UOP Flanges

Training Services

Flanges

EDS-2004/FL-1

Purpose „

Introduce the common types and uses of flanges, outline the methods to select or design a flange for a given application, describe some of the common reasons for flange leakage, and outline methods for correcting leakage.

EDS-2004/FL-2

The purpose of this presentation is to discuss the common types of flanges and gaskets used in refineries and petrochemical plants. Included is the means used to select an appropriate standard flange for a given service. The means of designing a flange for circumstances where a standard flange cannot be used are briefly introduced. The presentation closes with a discussion of the common causes of and corrections for leakage problems.

Outline „ „ „ „ „ „ „ „ „

Introduction Standards Materials Flange Selection Flange Facings Gaskets Finishes Flange Design Leakage Causes and Correction EDS-2004/FL-3

The presentation will cover the applicable Standards encountered in the determination of a flange class, materials in terms of product form, specified dimensions of a flange, flanged connection components with their associated tolerances, flange design basis criteria, and some common causes of flange leakage and proposed solutions.

Flanged Joint „

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A flanged joint connects piping or equipment by means of bolting, allowing “easy” disassembly and assembly (e.g., valves, instruments, manways) The joint provides a seal against the contained fluid at design conditions –

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Fluid molecule size plays a role (e.g., water is much bigger than hydrogen)

A flanged joint is composed of three components -flanges, gasket, and bolts Performance is influenced by another factor, assembly of the joint Because of their cost and the potential for leaks, use flanges only when absolutely necessary EDS-2004/FL-4

The flexibility of a flanged connection comes with a price. The joint is subject to leakage. Providing a seal while maintaining flexibility is the goal of the system design. Fluid molecule size is a factor in determining the difficulty of sealing a joint. It is more difficult to achieve adequate joint tightness to prevent leakage of material with a small molecule size. For example, hydrogen services are common in hydrocarbon processing plants, but are very difficult to seal due to the small size of the hydrogen molecule. Because of leakage concerns (either initially or during service), the use of flanged joints is limited to locations where the ability to easily disassemble the joint is important. Other joints are welded. The contained fluid may be a vapor or a liquid. The design considerations are nearly the same.

Flanged Joint (continued)

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The gasket provides the seal, bolts provide the forces necessary to seat the gasket and hold the joint together, flanges provide the surfaces for the gasket to seal against and carry the applied forces around the gasket. The joint allows for “easy” disassembly and reassembly of piping or removal of components (e.g., valves and instruments). Because of their cost and the potential for leaks, use flanges only when absolutely necessary.

EDS-2004/FL-5

The gasket provides the seal against the contained fluid. Seating of the gasket involves compressing the gasket so it flows and fills the flange face surface imperfections without being crushed. The resulting seal must be maintained throughout the operating cycle when internal pressure is attempting to separate the flange faces and find a leak path between the gasket and the flange. In elevated temperature services, differential thermal expansion of the joint components and the time dependent effects of creep conspire to create leaks by reducing the forces holding the flanges together. Proper assembly techniques must be observed and alignment of the flange faces must be maintained throughout the operating cycle. Connection by means of bolting allows a joint to be easily and quickly taken apart to accommodate access for installation, removal, maintenance, inspection, or disassembly of a vessel, piping system, or piece of equipment. Examples include vessel manways (for access), valves or expansion joints (for removal or replacement), filters or strainers (to allow removal of the internal element(s)), and unloading nozzles (to allow removal of the vessel contents such as catalyst).

Stud Bolts with Hex Nuts Gasket

Flange

Gasket – Compressible material providing the seal Bolts – Provide the force to compress the gasket and form the seal Flange – Transmits the force from the bolts to the gasket (must not distort or deflect) PPF-R00-01

EDS-2004/FL-6

A joint consists of two flanges, one on each side of a gasket, and bolts used to squeeze the assembly together. The squeezing force comes from tightening the bolts, which applies force to the opposing flanges. The flanges must remain, essentially, ridged in order to transmit the forces evenly to the gasket surface(s). The gasket is then compressed to provide and maintain the seal. A flanged joint is composed of these three separate and independent, although interrelated, components. Proper controls must be exercised in the selection and application of all three elements to attain a joint which has, and maintains, an acceptable leak tightness. Stud bolts and hex nuts are, by far, the most common bolting configuration. For cast iron flanges, which tend to be brittle, machine bolts are often used because they will fail (break) before the flange

Flanges „

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Flanges may be uniquely designed or selected from standardized designs in a recognized document giving dimensions and pressure – temperature capacities Design methods or standards referenced must be in accordance with the governing code

EDS-2004/FL-7

The flanged system can be uniquely designed for a specific application or selected from industry recognized and accepted standardized code compliant designs. The existence of localized stresses, stress concentrations, and discontinuity stresses of a relatively high order in all pressure equipment is well known. The code accounts for localized stresses by using compensating factors in the design formulas for stress.

Standard Flanges „ „

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Flanges from accepted standards have a proven record of widespread safe, reliable use They are economical because standardized dimensions allow vendors to “tool up” for efficient production Everyone uses the same basis and benefits from economies of scale Users may obtain flanges easily and quickly, and need only stock a limited number of varieties EDS-2004/FL-8

Standardized design avoids the costs and delays associated with customized design and fabrication. Standardized flanges should be used whenever possible. Unique designs are reserved for instances where standard designs are inadequate, e.g. limiting clearance constraints or sizes and design conditions outside of the scope of the available standards. Many flange fabricators have their own “standard” flanges. Taylor Forge’s large diameter Class 175 and Class 350 flanges are examples. The fabricator has the necessary dies and equipment to efficiently produce these flanges, which are not covered by industry standards. These flanges must be checked to insure that they are adequate for the intended service, but significant cost and delivery time savings can be realized if they can be used. Similarly, flanges with industry standard dimensions, but non standard materials, may be suitable. Again, the design must be reviewed for adequacy but, if acceptable, the flange can be easily made with existing dies, etc. Code compliance assures consistent safe engineering practice.

Referenced Standards The following standards are referenced by the Pressure Vessel Code (ASME Section VIII) and the Process Piping Code (ASME B31.3) „

ASME B16.5, “Pipe Flanges and Flanged Fittings” Covers flanges from nominal pipe size ½ to 24 inches (12 inches for Class 2500) – Most commonly used standard for refinery and petrochemical plant flanges –

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ASME B16.42, “Ductile Iron Pipe Flanges and Flanged Fittings Classes 150 and 300” –

Used for many ASME pumps (usually in nonhazardous service)

EDS-2004/FL-9

ASME (American Society of Mechanical Engineers) Section VIII, Division 1, Pressure Vessels, governs the design and fabrication of the majority of all refinery equipment. ASME B31.3, Process Piping, is the document to which the majority of the piping in a petroleum refinery or chemical plant is designed and fabricated. Flanges must either comply with one of the industry standards incorporated into the applicable Code, or be uniquely designed in accordance with that Code. In most cases, the applicable Code references the design rules/methods in ASME Section VIII, Division 1, Appendix 2 when a special design is necessary. ASME B16.5 is referenced for flange selection by both Section VIII, Division 1 and B31.3. Class 2500 flanges are for use in very high pressure service and have an upper size limit of 12". The concept of flange classes will be discussed later.

Referenced Standards (continued)

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ASME B16.47, “ Large Diameter Steel Flanges” Covers flanges from 26 to 60 inches, in Classes 150 through 900 – Range of included materials is more limited than in B16.5 (e.g., few nonferritic materials such as Inconel) –

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ASME B16.20, “Metallic Gaskets for Pipe Flanges Ring - Joint, Spiral - Wound, and Jacketed” –

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Unlike its predecessor, API 601, it does not specify default materials.

ASME B46.1, “Surface Texture (Surface Roughness, Waviness, and Lay)” EDS-2004/FL-10

The scope of ASME B16.47 begins where B16.5 ends. B16.47 covers a more limited range of materials than B16.5 (i.e., no high alloys such as Inconel). Two styles are included. Series A flanges are similar to flanges built to MSS-44, a standard often applied to pipelines. They are designed for connection to relatively thin piping and are limited to a maximum temperature of 450°F. Series A flanges may also be found on valve bodies intended for process services. Series B flanges follow the basis used for B16.5 (and the old API 605) and are used for refinery/petrochemical services. Series B is generally more compact than Series A. It is important to note that Series A and Series B flanges are incompatible, i.e., they cannot be bolted together. The edition of each referenced document that is specified (i.e., accepted) by the governing Code must be used. The referenced edition may not be the most recent edition. B16.20 is the standard covering the majority of gasketing used with B16.5 flanges. These are the gaskets commonly found in refineries and petrochemical plants. B16.20 includes gasket dimensions, materials, marking requirements, etc. B46.1 is referenced in B16.5 and B16.47 and defines the flange face surface finish specifications and tolerances.

Obsolete Reference Standards „

API 601, “Metallic Gaskets For Raised - Face Pipe Flanges and Flanged Connections (Double - Jacketed Corrugated and Spiral Wound)” – replaced by ASME B16.20.

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API 605, “Large Diameter Carbon Steel Flanges” – replaced by ASME B16.47.

EDS-2004/FL-11

Both of these are obsolete and are not maintained. These have been replaced by B16.20 and B16.47 respectively.

Scope of ASME B16.5 „ „ „ „ „ „

Materials Pressure - Temperature Ratings Dimensions Tolerances Marking Testing

EDS-2004/FL-12

Subject areas of B16.5 include acceptable flange materials, pressure-temperature ratings for flange class determination, tables of standardized dimensions (based upon flange class), tolerances associated with different components of a flange, required code compliant marking, and the testing required for flanges.

Materials for B16.5 „ „

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Permissible flange materials are listed in Table 1A, bolting materials in Table 1B Flange materials are organized into groups of materials with similar compositions and mechanical properties Ratings are based upon the material in each group with the lowest allowable stress

EDS-2004/FL-13

Materials tables have been grouped to provide compatible flanged joint ratings for materials likely to be used together. Groups frequently have more than one material covered in a respective group. With ratings based on the material in the group with the lowest allowable stress, ratings for some materials within a group are conservative. Material type is also dependent on product form: forging, casting, or plate.

Materials for B16.5 (continued)

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Bolt materials are divided into three groups based upon strength High strength (e.g., A193 B7 or B16) may always be used – Intermediate strength (e.g., A193 B8 Class 2) may be used, provided it has the ability to maintain a sealed joint – Low strength (e.g., A307 and A193 B8 Class 1) is limited to Class 150 and Class 300 flanges and certain gaskets –

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Stud bolts with 2 nuts are typically used EDS-2004/FL-14

Bolts must have adequate strength to be able to both seat the gasket and maintain a seal for the specific application throughout the operating cycle. Low strength bolts are used in the lower Class flange applications, which are generally lower temperature and pressure operating conditions. Stainless steel bolts are avoided because of low yield strength and high thermal expansion. Stud bolts, or bolts without heads and threaded over their full length, are used because they are less expensive and can be safer. A nut is used on each end. Two nuts on each end, tack welding of the nuts, or “spiking” (damaging of the bolt thread just outside of the nut) of the thread may be used to prevent backing off or loosening of the nuts when vibration is a concern. Bolt engagement must be enough so that at least two threads show outside of the nut to ensure full engagement. Otherwise, the bolt may project any distance beyond the nut and either nut may be engaged first, either before or after the bolt is inserted through the bolt hole from either direction. Either nut may be tightened to stress the bolt This provides more flexibility in assembly than a headed bolt. Headed bolts are normally used only with studding flanges (see slide 38) where use of a nut on both ends of the bolt is impossible. Even there, a stud bolt with one nut could be used.

Materials for B16.5 (continued)

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Flanges may be either forged or cast Forged flanges are preferred due to a lower likelihood of flaws or brittle material Cast flanges are usually provided as an integral part of cast valves and other components In forged and cast construction, the grain tends to be non-directional or circumferential, limiting the potential for large cross grain stresses

EDS-2004/FL-15

Forged flanges are generally considered to be a higher quality product. Cast material can have inclusions or imperfections that can affect material properties, even leading to brittle (sudden) failure. They are permitted as part of valves and other complex components because casting is the accepted (and cost efficient) method of producing these components, including integrated flanges. Rather than weld a separate flange to the component, the flanges are included in the casting. Welding would be more costly, would impose the potential problems found at welds, may require heat treatment, and would often increase the flange face to flange face length of the component,

Materials for B16.5 (continued)

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Only blind and certain reducing flanges (those without hubs) may be made from plate One reason is that a flat plate closely approximates a blind flange’s shape (e.g., there is no raised hub) Another reason is that the directional nature of the grain in these flanges is not a serious additional concern because there will be cross grain bending stresses in blind flanges regardless of how the grain is oriented

EDS-2004/FL-16

Although plate material is listed in ASME B16.5, there are severe limitations placed upon its use. It is rarely acceptable to make a flange out of plate material.

Flange Classes „ „

Flanges are organized into classes for identification Classes used by B16.5 are: Class 150 Class 300 Class 400 Class 600 Class 900 Class 1500 Class 2500

EDS-2004/FL-17

Classes provide an easy method to identify categories of flanges. The dimensions of each size of flange within each class are standardized. The design pressure and temperature for the flange form the required rating. The rating is used to determine the applicable flange class. Flange class and flange rating are not the same. An example of a flange class is the designation “Class 300”. An example of a rating is 250psi at 300°F. A rating of Class 300 is meaningless.

Flange Classes (continued)

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Class 150 flanges are lightly built and are often avoided, especially when imposed loads (e.g., from piping) or cyclic loads are present Class 150 flanges are not used above a design temperature of 700ºF because they may tend to deform or creep, possibly opening and leaking Class 400 (and sometimes Class 900) flanges are usually avoided because valves and fittings are not commonly available for them

EDS-2004/FL-18

Class 150 flanges are typically used in low temperature and pressure service where their light weight construction is suitable. They are not suitable for cyclic services or where large imposed loads are present. They are inexpensive and very commonly used in refineries and petrochemical plants. Use of Class 400 may be acceptable for systems that do not contain valves or other components not available in the classification. Consider, however, the need to stock a few Class 400 flanges for these lines. It is often cost efficient to use Class 600 even for these instances to avoid the need to have rarely used spare flanges, gaskets, and bolts in the warehouse. As a practical matter, these spares will probably not be found if and when they are needed.

Flange Classes (continued)

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A rating table is provided for each material group For a given material group, temperature, and nonshock pressure, the table indicates the appropriate flange class Each size flange in each class is built to a standard set of dimensions

EDS-2004/FL-19

Ratings are the maximum allowable non-shock working gage pressure at the design temperature for the applicable material. The appropriate flange class is the class with a pressure rating at the design temperature that is greater than the design pressure. Note that B16.5 and B16.47 each have their own set of rating tables. Although these tables are normally identical, there may be differences - especially just after one document’s tables have been revised. It is possible for a different flange class to be required for the same design conditions because of this difference in the selection tables.

B16.5 Rating Considerations „

Ability to withstand stresses necessary to seat the gasket –

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Special attention is required for some Class 150 and Class 300 flanges with spiral wound gaskets

Adequate thickness to sustain the stresses due to pressure and other loadings necessary to maintain a fluid seal Distortion due to loadings is transmitted through the piping or bolting

EDS-2004/FL-20

Gasket seating is the application of sufficient force to deform the gasket, causing it to flow into and fill imperfections in the flange surface. The characteristics of the gasket and the flange, i.e., hardness and roughness, must be matched to efficiently produce a seal and not deform the flange. During operation, the forces on the gasket are reduced due to the effects of the internal pressure. Enough force must remain to prevent the internal fluid from flowing between the gasket and the flange, i.e., leaking. As previously mentioned, deformation of the flange itself will affect the ability to produce and maintain a seal. The flange must remain stiff and undistorted.

Use of B16.5 Rating Tables „ „

Determine the applicable group for the material used (Table 1A) Determine the design temperature and pressure (including hydrostatic head) that apply

EDS-2004/FL-21

Material group determination includes consideration of the chemical composition and the product form. Pressure can be considerably different at different locations in a vessel considering liquid head and pressure drops. Temperature can also vary throughout a piece of equipment . Use internal pressure (or the external pressure applied as an internal pressure). External pressure is not a concern because it tends to increase gasket seating forces (and/or reduce the bolt force) and does does not “pry” the flange open as much as internal pressure. If determination of the required flange class considers a reduced design temperature for uninsulated flanges, as permitted by the Piping Code (B31.3), the affected flanges must be clearly identified. Future insulation of these flanges is restricted or prohibited.

Use of B16.5 Rating Tables (continued)

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Enter Table 2 and determine a flange class with a pressure rating equal to or greater than the design pressure for the applicable material and temperature Check the flange for hydrotest conditions (including hydrostatic head) with a maximum permitted pressure of 1.5 times the 100ºF rating rounded up to next multiple of 25 psi

EDS-2004/FL-22

The allowance of a hydrotest maximum permitted pressure of 1.5 times the 100oF (ambient) rating is based on the fact that this is a short-term loading condition, and the material properties are in the elastic range. Excluding the effects of hydrostatic head, hydrotest is not intended to govern the design of a flange. Determination of the test pressure involves the same allowable stress ratio (1.5) used to determine the required flange rating for hydrotest. Hydrostatic head may occasionally result in hydrotesting governing the required class. Section 2.5 of ASME B16.5 states; “Flanged joints and flanged fittings may be subjected to system hydrostatic tests at a pressure not to exceed 1.5 times the 100°F rating rounded off to the next higher 25 psig. Testing at any higher pressure is the responsibility of the user, subject to the requirements of the applicable code or regulation .” Section 8.3 requires flanged fittings to be tested at a minimum pressure of 1.5 times the pressure rating at 100°F, rounded up to the next multiple of 25 psig.

Use of B16.5 Rating Tables (continued)

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If the flanges are made of different materials, both must be checked –

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The highest resulting flange Class governs both flanges

Interpolation is permitted between the listed temperatures

EDS-2004/FL-23

Be sure to consider both flanges used in the system - the metallurgy's may differ. One example is a thermowell connection. The thermowell assembly, including the flange, is usually made as one piece using stainless steel. The flange may be paired with a low chrome or carbon steel flange on the vessel. The required flange class for both metallurgy's must be checked, and the greater class used. This may be a different class than is necessary for the remainder of the vessel!

Use of B16.5 Rating Tables (continued)

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Flanges used to be designated by “Pound” rather than “Class” (e.g., 600 Pound). Previously, this referred to the pressure capacity of a carbon steel flange at 850ºF (500ºF for 150 Pound). This is no longer true; therefore, the word Class is used and, except as noted below, the number is only an identifier.

EDS-2004/FL-24

The “pound” designation has a historical origin based on the empirical testing method development that equated a class with a certain allowable pressure at a standardized reference temperature.

Use of B16.5 Rating Tables (continued)

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Rating table pressures for Class 300 and above are based upon the formula: PT = PR x SI / 8750 ≤ PC where:

PT = rated pressure (psi) PR = Class (e.g., 300 for Class 300) SI = material allowable stress at temperature (psi), determined from the rules in Annex D of B16.5 PC = ceiling pressure per Annex D of B16.5 EDS-2004/FL-25

The allowable stresses used are not exactly as listed in other Codes (e.g., B31.3 or Section VIII).

Use of B16.5 Rating Tables (continued)

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Rating table pressures for Class 150 comply with the formula on the previous slide, except use 115 for PR and limit PT to 320 - 0.3T (T = temperature in ºF) B16.5 ratings originated with experience and were essentially empirical Recently (1996), the ratings have been revised to agree more closely with the formulas

EDS-2004/FL-26

Class 300 Temperature - Pressure Ratings Material Temp (ºF)

2 ¼ Cr - 1 Mo (psi)

321 S.S. (psi)

100 200 300 400 500

750 750 730 705 665

720 645 595 550 515

z z z

z z z

z z z

EDS-2004/FL-27

For each respective material, as the temperature increases, the allowable stress decreases and, accordingly, the allowable pressure (pressure-temperature rating) decreases. This trend of a decreasing allowable stress with an increasing temperature is the same for both materials. However, the magnitude of the decrease is different and dependent on the respective material composition and mechanical properties. Different materials have different capacities at the same temperature. Note that, below the creep range, the allowable pressure for stainless steel flanges declines more rapidly than for low alloy (or even carbon steel) flanges. This is because stainless steel is softer and more ductile than most other materials, hence, it may be more easily deformed and leak.

Class 300

PPF-R01-02 EDS-2004/FL-28

This figure illustrates the decline in allowable pressure with temperature in a graphical form. Stainless steel ratings are generally lower than for many other materials.

Example „ „ „ „

Material SA182 - F11 class 2 (1¼ Cr - ½ Mo) Design Pressure PD = 400 psig Design Temperature 1000ºF Allowable Stress (per the Pressure Vessel Code) @ 1000ºF SH = 6,300 psi @ ATM. SC = 20,000 psi Use Class 600 Flange EDS-2004/FL-29

A182-F11 Class 2; Low Chrome (1-1/4 Cr - 1/2 Mo) Forging material -- Use ASME B16.5 material group No. 1.9 to select the required flange class. Allowable stresses at temperature are taken from the governing Code, in this case, the ASME Boiler & Pressure Vessel Code, Section II, Part D - Properties; Table 1A, Maximum Allowable Stress Values S for Ferrous Materials. Allowable stress values are used for the check of hydrotest conditions.

Check for Hydrostatic Test Pressure PT = ( 1.3 ) PD ×

PT = ( 1.3 ) 400 ×

SC SH 20,000 6 ,300

∴ PT = 1,650 psi < 2 ,250 psi 1,500 * 1.5 Allowable Pressure @ Ambient EDS-2004/FL-30

The purpose of the hydrotest is to confirm the adequacy of the piece of equipment for the service conditions by performing the test at an inflated (elevated) pressure and ambient conditions. The objective is to get to a similar relative stress level (i.e., stress vs allowable stress) as that seen during operation (which has a higher design temperature and lower design pressure), in a controlled, safe, test environment at the low temperature ambient conditions. At the higher design temperature, the material has a lower allowable stress. At the ambient test conditions, the material has a higher allowable stress which is used to adjust the pressure to approach the relative stress level present at operating conditions.

Flange Material: A B C , SA182-F11 class 2 (1¼ Cr - ½ Mo) D , SA182-F316 (16 Cr-12 Ni-2 Mo)

B A

Design Pressure: PD = 850 psi Design Temperature: T = 850°F Allowable Stress (per the Pressure Vessel Code): A182-F11 @ 850°F : SH = 18,700 psi @ ATM. : SC = 20,000 psi A182-F316 @ 850°F : SH = 11,600 psi @ ATM. : SC = 20,000 psi For A & B, Use Class 600 For C & D, Use Class 900

C

D

PPF-R00-03 EDS-2004/FL-31

A182-F11 Class 2; Low Chrome (1-1/4 Cr – ½ Mo) Forging material -- Use ASME B16.5 material group No. 1.9 for selection of the required flange class. Allowable stresses at temperature are taken from the ASME Boiler & Pressure Vessel Code, Section II, Part D - Properties; Table 1A, Maximum Allowable Stress Values S for Ferrous Materials. A182-F316; Stainless Steel Forging material -- Use ASME B16.5 material group No. 2.2 for selection of the required flange class. The class of the low chrome flange C is increased to match the Class 900 required for the mating stainless steel flange D. By itself, the pressure-temperature rating of the low chrome flange C for Class 600 would be acceptable. In this case, the higher resulting flange class of the mating flanges governs both flanges. This is necessary so that the bolt size and locations for the two flanges match, and the sealing surfaces and gasket requirements are compatible.

Check for Hydrostatic Test Pressure

PT = (1.3) PD ×

SA 182-F11 PT = (1.3) 850 x

SC SH

20,000 18,700

PT = 1,182 psi < 2,250 psi

EDS-2004/FL-32

Check for Hydrostatic Test Pressure (continued)

SA 182 - F 316 PT = (1.3) 850 ×

20,000 11,600

PT = 1,905 psi < 3,250 psi 2,160 * 1.5 Allowable Pressure @ Ambient EDS-2004/FL-33

Flange Types „

Integral Flanges (flange is part of or buttwelded to the piping or vessel so the system acts as an integral structure) – – – – – –

Welding neck Long welding neck Integrally reinforced Ring Studding Specialty joints such as exchanger closures

EDS-2004/FL-34

This classification covers types of construction where the flange is integral (i.e., part of the same piece) with the neck or vessel wall, butt-welded to the neck or vessel wall, or attached to the neck or vessel wall by any other type of welded joint that is considered to be the equivalent of an integral structure. In welded construction, the neck or vessel wall is considered to act as a hub. The whole system acts as one.

Integral Flanges

Welding Neck

Weld Neck

Ring PPF-R00-04 EDS-2004/FL-35

Welding neck is the most common type of an integral flange. They are designed so that the outside diameter at the junction to the pipe matches the outside diameter of the joining pipe. The inside diameter must be specified. They are used where joining to a pipe. Ring weld is a ring butt-welded onto the end of a pipe. This is typically used only in low pressure service.

Integral Flanges (continued)

Long Welding Neck

PPF-R00-05 EDS-2004/FL-36

Long welding neck flanges are usually dimensioned by their inside diameter. The outside diameter varies with their wall thickness. They are one piece nozzles that provide much of the required reinforcement for the vessel opening in their neck. Because their dimensions do not match those of standard pipes, they are not suitable for welding to a pipe. They are normally welded to the vessel and used where control of the inside diameter is important. Two examples are manways and small nozzles through which instruments are inserted. They can use a constant ID and a varying OD because they do not attach to a pipe, hence they do not need to match a pipe’s OD.

Integral Flanges (continued)

Allow room for the nuts on the bolts (bolts are removed through the mating flange)

Integrally Reinforced PPF-R01-06 EDS-2004/FL-37

These flanges have a thick nozzle neck. The reinforcement for the vessel opening is integral to the flange. The reinforcement is provided by thickening the nozzle neck, sometimes to a greater dimension than the outside diameter of the flange itself! The thick hub makes them unsuitable for connection to piping. Therefore, they are dimensioned by their inside diameter for the same reason as a long welding neck flange, and welded directly to the vessel. Integral reinforcement is preferred over built-up pad reinforcement for several reasons: • • •

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The reinforcement is concentrated near the nozzle/shell junction, where local stresses are at their maximum The reinforcement is one piece, stresses and forces do not transfer from piece to piece across welds There are far fewer welds to make. Welds are costly, are prone to flaws, create residual thermal stresses, create heat affected zones with related metallurgical concerns, and can cause warpage of the joined pieces. There is no flange to pipe weld. This weld would be in a high stress zone caused by the flange rotation and local stresses , as the bolts are tightened.

On the other hand, integral nozzles are machined from a large forging, itself an expensive undertaking

Flared Nozzle

R Weld

PPF-R00-94 EDS-2004/FL-38

Often a “flare” is provided at the base to move the vessel/nozzle weld away from the stress concentration zone at the junction of the shell and nozzle. This places the stress concentrations due to geometry and stresses due to welding at different locations. The detail also allows a contoured, controlled junction geometry to be more easily provided because the transition is part of the forging, not the weld. Additionally, the “flared” detail provides the needed clearance to adequately radiograph the welded joint.

Although a clearly better detail than a conventional integral nozzle, flared nozzles are more costly than conventional integral nozzles. The differential becomes greatest when the flared portion extends beyond the flanged portion. This requires an increase in the initial forging size and additional machining to arrive at the required geometry. UOP uses the flared detail in high temperature services (i.e., the creep range of the material) where differing stresses and creep rates may redistribute (and concentrate) stresses to the weld. Significant cracking has been detected in services such as catalytic reforming. Flared nozzles are also used in high pressure, heavy wall (greater than 4 inches (100 mm)) services. Here the stresses are high and it’s difficult to ensure the proper material properties throughout the thickness. The ability to radiograph the joint is also important. Cyclic or fatigue services are another instance where UOP uses a flared nozzle detail.

Integral Flanges (continued)

Studding

PPF-R01-07 EDS-2004/FL-39

These flanges set into a vessel head or shell where clearance is critical. The design allows for compact installation applications. They are dimensioned by their inside diameter. This type of flange allows a low projection from the mating vessel shell. Often this design includes the nozzle reinforcement as part of the flange. When determining the flange dimensions to provide sufficient opening reinforcement, the effect of the bolt holes must be considered because they project into the area providing the reinforcement. A danger with this type of nozzle is that the bolt engagement is within the flange and is not visible. Use of a short, or wrong diameter, bolt is not visually apparent. A flange failure due to insufficient thread engagement is possible. When stud bolts are used with a through bolted flange, a short bolt is easily seen. A small diameter stud bolt may be seen by comparison with the bolt hole. If the bolt size is still adequate, nuts of the proper size may be used and the bolt will be fully engaged and will work. The thread size in a studded outlet cannot be adjusted to fit a bolt of the wrong size (e.g., only the tip of the threads may be engaged). UOP uses studded outlets only where there is a severe space or clearance problem in a low pressure service (e.g., CCR’s).

Flange Types „

Loose Flanges (no direct attachment between the flange and piping or vessel, does not act as one integral structure) Slip-on – Lap joint –

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Blind Flanges (closures) –

Flat, solid discs used to close an opening (e.g., a manway cover). Generally thick because they are flat, spanning the opening like a beam, developing through thickness bending moments EDS-2004/FL-40

Loose flanges cover types of flanged construction where there is no direct attachment between the flange and the pipe, neck, or vessel wall and where the means of attachment between the flange and pipe, neck, or vessel wall is not considered to be equivalent to an integral structure. In these cases, the pipe, neck, and/or vessel wall has less influence upon the response of the flange to applied and pressure loadings than in an integral design.

Loose Flanges

Vent

Slip-on

Lap Joint PPF-R01-08 EDS-2004/FL-41

A lap joint flange rests on the lap or stub of the piping. Slip-ons slide onto the end of a pipe and are welded to the pipe, usually after the flanges are bolted together. Slip-ons provide some ability to adjust the axial location of the flange. They are limited to low pressure, non-hydrogen, services with no applied moments or forces. Both types of flange may be rotated in place so that the bolt holes of the mating flanges line up. This is not possible with welded in place welding neck flanges (unless the butt welds are made insitu).

Types of Flange Facing Flat Face

Inexpensive „ Used with a full face gasket in low temperature/pressure services „ Easily sealed (i.e., containment of large molecules), non-dangerous, noncyclic services that require low bolt loads and sealing pressures „ ASME non-process pumps and utilities such as cooling water are examples „

PPF-R00-09 EDS-2004/FL-42

This style of flange may be used in refineries for low pressure utility lines and low pressure/temperature process services where ASME pumps are acceptable. This is especially true when the pumps are cast iron, which tends to be brittle. Flat face flanges and full face gaskets are used to reduce the imposed bending moment stresses by moving the bolt force and resultant gasket force closer together. Tightening of the bolts is likely to deflect the flange surfaces towards each other. This causes a non-uniform application of load to the gasket, possibly interfering with the ability to seat and/or seal the gasket. If the deflected flanges contact each other, a portion of the bolt forces will transfer directly from one flange to another without further seating/sealing the gasket. The large gasket surface area, coupled with the limited force available from the bolts, means that the gasket seating/sealing stress that can be achieved is limited. Therefore, these flanges are not applicable for gasket systems requiring “high” seating or sealing forces.

Types of Flange Facing Tongue and Groove

Mating flanges are different - one with a 3/16 inch recess, the other with a ¼ inch raised portion „ The gasket is confined on both edges and partially protected from the internal environment „ The projecting sealing surface is subject to damage „ Reduced bolt load when compared to raised face, due to the smaller gasket area „

PPF-R00-10 EDS-2004/FL-43

The gasket is contained in the mating flange’s groove. A potential detriment to this type of flange facing is that the small protruding portion on one of the flanges can be subject to damage during handling, reducing or destroying the ability to subsequently effect a seal.

Types of Flange Facing Male-Female

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Similar to tongue and groove except the gasket is confined only against blowout The sealing surface is not protected from the internal environment Projecting portion is larger and less likely to be damaged than on the tongue and groove style

PPF-R00-11 EDS-2004/FL-44

Blowout is the internal pressure force that directionally acts to push the gasket radially outward. Although the projecting portion of the flange is much sturdier than on the tongue and groove type, it can still be damaged. Even a radial scratch will affect sealing.

Types of Flange Facing Lap Joint

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Stub end fitting

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Allows use of a different metallurgy for the flange than for the piping Is not welded Avoid in cyclic or services other than low pressure Compensates for some misalignment Limit to low temperature services to avoid differential thermal expansion problems Sealing may be more difficult because the flange and sealing surface (stub) are independent PPF-R00-12 EDS-2004/FL-45

Because the flange rests on the lap (stub end) of the piping, it does not see the internal service fluid. This potentially allows different materials to be used for the flange and pipe/stub. The flange may be a lower grade of material (e.g., low chrome) that is acceptable for the temperature and pressure, but not the internal atmosphere. A higher grade piping material (e.g., Inconel) is required because it is directly exposed to the corrosive environment. Very significant cost savings can be realized in these cases if this style of flange is acceptable. Lap joint flanges are limited to low pressure, non-cyclic services where there are no external loads. These flanges are subject to severe distortion because the end of the hub is not restrained. Distortion or flange rotation under imposed loads or during gasket seating is likely and can reduce the seating and sealing pressures on the gasket, leading to leakage. Differential thermal expansion between the flange and the pipe can also pose a big problem. The differential expansion may be due to differing coefficients of thermal expansion between the two materials, and/or differing temperatures because the flange and stub are not directly connected, thereby limiting heat transfer.

Types of Flange Facing Slip-On

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Vent

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Allows adjustment of the flange position(s) in situ Must be double welded and vented Not used above Class 150 (except for manways and some reducing flanges) or 500°F Not used in hydrogen atmospheres and cyclic services

PPF-R02-13 EDS-2004/FL-46

The enclosed space between the flange and the pipe must be vented to relieve any trapped vapor. The vapor may come from gasses released during welding, or may gather from diffusion of the contained materials through the pipe or weld into the open space between welds. There, it can combine into molecules too large to get out. Hydrogen is a prime example of this phenomenon. If not vented, the trapped gas can crack the welds. Hydrogen accumulation may also cause blistering and hydrogen embrittlement. The system depends upon a couple of fillet welds to hold it together and prevent leakage between the flange and the pipe. Thermal stresses, piping movements, and the forces/moments developed when the flange is bolted together can damage, even break, one or both of the welds, permitting leakage, and/or rotation of the flange, reducing the gasket sealing forces also leading to leaks. UOP restricts the use of slip-on flanges to Class 150 in low temperature (