connections such as cast headers or threaded pipe headers.

18.7.4

Article 4: Tests to Establish Design Pressure

18.7.4.1 General Where the design pressure cannot be calculated using available formulas, the design pressure should be established using the rules that follow. Special attention should be given to the safety of testing personnel during the conduct of burst tests. These procedures should only be used when calculations cannot be used, that is, not in lieu of calculation. Any subsequent design changes will require retesting, and in all cases the maximum allowable working pressure cannot be greater than that determined by means of applicable design rules. Moreover, the test(s) have to be repeated every five years or less. Inventory of slow moving parts can be used beyond the five-year period provided that the test is rerun prior to the first production run after the five-year period.

18.7.4.2 Bursting Test Procedure (a) To establish the design pressure, a full-size sample of the part in question is to be hydrostatically pressurized until it ruptures. Alternatively, the test can be stopped when the test pressure reaches a value that will justify the design pressure dictated by the formula in (b). (b) Three representative boilers or parts are to be tested and the lowest value is to be used in determining PR in the following formula: PR  PB兾5  S兾(Sa or Sm)  S2兾S1 where PB  test pressure as per (a), psi (kPa) PR  design pressure, psi (kPa) S  specified minimum tensile strength, psi (kPa) Sa  average actual tensile strength of test specimens, (kPa) Sm  maximum tensile strength of range of specimens, (kPa) S1  maximum allowable stress at room temperature, (kPa) S2  maximum allowable strength at design temperature, (kPa)

psi psi psi psi

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18.7.4.3 Test Gages Indicating gages and additional recording gages are used. They must be calibrated for accuracy. 18.7.4.4 Witness, Recording, and Certifying Tests The Certified Individual witnesses the test and ensures that the data are recorded on the Manufacturer's Master Data Report for Boilers Constructed From Cast Aluminum. The forms are to be notarized and kept on file. 18.7.4.5 Rating of Production Boilers Based on Tests All boilers or boiler parts made of the tested material and design will be considered to have a design pressure equal to the maximum allowable working pressure determined by this test, and they will be subject to a hydrostatic test pressure as dictated in 18.7.4.6. 18.7.4.6 Hydrostatic Test All completed boilers need to pass a hydrostatic test in accordance with the following: Hot Water Boilers For hot water boilers the test pressure depends on the maximum allowable working pressure. For those boilers or sections with a maximum allowable working pressure of 30 psi or less, the hydrostatic test pressure is to be 60 psi or more. For those boilers or sections with a maximum allowable working pressure of more than 30 psi, the hydrostatic test pressure is to be two and a half times the maximum allowable working pressure. These tests are to be run at the shop where made. In addition, the assembled boiler has to be hydrostatically tested at a test pressure not less than one and a half times the maximum allowable working pressure. Required Test Pressure While conducting the tests in 18.7.4.6.1, the test pressure should be under sufficient control to ensure that the required test pressure is not exceeded by more than 10 psi in all cases.

18.7.5

Article 5 Quality Control and Inspection

18.7.5.1 General Each foundry or shop assembler must have and maintain a quality control system, which ensures that all Code requirements are met. This includes materials, design, testing, fabrication, and inspection. This system may include additional provisions that exceed those of the Code and/or non-Code requirements. The details of the system depend on the work to be performed and the complexity of the organization. They must be suitable for the circumstances. A written version shall be available for review. Since this written version may contain proprietary information, the Code does not require any distribution except as noted in 18.X.5.11.3 and in all cases the quality control system is considered to be confidential. 18.7.5.2 Features to be Included in the Quality Control System Guidance is given as to features that should be included in the written description of the quality control system.

Organization An organization chart is to be provided. It should show the relationships of the actual organization bearing in mind that the Code does not intend to encroach on the rights of the Manufacturer in this area. Drawings, Design Calculations, Test Results, and Specification Control The quality control system should ensure that the latest versions of drawings, design calculations, test results, and specifications are used. Material Control The system should require verification that the material to be used is a Code material and that only the intended material is used. Examination Program The system should describe all tests and fabrication procedures in sufficient detail to determine at which stages of the operation they are to be performed. Correction of Nonconformities The system should ensure that any condition that does not comply with the Code gets corrected. Calibration of Measurement and Test Equipment The system should detail how equipment, used for compliance with the Code, is calibrated. Sample Forms Exhibited forms should be marked “Sample” and completed in a way that is typical of actual production and test procedures. Retention of Records Manufacturer's Data Form should be retained for at least 15 years. ASME Designee The quality control system must refer to the ASME Designee and ensure that he has access to the written description of the quality control system. In addition, the Designee must have access to (but not necessarily separate copies of) all drawings, calculations, specifications, procedures, or any other documents necessary for his review in accordance with the Code. Certified Individual The Certified Individual provides oversight of all activities that might affect proper use of the Code symbol "H" used on cast aluminum sections as outlined in this Part. The Certified Individual must be an employee of the Manufacturer, be qualified, have a record containing objective evidence of his qualifications and training, and not be directly involved in the production of cast aluminum sections for which he is doing his oversight. Qualifications include knowledge of code requirements, knowledge of the quality control system, and training in the activities he is to oversee. The Certified Individual witnesses tests to determine design pressure, verifies sections have current reports, reviews tensile and composition test records to verify they meet Code requirements, and signs the Certification of Conformance outlined in 18.7.5.4.

Product or Work Description The quality control system should contain a brief description of the product the Manufacturer wants to make or the work he wants to do.

18.7.5.3 Examination Each boiler or part must comply with Article 2 of Part HA. Hydrostatic tests must be conducted as prescribed and there must be a way to identify acceptable sections or parts.

Authority and Responsibility It should clearly establish the responsibility and authority of those in charge of the quality control system. It is required that these persons have sufficient freedom to initiate actions and provide solutions to quality control problems.

18.7.5.4 Certificates of Conformance Cast aluminum boiler sections marked with the “H” symbol are to be recorded on Certificates of Conformance as follows:

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(a) The Manufacturer is to fill out Form HA-1 listing the pattern number, casting date, and the number of castings made and marked with the “H” symbol. Multiple sections may be listed on one form and castings with the same date of manufacture may be recorded on the same line. (b) The Manufacturer is also to fill out Form HA-2 listing the pattern number, maximum allowable working pressure, hydrostatic test pressure, and the quantity of sections that passed the hydrostatic test in 18.7.4.6. The Certified Individual also signs this form. And, again, multiple boiler sections may be recorded on the same form. (c) Certificates of conformance are to be kept on file for at least 5 years. (d) The Manufacturer and the Certified Individual cannot be the same person.

18.8

PART HLW: REQUIREMENTS FOR POTABLE-WATER HEATERS

18.8.1

Introduction

18.8.1.1 Types of Water Heaters: In general, water heaters are classified as residential and commercial. Residential-water heaters are used for supplying potable water for houses, apartments, condominiums and other residential buildings, whereas commercial water heaters are used for supplying potable water for industries, office buildings, and other commercial locations. 18.8.1.2 Differences Between Hot-Water-Heating Boilers and Water Heaters A hot-water-heating boiler is used to heat the space in any building, whereas a water heater is used to supply potable water to any building. The differences in application between the hot-water boiler and the water heater are as follows: (1) The water temperature of a water heater is limited to 210F (99C). (2) A corrosion-resistant lining or material is used in the construction of a water heater. (3) A water heater is used for supplying potable water, with make-up water from a potable-supply system. 18.8.1.3 Application of Part HLW Part HLW applies to water heaters of commercial or industrial size for supplying potable water at pressures not exceeding 160 psig (1,100 kPa) and temperatures not exceeding 210F (99 C). A brief outline of the contents of each article of Part HLW is given in the following text. Article 1: General This article covers the scope, any service restrictions and exceptions, and permissible stamping on water heaters. Article 2: Materials Included in this article are the material requirements for lining and primary pressure parts, as well as the acceptance of unidentified material. Article 3: Design In this article, the design criteria for water heaters is specified; for example, the maximum allowable working pressure is 160 psig (1,100 kPa), the minimum allowable working pressure is 100 psig (690 kPa), and the maximum water temperature allowed is 210F (99C).

Article 4: Weldments The provisions for weldment joint design are outlined in this article. Some acceptable types of joint designs commonly used for the construction of water heaters are provided. Article 5: Tests The proof test procedure, used to establish the MAWP of a water heater when the design pressure is unknown, is given in this article. Article 6: Inspection and Stamping Requirements for inspection and stamping are mentioned in this article. Accordingly, a water heater is stamped with the ASME Code HLW Symbol Stamp. Article 7: Controls A water heater should be equipped with an operating control, a high limit temperature-actuated control, safety controls, safety-limit switches, and burners or electric elements. Examples of these controls as required by nationally recognized standards are listed. Article 8: Installation A water heater may be installed in accordance with the American Gas Association Standard Z21.10.3, Installation of Gas Water Heaters. Provisions for acceptable piping installations and the installation of safety-relief valves and other valves are continued in this article.

18.8.2

Article 1: General

18.8.2.1 Scope The scope of Part HLW covers water heaters and water-storage tanks for supplying potable hot water. These heaters and tanks are constructed with corrosion-resistant materials. It is important to note that Part HLW is not applicable for hot-water-heating boilers. The requirements of linings for lined water heaters are specified in paragraph HLW-200. In Table HLW-301, the materials used for construction of unlined water heaters are listed. Both water heaters and tanks may be provided with cathodic protection. 18.8.2.2 Service Restrictions and Exceptions 18.8.2.2.1 Restrictions These requirements apply to water heaters and water-storage tanks for an MAWP of 160 psig (1,100 kPa) and a maximum water temperature of 210F (99C). 18.8.2.2.2 Exceptions Water heaters are exempted from the requirements of Part HLW if none of the following limitations is exceeded: (1) a heat input of 200,000 Btu/hr (58.6 kW); (2) a water temperature of 210F (99C); (3) a nominal water-containing capacity of 120 gal (454 L). Example A lined hot-water heater for commercial purposes is stamped with ASME Code Symbol HLW. The nameplate lists the MAWP as 160 psi and the maximum allowable input as 250,000 Btu/hr. What is the maximum service temperature of this hotwater heater? The hot-water heater can be used up to a maximum service temperature of 210F (99C). (See paragraph HLW-101.) 18.8.2.3 Permissible Stamping A water heater or water-storage tank constructed under Part HLW may be stamped with ASME Code Symbol HLW.

18.8.3

Article 2: Material Requirements

18.8.3.1 Lining A water heater or water-storage tank is provided with a corrosion-material lining for supplying potable water. The specifications of lining materials should conform to the requirements of Article 2. Many of the following types of lining

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are used for the construction of potable-water heaters and waterstorage tanks: (a) Glass Lining The surfaces of the water heater and storage tank that are exposed to hot water are lined with glass, of which the minimum average thickness should be 0.005 in. (0.13 mm). In fact, the glass lining may be applied to the surfaces before assembly. (b) Galvanizing As a corrosion-resistant material, the galvanized coating may be used on the water heater vessel. The minimum amount of coating should be 1 oz of zinc/ft2 of surface based on a coating thickness of 0.007 in. (0.043 mm). Because zinc is used for the coating, it should conform to ASTM B6— Specifications for Zinc (Slab Zinc)—and should be equal to the “Prime Western” grade. (c) Cement Lining A lining of cement may be used to resist 3 corrosion. It should be applied to a minimum thickness of 16 in. (4.8 mm). The lining should be completely cured and should cover the interior of the vessel. (d) Copper Lining Copper of weldable or brazeable quality may be applied as a corrosion-resistant material. The minimum thickness of such lining should be 0.005 in. (0.13 mm). Welding or brazing for lining attachments to steel backing should conform to the requirements of Section IX. (e) Fluorocarbon-Polymer Lining Because flurocarbon-polymer lining is corrosion-resistant and suitable for hot-water service, the minimum thickness of the lining should be 0.003 in. (0.076 mm). Before the application of the lining, surfaces must be cleaned and free from scale, oxidation, oil, and so on. Then, the lining should be cured at a proper temperature and duration to ensure its continuity. (f) Amine- or Polyamine-Epoxy Lining Amine- or polyamineepoxy linings may be used for electric-water heaters with immersion-type elements, for storage tanks, and for surfaces of water heaters that are not directly heated by the products of combustion. The minimum thickness should be 0.003 in. (0.076 mm), and the lining should be cured at a proper temperature and duration to ensure continuity of the lining. (g) Thermally Sprayed Metallic Lining This lining material comprises any type of copper or copper alloy suitable for spraying. All inner surfaces should be cleaned by grit blasting before spraying. The minimum lining thickness should be 0.005 in. (0.13 mm). To avoid the surface temperature exceeding 650F (343C), the spraying process should be controlled. (h) Polymeric Flexible Lining The National Sanitation Foundation International (NSFI) has specified the material that should be used to constitute this lining. In addition, the lining material should meet the requirements of ANSI/NSF 14-1900, a standard for plastic piping components and related materials, for potable-water service at a minimum temperature of 210F (99C). The minimum thickness of lining should be 0.020 in. (0.51 mm), and the inner surfaces of the vessel should be free from discontinuities that exceed 21 times the thickness of the liner. (i) Autocatalytic (Electroless) Nickel-Phosphorus Lining The composition of the nickel–phosphorus lining should conform to ASTM B 733-90 SC3, Type 1, Class 1. The minimum thickness should be 0.0003 in. (0.0076 mm). The minimum phosphorus content of the bath should be 9%; the maximum, 13%. 18.8.3.2 Pressure Parts The materials for primary pressure parts, such as shells, heads, flues, headers, and tubes, should conform to the specifications of Section II. Only those materials listed in Table HLW-300 (given here as Table 18.7) as well as in HLW301 and HF-300.2 are used. Moreover, the material test report is required for plate material to verify the chemical and

mechanical properties; the mill of origin shall provide this mill test report. Materials that are used for product forms require identification marking in accordance with the specifications of ASME Section II. Painted color identification or any other method of marking acceptable to the Authorized Inspector may be used. A welded assembly may be supplied as part of the completed water heater, in which case the Parts Manufacturer will submit the Manufacturer’s Partial Data Report Form HLW-7. 18.8.3.3 Unidentified Materials When there is no identification, each piece of material must show that the chemical composition and mechanical properties of Section II have been met. The materials are tested in accordance with the requirements of Section II, and the Manufacturer of the completed vessel is responsible for verifying all of these requirements.

18.8.4 Article 3: Design 18.8.4.1 Design Criteria Water heaters are fired with gas, oil, or electricity, and are designed in accordance with the requirements of this article. The design parameters of water heaters include the following: (1) a maximum allowable working pressure of 160 psi1,100 kPa); (2) a minimum allowable working pressure of 100 psi (690 kPa); and (3) a maximum water temperature of 210F (99C). All pressure parts of water heaters should be designed to prevent flame impingement. The design temperature should not be less than the mean metal temperature expected during operation. This metal temperature may be determined by calculations or by actual measurement of the temperature under equivalent operating conditions. If the MAWP of the water heater is not known, the proof test described in Article 5 may be used. The minimum thickness of plate material used for the construction of any lined or unlined water heater should be 18 in. (3.2 mm). 18.8.4.2 Shells Pressure parts, such as shells, headers, and pipes of water heaters, are subjected to internal pressure. The MAWP and thickness of the pressure parts under internal pressure are calculated as given in the following formulas: PR t = SE - 0.6P P =

SEt R + 0.6t

where P  the MAWP, psi (but not less than 100 psi) S  the maximum allowable stress values from Tables HLW 300, HLW-301, HF-300.1, and HF-300.2, psi t  the required wall thickness exclusive of liner, in. R  the inside radius of the cylinder, in. E  the efficiency of the longitudinal joint or ligament between tube holes, whichever is less. For seamless shells, E  1; for welded joints, the efficiency specified in paragraph HLW-402 may be used. Example What is the MAWP for a hot-water-heater vessel that has a 28 in. inside diameter, is of Material Specification SA-285, Grade C, and is 56 in. thick, where full-penetration double-butt welding has been performed on the longitudinal seam? (Note: the

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TABLE 18.7

MAXIMUM ALLOWABLE STRESS VALUES IN TENSION FOR LINED MATERIALS, KSI (Source: Table HLW-3000, Section IV of the ASME B&PV Code)

maximum temperature will not exceed 750F.) Find the MAWP in the vessel, given the following: S  13,800 psi for SA-285, Grade C from Table HLW-300 E  0.85 from paragraph HLW-402 t  0.3125 in. D  28 in. R  14 in. The MAWP is

SEt R + 0.6t 13,800 * 0.85 * 0.3125 P = 14 + 0.6 * 0.3125 3665.625 P = 14.1875 P = 258.37 psi P =

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TABLE 18.7

18.8.4.3 Dished Heads Blank unstayed dished heads, such as ellipsoidal and torispherical heads, may be used for pressure on either the concave or convex side. The following symbols are used in the formulas to calculate the MAWP and the thickness of a blank unstayed dished head: t  the required wall thickness exclusive of liner, in. P  the maximum allowable working pressure, but not less than 100 psi (690 kPa) D  the inside diameter of the head skirt, or inside length of the major axis of an ellipsoidal head, in. S  the maximum allowable stress values from Tables HLW300, HF-300.1, and HF-300.2, psi L  the inside spherical or crown radius, in. E  the lowest efficiency of any joint in the head. For seamless heads, E  1; for welded joints, the efficiency specified in paragraph HLW-402 may be used. 18.8.4.3.1 Ellipsoidal Heads The required thickness and MAWP of a dished head of semiellipsoidal form under pressure on the concave side are calculated by the following formulas: t =

PD 2SE - 0.2P

P =

2SEt D + 0.2t

18.8.4.3.2 Torispherical Heads The MAWP of a torispherical head under pressure on the concave side is calculated by the fol-

(CONTINUED)

lowing formulas: 0.885PL SE - 0.1P SEt P = 0.885L + 0.1t t =

Example What is the thickness of a seamless torispherical head designed for 150 psi for a hot-water-heater vessel of Material Specification SA-285, Grade B with an inside crown radius of 24 in.? The maximum design temperature is 750F. Find the thickness of the head, given the following: P  150 psi S  12,500 psi for SA-285, Grade B from Table HLW-301 E  1 for seamless head L  24 in. The thickness of the head is 0.885PL SE - 0.1P 0.885 * 150 * 24 t = 12, 500 * 1 - 0.1 * 150 t =

t = 0.26 in. 18.8.4.3.3 Crown Radius The inside crown radius of an unstayed formed head should not be more than the outside diameter of the skirt of the head. A torispherical head inside the knuckle radius

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should be a minimum of 6% of the skirt’s outside diameter but not less than three times the head thickness. 18.8.4.3.4 Hemispherical Heads Hemispherical heads are not allowed for the construction of potable-water heaters because of their complicated joint design. 18.8.4.3.5 Pressure on the Convex Side Unstayed dished heads with pressure on the convex side have an MAWP that is 60% of the MAWP of the same heads with pressure on the concave side. 18.8.4.4 Tubes The thickness of either seamless or welded tubes that are subjected to internal pressure should be calculated by using the formula in paragraph HG-301. The thickness of the same tubes that are subjected to external pressure should be calculated by using the formula in paragraph HG-312.2. 18.8.4.4 Openings All openings are reinforced in accordance with paragraph HG-321 except single openings, for which, according to the Code, reinforcement is not required if the welded connections are attached and not more than the following: (1) NPS 3 (DN 75) in shells or heads 83 in. (10 mm) or less, or (2) NPS 2 (DN 50) in shells or heads over 83 in. (10 mm). Reinforcement is also not required if the threaded, studded, or expanded connections are not more than NPS 2 (DN 50). 18.8.4.6 Tube Attachments Tubes may be attached to the tubesheet by rolling. The minimum thickness of any tubesheet for 3 tube installation should be 16 in. (4.8 mm). The tube attachment is accomplished by rolling the tubes into tube holes in the tubesheet. These holes may be formed by (1) using a method to the full diameter without producing irregularities, or (2) using a method to a lesser diameter and then increasing it to the full diameter by a secondary operation that will not produce irregularities.

18.8.5

Article 4: Design of Weldments

18.8.5.1 General Requirements All members of the joint should be properly prepared, fitted, aligned, and retained in position before welding. In accordance with the requirements of Section IX, all welds are made to a qualified welding procedure by qualified welders for each welding process. 18.8.5.1.1 Butt Joints A butt joint is used for longitudinal or circumferential joint for welding of plates of a drum, shell, or other pressure part. This butt joint is a double-welded butt or filler metal that is added from one side to obtain complete weld penetration. When there are two or more courses, the longitudinal joints of adjacent courses will be a minimum of 6 in. (152 mm) apart. If plates of unequal thickness are welded, the plate of one side of the joint is offset with the plate on the other side, which is in excess of one-fourth of the thickness of the thickest plate as shown in Fig. HLW-401.1. Also, the weld position may be in the tapered section or adjacent to it. 18.8.5.1.2 Corner or Tee Joints The typical corner or tee joints used for welding unflanged heads or tubesheets to the shell are shown in Fig. HLW-401.2. Tubes support the head or tubesheet, and the throat of the fillet should be a minimum of 0.7 times the thickness of the thinner plate.

18.8.5.1.3 Joint Efficiencies Joint efficiencies are required to be used in formulas of paragraphs HLW-302 and HLW-305 to calculate the minimum required thickness and design pressure. The following values of joint efficiency, E, are used for joints made by an arc- or gas-welding process: (1) E  85% for full-penetration butt joints obtained by double welding or other means. (2) E  80% for full-penetration single-welded butt joints with backing strips. The joint efficiency, E, is not used if the part is designed for external pressure. 18.8.5.2 Head or Tubesheet Attachments Typical welded joints in a water-heater construction are shown in Fig. HLW-411, given here as Fig. 18.24. Although flanged heads or tubesheets are attached by butt welding in accordance with Fig. HLW-415 (given here as Fig. 18.25), the fillet weld may be used for welding an outwardly or inwardly flanged head or tubesheet to a shell. 18.8.5.3 Tube Attachments Because tubes may be attached to the tubesheet by welding, the typical joints for such welding are shown in Fig. HLW-413. The edge of the plate at the tubesheet hole may be beveled or recessed to a depth at least equal to the tube thickness or 81 in. (3.2 mm)—whichever is greater—but not more than one-third of the tubesheet thickness. Moreover, projection of the tube beyond the tubesheet should not exceed a distance equal to the tube thickness. If a bevel or recess is not used, the tubes should extend beyond the tubesheet a minimum of 1.5 times the tube thickness and a maximum of 3 times the sum of the head thickness plus the tube thickness. 18.8.5.4 Head-to-Shell Attachments The skirt length is determined for different types of formed heads that are concave or convex to pressure. However, an ellipsoidal or torispherical head attached to shell as shown in the Fig. HLW-415(e) should not be provided with a skirt when the head thickness is not more than 114 times the shell thickness. If the head thickness is greater than that, a skirt is provided with a minimum length of 3 times the head thickness or 112 in. (38 mm), whichever is greater. In addition, an ellipsoidal or torispherical head that is concave or convex for a lap joint should have a skirt with a minimum length of 3 times the head thickness but not less than 1 in. (25 mm). 18.8.5.5 Welded Connections 18.8.5.5.1 Strength of Attachment Welds Arc or gas welding should be used to attach nozzles, connections, and their reinforcement to a water heater. Through shear or tension in the weld, sufficient welding is provided to develop the strength of the shell. The strength of the groove weld is based on the area subjected to shear or tension, and the strength of fillet weld is based on the area subjected to shear. 18.8.5.5.2 Stress Values for Weld Metal The allowable stress values for weld metal in terms of percentage of stress values for the vessel materials are as follows: • • • •

Nozzle wall: 70% Groove-weld tension: 74% Groove-weld shear: 60% Fillet-weld shear: 49%

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FIG. 18.24

TYPICAL WATER HEATER WELDED JOINTS (Source: Fig. HLW-411, Section iv of the ASME B&PV Code)

18.8.5.6 Requirements for Attachment Welds Acceptable types of welds for fittings, nozzles, and other connections to shells and heads are shown in Fig. HLW-431.1 and Fig. HLW-431.5. The symbols used in these figures are defined as follows: t  the nominal thickness of the shell or head, in. tn  the nominal thickness of the nozzle wall, in. te  the thickness of the reinforcement element, in. tw  the dimension of the partial-penetration attachment welds, in. tc  the smaller of 14 in. (6 mm) or 0.7 tn tmin  the smaller of 34 in. (19 mm) or the thickness of either of the parts joined by a fillet, single-bevel, or single-Jweld, in. t1,t2 - not less than 31 tmin or 41 in. (6 mm), and t1 t2 not less than 114 tmin. 18.8.5.6.1 Nozzles without Reinforcement Inserted-type nozzles without additional reinforcement may be welded by either a full-penetration groove weld or by two partial-penetration welds, one of which is on each face of the shell. Backing strips may be used with full-penetration welding from one side when the shell thickness is more than 38 in. (10 mm). When complete penetration cannot be verified by a visual inspection, the backing strip may also be used. 18.8.5.6.2 Nozzles with Reinforcement Inserted-type nozzles with added reinforcement may be welded at the nozzle neck periphery and at the outer edge of each reinforcement plate. A fillet weld with a minimum throat dimension of 12 \tmin is used for welding on the outer edge of each reinforcement plate. 18.8.5.6.3 Nozzles with Integral Reinforcement Nozzles with integral reinforcement may be attached by a full-penetration weld

or fillet weld along the outer edge and a fillet, single-bevel, or single-J-weld along the inner edge. The throat dimension of the outer weld should be a minimum 12 tmin, and dimension tw of the inner weld should not be less than 0.7 tmin. 18.8.5.6.4 Fittings with Internal Threads Internally threaded fittings should be attached by full-penetration groove welds or by two fillet or partial-penetration welds on each face of the shell. At the same time, a fillet weld deposited from the outside may be used for attaching internally threaded fittings or equivalent bolting pads not greater than NPS 4 (DN 100). 18.8.5.6.5 Resistance Welding Resistance welding may be used for the attachment of internally threaded fittings under the following conditions: (1) The welding process will be restricted to projection welding. (2) The parts’ materials to be welded will have a maximum carbon content of 15%. 5 (3) The thickness, t, will not exceed 16 in. (8 mm), and the fitting will not exceed NPS 2 (DN 50). (4) The MAWP for the vessel will be established by a proof test. 18.8.5.6.6 Stud Welding Stud welding may be used for attaching bolted unstayed flat heads, cover plates, blind flanges, handholes, and manholes with the following limitations: (1) The studs will not be in direct contact with products of combustion. (2) A full-face gasket will be used on flat heads, cover plates, and blind flanges if the pressure exerts a tensile load on the studs.

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FIG. 18.25

HEADS ATTACHED TO SHELLS (Source: Fig. HLW-415, Section IV of the ASME B&PV Code)

(3) The stud size will be of a minimum 41 in. (6 mm) and maximum 78 in. (22 mm) nominal diameter. (4) The stud type will be restricted to the round externally threaded type. (5) The base metal will be the ferrous material permitted in Section II. (6) The stud material should be low-carbon steel, with a maximum carbon content of 0.27% and a minimum tensile strength of 60,000 psi (410 MPa).

(7) The maximum spacing of studs will not exceed 12 times nominal diameter of the stud. (8) The maximum allowable stress for the stud will be 7,800 psi (54 MPa) 18.8.5.6.7 Friction Welding Inertia and continuous drive are types of friction-welding processes that are used. Friction welding may be used for material with assigned P-numbers in Section I.

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18.8.5.7 Brazed Connections Brazing of connections for copperlined vessels is required to be made in accordance with Subpart HB. Some acceptable types of brazed fittings, nozzles, and other connections to copper-lined shells and heads are shown in Fig. HLW-432.1. 18.8.5.8 Welding Processes The following welding processes are used for the welding of pressure parts for hot-water heaters: (1) Arc or Gas Welding, processes that are limited to shielded metal–arc, submerged–arc, gas metal–arc, gas tungsten–arc, plasma–arc, atomic hydrogen metal–arc, oxyhydrogen, and oxyacetylene welding. (2) Pressure Welding, processes that are limited to flash, induction, resistance, thermite, pressure–gas, and inertia and continuous–friction welding. Definitions of these welding processes are given in Appendix 18.E. 18.8.5.9 Welding Qualifications The welding procedures as well as the welders and welding operators engaged in the welding of pressure parts and in the welding of nonpressure parts to pressure parts are all required to be qualified in accordance with Section IX. Qualification tests for welders and welding operators conducted by one Manufacturer do not qualify a welder or welding operator to perform welding for another Manufacturer. 18.8.5.10 Production Work Qualifications Production work is undertaken if the welding procedures, welders, and the welding operators are qualified. The welders and welding operators are normally employed by the Manufacturer. When these welders (including brazers), welding operators, and brazing operators are not employed by the Manufacturer, they can be used to fabricate water heaters or the parts of water heaters, provided the following requirements are met: (1) The Manufacturer is responsible for all Code work. (2) All welding is made in accordance with the Manufacturer’s qualified welding procedures. (3) All welders are qualified by the Manufacturer. (4) The quality control system includes the Manufacturer’s authority to supervise, designate, and discharge welders and to assign identification symbols to welders. (5) The Authorized Inspection Agency (AIA) accepts the quality control program. (6) The Manufacturer is responsible for fabricating the vessel in accordance with the Code, and he or she applies the Code Symbol Stamp and completes the Data Report Forms. 18.8.5.11 Maintenance of Records The Manufacturer maintains a record of the welding procedures, welders, and welding operators employed by his or her organization. The record should show the date and results of the test, as well as the identification mark assigned to each welder or welding operator. These records should be certified by the Manufacturer and be made available to the Authorized Inspector. A welder or welding operator stamps the identification mark on or adjacent to the welding joints on which he or she is working at a maximum interval of 3 ft (0.9 m). Alternatively, the Manufacturer may keep a record of the welded joints and the names of the welders and welding operators who made the joints. 18.8.5.12 Specific Welding Requirements 18.8.5.12.1 Stud Welding A production-stud-weld test of the procedure and of the welding operator is performed on five studs

if stud welding is used to attach load-carrying studs. The production stud is welded and tested in accordance with either the bendor torque-stud-testing requirements of Section IX. Procedure and performance qualification testing are not required if the stud weld is used for attaching nonpressure parts to pressure parts by an automatic welding process performed in accordance with Section IX. A production-stud-weld test is specified by the Manufacturer and is performed on a separate plate if the stud welding is used for attaching non-load-carrying studs. 18.8.5.12.2 Tack Welds The alignment of welding-joint members is secured by tack welds. These welds may be either removed completely or left in place after their purpose has been served. Tack welds are used with a fillet- or butt-weld procedure qualified in accordance with Section IX. If tack welds are removed, their stopping and starting ends should be prepared by grinding so that they may be incorporated in the final weld. If they are to be left in place, however, the welding should be performed by welders qualified in accordance with Section IX. The tack welds are visually inspected and should be removed if they are found to be defective. 18.8.5.12.3 Friction Welding When this welding process is used, one of the two parts is held in a fixed position, and the other part is rotated. The axis of rotation of the two parts is made symmetrical, and the welded joint should be a full-penetration weld. The weld upset is maintained within 10% range, and the flash is removed to sound metal.

18.8.6

Article 5: Tests

18.8.6.1 General A proof test may be applied to determine the MAWP on the water heater. This test is accomplished by applying hydrostatic pressure to a full-sized sample of a water heater. On the other hand, one sample vessel may be proof-tested to establish the MAWP for a series of water heaters, but if the ligament is different for the different water heaters in a series of water heaters, two sample vessels must be proof-tested. Water-heater vessels are considered to be in series under the following conditions: (1) the heads are of the same geometry and thickness; (2) the cylindrical shell and tubes, differ only by length; and (3) the openings are of the same size and type as those on the proof-tested vessel. 18.8.6.2 Proof Test 18.8.6.2.1 Test Procedure Before the proof test, the outer surface of the water heater is cleaned and a brittle coating is applied. The hydrostatic test pressure is slowly increased until it is approximately half the anticipated MAWP; then, it is increased in steps of one-tenth the anticipated MAWP. The inspection is done at the end of every step to determine any permanent strain or displacement observed by the flaking of the brittle coating. It is important to note that the hydrostatic test pressure should be stopped when the intended test pressure is reached. 18.8.6.2.2 Test Based on Yield Strength The average yield strength is determined for use in the formulas for P (the MAWP). After completion of the test, three specimens are cut from the tested part. The average yield strength from these three specimens is used to calculate P by the following formula: P = 0.5H

Ts Ya

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where P  the hydrostatic test pressure at which the test was stopped, psi Ys  the specified minimum yield strength, psi Ya  the actual average yield strength from the test specimen, psi 18.8.6.2.3 Test Based on Tensile Strength If the test is stopped before any yielding, the MAWP may be calculated by one of the following given formulas: For carbon steel with a maximum tensile strength of 70,000 psi (481 MPa): S b P = 0.5H a S + 5,000 where H  the hydrostatic test pressure, psi S  the specified minimum tensile strength, psi For any other material: P  0.4H 18.8.6.2.4 Test Gages A gage is connected directly onto the water heater for indicating hydrostatic pressure. If the indicating gage is not clearly visible to the operator, an additional gage may be furnished. Also, a recording gage may be installed for large water heater. The dial range of the indicating gage should be 112 –4 times the pressure, and both the indicating and the recording gage should be calibrated against the master gage. 18.8.6.3 Collapsing of the Parts The water-heater parts should withstand (without major deformation) a hydrostatic test pressure that is a minimum of 3 times the desired MAWP. 18.8.6.4 Test Records The Manufacturer’s designated person is required to witness the proof tests to establish the MAWP of the water heaters. These tests are also witnessed and accepted by the Authorized Inspector. All results will be recorded on Form HLW8 (Manufacturer’s Master Data Report Test Report for Water Heaters or Storage Tanks). The Manufacturer’s designated person certifies the completed form, which is then kept on file. 18.8.6.5 Hydrostatic Test A hydrostatic test, in which the pressure should be 112 times the MAWP, is required to be performed on all water heaters. While the water heaters are under hydrostatic test pressure, all joints and connections are inspected for leakage. The test pressure is kept under control so that it cannot be exceeded by more than 10 psi (69 kPa), and the MAWP is marked at a suitable location on the water-heater vessel.

18.8.7

Article 6: Inspection and Stamping

province or city, all Authorized Inspectors are qualified by written examination and are employed by Authorized Inspection Agencies (AIAs) accredited by the ASME. The written examination to qualify Authorized Inspectors is prepared by the National Board of Boiler and Pressure Vessel Inspectors and conducted by the jurisdictions. The AIA may be the inspection organization of a U.S. state or municipality or Canadian province or municipality. In addition to the responsibility of certifying that water heaters have been constructed in accordance with the Code, the Authorized Inspector has the following responsibilities: (1) Conducts the inspections necessary to ensure that the Manufacturer has complied with all the requirements of Part HLW. (2) Confirms and reviews evidence that the welding procedures used in construction have been qualified in accordance with Section IX. (3) Verifies that all welding done by welders or welding operators has been qualified in accordance with Section IX. The Authorized Inspector reviews evidence of each welder’s or welding operator’s performance and qualification tests and may also call for and witness the test welding if deemed necessary. (4) Ensures that the inspection and quality control procedures (if any) for the fabrication of multiple duplicate water heaters and storage tanks have been followed. 18.8.7.3 Manufacturer’s Responsibility The Manufacturer’s overall responsibility is to comply with all the requirements of Part HLW if the water heater is to be stamped with the ASME Code Symbol HLW. In addition, the Manufacturer has other responsibilities that include the following: (1) Ensuring that Parts’ Manufacturers also comply with the requirements of the Code. (2) Providing necessary information to Authorized Inspectors so that they can perform their duties under the Code. (3) Confirming that the quality control system has been complied with. (4) Submitting or otherwise making available to Authorized Inspectors the following documents for their review: (a) a valid Certificate of Authorization for the use of the ASME Symbol HLW; (b) the design calculations or certified proof-test results; (c) the identification of materials; (d) the records of qualification of the welding and/or brazing procedures; (e) the evidence of qualifications of welders, welding operators, and/or brazers; (f) any Manufacturers’ Partial Data Reports (if required); (g) the traceability records of the material identification, thickness, and acceptability as required by the Code; and (h) the water heater or part for inspection at different stages as designated by the Authorized Inspector.

18.8.7.1 Inspection and Certification Water heaters are designed, constructed, and stamped in accordance with Part HLW of Section IV. The Manufacturer is responsible for complying with all the requirements of Part HLW. It is the responsibility of an Authorized Inspector to certify that the water heater has been constructed in accordance with the Code.

18.8.7.4 Data Reports Data reports are the documents of waterheater design, construction, fabrication, inspection, and stamping. There are three types of data reports: Manufacturer’s Data Reports, Partial Data Reports, and Supplementary Data Reports.

18.8.7.2 Authorized Inspector’s Responsibility Under the jurisdictional rules of any U.S. state or city and any Canadian

18.8.7.4.1 Manufacturer’s Data Reports The Manufacturer is required to complete a Manufacturer’s Data Report on Form HLW-6

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for each water heater. A single water heater or multiple identical water heaters with serial numbers in sequence and completed in a continuous eight-hour period may be included in the Data Report. The Manufacturer distributes the Manufacturer’s Data Report to the User, the AIA, the purchaser, and the jurisdiction. A copy of the Manufacturer’s Data Report is kept in the Manufacturer’s file for a minimum of five years; otherwise, the water heater may be registered and the original Data Report may be filed with the National Board of Boiler and Pressure Vessel Authorized Inspectors. 18.8.7.4.2 Partial Data Reports The Parts’ Manufacturer is required to complete a Manufacturer’s Partial Data Report on Form HLW-7 for each part requiring inspection under the Code. All parts fabricated by a Manufacturer other than the one who completed the water heater may be included in this Data Report. The Parts’ Manufacturer will forward the Data Reports in duplicate to the Manufacturer of the completed water heater, and the Authorized Inspector will witness the application of the Code Symbol Stamp on the completed water heater based on the Partial Data Report together with his or her own inspection. 18.8.7.4.3 Supplementary Reports When space on the Manufacturer’s Data Report Form HLW-6 is not sufficient to record all data, the Manufacturer’s Data Report Supplementary Form H-6 is used to record the additional data. This form is attached to the Manufacturer’s Data Report Form. 18.8.7.5 Stamping 18.8.7.5.1 Stamping of Water Heaters The Manufacturer who possesses a valid Code Symbol Stamp and a Certificate of Authorization applies the Code Symbol Stamp to the water heaters constructed in accordance with the Code. The water heater will be marked or stamped with the Code Symbol Stamp shown in Fig. HLW-602.1 (given here as Fig. 18.26) and the form of stamping shown in Fig. HLW-602.2 (given here as Fig. 18.27). The following data is required to be marked or stamped on the water heater: (1) the Manufacturer’s name to be inserted after the words “Certified by”; (2) the MAWP; (3) the maximum allowable input, Btu/hr (for electric heaters, kW or Btu/hr); (4) the Manufacturer’s serial number; and (5) the year built. 18.8.7.5.2 Stamping of a Proof-Tested Vessel A proof-tested vessel may be marked or stamped with the Code Symbol Stamp if (1) the proof test was stopped before any visible yielding; (2) the welding was qualified as required by the Code;

FIG. 18.27 FORM OF STAMPING ON COMPLETED WATER HEATERS (Source: Fig. HLW-602.2, Section IV of the ASME B&PV Code)

(3) the MAWP was calculated by the formula based on minimum tensile strength; (4) the vessel interior was inspected for damage; and (5) the complete vessel was hydrostatically tested. 18.8.7.5.3 Dimensions of Stamping Code Symbol Stamping is 5 required on the water heater with a minimum height of 16 in. (8 mm). The stamping may also be reproduced on a plate of a mini3 mum thickness of 64 in. (1.2 mm) thick, which may be permanently fastened to the water heater. If the stamping is to be covered by insulation, one of the following should be provided: (1) an opening made with a removable cover for viewing stamping, or (2) a nameplate with a duplicated Code Symbol and set of data, located in a conspicuous place. The nameplate dimension should be a minimum of 3 in.  4 in. (76 mm  102 mm) and marked with letters and numbers that are a minimum of 18 in. (3.2 mm) high.

18.8.8 Article 7: Controls 18.8.8.1 Temperature Control In addition to the operating controls, an automatically fired water heater is fitted with a separate high temperature limit-actuated combustion control is required, as it automatically cuts off the fuel supply when the water temperature reaches 210F (99C). The high temperature limit-actuated combustion control performs the following functions for different types of water heaters: (1) For gas-fired water heaters, it cuts off the fuel supply with a shutoff mechanism other than the operating-control valve. (2) For electrically heated boilers, it cuts off all power to the operating controls. (3) For oil-fired water heaters, it cuts off all current flow to the burner system. (4) For indirect-water heaters, it cuts off the source of heat. 18.8.8.2 Limit Controls Limit controls used with an electric circuit will break the hot or line sides of the control circuit.

FIG. 18.26 OFFICIAL SYMBOL TO DENOTE THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS’ STANDARD (Source: Fig. HLW-602.1, Section IV of the ASME B&PV Code)

18.8.8.3 Safety Controls Safety controls, such as primary safety controls, safety-limit switches, burners, and electric elements, are

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used for all water heaters. They are required by the following nationally recognized standards: • The Underwriters Laboratories (UL) 732, Standard for Safety, Oil-Fired Heaters • The Underwriters Laboratories (UL) 795, Standards for Safety, Commercial–Industrial Gas-Heating Equipment • The Underwriters Laboratories (UL) 1453, Standards for Safety, Electric Booster, and Commercial Storage Tank Water Heaters • The American National Standards Institute (ANSI) Z21.10.3, Standards for Gas-Water Heaters (vol. III: Storage Water Heaters, with Input Ratings Above 75,000 Btu per Hour, Circulating and Instantaneous) A certifying organization, which provides uniform testing, examination, and listing procedures under the established nationally recognized standards, will test the equipment under a nationally recognized standard. (The requirements of ASME CSD-1, Controls and Safety Devices for Automatically Fired Boilers, are not applicable for water heaters.) If the controls and heat-generating apparatuses are manufactured in accordance with that standard, the monogram or symbol of the certifying organization will be affixed onto the equipment. 18.8.8.4 Electrical Requirements Water heaters are provided with controls and an electrical apparatus either in the shop or in the field. All factory-mounted and -wired controls, heat-generating apparatuses, and other appurtenances are installed in accordance with the nationally recognized standards listed in paragraph HLW703. Provisions of the National Electrical Code (NFPA) 70, published by the National Fire Protection Association, or an electrical code enforced by local jurisdictions are applicable for the installation of all field-wired controls, heat-generating apparatuses, and other appurtenances. However, the National Electric Code will be applicable if there is no alternative electrical code.

18.8.9

Article 8: Installation Requirements

18.8.9.1 Safety-Relief Valves Hot-water heaters may be installed in accordance with the following codes: • The American National Standards Institute (ANSI) Z21.10.3, Standards for Gas-Water Heaters (vol. III: Storage Water Heaters, with Input Ratings Above 75,000 Btu per Hour, Circulating and Instantaneous) • The American National Standards Institute (ANSI) Z222.3, National Fuel Gas Code • The Canadian Standards Association (CAN/CGA) B149.1, Natural Gas Installation Code • The Underwriters Laboratories (UL) 1453, Standards for Safety, Electric Booster, and Commercial Storage Tank Water Heaters 18.8.9.1.1 Safety Relief–Valve Requirements At least one temperature-and-pressure (T&P) relief valve or safety-relief valve is required for each water heater. These valves should be ASMErated and marked with the Code Symbol V or HV. (V is used with boiler safety valves; HV is used with heating-boiler safety valves.) The minimum size of the safety-relief valves is NPS 34 (DN 20). 18.8.9.1.2 Set Pressure The pressure setting of the safety-relief valves should be less than or equal to the MAWP. If there are additional valves, the set pressure may not exceed 10% the set pressure

of the first valve. If there are different components of a hot-water system, such as expansion tanks, storage tanks, pumps, valves, or piping with working pressures different from those of the hotwater heaters, the set pressure of the safety-relief valve should be the lowest MAWP of any component. 18.8.9.1.3 Safety Relief–Valve Capacity The relieving capacity of the safety-relief valve shall not be less than the maximum allowable input of the water heater. The rated burner-input capacity may be used to determine the relieving capacity of the safety-relief valve. The unit for relieving capacity is Btu/hr for gas-or oil-fired water heaters; for electric-water heaters, this capacity may be expressed in Btu/hr by multiplying the kW input with 3,500 Btu/hr. At maximum capacity, the pressure cannot exceed 10% of the MAWP. The capacity of the safety valve must be recalculated if the operating conditions change or if any additional heating surface is installed. 18.8.9.2 Mounting Safety–Relief Valves Safety-relief valves may be installed in the shop by the Manufacturer or in the field by an installer. Before a water heater is placed into operation, either an installer in the field or the Manufacturer in the shop may install the safety-relief valve. 18.8.9.2.1 Permissible Mountings Safety-relief valves are installed on the top of water heaters or directly to a tapped or flanged opening in the water heater. The spindles of the safety-relief valves should be in an upright position except when the valve is mounted horizontally directly onto the water heater shell and the outlet is pointed down. Piping or fitting used to mount the safety-relief valve should not be of a nominal pipe size less than the valve-inlet size. The centerline of the valve connection should not be at a point lower than 4 in. (102 mm) from the top of the water-heater shell. 18.8.9.2.2 Common Connection for Multiple Valves The cross section of the common connection of multiple valves should not be less than the combined area of inlet connections of all the safety-relief valves. When two or more valves are used on a water heater, they may be single, directly mounted, or mounted on a Ybase. When the Y-base is installed, the inlet area should not be less than the combined outlet areas. 18.8.9.2.3 Threaded Connections A threaded connection may be used for attaching the safety-relief valves to water heaters. 18.8.9.2.4 Shutoff Valves A shutoff valve of any type should not be installed between the safety-relief valve and the water heater. Also, a shutoff valve must not be placed between the discharge pipe and the atmosphere. 18.8.9.2.5 Discharge Piping The internal cross-sectional area of the safety relief–valve discharge pipe should be not less than the full area of the valve inlet or of the total of the valve outlets. The discharge piping should be short and straight. If an elbow is used on the discharge pipe, it should be located close to the valve outlet. So there is no danger to people, the safety-valve discharge should be piped away from the water heater to a safe point—it should be drained properly without any threat to public safety. 18.8.9.3 Water Supply Feedwater is introduced into a water heater through an independent connection, not through a drain, a pressure or temperature gage opening, or any opening for cleaning. There are stop valves installed in the supply and discharge pipe connections to allow the draining of the water

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FIG. 18.28 A TYPICAL ACCEPTABLE PIPING INSTALLATION FOR STORAGE WATER HEATERS IN BATTERY (Source: Fig. HLW-809.1, Section IV of the ASME B&PV Code)

heater. A pressure-reducing valve is required if the pressure on the water-supply line exceeds 75% of the set pressure of the safetyrelief valve. 18.8.9.4 Storage Tanks A storage tank (if required) should be designed and constructed in accordance with Section VIII, Division 1 or to Section X. If a tank is constructed under Section X, the maximum allowable temperature should be equal to or more than 210F (99C).

18.8.9.6 Bottom-Drain Valve A bottom-drain-pipe connection fitted with a valve, of which the minimum size should be 43 in. (19 mm), is provided for each water heater. This pipe should be connected to the lowest possible water space, and the discharge piping connected to the bottom-drain connection should be of full size to the point of discharge. 18.8.9.7 Thermometer A thermometer for indicating the water temperature is installed at or near the water heater outlet. This thermometer should be located so that it is easily readable.

18.8.9.5 Provision for Expansion 18.8.9.5.1 Expansion Tank An expansion tank that is designed and constructed in accordance with Section VIII, Division 1 or to Section X is required if the hot-water system is equipped with a check valve or pressure-reducing valve in the cold-water line. The safety-relief valve may lift periodically from the thermal expansion of water if an expansion tank is not provided. A typical acceptable piping installation for an expansion tank in battery is shown in Fig. HLW-809.1 (given here as Fig. 18.28). 18.8.9.5.2 Piping Expansion Hot-water mains connected to water heaters are subjected to expansion and contraction. Substantial anchorage and swing joints are provided when water heaters are installed in batteries. Figure HLW-809.2 shows a typical acceptable piping installation for the flow through a water heater with provisions for piping expansion.

18.9

CONSIDERATIONS LIKELY TO BE IN FUTURE CODE EDITIONS

Materials of Construction: What was formerly a market, limited to boilers made of cast iron, steel, and copper, has now become a market for all of those materials plus aluminum and stainless steel with plastics and composites on the horizon. In upcoming years, additional (unlisted) alloys will likely come to the forefront. One of the challenges in this area is how to deal with materials that meet European norms but are not paralleled in ASTM specifications. Section IV does not deal with this challenge directly. That is, for Section II, but when such an alloy or “new” material is to be used in making a Section IV vessel, the inquiry starts with Section IV.

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Code Modification: The market is international. New materials need to be approved. New technology needs to be evaluated and the Code needs to stay current. Changes to how the Code is modified are under study and review. The challenge is to speed up the overall process while maintaining high standards for safe operation and sufficient time for review by competent individual volunteers along the way.

18.10

WHAT SHOULD THE ASME CODE COMMITTEES AND REGULATORS CONSIDER, RECOGNIZING THE INTENT OF THE ASME B&PV CODE?

The hydronics market in the United States is seeing the advent of several trends. Advanced Controls: simple on/off operating controls are being displaced by system controls that try to match system performance to the actual needs of the space being heated. Reset controls, while around for many years, are benefiting from computer enhancements and better insights into how they should respond. Add in variable speed pumping, burner delays, home owner interaction, internet access, and mixing of supply and return water for multiple temperature operation, and the complexity continues to increase. The challenge for ASME is to ensure that safety controls are not compromised by operating controls while, at the same time, allowing advances in control technology to take place in a timely manner. Emissions: As with every fuel burning appliance, pressure is currently coming from both the markets and governments around

18.11 Page iii xv-xvii 1 4 30, 31 38 54 59 61 62 74 81

90 92, 95 129 133

the world for reduced emissions through better efficiency and/or better burners. Advanced controls should also play a growing role in this area. Again, this is not a direct factor when considering Code-constructed vessels, but the secondary impacts on such things as flue gas composition and its impact on condensate acidity must be recognized and dealt with. Installation: The trend toward increasing system complexity brings with it a need for improved, repeatable installation techniques. The market responds with prepiped manifolds, plug-in wiring, touch screen programming, and a renewed emphasis on training for installers and designers. The code needs to deal with such advances, to the extent it can, to ensure that safety is not compromised. Heat Release Devices: The (knowledgeable) market calls for a variety of heat release devices in a building. Warm air delivery (for use with air-conditioning) is coupled with such heat release techniques as warm floors, traditional baseboard, radiant panels, and decorative convectors or radiators. Traditional baseboard systems get coupled with high-velocity air-conditioning. No obvious safety concerns are evident in this area, but watchfulness is called for. Efficiency: The system efficiency is one that counts the most. How all the components react to one another is the challenge of the future. Moreover, there is an increasingly fuzzy line between a water heater and a boiler. The rules for construction on these two devices are not the same based on the historical definitions and use patterns for them. With water heaters now being used for space heating in many applications and many boilers being limited to supply temperatures below boiling, this separation may need to be revisited for clarification or redefinition.

SUMMARY OF CHANGES Location

Changes

List of section Foreward HG-102 HG-306.1 HG-360.2 HG-360.3 HG-402.8(a) HG-604

Updated to reflect 04 Editorially revised Added Last line corrected by Errata Subparagraph (d) revised Subparagraph (d) revised Fourth line revised In subparagraph (a), third line corrected by Errata Footnote added Revised Deleted Second paragraph revised Last column corrected by Errata For SB-61, C92200; SB-62, CB3600; and SB-584, CB4400, under Form, corrected by Errata Subparagraph (c) corrected by Errata Last line corrected by Errata Last line revised by Errata Subparagraph (c) through (g) deleted Added Corrected in its entirety by Errata Designator corrected by Errata Designator corrected by Errata

HG-703 Fig. HG-703.1(b) Table HG-709.1 HG-709.2 Table HG-300.1 Table HG-300.2

HW-713 HW-731.2(b) HW-731.8 HLW-100 HLW-103 HLW-300 HLW-301 HLW-302

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134, 135

HLW-303 Table HLW-300

153 158 164 168 206–209 210–212

HLW-501 HLW-701.1 Table 2-100 Mandatory Appendix 6 Nonmandatory Appendix M Index

18.12

Designator corrected by Errata SA-513 Grade 1010 values for Tensile Strength corrected by Errata Second line corrected by Errata Fourth line corrected by Errata Revised Added Added Corrected by Errata

REFERENCES

1. Buxton, W. J., and Burrows, W. R., ASME Transactions, 1951. (Reprinted in Pressure Vessel Design and Piping, Collected Papers, 1927–1959).

4. Timonshanko and Woinowsky-Krieger, Theory of Plates and Shells, McGraw-Hill, New York, 2nd ed., pp. 55–57.

2. Kinzel, H. B., “Pressure Vessel Heads,” Mechanical Engineering, 1927

5. Jawad and Farr, Structural Analysis and Design of Process Equipment, pp. 323–332.

3. Jawad and Farr, Structural Analysis and Design of Process Equipment, p. 252.

6. Theory and Design of Pressure Vessels, Van Nostrand Reinhold Co., New York, 2nd ed., p. 605.

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18.A

METHOD OF CHECKING SAFETY VALUE AND SAFETY RELIEF–VALUE CAPACITY BY MEASURING MAXIMUM AMOUNT OF FUELTHAT CAN BE BURNED 1

1

Source: Appendix B, Section IV of the ASME B&PV Code.

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EXAMPLE OF METHODS OF CALCULATING A WELDED RING REINFORCED FURNACE1

1

Source: Appendix C, Section IV of the ASME B&PV Code.

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EXAMPLES OF METHODS OF COMPUTATION OF OPENINGS IN BOILER SHELLS1

1

Source: Appendix D. Section IV of the ASME B&PV Code.

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18.D

GLOSSARY

1.0

GENERAL TERMS

Accepted A boiler unit, piece of equipment, or device is accepted when it is listed, labeled, or otherwise determined to be suitable and safe by a nationally recognized testing agency. Field installations are accepted when they are approved by the authority having jurisdiction. Approved Acceptable to the authority having jurisdiction. Authorized Inspection Agency (AIA) This is an inspection agency accredited by the ASME.

2.0

BOILER TERMS

Boiler A closed vessel in which water is heated, steam is generated, steam is superheated, or any combination thereof, under pressure or vacuum by the direct application of heat. The term boiler shall include fired units for heating or vaporizing liquids (other than water) that are complete within themselves. Automatically Fired Boiler A boiler equipped with a means of introducing heat or fuel—solid, liquid, gaseous, or electric— into the boiler or boiler furnace. The means are regulated so greatly by the rate of flow, the generating pressure, or the temperature of the boiler fluid, vessel, or heated space that it maintains a determined, desired condition within a designated tolerance. Electric Resistance Heating Element–Type Boiler This boiler is either (1) of a design in which the electric-resistance element is directly attached to the external surface of the pressure vessel, or (2) of an immersed type in which the electric-resistance element is inserted through an opening in the pressure vesselso that the element is in direct contact with the water. Electric Submerged Electrode–Type Boiler This boiler incorporates a design wherein two or more metallic electrodes are directly suspended in the boiler water. When a source of electric power is connected to the electrodes, the current will flow between the electrodes and through the water, thus raising the water’s temperature to produce steam. High-Pressure Boiler A boiler in which steam or vapor is generated at a pressure exceeding 15 psig (103.4 kPa gage). Horizontal-Return-Tubular Boiler A firetube boiler consisting of a cylindrical shell, with tubes inside the shell attached to both end closures. The products of combustion pass under the bottom half of the shell and return through the tubes.

Hot-Water-Heating Boiler A boiler in which no steam is generated and from which hot water is circulated for heating purposes, then returned to the boiler. Hot-Water-Supply Boiler A boiler that furnishes hot water to be used external to itself at a pressure not exceeding 160 psig (1,100 kPa gage) or a temperature not exceeding 250F (120C) at or near the boiler outlet. Low-Pressure Boiler A boiler in which steam or vapor is generated at pressure not exceeding 15 psig (103.4 kPa gage). Modular Boiler A steam- or hot-water-heating assembly that consists of a grouping of individual boilers called modules intended to be installed as a unit with no intervening stop valves. Modules may be under one jacket or may be individually jacketed. The individual modules shall be limited to a maximum input of 400,000 Btu/hr (117,228 W) for gas, 3 gph (11.4 L/h) for oil, and 115 kW for electric. Steam-Heating Boiler A boiler designed to convert water into steam, which is supplied to an external space heating system. Vacuum Boiler A factory-sealed steam boiler that is operated below atmospheric pressure. Water Heater A closed vessel in which water is heated by the combustion of fuels, electricity, or any other source and is withdrawn for use external to the system at pressures not exceeding 160 psig (1,100 kPa gage). It shall include the apparatus by which heat is generated and all the controls and devices necessary to prevent the water temperature from exceeding 210F (99C). The following are two types of water heaters: (1) Lined A water heater with a corrosion-resistant lining designed to heat potable water. (2) Unlined A water heater made from corrosion-resistant material designed to heat potable water.

3.0

DESIGN TERMS

Accumulation-Test Pressure The steam pressure for which the capacity of a safety, safety-relief, or relief valve is determined. It is 3313 % over the set pressure of the steam-safety valve and 10% over the set pressure of the safety-relief valve. Design Pressure The pressure used in the design of a boiler for the purpose of calculating the minimum permissible thickness or physical characteristics of different parts of the boiler. Furnace The part of a boiler where combustion of fuel takes place or where the primary furnace gases are conveyed.

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Heating Surface The area of boiler surface exposed to the products of combustion. In computing the heating surface to determine the safety-or relief-valve requirements, only the tubes, fireboxes, shells, tubesheets, and the projected area of the headers need to be considered except for vertical firetube boilers, in which only the tube surface up to the middle point of the gage glass needs to be computed. Maximum Allowable Stress The maximum unit stress permitted in a given material used under these rules. Maximum Allowable Working Pressure (MAWP) The maximum gage pressure permissible in a completed boiler. The MAWP of the completed boiler shall be less than or equal to the lowest design pressure determined for any one of its parts. Operating Pressure The pressure of a boiler at which it normally operates. It shall not exceed the MAWP and is usually kept at a suitable level below the settings of the pressure-relieving devices to prevent their frequent opening. Popping Action The action of a safety or safety-relief valve when it opens under the steam pressure. The disk of the valve is designed so that the force of the steam lifting the disk is increased when the disk is lifted slightly off its seat. The increase in force accelerates the rising action of the disk to the wide-open position at or near the opening pressure. Primary Furnace Gas A gas in a zone where its anticipated temperature exceeds 850F (454C). Required Thickness The minimum thickness determined by the formulas in the Code. Safety Valve An automatic pressure-relieving device actuated by the static pressure that is upstream of the valve and characterized by full-opening pop action. It is used for gas or vapor service. Safety-Relief Valve An automatic pressure-relieving device actuated by the pressure that is upstream of the valve and characterized by opening pop action with further increase in lift with an increase in pressure over popping pressure. Temperature-and-Pressure (T&P) Safety-Relief Valve A safety-relief valve that also incorporates a thermal-sensing element actuated by an upstream water temperature of 210F (99C) or less.

4.0

WELDING TERMS

Arc Welding A group of welding processes wherein the coalescence is produced by heating with one or more electric arcs with or without the application of pressure and with or without the use of filler metal. Arc-Stud Welding An arc-welding process wherein the coalescence is produced by heating with an arc drawn between a metal stud (or similar part) until the surfaces to be joined are properly heated, at which time they are brought together under pressure. Partial shielding may be obtained by the use of a ceramic ferrule that surrounds the stud. Shielding gas or flux may or may not be used. Automatic Welding Welding with equipment that performs the entire welding operation with constant observation and adjustment of the controls made by an operator. The equipment may or may not perform the loading and unloading of the work. Backing Material (metal, weld metal, asbestos, carbon, granular flux, etc.) backing up the joint during welding to facilitate a sound weld at the root. Butt Joint A joint between two members lying approximately in the same plane.

Corner Joint A joint between two members located approximately at right angles to each other in an L-formation. Fillet Weld A weld of an approximately triangular cross section that joins two surfaces at approximately right angles to each other in a lap, tee, or corner joint. Flux Cored–Arc Welding A gas metal arc-welding process wherein the coalescence of metals is produced by heating them with an arc between a continuous-filler metal (consumable) electrode and the work. Shielding is provided by a flux contained within the tubular electrode. Additional shielding may or may not be obtained from an externally supplied gas or gas mixture. Gas Welding A group of welding processes wherein the coalescence is produced by heating with a gas or with flames with or without the application of pressure and with or without the use of filler metal. Gas Tungsten–Arc Welding An arc-welding process wherein the coalescence is produced by heating with an electric arc between a single tungsten (nonconsumable) electrode and the work. Shielding is obtained from one gas or a gas mixture that may contain an inert gas. Pressure may or may not be used. (This process is sometimes called TIG welding.) Lap Joint A joint between two overlapping members. Oxyacetylene Welding A gas-welding process wherein the coalescence is produced by heating with a gas flame or flames obtained from the combustion of acetylene with oxygen with or without the application of pressure and with or without the use of filler-metal. Pressure Welding Any welding process or method wherein the pressure is used to complete the weld. Resistance Welding A group of welding processes wherein the coalescence of overlapping faying surfaces is produced not only with the heat obtained from resistance of the work to the flow of current in a circuit of which the work is a part, but also by the application of pressure. Seal Weld Any weld used primarily to obtain tightness. Shielded Metal–Arc Welding An arc-welding process wherein the coalescence is produced by heating with an electric arc between a covered metal electrode and the work. Shielding is obtained from the decomposition of the electrode covering. Pressure is not used, and filler metal is obtained from the electrode. Submerged–Arc Welding An arc-welding process wherein the coalescence is produced by heating with one or more electric arcs between one or more bare metal electrodes and the work. The welding is shielded by a blanket of granular, fusible material on the work. Pressure is not used, and filler metal is obtained from the electrode and (sometimes) from a supplementary welding rod. Thermit Welding A group of welding processes wherein the coalescence is produced by heating with a superheated liquid metal and slag that result from a chemical reaction between a metal oxide and aluminum, with or without the application of pressure. Filler metal, when used, is obtained from the liquid metal. Welder One who is capable of performing manual or semiautomatic welding. Welding Operator One who operates a welding machine or automatic welding equipment.

5.0

BRAZING TERMS

Automatic Brazing Brazing with equipment that performs the brazing operation without constant observation and adjustment by

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a brazing operator. The equipment may or may not perform the loading and unloading of the work. Brazer One who performs a manual or semiautomatic brazing operation. Brazing A group of metal-joining processes wherein the coalescence of materials is produced by heating them to a suitable temperature, and also by using a filler metal having a liquidus above 840F but below the solidus of the base materials. The filler metal is distributed between the closely fitted surfaces of the joint by capillary action. Brazing Operator One who operates a brazing machine or automatic brazing equipment. Dip Brazing A brazing process in which the heat required is furnished by a molten-chemical or -metal bath. When a moltenchemical bath is used, the bath may act as the flux; when a molten-metal bath is used, the bath provides the filler metal.

Flux Material used to prevent, dissolve, or facilitate the removal of oxides and other undesirable surface substances. Furnace Brazing A brazing process in which the parts to be joined are placed in a furnace, which is then set to a suitable temperature. (When the heat source is placed internal to the workpiece, it may be considered a “furnace.”) Induction Brazing A brazing process in which the heat required is obtained from the resistance of the work to the induced electric current. Lap or Overlap The distance measured between the edges of two plates when they overlap to form the joint. Resistance Brazing A brazing process in which the heat required is obtained from the resistance to electric current in a circuit of which the work is a part. Torch Brazing A brazing process in which the heat required is furnished by a fuel-gas flame.

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18.E.11

Source: Appendix L, Section IV of the ASME B&PV Code.

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APPENDIX

1

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18.E.21

Source: Appendix L, Section IV of the ASME B&PV Code.

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COMPANION GUIDE TO THE ASME BOILER & PRESSURE VESSEL CODE • 77

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