Specifying Design Requirements for Heat Ex Changers

Engineering Encyclopedia Saudi Aramco DeskTop Standards

Specifying Design Requirements for Heat Exchangers

Note: The source of the technical material in this volume is the Professional Engineering Development Program (PEDP) of Engineering Services. Warning: The material contained in this document was developed for Saudi Aramco and is intended for the exclusive use of Saudi Aramco’s employees. Any material contained in this document which is not already in the public domain may not be copied, reproduced, sold, given, or disclosed to third parties, or otherwise used in whole, or in part, without the written permission of the Vice President, Engineering Services, Saudi Aramco.

Chapter : Vessels File Reference: MEX21003

For additional information on this subject, contact J.H. Thomas on 875-2230

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Vessels Specifying Design Requirements for Heat Exchangers

CONTENTS

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USE OF SAUDI ARAMCO DESIGN SPECIFICATION SHEETS IN HEAT EXCHANGER PROCUREMENT.......................................................................... 1 Use of Heat Exchanger Data Sheets................................................................................ 1 Data Sheet for Shell-and-Tube Heat Exchangers ............................................................ 1 General Procurement Information................................................................................ 4 Section A. Process/Performance Data of One Unit..................................................... 5 Section B. Construction Data of One Shell................................................................. 5 Section C. Miscellaneous ............................................................................................ 6 Data Sheet for Air-Cooled Heat Exchangers................................................................... 7 General Procurement Information................................................................................ 8 Performance Data Section............................................................................................ 8 Design-Materials-Construction Section ....................................................................... 8 EVALUATING CONTRACTOR-SPECIFIED DESIGN CONDITIONS FOR TEMA-TYPE AND AIR-COOLED HEAT EXCHANGER COMPONENTS ............................................................................................................... 10 TEMA-Type Shell-and-Tube Heat Exchangers ............................................................ 10 Shells and Heads ........................................................................................................ 12 Nozzles....................................................................................................................... 12 Girth Flanges.............................................................................................................. 13 Tubesheets.................................................................................................................. 13 Flat Covers ................................................................................................................. 14 Internal Components .................................................................................................. 14 Air-Cooled Heat Exchangers......................................................................................... 16 Tubes.......................................................................................................................... 17 Tube Fins ................................................................................................................... 17 Tube Bundles ............................................................................................................. 17 Tube Supports ............................................................................................................ 17 Header Boxes ............................................................................................................. 18

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EVALUATING CONTRACTOR-SPECIFIED DIMENSIONS FOR SHELL-AND-TUBE HEAT EXCHANGER COMPONENTS........................................ 19 General Dimensional Verification................................................................................. 19 Typical Errors............................................................................................................. 20 Compliance with Saudi Aramco, TEMA, API, and ASME Requirements ............................................................................................................. 20 Use of Computer Programs ........................................................................................... 20 Verifying Computer Programs ................................................................................... 20 Checking Computer Input Data.................................................................................. 21 Checking Computer Output ....................................................................................... 21 Heat Exchanger Components ........................................................................................ 22 Girth Flanges.............................................................................................................. 22 Overall ASME Flange Design Procedure .................................................................. 22 Parameters That Affect Flange Design and In-Service Performance......................... 24 Pass Partition Gaskets ................................................................................................ 30 Flat (Channel) Cover.................................................................................................. 31 Tubesheets.................................................................................................................. 32 Internal Floating Heads .............................................................................................. 36 Tubes.......................................................................................................................... 37 Pass Partition Plates ................................................................................................... 38 Nonpressure Containing Components........................................................................ 39 EVALUATING CONTRACTOR-SPECIFIED DESIGNS FOR AIRCOOLED HEAT EXCHANGER TUBE BUNDLES AND HEADERS .......................... 40 Tube Bundle Design Requirements............................................................................... 40 Overall Bundle Design Requirements........................................................................ 40 Tube Design ............................................................................................................... 40 Tube Support Design ................................................................................................. 41

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Header Design Requirements........................................................................................ 41 Basic Design Requirements ....................................................................................... 42 Header Type............................................................................................................... 42 Gasket Requirements ................................................................................................. 43 Nozzles and Other Connections ................................................................................. 43 Maximum Allowable Moments and Forces for Headers and Nozzles....................... 43 ASME Code Requirements ........................................................................................ 44 Computer Design of Header Boxes............................................................................ 45 Sample Problem 4: Evaluate Contractor-Specified Dimensions for the Inlet/Outlet Header Box of an Air-Cooled Heat Exchanger....................................... 46 COMPLETING A SAFETY INSTRUCTION SHEET FOR A SHELLAND-TUBE HEAT EXCHANGER ................................................................................. 47 Information Covered ..................................................................................................... 47 Where to Find Other Information.................................................................................. 50 WORK AID 1: PROCEDURE FOR EVALUATING CONTRACTORSPECIFIED DESIGN CONDITIONS FOR TEMA-TYPE AND AIRCOOLED HEAT EXCHANGER COMPONENTS ......................................................... 51 Part 1: TEMA-Type Heat Exchangers........................................................................... 51 Part 2: Air-Cooled Heat Exchangers ............................................................................. 52 WORK AID 2: PROCEDURE FOR EVALUATING CONTRACTORSPECIFIED DIMENSIONS FOR SHELL-AND-TUBE HEAT EXCHANGER COMPONENTS...................................................................................... 54 Part 1: General Requirements........................................................................................ 54 Part 2: Girth Flanges and Flat Channel Covers ............................................................ 55 Part 3: Stationary and Floating Head Tubesheets......................................................... 60 Part 4: Floating Heads With and Without Backing Rings............................................ 64 WORK AID 3: PROCEDURE FOR EVALUATING CONTRACTORSPECIFIED DESIGNS FOR AIR-COOLED HEAT EXCHANGER TUBE BUNDLES AND HEADERS ........................................................................................... 68 Part 1: General Requirements........................................................................................ 68

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Part 2: 32-SAMSS-011 and API-661 Requirements ..................................................... 69 Overall Tube Bundle Design Requirements............................................................... 69 Tube Wall Minimum Thickness................................................................................. 70 Selection of Tube Fins ............................................................................................... 70 Header Design Requirements..................................................................................... 71 Headers: Removable-Cover-Plate and Removable-Bonnet-Type .............................. 73 Headers: Plug-Type.................................................................................................... 73 Gasket Requirements ................................................................................................. 74 Nozzles and Other Connections ................................................................................. 74 Part 3: ASME Code Calculations for Header Box Plate Thicknesses .......................... 75 WORK AID 4: PROCEDURE FOR COMPLETING A SHELL-ANDTUBE HEAT EXCHANGER SAFETY INSTRUCTION SHEET................................... 80 GLOSSARY ..................................................................................................................... 84

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USE OF SAUDI ARAMCO DESIGN SPECIFICATION SHEETS IN HEAT EXCHANGER PROCUREMENT The Saudi Aramco specification sheets that are used for design of heat exchangers are also used in various stages of heat exchanger procurement. These sheets are also frequently referred to during heat exchanger operation, inspection, and maintenance inasmuch as they are a source of reference information. Saudi Aramco has specification sheets for shell-andtube, air-cooled, and plate-type heat exchangers. The specification sheets for shell-and-tube and air-cooled heat exchangers were previously introduced in MEX 210.02 with respect to material selection requirements, and will be discussed further in this module. The specification sheet for plate-type heat exchangers will not be discussed. Use of Heat Exchanger Data Sheets Heat exchanger data sheets that are required for capital projects are generally completed by contractors who are employed by Saudi Aramco. The Saudi Aramco engineer will normally review the contractor's work in order to ensure that the heat exchanger data sheet is completed correctly. In some cases, the Saudi Aramco engineer will complete the heat exchanger data sheet when no contractor is involved on the project, or when an existing exchanger must be rerated to new design conditions. The data sheets specify the design information that is necessary in order to request a quotation for a new exchanger and in order to document as-built details of the exchanger. The use of data sheets ensures that there will be a uniform bidding basis among the competing heat exchanger manufacturers and simplifies the bids that these manufacturers submit. Data Sheet for Shell-and-Tube Heat Exchangers Saudi Aramco Form 2714, Shell and Tube Heat Exchanger Specification, is used to specify the design requirements for TEMA-type shell-and-tube heat exchangers. This form is referenced in SAES-E-001, Basic Criteria for Unfired Heat Transfer Equipment. This form is shown in Figure 1, and a copy is contained in Course Handout 3. The form has several sections that are filled in by process and mechanical engineers during heat exchanger procurement. The following paragraphs briefly describe the main sections of this form.

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Form 2714 Figure 1

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Form 2714 Figure 1, cont’d

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General Procurement Information The upper left portion of the form contains an area where general information about the exchanger is specified. The following items would probably be completed before the form is sent out to manufacturers for bids: •

Equipment No.

•

Service

•

Horiz./Vert.

•

No. of Units

•

OR No.

•

Date

•

Type (TEMA Designation)

•

Sour Wet Service/Lethal

•

Service Condition (Cyclic/Noncyclic)

The following information is typically completed either by the manufacturer when he bids on the exchanger or by the contractor when he specifies the purchase information: •

Shell I.D.

•

Tube Length

•

Per unit (shells in series and shells in parallel)

•

Saudi Aramco Order No.

•

Manufacturer's Name

•

Manufacturer's Order Number

•

Manufacturers Drawing Number

•

Total Effective Surface Area and No. of Shells per Unit

•

Effective Surface per Shell

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Section A. Process/Performance Data of One Unit The contractor's process engineer typically completes the process information that is specified in this section. The heat exchanger manufacturer uses this information to design the exchanger from a process standpoint. Note that this section contains columns that are headed “IN” and “OUT” for both the shell-side and the tube-side fluids. The purpose of these columns is to allow the contractor's process engineer to indicate the change in various process parameters as the fluid travels from the inlet to the outlet on both the shell-side and tube-side of the exchanger. In most cases, all of the information that is necessary for the process design of the unit is provided when the specification is sent out for bids. Any discrepancies between the specified process information and what the manufacturer includes in his bid must be resolved before the exchanger is purchased, because these discrepancies could have a significant effect on whether the heat exchanger performs its required process function. From a mechanical design standpoint, the values that are of interest are the temperature, the inlet pressure, and the pressure drop. The mechanical design temperature must be higher than the process temperature. The mechanical design pressure must be higher than the inlet pressure, and some internals must be designed for the pressure drop that occurs in the exchanger. Section B. Construction Data of One Shell The mechanical design information that is necessary to construct the heat exchanger is specified in this section. The contractor's mechanical engineer should provided as much information as possible in order to obtain a uniform basis for bidding; however, in all cases, relevant requirements that are contained in SAES-E-001 must be completed by the contractor. Any information that is left out should be completed by the manufacturer when he submits his bid. There are two columns in the first part of this section, one for the shell-side data and one for the tube-side data. The following information must be specified when the specification sheet is sent out for bids: •

Corrosion Allowance

•

Design Temperature

•

Design Pressure

•

Nozzle Data (Size, Number, Rating, Facing)

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The following design information is normally completed by the contractor or the manufacturer before the exchanger is purchased: •

Test Pressure

•

Limited By

•

Number of Passes per Shell

•

Shell I.D. and O.D.

The second part of Section B contains three columns that cover materials and construction details for the exchanger. The first column is for Material and Specifications, the second column is for Thickness Base Metal/Cladding, and the last column is for PWHT/XR (Postweld Heat Treatment/ Degree of Radiography). Saudi Aramco material specification requirements were discussed in MEX 210.02. In most cases, this information is completed by the manufacturer at the time of bid; however, this information could also be completed by the contractor when bids are requested if the contractor has done a complete mechanical design. The second part of Section B also contains design information that must be specified for the tubes and baffles. Section C. Miscellaneous This section includes information (such as overall dimensions and weights) that is normally completed by the manufacturer when he submits his bid. The section also includes notes for the specification sheet and an area for remarks and general requirements, such as: •

ASME Boiler and Pressure Vessel Code Section VIII, Div. (1 or 2) and Edition (i.e., year)

•

Standards of the Tubular Exchangers Manufacturer's Association (TEMA) Type and Class

•

Saudi Aramco Material System Specification 32-SAMSS-007

•

Saudi Aramco Standard Heat Exchanger Type (Yes/No)

•

Reference Drawings

The lower right corner of the form contains a standard Saudi Aramco drawing title block and revision record.

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Data Sheet for Air-Cooled Heat Exchangers Saudi Aramco Form 2716, Specifications for Air Cooled Heat Exchanger, is referenced by SAES-E-001. This form is shown in Figure 2 and a copy is contained in Course Handout 3. The form has several sections that are completed by process and mechanical engineers at various stages of exchanger procurement. The following paragraphs briefly describe the main sections of this form.

Form 2716 Figure 2

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General Procurement Information This portion of the form contains general information about the heat exchanger. All of this information, except for the manufacturer’s name, is completed by the contractor. Performance Data Section This section contains process information that is completed by the contractor's process engineer. The heat exchanger manufacturer uses this information to design the exchanger from a process standpoint. Note that there is one column for tube-side data and another column for air-side data. The tube-side column contains additional columns that are headed “IN” and “OUT.” The purpose of these columns is to allow the contractor's process engineer to indicate various process parameters that may change as the tube-side fluid travels from the inlet to the outlet of the exchanger. In most cases, all of the information that is necessary to permit the process design of the exchanger is provided when the specification is sent out for bids. Any discrepancies between the specified process information and what the manufacturer includes in his bid must be resolved before the exchanger is purchased because these discrepancies could have a significant effect on whether the heat exchanger performs its required process function. From a mechanical design standpoint, the values that are of interest on the tube-side are the inlet temperature, the inlet pressure, and the pressure drop. The mechanical design temperature must be higher than the process inlet temperature. The mechanical design pressure must be higher than the process inlet pressure, and some internals must be designed for the pressure drop that occurs in the exchanger. The quantities that are of interest on the air side are the design inlet air temperature and the minimum design temperature. Design-Materials-Construction Section This section includes the mechanical design information that is necessary to construct the heat exchanger. The contractor's mechanical engineer should provide as much information as possible in order to obtain a uniform basis for bidding; however, in all cases, relevant requirements that are contained in SAES-E-001 must be completed by the contractor. Any information that is left out should be provided by the manufacturer when he submits his bid.

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The following information is normally specified when the specification sheet is sent out for bids: •

Design Pressure

•

Wind Load

•

Corrosion Allowance

•

Nozzle Data (Size, Number, Rating, Facing)

•

TI and PI connections (Sizes, Number, Reference Details)

•

Design Temperature

•

ASME Code Stamping Requirements (Yes/No)

The bottom and the left margin of the form contains a standard Saudi Aramco drawing title block and revision record.

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EVALUATING CONTRACTOR-SPECIFIED DESIGN CONDITIONS FOR TEMATYPE AND AIR-COOLED HEAT EXCHANGER COMPONENTS SAES-E-001 specifies how to determine the heat exchanger mechanical design conditions based on the operating conditions that are specified on Forms 2714 and 2716 . The process engineer always specifies the operating conditions and usually sets the mechanical design conditions as well; however, the mechanical engineer usually checks the design conditions as a part of his review of the Contractor Design Package. Work Aid 1 provides a procedure that may be used to evaluate the information that is contained in a Contractor Design Package, to determine if the design conditions are specified correctly. In most cases, the maximum operating pressure and temperature can be assumed to be equal to the values that are indicated in the process/performance section of Form 2714 or Form 2716. However, the specified conditions may not be the maximum operating conditions in some cases, such as when the heat transfer surface area must be sized to transfer heat at conditions that are lower than the maximum operating conditions. For the purpose of this course, it will be assumed that the operating conditions that are shown on Form 2714 and Form 2716 are the maximum operating conditions. In actual work, the maximum operating pressures and temperatures must be confirmed by the process engineer in order to ensure that the mechanical design of the heat exchanger is suitable for the most extreme operating conditions. Since heat exchangers transfer heat from one fluid to another, design conditions must be specified for each fluid. Some heat exchanger components are exposed to only one fluid, and other components are exposed to both fluids. Therefore, some components need only be designed for one set of design conditions, while other components must be designed for both sets of design conditions. From a practical standpoint, both sets of design conditions must only be directly considered for shell-and-tube heat exchangers. TEMA-Type Shell-and-Tube Heat Exchangers Figure 3 illustrates which design conditions are imposed on the major components of a shelland-tube heat exchanger, and Figure 4 summarizes the conditions that each major component must be designed for. The following sections discuss the design conditions for specific components.

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Heat Exchanger Design Conditions Figure 3

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Components Designed for Shell-Side Conditions

Components Designed for Tube-Side Conditions

Components Designed for Both Shell-Side and TubeSide Conditions

Shell

Channel

Tubes

Shell Cover

Channel Cover

Tubesheet(s)

Shell Flanges

Channel Flange

Tubesheet Flanges

Shell Nozzles

Channel Nozzles

Floating Head Pass Partition Plate

Design Conditions for Shell-and-Tube Heat Exchanger Components Figure 4 Shells and Heads The shell and shell cover must be designed for the shell-side conditions and the channel and channel cover must be designed for the tube-side conditions. These components are made of cylindrical shells, conical shells, or formed heads, and they are designed for the design pressure at the design temperature using the ASME Code Section VIII. Design procedures that are used for these components were discussed in MEX 202. Nozzles Shell-side nozzles are designed for the shell-side conditions and tube-side nozzles are designed for the tube-side conditions. The nozzles necks are cylindrical shells and are designed in accordance with the ASME Code for their respective design conditions. Because there are cut-outs in the shell due to the nozzle penetration, nozzle reinforcement requirements must be evaluated in accordance with the ASME Code. Nozzles typically have standard flanges in order to permit attachment to the connected pipe. These flanges are designed in accordance with ASME/ANSI B16.5 for up to 600 mm (24 in.) size and must meet other design standards for larger sizes. The flange Class (e.g., Class 150, 300, or 600) is specified based on the required design pressure and design temperature.

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External forces and moments may be exerted on the nozzles by piping that is attached to them, and the nozzles should be designed for these loads in addition to the design pressure. If the piping loads are high, they should be specified to the heat exchanger manufacturer so that he can determine if additional nozzle reinforcement is required. All these aspects of nozzle design were discussed in MEX 202. Girth Flanges Figure 3 shows that a typical shell-and-tube heat exchanger has several girth flanges. On the rear or floating head end of the exchanger, a flange may be used to bolt the shell cover to the shell. This shell cover flange is designed for shell-side conditions. On the front or stationary end of the exchanger, a girth flange may be used to bolt a flat cover onto the channel. This channel flange is designed for the tube-side conditions. A girth flange may also be used to bolt the channel to the shell. In many cases, the tubesheet at the stationary end of the exchanger may be clamped between a pair of girth flanges. In these clamped tubesheet designs, one of the girth flanges is attached to the channel and the other girth flange is attached to the shell. The shell-side flange at the stationary-end tubesheet must be designed for the shell-side conditions, and the tube-side flange at the tubesheet must be designed for the tube-side conditions. In addition, since both flanges are connected by the same set of bolts, the flanges must be designed for a common bolt load. This bolt load may be governed by either the shell-side or tube-side flange design, whichever results in the larger bolt load. The actual design of such flanges will be discussed in more detail in a later section. Girth flanges are normally of nonstandard sizes, and are designed using procedures that are contained in the ASME Code. These flange design procedures are discussed in a later section of this module. Tubesheets Tubesheets are exposed to both the shell-side and the tube-side design conditions. In actual operation, the tubesheets are normally exposed only to a differential pressure (i.e., the difference between the tube-side pressure and the shell-side pressure) and are at a temperature that is between the shell-side and the tube-side temperatures. While the tubesheets could be designed on this basis, tubesheets are major components of the exchanger and are typically designed for the more severe of either the shell-side or the tube-side conditions.

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While conservative, this design approach is realistic inasmuch as it is often possible for one side of the exchanger or the other side to be exposed to its operating conditions while the other side is not. There are some services where it is impossible for only one side of the exchanger to be at its operating conditions while the other side is not (e.g., for a reactor feed-effluent exchanger where both sides are automatically either in operation or not). In other cases, it may be very expensive to design the tubesheet for the worst design conditions. In these special situations, the tubesheet may be designed for only the differential pressure between the tube-side and the shell-side. An additional factor is that hydrotest of the heat exchanger is normally done on each side separately. Thus, one side will have the full hydrotest pressure while the opposite side has no pressure. Tubesheets typically operate at a temperature that is between the shell-side and the tube-side temperatures. The TEMA standard allows tubesheets to be designed for the mean metal temperature unless the owner specifies otherwise. If a mean temperature is used, it should be based on heat transfer calculations that account for the heat transfer coefficients and various modes of operation. Except for fixed tubesheet heat exchangers, tubesheets are usually designed for the higher of either the tube-side or the shell-side temperatures unless it is impossible for the exchanger to be exposed to the higher temperature (e.g., if a refractory lining is installed on the tubesheet to reduce its metal temperature). In the case of fixed tubesheet exchangers, it may not be practical to design the fixed tubesheet if the design conditions are too conservative. Therefore, the tubesheets of fixed tubesheet exchangers are usually designed for a calculated mean temperature. Flat Covers Flat covers are typically used on the channel side of TEMA Type A and Type C exchangers and are designed for the tube-side pressure and temperature conditions. Covers for exchangers that have internal pass partition plates must also be designed to limit the deflection of the cover in order to minimize leakage across the pass partition plate. Deflection limits are specified in TEMA and are discussed in a later section. Internal Components Internal components of a heat exchanger may be subjected to pressure from both sides or may not be subjected to any significant pressure. In general, the design temperature of the component is taken as the higher design temperature of the fluids with which it is in contact. The TEMA standard also permits internal components to be designed for a mean metal temperature unless the owner specifies otherwise. In most cases, internal components are designed for the more severe set of conditions.

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Floating Heads - The tube-side conditions impose an internal pressure on the floating head, and

the shell-side conditions impose an external pressure on the floating head. Both sets of conditions must be checked separately in order to determine which one governs the design of the floating head and its associated flange and backing ring. As with tubesheets, floating heads are usually designed for the more severe of either the shell-side or the tube-side conditions. Recall from MEX 202 that the design of heads and cylinders for external pressure conditions is done using a different procedure than is used for internal pressure conditions. Therefore, the governing condition for the head thickness may not necessarily be the higher pressure side of the exchanger. Tubes - The tubes of shell-and-tube heat exchangers are typically designed independently for

internal pressure at the tube-side conditions and for external pressure at the shell-side conditions. The tube design is governed by the set of conditions that requires the larger tube thickness. The longitudinal stress due to weight and pressure may govern the design in some cases; however, it is usually more economical to reduce the baffle or tube support spacing rather than to increase the tube wall thickness. In fixed tubesheet exchangers, consideration must also be given to designing the tubes for forces that are due to the differential temperature between the tubes and the shell. If the tube loads are too high, normal practice is to use a shell expansion joint rather than to increase the tube wall thickness. Tube vibration may also be a consideration in the design of tubes. Tube vibration is discussed in MEX 210.05. Pass Partition Plates and Longitudinal Baffles - Pass partition plates are located in the channel and

the floating heads of some exchangers. Typically, these plates are designed for the maximum normal pressure drop across the tube side. Some exchanger configurations include shell-side longitudinal baffles, and these baffles must be designed for the shell-side pressure drop. Nonpressure Containing Components - Nonpressure containing components include tie-rods,

spacers, impingement plates, baffles, and support plates. The design of these components is typically based on minimum sizes that are specified in TEMA based on nominal shell diameter. Tube support plates that are thicker than the TEMA minimum values may be required in some cases where there is a large shell-side corrosion allowance or if flow pulsation or tube vibration is a special design consideration.

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Air-Cooled Heat Exchangers As described in MEX 210.01, air-cooled heat exchangers are composed of a tube bundle, one or more header boxes, a steel frame, steel ductwork, and machinery for the fan. Several of these primary components are illustrated in Figure 5. The basic minimum thicknesses for many of the components are given in the SAMSS or API standards, and the tubes and the header boxes are designed for internal pressure in accordance with the ASME Code. The design of the machinery and structural steel parts is outside the scope of this course. The design conditions that are used for the tubes, tube fins, tube bundle, tube supports, and header boxes are briefly discussed below.

Typical Air-Cooled Heat Exchanger Tube Bundle Components Figure 5

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Tubes The tubes of an air-cooled heat exchanger are typically designed with respect to strength, based on the process-side design pressure and design temperature. Design of the tubes must also take into consideration the additional longitudinal stress that is caused by the weight loads from the tubes, tube fins, and tube contents. Note that it is usually more economical to shorten the tube support spacing, rather than increase the tube wall thickness in cases where excessive longitudinal stress or tube sagging are a problem. The needed tube surface area of the exchanger is usually determined based on the air-side design temperature conditions. Tube Fins Several different designs are available that may be used to attach fins to the tubes. The tube metal temperature typically governs which fin attachment option is used for a specific heat exchanger. The fin attachment design is typically selected based on the maximum processside design temperature, because it is usually possible to stop the air flow while the process fluid continues to flow. Tube Bundles The tube bundle must be designed for the process-side design temperature in case the air flow is stopped. The bundle must be designed for differential thermal expansion between it and the supporting frame and structure. The tube bundle must be designed to be rigid in order to permit handling it as a complete assembly both in the shop and in the field. The tube bundle and side frame assemblies must also be designed to withstand the required wind loads and earthquake loads. Tube Supports The tubes are supported at intervals that are short enough to prevent excessive sagging due to the imposed weight loads. Excessive sagging could cause flow distribution problems, or cause meshing or crushing of the fins. The fluid property information, design temperature, and tube design details that are specified on Form 2716 are used to help determine the required tube support spacing.

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Header Boxes The header boxes are designed for internal pressure at the process-side design conditions. The specific heat exchanger service and design conditions may affect design details of the header box. Header box design details are discussed later in this module. API-661 limits the loads that may be imposed by connected piping on heat exchanger nozzles in order to avoid overstressing the nozzles and the header boxes. The maximum permitted nozzle loads are a function of nozzle diameter. The header boxes must also be designed to transmit piping loads from the nozzles to the exchanger-side frame and support structure.

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EVALUATING CONTRACTOR-SPECIFIED DIMENSIONS FOR SHELL-ANDTUBE HEAT EXCHANGER COMPONENTS A shell-and-tube heat exchanger is composed of many components, such as cylindrical or conical shells, flat plates, and formed heads. Although minimum thicknesses for these components are given in 32-SAMSS-007, API-660, TEMA, or the ASME Code, these components must normally be designed and dimensioned for the specific heat exchanger design requirements. The design of components such as cylindrical shells and formed heads was covered in MEX 202 and will not be discussed. Components that are unique to shelland-tube heat exchangers (e.g., girth flanges, flat [channel] covers, internal floating heads, tubesheets, tubes, and pass partition plates) will be discussed. To evaluate the dimensions that a contractor or manufacturer specifies for shell-and-tube heat exchanger components, the Saudi Aramco engineer typically checks that all dimensions are: •

Consistent on all drawings and in all specifications and calculations that are made by the manufacturer and that are included in the Contractor Design Package.

•

In accordance with the design and calculation requirements that are specified in Form 2714, 32-SAMSS-007, API-660, TEMA, and the ASME Code.

Work Aid 2 provides an overall procedure that may be used to evaluate the dimensions that are specified for the major components of shell-and-tube heat exchangers. The sections that follow elaborate on several aspects of this procedure and discuss several of the design requirements for specific heat exchanger components. General Dimensional Verification The dimensions that are specified for heat exchanger components must be checked to ensure that they are consistent and that they comply with Saudi Aramco and industry requirements. Fundamental and simple errors are often made that are not related to design calculations.

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Typical Errors Many mistakes are made when copying dimensions from calculation sheets to fabrication drawings or from one drawing to another. Corrosion allowance is sometimes left out or may be counted twice when component thicknesses are indicated on the drawing. In some cases, details may not be consistent between the overall heat exchanger assembly drawing and other drawings that specify individual component details. Another typical mistake occurs when a detail on one drawing is revised, but other details in the Contractor Design Package are not revised to be consistent with the change. Compliance with Saudi Aramco, TEMA, API, and ASME Requirements While manufacturers are all familiar with TEMA, API-660, and ASME Code requirements, the manufacturer may not be familiar with Saudi Aramco's specific requirements. In some cases, dimensional requirements or dimensional limits that are given on Form 2714 or in 32SAMSS-007 may be neglected. In other cases, the manufacturer may misinterpret a Saudi Aramco requirement. Therefore, several problems can usually be identified if a review for compliance is made with respect to specific Saudi Aramco requirements. Use of Computer Programs The required mechanical design calculations for heat exchanger components are normally done using computer programs. Therefore, the Saudi Aramco engineer will normally have to check computer-generated calculations, in addition to checking the fabrication exchanger drawings, in order to confirm that the heat exchanger design is acceptable. Verifying Computer Programs The required design calculations must be done in accordance with the appropriate TEMA and ASME Code requirements. In order to check a manufacturer's computer program, it is usually sufficient to review a verification example problem that was made for the program. If no verification problem is available, another approach is to select a typical exchanger and thoroughly check the calculations for the selected exchanger. This check can be done by redoing the calculations by hand or by using another, commercially-available computer program for heat exchanger design that has already been independently verified. Commercial programs that are widely used are usually updated frequently and corrected quickly when errors are found.

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All of the heat exchanger calculations that are used in this module were made using the CODECALC computer program by Coade, Inc. This program is available within Saudi Aramco. It may be assumed that the CODECALC program has been thoroughly tested and verified. All computer programs require the same input, use the same TEMA or ASME Code equations, and give similar output. The purpose of this course is not to instruct Participants in how to run a specific computer program, but in how to evaluate whether the contractor or exchanger manufacturer has done his job properly. Therefore, the Work Aids were developed to facilitate the process of checking the input and output of a typical computer program. However, the terminology that is used in the input and output of the CODECALC program is explained where necessary. Checking Computer Input Data Checking for consistency between the computer program input data and the information that is included in various parts of the Contractor Design Package is tedious but is necessary. The necessary input includes design conditions, some dimensional information, material properties, and other Code design information. Some computer programs require that necessary design factors be manually entered from tables or figures that are in the standard or Code, whereas other programs have internal data bases that contain the needed information. A small mistake in the computer program input can result in completely incorrect calculations. Checking Computer Output Checking that the contractor or manufacturer has correctly interpreted the computer program output is tedious, but this checking is still necessary because errors can still be made at this stage. Examples of errors that can be made at this stage include overlooking corrosion allowances or specifying information on the fabrication drawings that does not coincide with the program output (e.g., an incorrect thickness). Heat exchanger programs can also calculate the Maximum Allowable Working Pressure (MAWP) of exchanger components based on a specified component thickness and other asbuilt dimensions. The basic approach that is used to solve for MAWP was discussed in MEX 202. For heat exchangers, the MAWP is determined by solving the appropriate TEMA or ASME Code equations for pressure in terms of the as-built thickness and other dimensions. The MAWP is then shown in the program output. Knowing the MAWP is useful if it is required to rerate an exchanger. Rerating a heat exchanger is discussed in MEX 210.05.

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Heat Exchanger Components This section will review the design requirements for the following components of shell-andtube heat exchangers and air-cooled heat exchanger. •

Girth flanges

•

Pass partition gaskets

•

Flat (channel) cover

•

Tubesheets

•

Internal floating heads

•

Tubes

•

Pass partition plates

•

Nonpressure containing parts

Girth Flanges Girth flanges are custom-designed for most shell-and-tube heat exchangers, although some manufacturers attempt to standardize some aspect of their girth flange designs. All girth flanges should be checked for compliance with the ASME Code, Section VIII Div. 1, Appendix 2. The procedure is quite involved and is best done by using a computer program. Work Aid 2 contains an overall procedure that may be used to check design calculations that are provided by a contractor or manufacturer for exchanger girth flanges. The following sections briefly describe: •

The steps in the overall ASME flange design procedure.

•

The parameters that affect flange design and in-service performance.

•

The tubesheet girth flange design requirements for TEMA Type A and Type B exchangers.

Overall ASME Flange Design Procedure The flange design procedure consists of the following steps: •

Determining bolting requirements.

•

Determining flange design loads and moments.

•

Determining stresses in two flange ring and flange hub.

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The first main step in flange design is usually to determine the number and size of bolts that are required for the flange. Bolting requirements are determined by calculating the loads on the bolts during both normal operation (i.e., based on the design conditions), Wm1, and during the initial flange boltup (i.e., the gasket seating conditions), Wm2. The bolt area that is required for each of these loads is then calculated by dividing each bolt load by the allowable stress of the bolts at design temperature and room temperature, respectively. Either the operating case or the gasket seating case may yield the minimum required bolt area, Am. Inasmuch as bolts come in standard sizes, and inasmuch as there are limitations on the spacing between bolts, the actual bolt area, Ab, is usually greater than the maximum required bolt area. The next step is to determine the design loads and moments on the flange. These loads include the design bolt load on the flange (W), the hydrostatic pressure loads that act on the flange (HD and HT), and the gasket sealing force (HG). Because these loads do not all act at the same location on the flange, effective moment arms (hD, hT, and hG) are calculated based on the locations of the bolts and gasket and on the flange geometry (See Figure 6). The appropriate loads are then multiplied by the effective lever arms in order to determine flange design moments for the operating case and the gasket seating case.

Flange Loads and Moment Arms Figure 6

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Finally, the stresses in the flange ring and the flange hub are calculated using stress factors that are in the ASME Code (which are based on the flange geometry), the applied moments, and the flange geometry. These stresses are calculated for both the operating case and the gasket seating case and are then compared to the appropriate Code allowable stress. If the flange is properly designed, all of the flange stresses will be lower than the appropriate allowable stresses. It may be necessary to increase the flange thickness, change the hub dimensions, or make other changes to the flange design parameters in order to keep the flange stresses within their allowable limits. The computer programs that are used for flange design use iterative calculation procedures in order to optimize flange design. Parameters That Affect Flange Design and In-Service Performance The following additionally significant parameters are discussed below: •

ASME Code m and y parameters.

•

Specified widths for peripheral ring gaskets and pass partition gaskets.

•

Flange facing and nubbin width w.

•

Bolt size, number, and spacing.

The gasket factor, m, is a parameter that determines the amount of force that is required to keep the gasketed joint tight. The minimum design seating stress, y, is a parameter that determines how much gasket stress is required to initially seat or deform the gasket. Both of these parameters are used in the flange design calculations. The ASME Code specifies m and y based on gasket type in Table 2-5.1 (excerpted in Figure 7). Higher values of m and y typically indicate that a gasket is harder to seal or seat. While this is a consideration in gasket selection, gasket type and gasket material are usually selected based on historical service experience and corrosion resistance. For example, both TEMA and 32-SAMSS-007 specify gasket requirements based on service conditions as discussed in MEX 210.02. In addition, m and y are only two of many parameters in the flange design calculations.

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Gasket Material

Gasket Factor m

Min. Design Seating Stress y, psi

Facing Sketch and Column in Table 2-5.2

Flat metal, jacketed asbestos filled: Soft aluminum

3.25

5 500

Soft copper or brass

3.50

6 500

Iron or soft steel

3.75

7 600

Monel

3.50

8 000

4-6% chrome

3.75

9 000

Stainless steels and nickel-base alloys

3.75

9 000

Soft aluminum

4.00

8 800

Soft copper or brass

4.75

13 000

Iron or soft steel

5.50

18 000

Monel or 4-6% chrome

6.00

21 800

Stainless steels and nickel-base alloys

6.50

26 000

(1a), (1b), (1c), (1d); (2); Column II

Solid flat metal:

(1a), (1b), (1c), (1d); (2), (3), (4), (5); Column I

ASME Code m and y Factors Figure 7 TEMA specifies a minimum required width for the peripheral ring gaskets at external joints and for pass partition gaskets. Although TEMA exchangers operate over a very wide range of service conditions, these minimum gasket widths have been used for many years and are typically specified.

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The gasket widths that are referred to in TEMA are actual minimum widths. In addition to the actual minimum width, N, two other gasket widths are referred to in the ASME Code: the basic seating width, bo, and the effective seating width, b. The effective seating width is a function of the basic seating width, and the basic seating width is a function of the actual width and the type of flange face. See Table 2-5.2 in the ASME Code (Excerpted in Figure 8). In general, wider gaskets provide better sealing, but a wider gasket also requires more bolting to seat and seal the gasket. The required flange thickness increases as the amount of bolting increases.

Effective Gasket Seating Width, b b = bo when b o ≤ 1/ 4 in.; b = b o when bo > 1/ 4 in. ASME Code Gasket Widths Figure 8

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The effective seating width, b, discussed above is also a function of the flange facing type and the nubbin width, w, for flat metal gaskets. Table 2-5.1 (excerpted in Figure 7) in the Code indicates which facing sketch is applicable for a given gasket type and material, and Table 25.2 (Figure 8) shows the equations for determining b based on w, N, and the type of flange facing. Note that b is the factor used in the subsequent Code equations to determine the load required for sealing the gasket during operation, WM1, and the load required for seating the gasket initially, WM2. Once a gasket type, material, width, and facing are selected, the required bolting area can be determined. The bolt size, number and spacing that are used to clamp the flanges together are interrelated parameters that affect the overall design of the flanges. Bolting is typically selected per TEMA Table D-5 (See Figure 9), with the added restrictions in TEMA Par. R-11.1 that the minimum bolt size is 19 mm (3/4 in.). Bolt Size

Threads

Nut Dimensions

Bolt Spacing

Radial Distance

Radial Distance

Edge Distance

Wrench Diameter

Bolt Size

dB

No. of Threads

Root Area, in.2

Across Flats

Across Corners

B

Rh

Rr

E

a

dB

1/2

13

0.126

7/8

0.969

1 1/4

13/16

5/8

5/8

1 1/2

1/2

5/8

11

0.202

1 1/16

1.175

1 1/2

15/16

3/4

3/4

1 3/4

5/8

3/4

10

0.302

1 1/4

1.383

1 3/4

1 1/8

13/16

13/16

2 1/16

3/4

7/8

9

0.419

1 7/16

1.589

2 1/16

1 1/4

15/16

15/16

2 3/8

7/8

1

8

0.551

1 5/8

1.796

2 1/4

1 3/8

1 1/16

1 1/16

2 5/8

1

Bolting Data Figure 9

TEMA Table D-5 indicates the number of threads per inch and the tensile stress area at the root of the threads. The number of bolts multiplied by the bolt root area of a single bolt must be greater than the minimum required bolt area, Am. The bolts must be far enough away from the shell or hub of the flange and be far enough apart circumferentially so that there is adequate clearance to permit access for a wrench to tighten and loosen the bolts. TEMA Table D-5 also indicates minimum dimensions to ensure adequate access for standard wrenches. While it may appear that maintaining these minimum dimensions can easily be achieved if a few large bolts are used, the bolts should also be spaced as close together as practical for several reasons.

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•

Having fewer bolts increases the bolt load moment arms. Larger moment arms increase the bending moments for which the flange must be designed and thus increase the required flange thickness.

•

TEMA also requires in Par. 11.2 that the flange design moment be increased if the bolts are widely spaced. Here again, this results in a thicker flange.

•

Excessive bolt spacing could make the flange more prone to leakage since the portions of the gasket that are located between the bolts might not be compressed sufficiently by the bolts to maintain a tight seal.

A final TEMA requirement in Par. 11.24 is that the total number of bolts be an integral multiple of four. A manufacturer's computer program will typically design the bolting and the flange subject to all the above conditions. The responsibilities of the Saudi Aramco engineer would then be to check the computer program input, to determine that the appropriate TEMA and ASME Code factors and allowable stresses were used, and to confirm that the computer program output has been correctly interpreted and incorporated into the design. Tubesheet Girth Flange Design Requirements for TEMA Type A and Type B Exchangers - TEMA

Type A and Type B exchangers have the fixed tubesheet compressed between two girth flanges. These girth flanges require special design consideration. Each flange must be designed for the appropriate design conditions on each side of the tubesheet, and for the common bolt load that is imposed on each flange. The common bolt load may be based on the operating or gasket seating loads, and these loads may be different on each side of the tubesheet. The proper design of these girth flanges typically requires that at least three separate flange calculations be made. •

The first calculation is done to design the flange on the channel side of the tubesheet for the tube-side design conditions.

•

The second calculation is done to design the flange on the shell-side for the shell-side design conditions.

•

After reviewing the first two calculations, one flange will typically be found to require more bolting than the other. In this case, the flange that requires less bolting must be redesigned for the larger amount of bolting.

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Sample Problem 1 covers how to evaluate the design of this type of tubesheet girth flange. Sample Problem 1: Evaluate Contractor-Specified Dimensions for the Mating Girth Flanges at the Tubesheet of a TEMA-Type AET Heat Exchanger - You must evaluate the contractor-specified

dimensions for the mating girth flanges at the fixed tubesheet end of a Type AET heat exchanger. All the information that is needed to solve this problem is in Contractor Design Package 4 in Course Handout 4. This information includes the heat exchanger specification sheet, flange dimensions, and the CODECALC computer program output for the shell girth flange and the mating channel girth flange. Part 2 of Work Aid 2 is used to solve this problem. The first step in evaluating a design is to compare the common dimensions between the two mating flanges and the number and size of bolts that are shown in the detail drawings for the flanges. Flange dimensions are also checked for consistency between the drawing details and the computer program input and output. Note that additional design information is included in the computer program input, such as ASME Code gasket factors and the allowable stresses for the flange material and the bolting. This additional design information must be checked against the ASME Code requirements. All of the computer input appears to be correct in this problem. The next step is to evaluate the overall design. The tube side and shell side of the exchanger have different design conditions; therefore, calculations were first made for the shell flange for the shell-side conditions, and then made for the channel flange for the tube-side conditions. By comparing the computer output for the required bolt area, Am, between the two computer runs, it is seen that the shell flange governs the bolting requirement for these mating flanges because it requires a larger value for Am. Therefore, a second analysis was made for the channel flange to account for the bolt load that is required by the shell flange. In reviewing the input for the second channel flange design case, it can be seen that the appropriate values for the operating bolt load, gasket seating bolt load, and the flange design bolt load have been entered for the mating flange bolt loads. These bolt loads were taken from the previous calculations that were done for the shell flange. Because the computer program input and output have been checked and the program has been verified, it is concluded that the dimensions specified by the manufacturer for the girth flanges are correct inasmuch as the dimensions are in accordance with the computer program output.

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Pass Partition Gaskets Most exchangers have at least two tube-side passes. A pass partition gasket is used in the channel for these exchangers in order to provide internal sealing between the tube passes at the pass partition plate (see Figure 10). A pass partition gasket is also required at the floating head end for exchangers that have more than two tube-side passes. The pass partition gasket has more surface area that must be compressed when compared to a conventional gasket that only has material at its periphery. Therefore, the flange bolting must be sufficient to compress the gasket enough at both its periphery and at the pass partition plate. If the exchanger has more than two tube passes, the pass partition gasket has even more surface area that must be compressed.

Pass Partition Gasket Figure 10 Although not specifically referred to in the ASME Code calculations or in TEMA, girth flanges should be designed to provide additional bolting in order to adequately compress pass partition gaskets and achieve a tight seal. Properly designed bolting should be able to compress the gasket at both its periphery and at the pass partition.

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Bolting design can be handled in several ways. In the CODECALC program, the length of the pass partition gasket may be entered as a separate parameter. If the width of the pass partition gasket (Npp) differs from the width of the peripheral gasket (N), the length that is input (Lpp) is adjusted as follows:  Npp  Lpp = (Gasket Inside Diameter) ×   N  The bolt area that is required is then increased to account for the additional gasket area.

Flat (Channel) Cover Flat covers are used on the channels of TEMA Type A and Type C exchangers in order to close the end of the channel (Refer to Figure 11).

Flat (Channel) Cover Figure 11

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The ASME Code design procedure for flat covers is specified in Par. UG-34 and is based on determining the minimum cover thickness that is required to limit the stress in the cover plate to the material allowable stress. In the ASME procedure, the thickness of the flat cover, t, is determined as a function of the pressure, P, the cover plate allowable stress, S, the flange design bolt load, W, the diameter of the gasket, d, and the gasket moment arm, hG. In addition, TEMA also restricts the maximum deflection that can occur at the center of the cover if the exchanger has pass partition baffles. The limit on cover deflection is specified in order to minimize leakage that can occur across the pass partition baffle. TEMA Par. RCB9.21 limits the maximum cover deflection to the following limits: •

0.76 mm (0.03 in.) for nominal cover diameters through 600 mm (24 in.).

•

0.125% of the nominal cover diameter for larger sizes.

An equation for calculating the deflection at the center of the cover is provided in TEMA Par. RCB-9.21. Computer programs are often used to make the calculations for a flat channel cover even though the calculations are not highly complicated. The cover deflection limit, rather than the ASME Code allowable stress, will generally govern the channel cover thickness for heat exchangers that have a pass partition plate. The procedure that is in Work Aid 2 for girth flanges also may be used to check design calculations that are provided by a contractor or manufacturer for exchanger flat (channel) covers. Tubesheets Different types of tubesheets may be used in heat exchangers. The most frequently used and simplest types of tubesheets to design are those associated with TEMA Type S, Type T, and U-tube type exchangers. The procedures that are most often used for the design of tubesheets in these exchangers is in accordance with TEMA Paras. RCB-7-1 through RCB-7-13. The ASME Code also has a tubesheet design procedure in nonmandatory Appendix AA. The ASME procedure is applicable for U-tube type and fixed tubesheet types of exchangers. Note that the ASME Code procedure is more complicated than the TEMA procedure, and that the TEMA procedure is used to design most heat exchanger tubesheets. Work Aid 2 covers only the TEMA procedure. The following paragraphs discuss several considerations for tubesheet design.

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Tubesheet Thickness - TEMA Par. RCB-7.12 requires that the tubesheet thickness be measured

at the bottom of the pass partition baffle groove or the shell-side longitudinal baffle groove, if so equipped. This is the thinnest portion of the tubesheet, as illustrated in Figure 12.

Tubesheet Thickness Figure 12

The effective thickness must also exclude any corrosion allowance that is required that is in excess of the partition groove depths. The effective thickness should be exclusive of any applied facings, but the thickness of cladding or weld overlay that is in excess of the specified corrosion allowance may be considered as effective in accordance with TEMA and ASME procedures.

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Basic Minimum Thicknesses - TEMA specifies basic minimum thicknesses for the tubesheet

based on overall fabrication and handling requirements when the tubes are expanded into the tubesheet. Par. RCB-7.13 requires that the tubesheet thickness, exclusive of corrosion allowance, should be at least equal to the nominal tube diameter but that the tubesheet thickness including corrosion allowance cannot be less than 19 mm (3/4 in.). Effective Thickness - The required effective thickness of the tubesheet is determined based on

limiting the bending and shear stresses in the tubesheet to the appropriate ASME Code allowable stress. The appropriate TEMA paragraph references are as follows: •

Par. RCB-7.132 determines tubesheet thickness based on limiting the bending stress in the center of the tubesheet.

•

Par. RCB-7.133 determines the tubesheet thickness based on limiting the shear stress in the tubesheet at the periphery of the tube bundle.

•

Some tubesheets may be extended as a flange, as in a T-type floating end tubesheet. Par. RCB-7.134 determines the thickness of the flanged extension portion of the tubesheet.

Fixed Tubesheet Exchangers - A significant design issue in fixed tubesheet type exchangers is

differential thermal expansion between the shell and the tubes. Fixed tubesheet exchangers are exchangers where both the front (i.e., channel) end tubesheet and the rear (i.e., shell) end tubesheet on the exchanger are rigidly attached to the shell. These exchangers, designated as L-, M-, or N-types, are much more complicated to design than S-, T-, or U- type exchangers because the tubes and shell interact with the tubesheets. Excessively high differential temperatures between the shell side and tube side of the exchanger can result in the following: •

High thermal stresses in the tubesheet or shell that can and cause a fatigue failure.

•

High longitudinal loads in the tubes that could buckle the tubes and/or cause leakage at the tube-to-tubesheet joints.

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Because of these concerns, some fixed tubesheet exchangers may be equipped with an expansion joint in the shell. The expansion joint permits differential thermal expansion between the shell side and the tube side without causing excessive loads or stresses. An expansion joint is normally necessary if the temperature differential between the tube wall temperature of any one tube pass and the average shell side temperature exceeds approximately 28°C (50°F). However, when the shell and tube materials have different thermal expansion coefficients, a stress analysis is required even when the temperature differential is less than 28°C (50°F). Fixed tubesheet exchangers are usually designed using a computer program that determines the interactions between the tubes, the shell, and the tubesheet. These programs typically make the calculations in accordance with TEMA Par. RCB-7.16 and with Nonmandatory Appendix AA of the ASME Code. Tubesheets that have a nonuniform thickness, or that incorporate flexible knuckles at their periphery, may be used on some exchangers. These tubesheets are considered as special cases in TEMA Par. RCB-7.3 and should be designed in accordance with Div. 1 or Div. 2 of the ASME Code. Sample Problem 2: Evaluate Contractor-Specified Dimensions for the Floating End Tubesheet of a TEMA-Type AET Heat Exchanger - You must evaluate the contractor-specified dimensions for

the floating end tubesheet of a Type AET exchanger. All the information that is needed to solve this problem is in Contractor Design Package 4 in Course Handout 4. This information includes the heat exchanger specification sheet, dimensions, and the CODECALC computer program output for the floating end tubesheet. Part 3 of Work Aid 2 is used to solve this problem. The first step in evaluating the design is to compare the dimensions that are specified in the drawing of the tubesheet to the computer program input. This comparison includes items such as the facing ID, tubesheet OD, and bolt circle diameter. Additional design information that is included in the computer program input, such as the gasket m and y factors and the tubesheet allowable stress, is also checked with the ASME Code. All of the computer input appears to be correct in this problem. Inasmuch as the computer program input has been checked and the program has been verified, it is concluded that the thickness specified for the floating end tubesheet is correct because the CODECALC output shows no overstress, and the dimensions that are shown in the tubesheet drawing coincide with the program output.

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Internal Floating Heads Internal floating heads are used on TEMA-Type AES and Type AET exchangers. The S-type floating head requires a split backing ring to clamp the floating head to the tubesheet. The Ttype floating head is bolted directly to the tubesheet. These head types are illustrated in Figure 13. The required thicknesses of the flange ring and of the dished head for both types of floating heads may be determined using Appendix 1-6 of the ASME Code.

Types of Floating Heads Figure 13 If the floating head is subjected to a high external (i.e., shell side) pressure, the head must also be checked for buckling in accordance with the ASME Code Section UG-33.

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The Appendix 1-6 method is relatively simple and can be done on a calculator, but computer programs are normally used to design floating heads. Although acceptable to the ASME Code, this method is approximate in that it does not consider the continuity between the flange ring and the dished head. The ASME Code indicates that a more exact method of analysis which considers the continuity between the flange ring and the head may be used if it meets the requirements of Section U-2 of the Code. A procedure that was published by Soehren in ASME paper ASME 57-A-7-47, The Design of Floating Heads for Heat Exchangers, is one such method that is acceptable to the Code. In many cases the Soehren method yields a thinner, more economical flange ring and floating head design than does the Appendix 1-6 method. However, the Soehren method is more complicated, requires the solution of simultaneous equations, and is best calculated using a computer program. Sample Problem 3: Evaluate Contractor-Specified Dimensions for the Floating Head Cover of a TEMAType AET Heat Exchanger - You must evaluate the contractor-specified dimensions for the

floating head of a Type AET exchanger. All the information that is needed to solve this problem is in Contractor Design Package 4 in Course Handout 4. This information includes the heat exchanger specification sheet, the dimensions of the floating head, and the CODECALC computer program output for the floating head. Part 4 of Work Aid 2 may be used to solve this problem. The first step in evaluating the design is to compare the dimensions on the tubesheet and the floating head, such as facing ID, OD, and bolt circle diameter. Dimensions are also checked for consistency between the dimensions that are shown in the detail drawings and the dimensions in the computer program input. Additional design information is included in the computer program input, such as the gasket m and y factors and the allowable stresses for the ring and the dished head materials. This additional information should be checked against the ASME Code. All of the computer input appears to be correct in this problem. Since the computer program input and output have been checked and the program has been verified, it is concluded that the specified dimensions for the floating head are correct because the dimensions shown on the drawing are in accordance with the computer program output. Tubes The tubes in TEMA P-, U-, S-, T-, and W-types of exchangers are typically designed in accordance with the ASME Code Par. UG 31. Par. UG 31 references Par. UG 27 for internal pressure and Par. UG 28 for external pressure. TEMA Par. 7.2 provides requirements for determining the axial tensile and compressive loads in the tubes for TEMA L-, M-, and Ntype fixed tubesheet exchangers.

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Wall Thickness and Corrosion Allowance - 32-SAMSS-007 requires tubes to be 19 mm (3/4 in.)

outside diameter with minimum thicknesses as shown in Figure 14. Tube Material

Minimum Required Thickness, mm (in.)

Carbon or Alloy Steel

14 BWG [2.1 mm (0.083 in.)]

Nonferrous Material

16 BWG [1.65 mm (0.065 in.)]

Minimum Required Tube Thickness Figure 14 Although tubes are also subject to corrosion, corrosion allowances are not explicitly applied to tubes per TEMA Par. RCB 1.517. The tube thickness that is required for internal or external pressure is small, and the difference between the minimum supplied wall thickness of the tube and the minimum required thickness is available for corrosion allowance. Tubes are also considered to be replaceable parts, and therefore do not need as large a corrosion allowance as other exchanger components. Consideration should be given to using a thicker tube gage or using a higher alloy tube material in services where high corrosion rates are expected where the design conditions require an unusually large tube wall thickness. Pass Partition Plates The required thickness of a pass partition plate is typically determined in accordance with TEMA Par. RCB-9.132. The thickness of the plate is a function of the dimensions of the plate, a and b, the pressure drop across the plate, q, the ASME Code allowable stress for the plate material, S, and a factor that is based on the conditions of the plate edges, B (see Figure 15).

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Pass Partition Plate Figure 15 Note that pass partition plates do not require a corrosion allowance per TEMA Par. RCB1.518. If a corrosion allowance is desired, it should be applied to both sides of the pass partition plate because both sides are exposed to the process fluid. Nonpressure Containing Components Nonpressure containing components include tie-rods, spacers, impingement plates, baffles, and support plates. These components are typically supplied with the minimum thicknesses that are specified in TEMA Paras. RCB-4.4 through 4.7, based on the nominal shell diameter. API-660 requires that the thickness of transverse baffles and support plates not be less than the shell-side corrosion allowance and that the thickness of impingement baffles should not be less than 6.5 mm (1/4 in.). Thicker tube support plates may be required in some cases, per RCB-4.43, for services that are prone to flow pulsation or tube vibration. Nonpressure containing parts also do not require a corrosion allowance per TEMA RCB-1.516. If a corrosion allowance or a more robust design is required for a particular application, this requirement should be specifically stated in the purchase order.

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EVALUATING CONTRACTOR-SPECIFIED DESIGNS FOR AIR-COOLED HEAT EXCHANGER TUBE BUNDLES AND HEADERS The general approach that is used to evaluate contractor-specified designs for air-cooled heat exchanger tube bundles and headers is the same as is used for shell-and-tube heat exchangers. Dimensional consistency must be verified, and all calculations and design procedures must be done in accordance with the applicable Saudi Aramco and industry engineering documents. These engineering documents include 32-SAMSS-011, API-661, and the ASME Code. Work Aid 3 provides an overall procedure that may be used to evaluate the designs that are specified for air-cooled heat exchanger tube bundles and headers. The sections that follow elaborate on several aspects of this procedure and discuss several of the design requirements. Tube Bundle Design Requirements Tube bundle design requirements are specified in Section 5 of API-661 and in 32-SAMSS-011. As previously noted, the sections and paragraph numbers in the SAMSS correspond to the same locations in API-661. Overall Bundle Design Requirements The tube bundle should be designed to be rigid so that it may be handled as a complete assembly without distorting and being damaged. The tube bundle grows in both length and width due to thermal expansion of the metal when the exchanger is in operation. Provision must be made in the design to permit the thermal expansion of the bundle because restrained thermal expansion could cause excessive stresses in the bundle that might eventually result in a failure. 32-SAMSS-011, Par. 5.1.1.4, requires that one header (usually the return header) be free to move due to thermal expansion and that the bundle and the structural mounting must have Teflon slide plates. Teflon has a much lower friction coefficient than steel, and its use permits the bundle to slide more easily. Tube Design The tubes are typically designed in accordance with the ASME Code Par. UG 31. Par. UG 31 references Par. UG 27 for internal pressure design and Par. UG 28 for external pressure design. The tubes must also be designed for the combination of the longitudinal stress due to internal pressure and bending stress due to the tube weight. It is usually more economical to change tube support spacing rather than to increase tube wall thickness in cases where longitudinal overstress or sagging are a problem.

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Tube Diameter Wall Thickness, and Corrosion Allowance - API-661 recommends a minimum prime

tube diameter of 25.4 mm (1 in.) in order to provide basic mechanical integrity to the bundle. API-661 specifies minimum required nominal tube wall thicknesses in order to provide basic mechanical strength, corrosion allowance, and for standardization purposes. These minimum thicknesses are summarized in Work Aid 3. Note that the required tube thickness varies with the tube material. This variation is due to differences in both the corrosion resistance and the strength of the different tube materials. As with shell-and-tube heat exchangers, corrosion allowances are not explicitly applied to the tubes of air-cooled heat exchangers because the thickness that is required for pressure is small, and the tubes are considered to be replaceable parts. Selection of Tube Fins - The tubes of air-cooled heat exchangers normally have external fins in

order to increase their external heat transfer area. API-661 describes the various types of tube fins that are available. 32-SAMSS-011 specifies temperature limits and restrictions on the use of the various fin types and attachment methods based on Saudi Aramco experience. These limits and restrictions are summarized in Work Aid 3. Tube Support Design The tubes are supported in the bundle in order to prevent sagging of the tubes and meshing of the fins. Meshing of the fins limits their effectiveness from a heat transfer standpoint and could also result in mechanical damage to the tubes. API-661 specifies a maximum center-tocenter distance between tube supports in order to minimize the possibility that these problems will occur. API-661 requires that structural hold-downs be provided at each tube support in order to prevent the tubes from lifting due to high winds or abnormal flow conditions. API-661 requires that tube spacers be designed so that they do not rely on the outer periphery of the fin for bearing in order to not damage the fins. The spacers must also prevent the fins from meshing together. Header Design Requirements Header design requirements are specified in 32-SAMSS-011, API-661, and the ASME Code. These requirements consist of design details for the type of header and its individual components and procedures to calculate the required wall thicknesses of the flat plates that are used to fabricate the header.

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Basic Design Requirements API-661 and 32-SAMSS-011 cover basic design requirements for the design of headers. API-661 requires that, if the temperature differential between any adjacent tube passes is greater than 200°F (111°C), split headers, U-tubes, or other means must be used to accommodate the differential thermal expansion that will occur between the tube passes. This accommodation is required in order to avoid excessive stress in the tubes that could cause the tubes to fail and to avoid excessive forces at the tube-to-tubesheet joints that could result in leakage. API-661 specifies basic minimum thicknesses for header components based on their material, as summarized in Work Aid 3. Note that these thicknesses already include a nominal corrosion allowance of 3.2 mm (1/8 in.) for carbon and low-alloy steel components. SAMSS011 increases the required thickness of the tubesheet beyond what is required by API-661. These basic minimum thickness requirements are specified in order to ensure basic strength and rigidity of the header box structure, to accommodate typical tube-to-tubesheet and plugto-plug sheet design details, and to better resist the loads that are applied by the connected piping system. Header Type 32-SAMSS-011 requires that plug-type headers be used for process-type coolers and that removable cover plate-type headers be used for lube oil and seal oil coolers below 1 725 kPa (250 psig). Plug-type headers are used for process applications and for the higher pressure oil cooler applications because plug-type headers are less prone to leakage and are preferred for more severe process applications. Plug-Type Header - Requirements for plug-type headers are specified in API-661. The tube

plug holes are specified to be slightly larger than the tube diameter in order to provide sufficient clearance to enter the inside of the tube with inspection or cleaning tools. Removable Cover Plate-Type and Removable Bonnet-Type Headers - API-661 specifies design requirements for removable cover plate-type and removable bonnet-type headers. An important consideration in the design of the flat cover or bonnet cover of these header types is the spacing of the bolts that attach the cover or bonnet to the header. If the bolts are spaced too far apart, insufficient compressive load may be exerted on the portion of the gasket that is between the bolts. Insufficient gasket compression will make the cover prone to leakage. API-661 provides an equation to determine the maximum permitted bolt spacing. Because the bolts must be tightened with a wrench, the bolts must also be spaced a minimum distance apart in order to provide sufficient space for the wrench. API-661 also specifies minimum bolt spacing requirements in Table 1.

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Gasket Requirements The gasket surface of the tubesheet plug hole must be spot-faced in order to provide a smooth and confined seating surface for the gasket. Gaskets that are used for tube plugs should be either the solid metal or double-metal-jacketed type and be of the same material classification as the plug. The use of these gasket types ensures that the gasket is of relatively strong construction and will have the same corrosion resistance as the plug. Gaskets that are used for flat covers and bonnets must also be the double-jacketed, nonasbestos filled type, except that synthetic fiber gaskets can be used in water, lube oil, and seal oil service if the pressure does not exceed 2 100 kPa (300 psig) and a parting agent is used on both sides of the gasket. The minimum width of cover plate gaskets must be 9 mm (3/8 in.) in order to provide enough sealing surface area, and gaskets must be of one-piece construction. Nozzles and Other Connections API-661 specifies flange and fabrication requirements for nozzles and other connections. 32SAMSS-011 specifies additional requirements that relate to nozzle strength, type of connection, material selection, and fabrication details. Maximum Allowable Moments and Forces for Headers and Nozzles API-661 specifies maximum allowable forces and moments that may be imposed on nozzles by the attached piping. Each nozzle must be designed by the manufacturer to withstand a certain amount of force and moment that generally increases with nozzle size. Since more than one nozzle is usually attached to a header, the manufacturer must also design the header itself to withstand a certain amount of total load from all the nozzles. If there is more than one bundle per heat exchanger bay, the total of all nozzle loads should not exceed three times the loading for one header. The piping designer uses these permissible loads as additional design criteria when he is designing the associated piping systems. The manufacturer must ensure that the nozzle is not overstressed when these permitted loads are applied. Note that neither API-661 nor the ASME Code specifies how the manufacturer must design the nozzles and headers for these loads. These load limits were set by a consensus agreement between the manufacturers and the users, and these limits have historically proven to be acceptable. Therefore, the use of standard nozzle and header design details is usually considered to be sufficient.

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ASME Code Requirements Tubesheets, plug sheets, and covers must also be designed in accordance with the ASME Code Section VIII, Div. 1, Par. UG-34 and Appendix 13. The rules of Par. UG-34 can be applied to the design of the flat rectangular plates that make up the header box, a bonnet-type cover, and a removable flat cover. The equations in UG-34 are explicit and can be used to calculate the component thicknesses directly based on overall dimensions, design pressure, and allowable stress. Design of Rectangular Header Boxes - Appendix 13 of the ASME Code applies to the design of

rectangular vessels in general. This Appendix specifically treats the design of tubesheets, plug sheets, and the top, bottom, and end plates of the rectangular header boxes or bonnet covers of air-cooled heat exchangers. The design procedures that are in Appendix 13 usually yield a thinner, more economical design than would result from using the UG-34 procedures; however, the equations are not explicit (i.e., the equations cannot be directly solved for the thickness of a single component in terms of other quantities). Appendix 13 treats the header box as a complete structure, and the internal pressure load causes membrane stresses and bending stresses in each of the plates that form the box (i.e., the tubesheet, plug sheet, end plates, top and bottom plates, [see Figure 16]). The bending stresses in the plates are a function of the moment distribution factors that are in turn a function of the thickness and the dimensions of all of the plates that make up the box. This is a relatively complicated design procedure to apply.

Typical Header Box Details Figure 16

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The design procedure in Appendix 13 also requires that the stiffness and stresses in the tubesheet and plug sheet be adjusted to account for the tube holes and plug holes. These holes weaken the tubesheet and plug sheet. A ligament efficiency is used to adjust the stiffness and stresses that are calculated, and the ligament efficiency is based on the tube hole or plug hole dimensions and the pitch between the holes. (See Figure 17).

 p − d  Ligament Efficiency =  p  Ligament Efficiency in Tubesheet or Plug Sheet Figure 17

Computer Design of Header Boxes Whereas the required thicknesses of header box components can be readily checked once a design has been developed, a trial-and-error method must be used for the initial design. In the trial-and-error method, an initial estimate of the component thicknesses is made based on assuming that the end of each side of the box is rigidly supported. The thickness of the plates is then incremented until all of the components that make up the box are below the allowable stress. The design of such components is therefore easily programmed into a computer.

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Sample Problem 4: Evaluate Contractor-Specified Dimensions for the Inlet/Outlet Header Box of an Air-Cooled Heat Exchanger You must evaluate the contractor-specified dimensions for the inlet/outlet header box of an air-cooled heat exchanger. All the information that is needed to solve this problem is in Contractor Design Package 5 in Course Handout 4. This information includes the specification sheet for the air-cooled heat exchanger, the dimensions of the inlet/outlet header box, and the CODECALC computer program output. Work Aid 3 is used to solve this problem. The first step in evaluating the manufacturer's design is to compare the dimensions that are specified in the drawings of the inlet/outlet header with the computer program input. These dimensions include the length, width, and depth of the header box, the component thicknesses, and the tube hole and plug hole dimensions. Additional design information that may be required, such as the allowable stress, should also be verified against the ASME Code. All of the computer input appears to be correct in this example. Inasmuch as the computer program input has been checked and the program has been verified, it is concluded that the dimensions specified by the manufacturer for the header box plates are correct based on stress analysis considerations because the CODECALC output shows that the header box components are not overstressed. However, note that the 0.375 in. thickness specified for the stay plate is less than the 0.5 in. minimum thickness that is required by API-661. Therefore, the stay plate thickness must be increased to 0.5 in. Because the stresses are acceptable and the component dimensions are consistent between the program and the detailed drawings, the header box design is acceptable once the stay plate thickness is increased.

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COMPLETING A SAFETY INSTRUCTION SHEET FOR A SHELL-AND-TUBE HEAT EXCHANGER As discussed in MEX 202, the purpose of a Safety Instruction Sheet is to ensure that operations, maintenance, and inspection personnel have adequate information in a consistent format. This information concerns safe operating limits, protective devices, and any special safety precautions that may be required. SAES-E-001 requires that a Safety Instruction Sheet be completed for every new process heat exchanger. In most cases, a contractor who is working for Saudi Aramco is responsible for completing the Safety Instruction Sheet. The Saudi Aramco Engineer is then responsible for checking the contractor's work. In all cases, the Safety Instruction Sheet is completed based on the final, certified, as-built, manufacturer’s data for the heat exchanger, not the data that is on the heat exchanger specification sheet. The Safety Instruction Sheet must also be revised whenever the heat exchanger is rerated or modified. The Saudi Aramco engineer may be responsible for revising the Safety Instruction Sheet when heat exchangers are rerated or modified. Saudi Aramco has Safety Instruction Sheets for both shell-and-tube and air-cooled heat exchangers. This module only discusses the Safety Instruction Sheet for shell-and-tube heat exchangers. SAES-A-005, Preparation of Safety Instruction Sheets, outlines the procedures for preparing Safety Instruction Sheets. These procedures are referenced in Work Aid 4. A copy of SAES-A-005 is contained in Course Handout 2. Information Covered A copy of the Safety Instruction Sheet for shell-and-tube heat exchangers, Form 2713, is shown in Figure 18, and additional copies are provided in Course Handout 3. Form 2713 includes general information, basic process design information, mechanical design information, and operating limits, The following paragraphs highlight several of the primary types of information that are required on Form 2713. Refer to Figure 18 or Course Handout 3.

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Safety Instruction Sheet Form 2713 Figure 18

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•

The top part of Form 2713 contains basic equipment information such as service, manufacturer, serial number, applicable construction Code and edition, and reference drawings.

•

Shell-side, tube-side, and tube-bundle details are provided in the next sections of the form. These sections contain mechanical design information and summarize information on pressure testing of the exchanger, such as the following:

•

-

Shell diameter, thickness, and material

-

Tube material, diameter, and thickness

-

Initial test pressure

-

Limiting component in the test

-

Basis for the calculated test pressure

The lower part of the form contains information on the operating limits of the shell side and tube side of the exchanger, such as the following: -

Design pressure and design temperature

-

Basis for the design pressure

-

Pressure relief valve location

-

Relief valve set pressure

-

Routine test pressure

-

Minimum required thicknesses of the components, "tm"

-

Actual available corrosion allowances of the components, “C”

-

Reference drawing numbers

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•

The next section is used to specify any special hazards, recommendations, inspections, or tests that are important for the safe operation of the exchanger.

•

The bottom part of the form contains standard Saudi Aramco drawing information, and the left side contains revision record and approval information.

Form 2713 provides much information about a shell-and-tube heat exchanger. It makes it possible for operations, maintenance, and inspection personnel to get needed information from one source without reviewing many drawings. There will be situations when the detailed exchanger fabrication drawings must be checked to resolve questions. However, having the information on this one form reduces the need to refer to the drawings and focuses the research on the necessary items. Where to Find Other Information Almost all of the information that is required on the Safety Instruction Sheet is obtained from the final version of the heat exchanger specification sheet, the as-built exchanger drawings, and the mechanical design calculations. The paragraphs that follow highlight other items that might have to be obtained from other sources: •

Any special design considerations or unusual construction features that should be highlighted would have been developed either during the initial specification of the exchanger or during its detailed engineering. Pertinent information could be obtained from the process and mechanical engineers who were assigned to the work.

•

Information as to the locations of the relief valves that protect the shell side and the tube side of the exchanger is available from the contractor. The Process and Instrument Diagram (P & ID) for the system will typically show the relief valve locations.

•

Information and guidance with regard to any special safety hazards, recommendations, inspections, and tests can be obtained from General Safety Instructions, Saudi Aramco GI No. 2608, and discussions with process, safety, maintenance, and inspection personnel who are assigned to the project and are familiar with the heat exchanger and its application.

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WORK AID 1: PROCEDURE FOR EVALUATING CONTRACTOR-SPECIFIED DESIGN CONDITIONS FOR TEMA-TYPE AND AIR-COOLED HEAT EXCHANGER COMPONENTS The procedures in this Work Aid may be used to evaluate whether design conditions that are specified in a Contractor Design Package for a heat exchanger meet the Saudi Aramco requirements that are specified in SAES-E-001. A copy of SAES-E-001 is included in Course Handout 2. Part 1 of this Work Aid is used for TEMA-type heat exchangers, and Part 2 is used for air-cooled heat exchangers. Part 1: TEMA-Type Heat Exchangers 1.

Determine the process operating conditions for the shell side and tube side. List the process operating conditions in Figure 19 under Operating Conditions. Operating conditions are specified in Section A of Form 2714.

2.

Determine the mechanical design conditions specified by the contractor for the shell side and tube side. List the design conditions in Figure 19 under Design Conditions. Mechanical design conditions are specified in Section B of Form 2714.

3.

Determine if the design conditions meet the requirements that are specified in SAESE-001. These requirements are summarized as follows: •

The design pressure must be at least the greater of the maximum operating pressure plus 104 kPa(ga) (15 psig), or 110 percent of the maximum operating pressure.

•

The design temperature must be at least the maximum operating temperature plus 28°C (50°F). Metal design temperatures shall be based on "steaming out" conditions if applicable.

•

The minimum design temperature must be the minimum metal temperature that is coincident with any pressure greater than 25 percent of the design pressure. The possibility of auto-refrigeration during start-up, shutdown, or upset must be considered in determining the minimum design temperature.

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4.

Indicate the results of your evaluation in the last column of Figure 19. DESCRIPTION

Operating Conditions

Design Conditions

Acceptable (Yes/No)

Shell Side Max. Temperature, °C (°F) Shell Side Min. Temperature, °C (°F) Shell Side Pressure, kPa (psig) Tube Side Max. Temperature, °C (°F) Tube Side Min. Temperature, °C (°F) Tube Side Pressure, kPa (psig) TEMA-Type Heat Exchanger Design Condition Evaluation Figure 19 Part 2: Air-Cooled Heat Exchangers 1.

Determine the operating conditions for the process side. List these in Figure 20 under Operating Conditions. Process operating conditions are indicated on Lines 16 and 23 of Form 2716.

2.

Determine the design air inlet, outlet, and ambient temperatures. List these in Figure 20 under Design Conditions. Air temperatures are indicated in the column headed “Performance Data - Air Side” of Form 2716.

3.

Determine the process-side design conditions specified by the contractor and list these in Figure 20 under Design Conditions. Process-side design conditions are indicated on Line 42 of Form 2716.

4.

Determine if the process-side design conditions meet the requirements that are specified in SAES-E-001. Refer to Step 3 of Part 1.

5.

Determine if the air-side design inlet, outlet, and ambient temperatures meet the requirements that are specified in Para. 3.14 of SAES-E-001.

6.

Indicate the results of your evaluation in the last column of Figure 20.

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Description

Operating Conditions

Design Conditions

Acceptable (Yes/No)

Process Max. Temperature, °C (°F) Process Min. Temperature, °C (°F) Process Inlet Pressure, kPa (psig) Inlet Air Temperature, °C (°F)

-

Outlet Air Temperature, °C (°F)

-

Min. Ambient Temperature, °C (°F)

-

Air-Cooled Heat Exchanger Design Condition Evaluation Figure 20

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WORK AID 2: PROCEDURE FOR EVALUATING CONTRACTOR-SPECIFIED DIMENSIONS FOR SHELL-AND-TUBE HEAT EXCHANGER COMPONENTS The procedures in this Work Aid may be used to evaluate whether the dimensions that are specified in a Contractor Design Package for a shell-and-tube heat exchanger meet Saudi Aramco, TEMA, API-660, and ASME requirements. This Work Aid is divided into four major parts as follows: •

Part 1 provides a general procedural-type checklist that should be used in all cases.

•

Part 2 is used for girth flanges and flat channel covers.

•

Part 3 is used for stationary and floating end tubesheets.

•

Part 4 is used for floating heads.

Part 1: General Requirements The following procedural items should be checked in all cases. 1.

Confirm that the specified dimensions are consistent in all drawings, specifications, and calculations that are provided in the Contractor Design Package. This will be done while checking the design details and dimensions in accordance with Parts 2 through 4 of this Work Aid.

2.

Confirm that the dimensions and design details are in accordance with requirements specified in 32-SAMSS-007, API-660, and the ASME Code. Further details on this check are provided in Parts 2 through 4 of this Work Aid.

3.

Confirm that all calculations are done in accordance with ASME Code procedures. This may involve verification of the computer program that is used by the exchanger manufacturer. For the purposes of this course, it may be assumed that the CODECALC computer program that is being used has been verified.

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Part 2: Girth Flanges and Flat Channel Covers Use the following procedure to check computer calculations that have been made to verify the design of a girth flange or a channel cover. This procedure is generic in that it may be applied to calculations that have been done using most computer programs. However, because the CODECALC program is used for all calculations that are done in this course, the parameter names that are used in the CODECALC program are identified in parentheses where appropriate. The program input must be checked to ensure that it conforms to the flange design requirements. The program output must be checked to ensure that it verifies the design that has been used for the girth flange or cover plate. In using this procedure, refer to Figure 21 for flange geometry and nomenclature.

Flange Geometry and Nomenclature Figure 21

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1.

Verify that the correct flange type is specified. Heat exchanger girth flanges are typically the integral weld neck flange. Permissible flange types are specified in Appendix 2 of the ASME Code.

2.

Verify that the specified design pressure (P) is equal to the pressure that is listed on the specification sheet.

3.

Verify that the specified design temperature is equal to the temperature listed on the specification sheet.

4.

For the girth flange, verify that the corrosion allowance (FCOR) is equal to the corrosion allowance that is listed on the specification sheet. For the flat channel cover, verify that the corrosion allowance is equal to the depth of the pass partition groove in the channel cover.

5.

Verify that the flange material is the same as the material listed on the specification sheet.

6.

Verify that the allowable stress for the flange or flat cover material conforms to the allowable stress specified in the ASME Code. Note that many programs such as CODECALC have the ASME allowable stress tables built into them and automatically use the correct allowable stress.

7.

Verify that the bolt material is the same as the material listed on the specification sheet.

8.

Verify that the allowable stress for the bolt material conforms to the allowable stress specified in the ASME Code. Note that many programs such as CODECALC have the ASME allowable stress tables built into them and automatically use the correct allowable stress.

9.

Verify that the flange inside diameter (B) is equal to the uncorroded (new) diameter shown on the detailed drawing. This is not applicable for the flat channel cover.

10.

Verify that the flange outside diameter (A) is equal to the uncorroded (new) diameter shown on the detailed drawing.

11.

Verify that the hub thickness at the small end of the flange (shell end, G0) is equal to the uncorroded (new) thickness shown on the detailed drawing. This is not applicable for the flat channel cover.

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12. Verify that the hub thickness at the back of the flange (large end, G1) is equal to the uncorroded (new) thickness shown on the detailed drawing. This is not applicable for the flat channel cover. 13.

Verify that the flange thickness (T) is equal to the uncorroded (new) thickness shown on the detailed drawing.

14.

Verify that the hub length (HL) is equal to the length shown on the detailed drawing. This is not applicable for the flat channel cover.

15.

Verify that the diameter of the bolt circle (C) is equal to the diameter shown on the detailed drawing.

16.

Verify that the bolt diameter (DB) is equal to the diameter shown on the detailed drawing.

17.

Verify that the thread series (SERIES) is identified as "TEMA."

18.

Verify that the number of bolts is equal to the number shown on the detailed drawing.

19.

For mating girth flanges that have a fixed tubesheet in between them, verify that the following bolt loads have been specified based on calculations that have been made for the opposite flange: •

Operating Bolt Load

•

Gasket Seating Bolt Load

•

Flange Design Bolt Load

These values are found from output information that is found in preliminary calculations that are done for the flanges. 20.

Verify that the gasket outside diameter is equal to the diameter shown on the detailed drawing.

21.

Verify that the flange face outside diameter (FOD) is equal to the diameter shown on the detailed drawing.

22.

Verify that the gasket inside diameter is equal to the diameter shown on the detailed drawing.

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23.

Verify that the flange face inside diameter (FID) is equal to the diameter shown on the detailed drawing.

24.

Verify that the gasket factor, m, is equal to the factor that is specified indicated in the ASME Code, Section VIII, Division 1, Appendix 2, Table 2-5.1, for the specified gasket type.

25.

Verify that the gasket design seating stress, y, is equal to the stress indicated in the ASME Code, Section VIII, Division 1, Appendix 2, Table 2-5.1 for the specified gasket type.

26.

Verify that the sketch number that is specified for the flange facing agrees with the sketch number listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the type of flange facing that is shown on the detailed drawing.

27.

Verify that the column number (I or II) for the facing sketch agrees with the column number listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the specified gasket type.

28.

Verify that the gasket thickness is equal to the dimension shown on the detailed drawing.

29.

Verify that the nubbin width (when a nubbin flange face is specified) is equal to the dimension shown on the detailed drawing.

30.

Verify that the length of the pass partition gasket is equal to the gasket inner diameter, multiplied by the fraction Npp/Ng, where Npp is the width of the pass partition gasket and Ng is the width of the girth flange gasket. This only applies for channel covers when there is a pass partition plate in the channel.

31.

Verify that the required bolt area (AM) is less than the actual total bolt area.

32.

Verify that the actual bolt spacing lies between the minimum and maximum permitted bolt spacings. The permitted spacings should have been determined based on TEMA requirements.

33.

Flange Stresses. Calculated and allowable stresses are output for the operating case and for the gasket seating case. Confirm that the calculated stresses are all less than the allowable stresses for each case. The following stresses must be checked:

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•

Longitudinal Hub Stress

•

Radial Flange Stress

•

Tangential Flange Stress

•

Maximum Average Stress

•

Bolt Stress

34.

Verify that the Maximum Allowable Working Pressure for the corroded flange (MAWP) is at least equal to the design pressure.

35.

Verify that the required flange thickness, including corrosion allowance, is less than or equal to the specified thickness (T) and the thickness that is shown on the detailed drawing.

36.

For channel covers, verify that the actual cover deflection is no more than the deflection that is permitted by TEMA.

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Part 3: Stationary and Floating Head Tubesheets Use the following procedure to check computer calculations that have been made to verify the design of a tubesheet that is either stationary or at a floating head. This procedure is generic in that it may be applied to calculations that have been done using most computer programs. However, because the CODECALC program is used for all calculations that are done in this course, the parameter names that are used in the CODECALC program are identified in parentheses where appropriate. The program input must be checked to ensure that it conforms to the tubesheet design requirements. The program output must be checked to ensure that it verifies the design that has been used for the tubesheet. In using this procedure, refer to Figure 22 for tubesheet geometry and nomenclature.

Tubesheet Geometry and Nomenclature Figure 22

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1.

Verify that the correct tubesheet type is specified and is consistent with information that is contained in the detailed drawing. Several common tubesheets options are as follows: •

Stationary, gasketed on both sides

•

Stationary, integral with the shell

•

Stationary, integral with the channel

•

U-tube, gasketed on both sides

•

U-tube, integral with the shell

•

U-tube, integral with the channel

•

Pull-through floating head

•

Floating head with backing device

2.

Verify that the specified design pressures for the shell side (PS) and channel sides (PC) are each equal to the applicable pressures that are listed on the specification sheet.

3.

Verify that the specified design temperature (TEMPTS) is equal to the temperature listed on the specification sheet.

4.

Verify that the materials for the shell, tubesheet, and channel are the same as the materials listed on the specification sheet.

5.

Verify that the allowable stresses for the shell, tubesheet, and channel conform to the allowable stresses specified in the ASME Code. Note that many programs such as CODECALC have the ASME allowable stress tables built into them and automatically use the correct allowable stress.

6.

Verify that the tubesheet thickness (TTS) is equal to the uncorroded (new) thickness shown on the detailed drawing.

7.

Verify that the shell-side and tube-side corrosion allowances (CAS and CAC) are equal to the corrosion allowances listed on the specification sheet.

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8.

9.

For gasketed tubesheets: a.

Verify that the gasket inside diameter and outside diameter equal the diameters indicated in the detail drawing.

b.

Verify that the flange face inside diameter (FID) and outside diameter (FOD) equal the diameters indicated in the detail drawing.

c.

Verify that the gasket factor, m, is equal to the factor that is specified indicated in the ASME Code, Section VIII, Division 1, Appendix 2, Table 2-5.1, for the specified gasket type.

d.

Verify that the gasket design seating stress, y, is equal to the stress indicated in the ASME Code, Section VIII, Division 1, Appendix 2, Table 2-5.1 for the specified gasket type.

e.

Verify that the sketch number that is specified for the flange facing agrees with the sketch number listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the type of flange facing that is shown on the detailed drawing.

f.

Verify that the column number (I or II) for the facing sketch agrees with the column number listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the specified gasket type.

g.

Verify that the gasket thickness is equal to the dimension shown on the detailed drawing.

h.

Verify that the nubbin width (when a nubbin flange face is specified) is equal to the dimension shown on the detailed drawing.

I.

Verify that the length of the pass partition gasket is equal to the gasket inner diameter, multiplied by the fraction Npp/Ng, where Npp is the width of the pass partition gasket and Ng is the width of the girth flange gasket. This requirement only applies for channel covers when there is a pass partition plate in the channel.

Verify that the tube outside diameter (DT) is equal to the diameter shown on the detailed drawing.

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10.

Verify that the tube thickness (TT) is equal to the diameter thickness shown on the detailed drawing.

11.

Verify that the tube pitch (PT) matches the pitch shown on the detailed drawing.

12.

Verify that the tube pattern (i.e., square or triangular) matches the pattern shown on the detailed drawing.

13.

Verify that the depth of the pass partition groove (GROOVE) is equal to the depth shown on the detailed drawing.

14.

If the tubesheet is extended as a flange, verify that the outside diameter of the flanged portion (DF) is consistent with what is shown on the detailed drawing.

15.

If the tubesheet is extended as a flange, verify that the thickness of the flanged portion (TF) is consistent with what is shown on the detailed drawing.

16.

Verify that the diameter of the bolt circle (DB) is equal to the diameter shown on the detailed drawing.

17.

Verify that the bolt diameter (DBOLT) is equal to the diameter shown on the detailed drawing.

18.

Verify that the thread series is identified as "TEMA."

19.

Verify that the number of bolts (NUMBER) is equal to the number shown on the detailed drawing.

20.

Verify that the actual tubesheet thickness is at least equal to the required thickness and is consistent with what is shown on the detailed drawing.

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Part 4: Floating Heads With and Without Backing Rings Use the following procedure to check computer calculations that have been made to verify the design of a floating head. This procedure is generic in that it may be applied to calculations that have been done using most computer programs. However, because the CODECALC program is used for all calculations that are done in this course, the parameter names that are used in the CODECALC program are identified in parentheses where appropriate. The program input must be checked to ensure that it conforms to the floating head design requirements. The program output must be checked to ensure that it verifies the design that has been used for the floating head. In using this procedure, refer to Figure 23 for floating head geometry and nomenclature.

Floating Head Geometry and Nomenclature Figure 23 1.

Verify that the specified floating head type is consistent with what is shown in the detailed drawing. The most common type is Type (d) as described in Appendix 1-6 in the ASME Code.

2.

Verify that the specified design temperature (TEMP) is equal to the temperature listed on the specification sheet.

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3.

Verify that the specified tube-side design pressure (P.S.) is equal to the pressure listed on the specification sheet.

4.

Verify that the specified shell-side design pressures (PSS) is equal to the pressure listed on the specification sheet.

5.

Verify that the specified tube-side corrosion allowance (CATS) is equal to the corrosion allowance listed on the specification sheet.

6.

Verify that the shell-side corrosion allowance (CASS) is equal to the corrosion allowance listed on the specification sheet.

7.

Verify that the materials for the head, flange, bolts, and backing ring are the same as the materials listed on the specification sheet.

8.

Verify that the allowable stresses for the head, flange, bolts, and backing ring conform to the allowable stresses specified in the ASME Code. Note that many programs such as CODECALC have the ASME allowable stress tables built into them and automatically use the correct allowable stress.

9.

Verify that the crown radius of the head (CR) is consistent with what is specified on the detailed drawing.

10.

Verify that the inside diameter of the flange (FID) is consistent with what is specified on the detailed drawing.

11.

Verify that the outside diameter of the flange (FOD) is consistent with what is specified on the detailed drawing.

12.

Verify that the inside diameter of the backing ring (DR) is consistent with what is specified on the detailed drawing.

13.

Verify that the actual thickness of the head (TH) is consistent with what is specified on the detailed drawing.

14.

Verify that the actual thickness of the flange (TC) is consistent with what is specified on the detailed drawing.

15.

Verify that the actual thickness of the backing ring (TR) is consistent with what is specified on the detailed drawing.

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16.

Verify that the number of splits in the backing ring (NSPLIT) is consistent with what is specified on the detailed drawing.

17.

Verify that the distance between the centroid of the flange and the attachment point at the head centerline is consistent with what is specified on the detailed drawing.

18.

Refer to the detailed drawing to determine whether the flange is or is not slotted and verify that the appropriate detail is specified in the calculations. The flange will normally not be slotted.

19.

Verify that the diameter of the bolt circle (DB) is equal to the diameter shown on the detailed drawing.

20.

Verify that the bolt diameter (DBOLT) is equal to the diameter shown on the detailed drawing.

21.

Verify that the thread series is identified as "TEMA."

22.

Verify that the number of bolts is equal to the number shown on the detailed drawing.

23.

Verify that the gasket type and material that is used is consistent with what is shown on the detailed drawing.

24.

Verify that the gasket outside diameter is equal to the diameter shown on the detailed drawing.

25.

Verify that the flange face outside diameter (FOD) is equal to the diameter shown on the detailed drawing.

26.

Verify that the gasket inside diameter is equal to the diameter shown on the detailed drawing.

27.

Verify that the flange face inside diameter (FID) is equal to the diameter shown on the detailed drawing.

28.

Verify that the gasket factor, m, is equal to the factor that is specified indicated in the ASME Code, Section VIII, Division 1, Appendix 2, Table 2-5.1, for the specified gasket type.

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29.

Verify that the gasket design seating stress, y, is equal to the stress indicated in the ASME Code, Section VIII, Division 1, Appendix 2, Table 2-5.1 for the specified gasket type.

30.

Verify that the sketch number that is specified for the flange facing agrees with the sketch number listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the type of flange facing that is shown on the detailed drawing.

31.

Verify that the column number (I or II) for the facing sketch agrees with the column number listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the specified gasket type.

32.

Verify that the gasket thickness is equal to the dimension shown on the detailed drawing.

33.

Verify that the nubbin width (when a nubbin flange face is specified) is equal to the dimension shown on the detailed drawing.

34.

Verify that the length of the pass partition gasket is equal to the gasket inner diameter, multiplied by the fraction Npp/Ng, where Npp is the width of the pass partition gasket and Ng is the width of the girth flange gasket. This only applies for channel covers when there is a pass partition plate in the channel.

35.

Verify that the actual thickness of the head is at least equal to the minimum required thickness (considering the corrosion allowances) and is consistent with what is shown on the detailed drawing.

36.

Verify that the actual thickness of the flange is at least equal to the minimum required thickness (considering the corrosion allowances) and is consistent with what is shown on the detailed drawing.

37.

Verify that the actual thickness of the backing ring is at least equal to the minimum required thickness (considering the corrosion allowances) and is consistent with what is shown on the detailed drawing.

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WORK AID 3: PROCEDURE FOR EVALUATING CONTRACTOR-SPECIFIED DESIGNS FOR AIR-COOLED HEAT EXCHANGER TUBE BUNDLES AND HEADERS The procedures in this Work Aid may be used to evaluate whether the tube bundle and header designs that are specified in a Contractor Design Package for an air-cooled heat exchanger meet Saudi Aramco, API-661, and ASME requirements. This Work Aid is divided into three major parts as follows: •

Part 1 provides a general procedural-type checklist that should be used in all cases.

•

Part 2 provides a procedure for checking compliance with the requirements that are contained in 32-SAMSS-011 and API-661.

•

Part 3 provides a procedure for evaluating whether the mechanical design calculations are in accordance with the ASME Code. It is assumed that a computer program has been used for these calculations.

Part 1: General Requirements The following procedural items should be checked in all cases. 1.

Confirm that the specified dimensions are consistent in all drawings, specifications, and calculations that are provided in the Contractor Design Package. This will be done while checking the design details and dimensions in accordance with Parts 2 and 3 of this Work Aid.

2.

Confirm that the dimensions and design details are in accordance with requirements specified in 32-SAMSS-011, API-661, and the ASME Code. Further details on this check are provided in Part 2 of this Work Aid.

3.

Confirm that all calculations are done in accordance with ASME Code procedures. This may involve verification of the computer program that is used by the exchanger manufacturer. For the purposes of this course, it may be assumed that the CODECALC computer program that is being used has been verified.

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Part 2: 32-SAMSS-011 and API-661 Requirements Use the procedure that follows to determine whether the requirements that are specified in 32SAMSS-011 and API-661 have been met. The paragraph references that are indicated are in API-661 unless otherwise noted. For each requirement, circle “Yes” or “No” depending on whether the requirement has been met or not. Overall Tube Bundle Design Requirements 1.

Par. 5.1.1.1. Is the tube bundle designed to be rigid for handling as a complete assembly? Yes/No.

2.

Par. 5.1.1.3. Has provision for at least 6 mm (1/4 in.) of lateral movement in both directions and 13 mm ( 1/2 in.) of lateral movement in one direction been provided? Yes/No.

3.

Par. 5.1.1.4. Has provision been made in the design to accommodate the thermal expansion of the tubes? Yes/No.

4.

32-SAMSS-011, Par. 5.1.1.4. Do the bundle and the structural mounting have Teflon slide plates at the moving end? Yes/No.

5.

Par. 5.1.1.5. Are the tube supports no more than 1.83 m (6 ft.) from center to center? Yes/No.

6.

Par. 5.1.1.6. Are structural hold-downs provided at each tube support? Yes/No.

7.

Par. 5.1.1.7. Are tubes of single-pass condensers and all heating coils sloped downward at 10 mm per meter (1/8 in. per ft.) toward the outlet header? Yes/No.

8.

Par. 5.1.1.8. Are air seals provided throughout the bundle to minimize air leakage? Yes/No. Any air gap that is more than 10 mm (3/8 in.) wide is excessive.

9.

Par. 5.1.1.9. Is 12 gage (2.8 mm [0.105 in.]) minimum thickness used for air seal construction? Yes/No.

10.

Par. 5.1.1.10. Are bolts for removable air seals at least 10 mm (3/8 in.) nominal diameter? Yes/No.

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11.

32-SAMSS-011, Par. 5.1.1.11. Do the tube ends extend beyond the tubesheet 3 mm ±1.5 mm (1/8 in. ± 1/16 in.)? Yes/No.

12.

32-SAMSS-011, Par. 5.1.1.12. Are tube spacers designed so that they do not rely on the outer periphery of the fins for bearing, and do the spacers prevent the fins from meshing? Yes/No.

Tube Wall Minimum Thickness 13.

Par. 5.1.12.1. Does the diameter of the prime tube equal the recommended minimum of 25.4 mm (1 in.)? Yes/No.

14.

Par. 5.1.12.3. Does the minimum tube wall thickness meet the requirements shown in Figure 24? Yes/No. Tube Material

Minimum Required Thickness, mm (in.)

Carbon and Low-Alloy Steels (Through 9% Chrome)

2.74 (0.108)

High-Alloys Steels (Austenitic and Ferritic)

1.65 (0.065)

Copper or Aluminum Alloy

2.11 (0.083)

Titanium

1.24 (0.049)

Minimum Required Tube Thicknesses Figure 24 Selection of Tube Fins 15.

32-SAMSS-011, Par. 5.1.12.7. Do the type of tube fins meet the requirements specified in Figure 25? Yes/No.

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Fin Type

Use Limitations

Tension wound

Auxiliary coolers and lube oil coolers at temperatures less than 95°C (200°F)

Extruded

Temperatures less than 260°C (500°F)

Embedded

Temperatures less than 400°C (750°F)

Other types

Must be approved by the buyer. Consult CSD as required.

Limitations on Fin Types Figure 25 Header Design Requirements 16.

Par. 5.1.5.2. If the differential design temperature of any adjacent tube pass is over 111°C (200°F), is a split header design, U-tube design, or other means used to accommodate differential thermal expansion between the adjacent tube passes? Yes/No.

17.

Par. 5.1.5.5. Are the minimum thicknesses of header box components in accordance with Figure 26 ? Yes/No.

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Component

Carbon or Low-Alloy Steel

High-Alloy Steel or Other Materials

Tubesheet

20 mm (3/4 in.)*

16 mm (5/8 in. )*

Plug sheet

20 mm (3/4 in.)

16 mm (5/8 in.)

12 mm (1/2 in.)

10 mm (3/8 in.)

25 mm (1 in.)

25 mm (1 in.)

Top, bottom, and end plates Removable cover plates

* 25.4 mm (1 in.) minimum thickness including corrosion allowance per Par. 5.1.5.5 of 32-SAMSS-011.

Minimum Required Thickness of Header Box Components Figure 26 18.

Par 5.1.5.6. Does the minimum pass partition plate thickness meet the requirements in Figure 27? Yes/No. Pass Partition Plate Material

Minimum Required Thickness, mm (in.)

Carbon and Low-Alloy Steels

12 (1/2) *

Nonferrous High-Alloy Steel

6 (1/4)

* Includes up to 3 mm (1/8 in.) corrosion allowance on each side.

Pass Partition Plate Thickness Figure 27 19.

32-SAMSS-011, Par 5.1.5.7. Does the header box type meet the requirements in Figure 28? Yes/No.

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Exchanger Service

Header Box Type

Process Cooler

Plug Type Header

Lube Oil Cooler or Seal Oil Cooler

Removable Cover or Cover Plate if less than 1 750 kPa (250 psig)

Header Box Type Figure 28 Headers: Removable-Cover-Plate and Removable-Bonnet-Type 20.

Par 5.1.6.5. Are jackscrews or a 5 mm (3/16 in.) clearance provided at the cover periphery to facilitate dismantling? Yes/No.

21.

Par 5.1.6.8. Is the minimum diameter of stud bolts 20 mm (3/4 in.)? Yes/No. Is the minimum diameter of through bolts 16 mm (5/8 in.)? Yes/No.

22.

Par 5.1.6.9. Does the bolt spacing exceed the maximum spacing requirements (refer to API-661 directly)? Yes/No.

23.

Par 5.1.6.10. Is the bolt spacing less than the minimum spacing that is specified in Table 1 of API-661? Yes/No.

24.

Par 5.1.6.11. For bolts that straddle the corners, does the diagonal distance meet the maximum bolt spacing criteria? Yes/No.

Headers: Plug-Type 25.

Par 5.1.7.2. Does the diameter of the tube plug holes equal the nominal outside diameter of the tube plus 0.8 mm (1/32 in.) minimum? Yes/No.

26.

Par 5.1.7.3. Is the gasket surface of the tubesheet plug hole spot faced? Yes/No.

27.

Par 5.1.8.7. Are threaded plugs that are 40 mm (1-1/2 in.) and less in diameter Unified Fine Thread in accordance with ANSI B1.1? Yes/No.

28.

Par 5.1.8.8. Are threaded plugs that are greater than 40 mm (1-1/2 in.) in diameter 12 thread series per ANSI B1.1? Yes/No.

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Gasket Requirements 29.

Par 5.1.9.1. Are gaskets for tube access plugs solid metal or double-metal-jacketed type and of the same material classification as the plug? Yes/No.

30.

Par 5.1.9.2. Are cover plate gaskets for flat covers and bonnets double-jacketed, nonasbestos filled type? Yes/No. Per 32-SAMSS-011, if the pressure does not exceed 2 100 kPa (300 psig), a synthetic gasket with parting agent on both sides of the gasket may be used in water, lube oil, and seal oil services.

31.

Par 5.1.9.3 and Par 5.1.9.4. Are cover plate gaskets a minimum width of 9 mm (3/8 in.), and are the gaskets of one piece construction? Yes/No.

Nozzles and Other Connections 32.

32-SAMSS-011, Par. 5.1.10.4. If nozzles are made from pipe, is only seamless pipe used? Yes/No. If the connections are 50 mm (2 in.) or smaller, is the thickness Schedule 80 minimum? Yes/No.

33.

32-SAMSS-011, Par 5.1.10.15. For small diameter connections, are bosses used per Saudi Aramco Standard Drawings AE-036175 or AE-036367? Yes/No.

34.

32-SAMSS-011, Par. 5.1.10.18. Do nozzles protrude beyond the inside surface of the header? Yes/No. If “Yes,” they are in violation of this requirement.

35.

32-SAMSS-011, Par. 5.1.10.19. If the header is lined with a corrosion resistant material, are the nozzles also lined in the same manner? Yes/No.

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Part 3: ASME Code Calculations for Header Box Plate Thicknesses Use the procedure that is summarized in Figure 29 to check computer calculations that have been made to verify the design of a header box for an air-cooled heat exchanger. This procedure is generic in that it may be applied to calculations that have been done using most computer programs. However, because the CODECALC program is used for all calculations that are done in this course, the parameter names that are used in the CODECALC program are identified in parentheses where appropriate. The program input must be checked to ensure that it conforms to the header box design requirements. The program output must be checked to ensure that it verifies the design that has been used for the header box. In using this procedure, refer to Figure 30 for header box geometry and nomenclature. Step

Item to Verify

Information Source

1

Correct Header Box Type Has Been Selected for Analysis. Several common options are as follows:

Detailed Drawing

•

Equal or unequal thicknesses of the long-side plates.

•

One or two internal stay plates.

•

External reinforcement.

2

Design Pressure (P)

Form 2716

3

Design Temperature (TEMP)

Form 2716

4

Material Specifications for the Header Box Components and Stay Plates

Form 2716

Header Box Calculation Verification Procedure Figure 29

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Step 5

Item to Verify

Information Source

Allowable Stresses and Minimum Yield Stresses for Header Box Components and Stay Plates Conform to ASME Code.

ASME Code

Note: Many programs such as CODECALC have the ASME allowable stress tables built into them and automatically use the correct allowable stress. 6

Short-Side Length Dimension (H). The new, uncorroded length should be input.

Detailed Drawing

7

Minimum Thickness of the Short-Side Plates (t1). The new, uncorroded thickness should be input.

Detailed Drawing

8

Mid-side joint efficiency on the short side (E) in accordance with the ASME Code and consistent with the radiographic inspection specified on the detailed drawing.

ASME Code

9

•

If no long seam, then E = 1.0.

•

If 100% RT, then E = 1.0.

•

If Spot RT, then E = 0.85.

•

If no RT, then E = 0.70.

Detailed Drawing

Corner joint efficiency on the short side (EC) in accordance with the ASME Code and consistent with the radiographic inspection specified on the detailed drawing. See Step 8.

Detailed Drawing

10

Long-Side Length Dimension (h).

Detailed Drawing

11

Minimum Thickness of the Long-Side Plates (t2). The new, uncorroded thickness should be input.

Detailed Drawing

ASME Code

Header Box Calculation Verification Procedure, cont'd Figure 29

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Step 12

Item to Verify

Information Source

Mid-side joint efficiency on the long side (E) is in accordance with the ASME Code and consistent with the radiographic inspection specified on the detailed drawing. See Step 8.

ASME Code Detailed Drawing

13

Minimum Thickness of the End Plates (t5). The new, uncorroded thickness should be input.

Detailed Drawing

14

Corrosion Allowance of the Shell

15

Tube Hole Pitch Distance (p)

Detailed Drawing

16

Tube Hole Diameter. Each hole may have multiple diameters (i.e., d0, d1, d2).

Detailed Drawing

17

Depth of the Holes. Each hole diameter will have a specific depth (i.e., T0, T1, T2).

Detailed Drawing

18

Plug Hole Pitch Distance (p)

Detailed Drawing

19

Plug Hole Dimensions

Detailed Drawing

20

Minimum Thickness of Stay Plate (t3, t4)

Detailed Drawing

21

Corrosion Allowance of Stay Plate

22

Membrane Stress, Bending Stress, and Total Stress in the Short-Side Plates, Long-Side Plates, End Plates, and at the Corner Sections. Check that actual stresses are below the corresponding allowable stresses.

Computer Output

23

MAWP based on Membrane Stress, Bending Stress, and Total Stress. MAWP for the exchanger is the lowest of the calculated values, and should be above the design pressure.

Computer Output

Form 2716

Form 2716

Header Box Calculation Verification Procedure, cont'd Figure 29

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Header Box Geometry and Nomenclature Figure 30

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PLATE WITH MULTIDIAMETER HOLES

Header Box Geometry and Nomenclature, cont'd Figure 30, cont'd

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WORK AID 4: PROCEDURE FOR COMPLETING A SHELL-AND-TUBE HEAT EXCHANGER SAFETY INSTRUCTION SHEET Use the procedural steps that are contained in SAES-A-005, Preparation of Safety Instruction Sheets, to complete Safety Instruction Sheets for shell-and-tube heat exchangers, Form 2713. The key numbers that are indicated in the procedure are shown on the edited Form 2713 in Figure 33. A copy of SAES-A-005 is contained in Course Handout 2. Most of the procedural steps that are contained in SAES-A-005 are straightforward and do not require further explanation. The following additional procedural information is provided to assist in completing several of the key number items. 1.

Key Number 22 - Determine the Basis for Calculated Test Pressure on the Shell Side Review the manufacturer's calculations and determine the Maximum Allowable Pressure New and Cold ( MAPNC) for the components that are listed in Figure 31. List these values in the column headed MAPNC: Component

MAPNC

Shell Shell Cover Shell Cover Flange Shell Flange Mating to Cover Flange Shell Girth Flange at Tubesheet Fixed Tubesheet (maximum shell-side pressure) Tubes (maximum external pressure) Floating Tubesheet (maximum shell-side pressure) Floating Head (maximum shell-side pressure) Floating Head Flange (maximum shell-side pressure) Components That May Determine Shell-Side MAPNC Figure 31

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The basis for calculated test pressure on the shell side is the minimum of the MAPNCs listed above. Use the shell-side design pressure if the MAPNCs for the components are not provided in the contractor calculations. 2.

Key Number 34 - Determine the Basis for Calculated Test Pressure on the Tube Side Review the manufacturer's calculations and determine the MAPNC for the components in Figure 32. List these values under the Column headed MAPNC: Component

MAPNC

Channel Channel Cover Channel Cover Flange Channel Girth Flange at Tubesheet Fixed Tubesheet (maximum tube-side pressure) Tubes (maximum internal pressure) Floating Tubesheet ( maximum tube-side pressure) Floating Head (maximum tube-side pressure) Floating Head Flange (maximum tube-side pressure)

Components That May Determine Tube-Side MAPNC Figure 32 The basis for calculated test pressure on the tube side is the minimum of the MAPNCs listed above. Use the tube-side design pressure if the MAPNCs for the components are not provided in the contractor calculations. 3.

Key Numbers 62 and 72 - Determine the tm's for Each Component.

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Review the contractor's calculations and look for the minimum required thickness, tm, of each component. •

If the minimum required thickness is indicated exclusive of the nominal corrosion allowance, this is the tm for the component.

•

If the minimum required thickness includes a corrosion allowance, subtract the nominal corrosion allowance from the minimum thickness that was determined by the manufacturer. This is the tm.

•

If the minimum required thickness of the part is not known, subtract the nominal corrosion allowance from the nominal thickness and assume that this is the tm for the component.

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WORK AID 4: PROCEDURE FOR COMPLETING A SHELL-AND-TUBE HEAT EXCHANGER SAFETY INSTRUCTION SHEET, CONT'D

Shell-and-Tube Heat Exchanger Safety Instruction Sheet Form 2713 Figure 33

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GLOSSARY BWG

Birmingham Wire Gauge. A standard measure of plate thickness as designated by a specific BWG number. Each BWG number corresponds to a specific thickness in inches.

embedded fin

A rectangular cross section, aluminum fin that is wrapped under tension and mechanically embedded in a groove that is spirally cut into the surface of the tube.

footed fin

An L-shaped aluminum fin that is wrapped under tension over the outside surface of a tube with the tube fully covered by the feet between the fins. The fin ends are secured to prevent loosening or unraveling of the fins under the design conditions.

integral fin

An aluminum outer tube from which fins have been formed by extrusion and then mechanically bonded to an inner tube.

overlapped footed fin

An L-shaped aluminum fin that is wrapped under tension over the outside surface of a tube, with the tube fully covered by the overlapped feet that are under and between the fins. The fin ends are secured to prevent loosening or unraveling of the fins under the design conditions.

Saudi Aramco DeskTop Standards

84