Specifying Design Requirements for Heat Ex Changers

Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramco’semployees. Any material contained in this document which is not alreadyin the public domain may not be copied, reproduced, sold, given, ordisclosed to third parties, or otherwise used in whole, or in part, withoutthe written permission of the Vice President, Engineering Services, SaudiAramco.

Chapter : Vessels For additional information on this subject, contactFile Reference: MEX21003 J.H. Thomas on 875-2230

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Specifying DesignRequirements for Heat Exchangers

Engineering Encyclopedia Vessels

Specifying Design Requirements for Heat Exchangers

Saudi Aramco DeskTop Standards

CONTENTS PAGE

USE OF SAUDI ARAMCO DESIGN SPECIFICATION SHEETS INHEAT 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 CONDITIONSFOR TEMA-TYPE AND AIR-COOLED HEAT EXCHANGERCOMPONENTS ............................................................................................................... 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




EVALUATING CONTRACTOR-SPECIFIED DIMENSIONS FORSHELL-AND-TUBE HEAT EXCHANGER COMPONENTS........................................ 19

General Dimensional Verification................................................................................. 19

Typical Errors............................................................................................................. 20

Compliance with Saudi Aramco, TEMA, API, and ASMERequirements ............................................................................................................. 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 AIR-COOLED HEAT EXCHANGER TUBE BUNDLES AND HEADERS ..........................40

Tube Bundle Design Requirements............................................................................... 40

Overall Bundle Design Requirements........................................................................ 40

Tube Design ............................................................................................................... 40

Tube Support Design ................................................................................................. 41




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 theInlet/Outlet Header Box of an Air-Cooled Heat Exchanger....................................... 46

COMPLETING A SAFETY INSTRUCTION SHEET FOR A SHELL-AND-TUBE HEAT EXCHANGER ................................................................................. 47

Information Covered ..................................................................................................... 47

Where to Find Other Information.................................................................................. 50

WORK AID 1: PROCEDURE FOR EVALUATING CONTRACTOR-SPECIFIED DESIGN CONDITIONS FOR TEMA-TYPE AND AIR-COOLED HEAT EXCHANGER COMPONENTS .........................................................51

Part 1: TEMA-Type Heat Exchangers........................................................................... 51

Part 2: Air-Cooled Heat Exchangers ............................................................................. 52

WORK AID 2: PROCEDURE FOR EVALUATING CONTRACTOR-SPECIFIED DIMENSIONS FOR SHELL-AND-TUBE HEATEXCHANGER 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 CONTRACTOR-SPECIFIED DESIGNS FOR AIR-COOLED HEAT EXCHANGER TUBEBUNDLES AND HEADERS...........................................................................................68

Part 1: General Requirements........................................................................................68




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-AND-TUBE HEAT EXCHANGER SAFETY INSTRUCTION SHEET................................... 80

GLOSSARY.....................................................................................................................84



Saudi Aramco DeskTop Standards 1

USE OF SAUDI ARAMCO DESIGN SPECIFICATION SHEETS IN HEATEXCHANGER PROCUREMENT

The Saudi Aramco specification sheets that are used for design of heat exchangers are alsoused in various stages of heat exchanger procurement. These sheets are also frequentlyreferred to during heat exchanger operation, inspection, and maintenance inasmuch as theyare a source of reference information. Saudi Aramco has specification sheets for shell-and-tube, air-cooled, and plate-type heat exchangers. The specification sheets for shell-and-tubeand air-cooled heat exchangers were previously introduced in MEX 210.02 with respect tomaterial selection requirements, and will be discussed further in this module. Thespecification 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 bycontractors who are employed by Saudi Aramco. The Saudi Aramco engineer will normallyreview the contractor's work in order to ensure that the heat exchanger data sheet is completedcorrectly. In some cases, the Saudi Aramco engineer will complete the heat exchanger datasheet when no contractor is involved on the project, or when an existing exchanger must bererated to new design conditions.

The data sheets specify the design information that is necessary in order to request a quotationfor a new exchanger and in order to document as-built details of the exchanger. The use ofdata sheets ensures that there will be a uniform bidding basis among the competing heatexchanger 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 specifythe design requirements for TEMA-type shell-and-tube heat exchangers. This form isreferenced in SAES-E-001, Basic Criteria for Unfired Heat Transfer Equipment. This form isshown in Figure 1, and a copy is contained in Course Handout 3. The form has severalsections that are filled in by process and mechanical engineers during heat exchangerprocurement. The following paragraphs briefly describe the main sections of this form.




Form 2714

Figure 1




Form 2714

Figure 1, cont’d




General Procurement Information

The upper left portion of the form contains an area where general information about theexchanger is specified. The following items would probably be completed before the form issent 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 onthe 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




Section A. Process/Performance Data of One Unit

The contractor's process engineer typically completes the process information that is specifiedin this section. The heat exchanger manufacturer uses this information to design theexchanger 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 thesecolumns is to allow the contractor's process engineer to indicate the change in various processparameters as the fluid travels from the inlet to the outlet on both the shell-side and tube-sideof the exchanger. In most cases, all of the information that is necessary for the process designof the unit is provided when the specification is sent out for bids. Any discrepancies betweenthe specified process information and what the manufacturer includes in his bid must beresolved before the exchanger is purchased, because these discrepancies could have asignificant 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, theinlet pressure, and the pressure drop. The mechanical design temperature must be higher thanthe process temperature. The mechanical design pressure must be higher than the inletpressure, and some internals must be designed for the pressure drop that occurs in theexchanger.

Section B. Construction Data of One Shell

The mechanical design information that is necessary to construct the heat exchanger isspecified in this section. The contractor's mechanical engineer should provided as muchinformation 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 hisbid.

There are two columns in the first part of this section, one for the shell-side data and one forthe tube-side data. The following information must be specified when the specification sheetis sent out for bids:

• Corrosion Allowance

• Design Temperature

• Design Pressure

• Nozzle Data (Size, Number, Rating, Facing)




The following design information is normally completed by the contractor or themanufacturer 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 constructiondetails for the exchanger. The first column is for Material and Specifications, the secondcolumn is for Thickness Base Metal/Cladding, and the last column is for PWHT/XR(Postweld Heat Treatment/ Degree of Radiography). Saudi Aramco material specificationrequirements were discussed in MEX 210.02. In most cases, this information is completed bythe manufacturer at the time of bid; however, this information could also be completed by thecontractor 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 thetubes and baffles.

Section C. Miscellaneous

This section includes information (such as overall dimensions and weights) that is normallycompleted by the manufacturer when he submits his bid. The section also includes notes forthe 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 andrevision record.




Data Sheet for Air-Cooled Heat Exchangers

Saudi Aramco Form 2716, Specifications for Air Cooled Heat Exchanger, is referenced bySAES-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 atvarious stages of exchanger procurement. The following paragraphs briefly describe the mainsections of this form.

Form 2716

Figure 2




General Procurement Information

This portion of the form contains general information about the heat exchanger. All of thisinformation, 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 processengineer. The heat exchanger manufacturer uses this information to design the exchangerfrom a process standpoint. Note that there is one column for tube-side data and anothercolumn 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 engineerto indicate various process parameters that may change as the tube-side fluid travels from theinlet to the outlet of the exchanger. In most cases, all of the information that is necessary topermit the process design of the exchanger is provided when the specification is sent out forbids. Any discrepancies between the specified process information and what themanufacturer includes in his bid must be resolved before the exchanger is purchased becausethese discrepancies could have a significant effect on whether the heat exchanger performs itsrequired process function.

From a mechanical design standpoint, the values that are of interest on the tube-side are theinlet temperature, the inlet pressure, and the pressure drop. The mechanical designtemperature must be higher than the process inlet temperature. The mechanical designpressure must be higher than the process inlet pressure, and some internals must be designedfor the pressure drop that occurs in the exchanger. The quantities that are of interest on the airside 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 heatexchanger. The contractor's mechanical engineer should provide as much information aspossible in order to obtain a uniform basis for bidding; however, in all cases, relevantrequirements that are contained in SAES-E-001 must be completed by the contractor. Anyinformation that is left out should be provided by the manufacturer when he submits his bid.




The following information is normally specified when the specification sheet is sent out forbids:

• 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 titleblock and revision record.




EVALUATING CONTRACTOR-SPECIFIED DESIGN CONDITIONS FOR TEMA-TYPE AND AIR-COOLED HEAT EXCHANGER COMPONENTS

SAES-E-001 specifies how to determine the heat exchanger mechanical design conditionsbased on the operating conditions that are specified on Forms 2714 and 2716 . The processengineer always specifies the operating conditions and usually sets the mechanical designconditions as well; however, the mechanical engineer usually checks the design conditions asa part of his review of the Contractor Design Package. Work Aid 1 provides a procedure thatmay be used to evaluate the information that is contained in a Contractor Design Package, todetermine if the design conditions are specified correctly.

In most cases, the maximum operating pressure and temperature can be assumed to be equalto the values that are indicated in the process/performance section of Form 2714 or Form2716. However, the specified conditions may not be the maximum operating conditions insome cases, such as when the heat transfer surface area must be sized to transfer heat atconditions that are lower than the maximum operating conditions. For the purpose of thiscourse, it will be assumed that the operating conditions that are shown on Form 2714 andForm 2716 are the maximum operating conditions. In actual work, the maximum operatingpressures and temperatures must be confirmed by the process engineer in order to ensure thatthe mechanical design of the heat exchanger is suitable for the most extreme operatingconditions.

Since heat exchangers transfer heat from one fluid to another, design conditions must bespecified for each fluid. Some heat exchanger components are exposed to only one fluid, andother components are exposed to both fluids. Therefore, some components need only bedesigned for one set of design conditions, while other components must be designed for bothsets of design conditions. From a practical standpoint, both sets of design conditions mustonly 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 shell-and-tube heat exchanger, and Figure 4 summarizes the conditions that each major componentmust be designed for. The following sections discuss the design conditions for specificcomponents.




Heat Exchanger Design Conditions

Figure 3




Components Designed forShell-Side Conditions

Components Designed forTube-Side Conditions

Components Designed forBoth Shell-Side and Tube-

Side Conditions

Shell

Shell Cover

Shell Flanges

Shell Nozzles

Channel

Channel Cover

Channel Flange

Channel Nozzles

Tubes

Tubesheet(s)

Tubesheet Flanges

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 andchannel cover must be designed for the tube-side conditions. These components are made ofcylindrical shells, conical shells, or formed heads, and they are designed for the designpressure at the design temperature using the ASME Code Section VIII. Design proceduresthat 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 aredesigned for the tube-side conditions. The nozzles necks are cylindrical shells and aredesigned in accordance with the ASME Code for their respective design conditions. Becausethere are cut-outs in the shell due to the nozzle penetration, nozzle reinforcementrequirements 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.




External forces and moments may be exerted on the nozzles by piping that is attached tothem, and the nozzles should be designed for these loads in addition to the design pressure. Ifthe piping loads are high, they should be specified to the heat exchanger manufacturer so thathe 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 therear or floating head end of the exchanger, a flange may be used to bolt the shell cover to theshell. This shell cover flange is designed for shell-side conditions. On the front or stationaryend of the exchanger, a girth flange may be used to bolt a flat cover onto the channel. Thischannel flange is designed for the tube-side conditions. A girth flange may also be used tobolt the channel to the shell.

In many cases, the tubesheet at the stationary end of the exchanger may be clamped betweena pair of girth flanges. In these clamped tubesheet designs, one of the girth flanges is attachedto the channel and the other girth flange is attached to the shell. The shell-side flange at thestationary-end tubesheet must be designed for the shell-side conditions, and the tube-sideflange at the tubesheet must be designed for the tube-side conditions. In addition, since bothflanges are connected by the same set of bolts, the flanges must be designed for a commonbolt 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 discussedin more detail in a later section.

Girth flanges are normally of nonstandard sizes, and are designed using procedures that arecontained in the ASME Code. These flange design procedures are discussed in a later sectionof this module.

Tubesheets

Tubesheets are exposed to both the shell-side and the tube-side design conditions. In actualoperation, the tubesheets are normally exposed only to a differential pressure (i.e., thedifference between the tube-side pressure and the shell-side pressure) and are at a temperaturethat is between the shell-side and the tube-side temperatures. While the tubesheets could bedesigned on this basis, tubesheets are major components of the exchanger and are typicallydesigned for the more severe of either the shell-side or the tube-side conditions.




While conservative, this design approach is realistic inasmuch as it is often possible for oneside of the exchanger or the other side to be exposed to its operating conditions while theother side is not.

There are some services where it is impossible for only one side of the exchanger to be at itsoperating conditions while the other side is not (e.g., for a reactor feed-effluent exchangerwhere both sides are automatically either in operation or not). In other cases, it may be veryexpensive 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 theshell-side.

An additional factor is that hydrotest of the heat exchanger is normally done on each sideseparately. Thus, one side will have the full hydrotest pressure while the opposite side has nopressure.

Tubesheets typically operate at a temperature that is between the shell-side and the tube-sidetemperatures. The TEMA standard allows tubesheets to be designed for the mean metaltemperature unless the owner specifies otherwise. If a mean temperature is used, it should bebased on heat transfer calculations that account for the heat transfer coefficients and variousmodes of operation. Except for fixed tubesheet heat exchangers, tubesheets are usuallydesigned for the higher of either the tube-side or the shell-side temperatures unless it isimpossible for the exchanger to be exposed to the higher temperature (e.g., if a refractorylining is installed on the tubesheet to reduce its metal temperature). In the case of fixedtubesheet exchangers, it may not be practical to design the fixed tubesheet if the designconditions are too conservative. Therefore, the tubesheets of fixed tubesheet exchangers areusually designed for a calculated mean temperature.

Flat Covers

Flat covers are typically used on the channel side of TEMA Type A and Type C exchangersand are designed for the tube-side pressure and temperature conditions. Covers forexchangers that have internal pass partition plates must also be designed to limit thedeflection of the cover in order to minimize leakage across the pass partition plate. Deflectionlimits 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 maynot be subjected to any significant pressure. In general, the design temperature of thecomponent 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 metaltemperature unless the owner specifies otherwise. In most cases, internal components aredesigned for the more severe set of conditions.




Floating Heads - The tube-side conditions impose an internal pressure on the floating head, andthe shell-side conditions impose an external pressure on the floating head. Both sets ofconditions must be checked separately in order to determine which one governs the design ofthe floating head and its associated flange and backing ring. As with tubesheets, floatingheads are usually designed for the more severe of either the shell-side or the tube-sideconditions. Recall from MEX 202 that the design of heads and cylinders for external pressureconditions 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 higherpressure side of the exchanger.

Tubes - The tubes of shell-and-tube heat exchangers are typically designed independently forinternal pressure at the tube-side conditions and for external pressure at the shell-sideconditions. The tube design is governed by the set of conditions that requires the larger tubethickness. The longitudinal stress due to weight and pressure may govern the design in somecases; however, it is usually more economical to reduce the baffle or tube support spacingrather than to increase the tube wall thickness.

In fixed tubesheet exchangers, consideration must also be given to designing the tubes forforces that are due to the differential temperature between the tubes and the shell. If the tubeloads are too high, normal practice is to use a shell expansion joint rather than to increase thetube wall thickness. Tube vibration may also be a consideration in the design of tubes. Tubevibration is discussed in MEX 210.05.

Pass Partition Plates and Longitudinal Baffles - Pass partition plates are located in the channel andthe floating heads of some exchangers. Typically, these plates are designed for the maximumnormal pressure drop across the tube side. Some exchanger configurations include shell-sidelongitudinal 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 istypically based on minimum sizes that are specified in TEMA based on nominal shelldiameter. Tube support plates that are thicker than the TEMA minimum values may berequired in some cases where there is a large shell-side corrosion allowance or if flowpulsation or tube vibration is a special design consideration.




Air-Cooled Heat Exchangers

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

Typical Air-Cooled Heat Exchanger Tube Bundle Components

Figure 5




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 mustalso take into consideration the additional longitudinal stress that is caused by the weightloads from the tubes, tube fins, and tube contents. Note that it is usually more economical toshorten the tube support spacing, rather than increase the tube wall thickness in cases whereexcessive longitudinal stress or tube sagging are a problem. The needed tube surface area ofthe 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 tubemetal temperature typically governs which fin attachment option is used for a specific heatexchanger. The fin attachment design is typically selected based on the maximum process-side design temperature, because it is usually possible to stop the air flow while the processfluid continues to flow.

Tube Bundles

The tube bundle must be designed for the process-side design temperature in case the air flowis stopped. The bundle must be designed for differential thermal expansion between it and thesupporting frame and structure. The tube bundle must be designed to be rigid in order topermit handling it as a complete assembly both in the shop and in the field. The tube bundleand side frame assemblies must also be designed to withstand the required wind loads andearthquake loads.

Tube Supports

The tubes are supported at intervals that are short enough to prevent excessive sagging due tothe imposed weight loads. Excessive sagging could cause flow distribution problems, orcause 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 therequired tube support spacing.




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 theheader 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 nozzlesin order to avoid overstressing the nozzles and the header boxes. The maximum permittednozzle loads are a function of nozzle diameter. The header boxes must also be designed totransmit piping loads from the nozzles to the exchanger-side frame and support structure.




EVALUATING CONTRACTOR-SPECIFIED DIMENSIONS FOR SHELL-AND-TUBE HEAT EXCHANGER COMPONENTS

A shell-and-tube heat exchanger is composed of many components, such as cylindrical orconical shells, flat plates, and formed heads. Although minimum thicknesses for thesecomponents are given in 32-SAMSS-007, API-660, TEMA, or the ASME Code, thesecomponents must normally be designed and dimensioned for the specific heat exchangerdesign requirements. The design of components such as cylindrical shells and formed headswas covered in MEX 202 and will not be discussed. Components that are unique to shell-and-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 heatexchanger components, the Saudi Aramco engineer typically checks that all dimensions are:

• Consistent on all drawings and in all specifications and calculations that aremade by the manufacturer and that are included in the Contractor DesignPackage.

• In accordance with the design and calculation requirements that are specified inForm 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 thatare specified for the major components of shell-and-tube heat exchangers. The sections thatfollow elaborate on several aspects of this procedure and discuss several of the designrequirements for specific heat exchanger components.

General Dimensional Verification

The dimensions that are specified for heat exchanger components must be checked to ensurethat 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.




Typical Errors

Many mistakes are made when copying dimensions from calculation sheets to fabricationdrawings or from one drawing to another. Corrosion allowance is sometimes left out or maybe 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 otherdrawings that specify individual component details. Another typical mistake occurs when adetail on one drawing is revised, but other details in the Contractor Design Package are notrevised 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 somecases, dimensional requirements or dimensional limits that are given on Form 2714 or in 32-SAMSS-007 may be neglected. In other cases, the manufacturer may misinterpret a SaudiAramco requirement. Therefore, several problems can usually be identified if a review forcompliance is made with respect to specific Saudi Aramco requirements.

Use of Computer Programs

The required mechanical design calculations for heat exchanger components are normallydone using computer programs. Therefore, the Saudi Aramco engineer will normally have tocheck computer-generated calculations, in addition to checking the fabrication exchangerdrawings, 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 andASME Code requirements. In order to check a manufacturer's computer program, it is usuallysufficient to review a verification example problem that was made for the program. If noverification problem is available, another approach is to select a typical exchanger andthoroughly check the calculations for the selected exchanger. This check can be done byredoing the calculations by hand or by using another, commercially-available computerprogram for heat exchanger design that has already been independently verified. Commercialprograms that are widely used are usually updated frequently and corrected quickly whenerrors are found.




All of the heat exchanger calculations that are used in this module were made using theCODECALC computer program by Coade, Inc. This program is available within SaudiAramco. It may be assumed that the CODECALC program has been thoroughly tested andverified. All computer programs require the same input, use the same TEMA or ASME Codeequations, and give similar output. The purpose of this course is not to instruct Participants inhow to run a specific computer program, but in how to evaluate whether the contractor orexchanger manufacturer has done his job properly. Therefore, the Work Aids were developedto 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 isexplained where necessary.

Checking Computer Input Data

Checking for consistency between the computer program input data and the information thatis included in various parts of the Contractor Design Package is tedious but is necessary. Thenecessary input includes design conditions, some dimensional information, materialproperties, and other Code design information.

Some computer programs require that necessary design factors be manually entered fromtables or figures that are in the standard or Code, whereas other programs have internal databases that contain the needed information. A small mistake in the computer program inputcan result in completely incorrect calculations.

Checking Computer Output

Checking that the contractor or manufacturer has correctly interpreted the computer programoutput is tedious, but this checking is still necessary because errors can still be made at thisstage. Examples of errors that can be made at this stage include overlooking corrosionallowances or specifying information on the fabrication drawings that does not coincide withthe 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 as-built dimensions. The basic approach that is used to solve for MAWP was discussed in MEX202. For heat exchangers, the MAWP is determined by solving the appropriate TEMA orASME 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 isrequired to rerate an exchanger. Rerating a heat exchanger is discussed in MEX 210.05.




Heat Exchanger Components

This section will review the design requirements for the following components of shell-and-tube 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 somemanufacturers attempt to standardize some aspect of their girth flange designs. All girthflanges 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 thatare provided by a contractor or manufacturer for exchanger girth flanges. The followingsections 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 Bexchangers.

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.




The first main step in flange design is usually to determine the number and size of bolts thatare required for the flange. Bolting requirements are determined by calculating the loads onthe bolts during both normal operation (i.e., based on the design conditions), Wm1, and duringthe initial flange boltup (i.e., the gasket seating conditions), Wm2. The bolt area that isrequired for each of these loads is then calculated by dividing each bolt load by the allowablestress of the bolts at design temperature and room temperature, respectively. Either theoperating 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 thespacing between bolts, the actual bolt area, Ab, is usually greater than the maximum requiredbolt area.

The next step is to determine the design loads and moments on the flange. These loadsinclude the design bolt load on the flange (W), the hydrostatic pressure loads that act on theflange (HD and HT), and the gasket sealing force (HG). Because these loads do not all act atthe same location on the flange, effective moment arms (hD, hT, and hG) are calculated basedon the locations of the bolts and gasket and on the flange geometry (See Figure 6). Theappropriate loads are then multiplied by the effective lever arms in order to determine flangedesign moments for the operating case and the gasket seating case.

Flange Loads and Moment Arms

Figure 6




Finally, the stresses in the flange ring and the flange hub are calculated using stress factorsthat 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 thegasket seating case and are then compared to the appropriate Code allowable stress. If theflange is properly designed, all of the flange stresses will be lower than the appropriateallowable stresses. It may be necessary to increase the flange thickness, change the hubdimensions, or make other changes to the flange design parameters in order to keep the flangestresses within their allowable limits. The computer programs that are used for flange designuse 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 tokeep the gasketed joint tight. The minimum design seating stress, y, is a parameter thatdetermines how much gasket stress is required to initially seat or deform the gasket. Both ofthese 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 Figure7). Higher values of m and y typically indicate that a gasket is harder to seal or seat. Whilethis is a consideration in gasket selection, gasket type and gasket material are usually selectedbased on historical service experience and corrosion resistance. For example, both TEMAand 32-SAMSS-007 specify gasket requirements based on service conditions as discussed inMEX 210.02. In addition, m and y are only two of many parameters in the flange designcalculations.




Gasket Material GasketFactor m

Min.DesignSeatingStress y,

psi

Facing Sketch andColumn in Table 2-5.2

Flat metal, jacketed asbestos filled:

Soft aluminum

Soft copper or brass

Iron or soft steel

Monel

4-6% chrome

Stainless steels and nickel-base alloys

3.25

3.50

3.75

3.50

3.75

3.75

5 500

6 500

7 600

8 000

9 000

9 000

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

Solid flat metal:

Soft aluminum

Soft copper or brass

Iron or soft steel

Monel or 4-6% chrome

Stainless steels and nickel-base alloys

4.00

4.75

5.50

6.00

6.50

8 800

13 000

18 000

21 800

26 000

(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 jointsand for pass partition gaskets. Although TEMA exchangers operate over a very wide range ofservice conditions, these minimum gasket widths have been used for many years and aretypically specified.




The gasket widths that are referred to in TEMA are actual minimum widths. In addition to theactual minimum width, N, two other gasket widths are referred to in the ASME Code: thebasic seating width, bo, and the effective seating width, b. The effective seating width is afunction of the basic seating width, and the basic seating width is a function of the actualwidth and the type of flange face. See Table 2-5.2 in the ASME Code (Excerpted in Figure8). In general, wider gaskets provide better sealing, but a wider gasket also requires morebolting to seat and seal the gasket. The required flange thickness increases as the amount ofbolting increases.

Effective Gasket Seating Width, b

b = bo when bo ≤ 1/ 4 in.; b = bo when bo > 1/ 4 in.

ASME Code Gasket Widths

Figure 8




The effective seating width, b, discussed above is also a function of the flange facing type andthe nubbin width, w, for flat metal gaskets. Table 2-5.1 (excerpted in Figure 7) in the Codeindicates which facing sketch is applicable for a given gasket type and material, and Table 2-5.2 (Figure 8) shows the equations for determining b based on w, N, and the type of flangefacing. Note that b is the factor used in the subsequent Code equations to determine the loadrequired for sealing the gasket during operation, WM1, and the load required for seating thegasket initially, WM2. Once a gasket type, material, width, and facing are selected, therequired bolting area can be determined.

The bolt size, number and spacing that are used to clamp the flanges together are interrelatedparameters that affect the overall design of the flanges. Bolting is typically selected perTEMA Table D-5 (See Figure 9), with the added restrictions in TEMA Par. R-11.1 that theminimum bolt size is 19 mm (3/4 in.).

Bolt Size Threads Nut Dimensions BoltSpacing

RadialDistance

RadialDistance

EdgeDistance

WrenchDiameter

BoltSize

dB No. ofThreads

RootArea,in.2

AcrossFlats

AcrossCorners

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 theroot of the threads. The number of bolts multiplied by the bolt root area of a single bolt mustbe greater than the minimum required bolt area, Am. The bolts must be far enough away fromthe shell or hub of the flange and be far enough apart circumferentially so that there isadequate clearance to permit access for a wrench to tighten and loosen the bolts. TEMATable D-5 also indicates minimum dimensions to ensure adequate access for standardwrenches.

While it may appear that maintaining these minimum dimensions can easily be achieved if afew large bolts are used, the bolts should also be spaced as close together as practical forseveral reasons.




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

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

• Excessive bolt spacing could make the flange more prone to leakage since theportions of the gasket that are located between the bolts might not becompressed 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 integralmultiple of four.

A manufacturer's computer program will typically design the bolting and the flange subject toall the above conditions. The responsibilities of the Saudi Aramco engineer would then be tocheck the computer program input, to determine that the appropriate TEMA and ASME Codefactors and allowable stresses were used, and to confirm that the computer program outputhas been correctly interpreted and incorporated into the design.

Tubesheet Girth Flange Design Requirements for TEMA Type A and Type B Exchangers - TEMAType A and Type B exchangers have the fixed tubesheet compressed between two girthflanges. These girth flanges require special design consideration. Each flange must bedesigned for the appropriate design conditions on each side of the tubesheet, and for thecommon bolt load that is imposed on each flange. The common bolt load may be based onthe operating or gasket seating loads, and these loads may be different on each side of thetubesheet.

The proper design of these girth flanges typically requires that at least three separate flangecalculations be made.

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

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

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




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 theTubesheet of a TEMA-Type AET Heat Exchanger - You must evaluate the contractor-specifieddimensions for the mating girth flanges at the fixed tubesheet end of a Type AET heatexchanger. All the information that is needed to solve this problem is in Contractor DesignPackage 4 in Course Handout 4. This information includes the heat exchanger specificationsheet, flange dimensions, and the CODECALC computer program output for the shell girthflange and the mating channel girth flange. Part 2 of Work Aid 2 is used to solve thisproblem.

The first step in evaluating a design is to compare the common dimensions between the twomating flanges and the number and size of bolts that are shown in the detail drawings for theflanges. Flange dimensions are also checked for consistency between the drawing details andthe computer program input and output.

Note that additional design information is included in the computer program input, such asASME 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 exchangerhave different design conditions; therefore, calculations were first made for the shell flangefor the shell-side conditions, and then made for the channel flange for the tube-sideconditions. By comparing the computer output for the required bolt area, Am, between thetwo computer runs, it is seen that the shell flange governs the bolting requirement for thesemating flanges because it requires a larger value for Am. Therefore, a second analysis wasmade 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 theappropriate values for the operating bolt load, gasket seating bolt load, and the flange designbolt load have been entered for the mating flange bolt loads. These bolt loads were takenfrom the previous calculations that were done for the shell flange.

Because the computer program input and output have been checked and the program has beenverified, it is concluded that the dimensions specified by the manufacturer for the girth flangesare correct inasmuch as the dimensions are in accordance with the computer program output.




Pass Partition Gaskets

Most exchangers have at least two tube-side passes. A pass partition gasket is used in thechannel for these exchangers in order to provide internal sealing between the tube passes atthe pass partition plate (see Figure 10). A pass partition gasket is also required at the floatinghead end for exchangers that have more than two tube-side passes. The pass partition gaskethas more surface area that must be compressed when compared to a conventional gasket thatonly has material at its periphery. Therefore, the flange bolting must be sufficient tocompress the gasket enough at both its periphery and at the pass partition plate. If theexchanger has more than two tube passes, the pass partition gasket has even more surface areathat must be compressed.

Pass Partition Gasket

Figure 10

Although not specifically referred to in the ASME Code calculations or in TEMA, girthflanges should be designed to provide additional bolting in order to adequately compress passpartition gaskets and achieve a tight seal. Properly designed bolting should be able tocompress the gasket at both its periphery and at the pass partition.




Bolting design can be handled in several ways. In the CODECALC program, the length ofthe pass partition gasket may be entered as a separate parameter. If the width of the passpartition gasket (Npp) differs from the width of the peripheral gasket (N), the length that isinput (Lpp) is adjusted as follows:

Lpp = (Gasket InsideDiameter) ×Npp

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 toclose the end of the channel (Refer to Figure 11).

Flat (Channel) Cover

Figure 11




The ASME Code design procedure for flat covers is specified in Par. UG-34 and is based ondetermining the minimum cover thickness that is required to limit the stress in the cover plateto the material allowable stress. In the ASME procedure, the thickness of the flat cover, t, isdetermined as a function of the pressure, P, the cover plate allowable stress, S, the flangedesign 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 thecover if the exchanger has pass partition baffles. The limit on cover deflection is specified inorder to minimize leakage that can occur across the pass partition baffle. TEMA Par. RCB-9.21 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 channelcover even though the calculations are not highly complicated. The cover deflection limit,rather than the ASME Code allowable stress, will generally govern the channel coverthickness 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 designcalculations 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 andsimplest types of tubesheets to design are those associated with TEMA Type S, Type T, andU-tube type exchangers. The procedures that are most often used for the design of tubesheetsin 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. TheASME procedure is applicable for U-tube type and fixed tubesheet types of exchangers. Notethat the ASME Code procedure is more complicated than the TEMA procedure, and that theTEMA procedure is used to design most heat exchanger tubesheets. Work Aid 2 covers onlythe TEMA procedure. The following paragraphs discuss several considerations for tubesheetdesign.




Tubesheet Thickness - TEMA Par. RCB-7.12 requires that the tubesheet thickness be measuredat the bottom of the pass partition baffle groove or the shell-side longitudinal baffle groove, ifso 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 inexcess of the partition groove depths. The effective thickness should be exclusive of anyapplied facings, but the thickness of cladding or weld overlay that is in excess of the specifiedcorrosion allowance may be considered as effective in accordance with TEMA and ASMEprocedures.




Basic Minimum Thicknesses - TEMA specifies basic minimum thicknesses for the tubesheetbased on overall fabrication and handling requirements when the tubes are expanded into thetubesheet. Par. RCB-7.13 requires that the tubesheet thickness, exclusive of corrosionallowance, should be at least equal to the nominal tube diameter but that the tubesheetthickness including corrosion allowance cannot be less than 19 mm (3/4 in.).

Effective Thickness - The required effective thickness of the tubesheet is determined based onlimiting the bending and shear stresses in the tubesheet to the appropriate ASME Codeallowable stress. The appropriate TEMA paragraph references are as follows:

• Par. RCB-7.132 determines tubesheet thickness based on limiting the bendingstress in the center of the tubesheet.

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

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

Fixed Tubesheet Exchangers - A significant design issue in fixed tubesheet type exchangers isdifferential thermal expansion between the shell and the tubes. Fixed tubesheet exchangersare exchangers where both the front (i.e., channel) end tubesheet and the rear (i.e., shell) endtubesheet on the exchanger are rigidly attached to the shell. These exchangers, designated asL-, M-, or N-types, are much more complicated to design than S-, T-, or U- type exchangersbecause the tubes and shell interact with the tubesheets.

Excessively high differential temperatures between the shell side and tube side of theexchanger can result in the following:

• High thermal stresses in the tubesheet or shell that can and cause a fatiguefailure.

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




Because of these concerns, some fixed tubesheet exchangers may be equipped with anexpansion joint in the shell. The expansion joint permits differential thermal expansionbetween the shell side and the tube side without causing excessive loads or stresses. Anexpansion joint is normally necessary if the temperature differential between the tube walltemperature of any one tube pass and the average shell side temperature exceedsapproximately 28°C (50°F). However, when the shell and tube materials have differentthermal expansion coefficients, a stress analysis is required even when the temperaturedifferential is less than 28°C (50°F).

Fixed tubesheet exchangers are usually designed using a computer program that determinesthe interactions between the tubes, the shell, and the tubesheet. These programs typicallymake the calculations in accordance with TEMA Par. RCB-7.16 and with NonmandatoryAppendix AA of the ASME Code.

Tubesheets that have a nonuniform thickness, or that incorporate flexible knuckles at theirperiphery, may be used on some exchangers. These tubesheets are considered as specialcases in TEMA Par. RCB-7.3 and should be designed in accordance with Div. 1 or Div. 2 ofthe ASME Code.

Sample Problem 2: Evaluate Contractor-Specified Dimensions for the Floating End Tubesheet of aTEMA-Type AET Heat Exchanger - You must evaluate the contractor-specified dimensions forthe floating end tubesheet of a Type AET exchanger. All the information that is needed tosolve this problem is in Contractor Design Package 4 in Course Handout 4. This informationincludes the heat exchanger specification sheet, dimensions, and the CODECALC computerprogram output for the floating end tubesheet. Part 3 of Work Aid 2 is used to solve thisproblem.

The first step in evaluating the design is to compare the dimensions that are specified in thedrawing of the tubesheet to the computer program input. This comparison includes itemssuch as the facing ID, tubesheet OD, and bolt circle diameter. Additional design informationthat is included in the computer program input, such as the gasket m and y factors and thetubesheet allowable stress, is also checked with the ASME Code. All of the computer inputappears to be correct in this problem.

Inasmuch as the computer program input has been checked and the program has beenverified, it is concluded that the thickness specified for the floating end tubesheet is correctbecause the CODECALC output shows no overstress, and the dimensions that are shown inthe tubesheet drawing coincide with the program output.




Internal Floating Heads

Internal floating heads are used on TEMA-Type AES and Type AET exchangers. The S-typefloating head requires a split backing ring to clamp the floating head to the tubesheet. The T-type floating head is bolted directly to the tubesheet. These head types are illustrated inFigure 13. The required thicknesses of the flange ring and of the dished head for both typesof 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 alsobe checked for buckling in accordance with the ASME Code Section UG-33.




The Appendix 1-6 method is relatively simple and can be done on a calculator, but computerprograms are normally used to design floating heads. Although acceptable to the ASMECode, this method is approximate in that it does not consider the continuity between theflange ring and the dished head. The ASME Code indicates that a more exact method ofanalysis which considers the continuity between the flange ring and the head may be used if itmeets the requirements of Section U-2 of the Code. A procedure that was published bySoehren in ASME paper ASME 57-A-7-47, The Design of Floating Heads for HeatExchangers, is one such method that is acceptable to the Code. In many cases the Soehrenmethod yields a thinner, more economical flange ring and floating head design than does theAppendix 1-6 method. However, the Soehren method is more complicated, requires thesolution 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 TEMA-Type AET Heat Exchanger - You must evaluate the contractor-specified dimensions for thefloating head of a Type AET exchanger. All the information that is needed to solve thisproblem is in Contractor Design Package 4 in Course Handout 4. This information includesthe heat exchanger specification sheet, the dimensions of the floating head, and theCODECALC computer program output for the floating head. Part 4 of Work Aid 2 may beused to solve this problem.

The first step in evaluating the design is to compare the dimensions on the tubesheet and thefloating head, such as facing ID, OD, and bolt circle diameter. Dimensions are also checkedfor consistency between the dimensions that are shown in the detail drawings and thedimensions in the computer program input. Additional design information is included in thecomputer program input, such as the gasket m and y factors and the allowable stresses for thering and the dished head materials. This additional information should be checked against theASME 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 beenverified, it is concluded that the specified dimensions for the floating head are correct becausethe 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 inaccordance with the ASME Code Par. UG 31. Par. UG 31 references Par. UG 27 for internalpressure and Par. UG 28 for external pressure. TEMA Par. 7.2 provides requirements fordetermining the axial tensile and compressive loads in the tubes for TEMA L-, M-, and N-type fixed tubesheet exchangers.




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 appliedto tubes per TEMA Par. RCB 1.517. The tube thickness that is required for internal orexternal pressure is small, and the difference between the minimum supplied wall thicknessof the tube and the minimum required thickness is available for corrosion allowance. Tubesare also considered to be replaceable parts, and therefore do not need as large a corrosionallowance as other exchanger components. Consideration should be given to using a thickertube gage or using a higher alloy tube material in services where high corrosion rates areexpected 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 withTEMA Par. RCB-9.132. The thickness of the plate is a function of the dimensions of theplate, a and b, the pressure drop across the plate, q, the ASME Code allowable stress for theplate material, S, and a factor that is based on the conditions of the plate edges, B (see Figure15).




Pass Partition Plate

Figure 15

Note that pass partition plates do not require a corrosion allowance per TEMA Par. RCB-1.518. If a corrosion allowance is desired, it should be applied to both sides of the passpartition 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 thicknessesthat 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 thanthe shell-side corrosion allowance and that the thickness of impingement baffles should not beless than 6.5 mm (1/4 in.). Thicker tube support plates may be required in some cases, perRCB-4.43, for services that are prone to flow pulsation or tube vibration. Nonpressurecontaining parts also do not require a corrosion allowance per TEMA RCB-1.516. If acorrosion allowance or a more robust design is required for a particular application, thisrequirement should be specifically stated in the purchase order.




EVALUATING CONTRACTOR-SPECIFIED DESIGNS FOR AIR-COOLED HEATEXCHANGER TUBE BUNDLES AND HEADERS

The general approach that is used to evaluate contractor-specified designs forair-cooled heat exchanger tube bundles and headers is the same as is used for shell-and-tubeheat exchangers. Dimensional consistency must be verified, and all calculations and designprocedures must be done in accordance with the applicable Saudi Aramco and industryengineering 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 arespecified for air-cooled heat exchanger tube bundles and headers. The sections that followelaborate 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 in32-SAMSS-011. As previously noted, the sections and paragraph numbers in the SAMSScorrespond 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 completeassembly without distorting and being damaged. The tube bundle grows in both length andwidth due to thermal expansion of the metal when the exchanger is in operation. Provisionmust be made in the design to permit the thermal expansion of the bundle because restrainedthermal expansion could cause excessive stresses in the bundle that might eventually result ina failure. 32-SAMSS-011, Par. 5.1.1.4, requires that one header (usually the return header) befree to move due to thermal expansion and that the bundle and the structural mounting musthave Teflon slide plates. Teflon has a much lower friction coefficient than steel, and its usepermits the bundle to slide more easily.

Tube Design

The tubes are typically designed in accordance with the ASME Code Par. UG 31. Par. UG 31references Par. UG 27 for internal pressure design and Par. UG 28 for external pressuredesign. The tubes must also be designed for the combination of the longitudinal stress due tointernal pressure and bending stress due to the tube weight. It is usually more economical tochange tube support spacing rather than to increase tube wall thickness in cases wherelongitudinal overstress or sagging are a problem.




Tube Diameter Wall Thickness, and Corrosion Allowance - API-661 recommends a minimum primetube 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 basicmechanical strength, corrosion allowance, and for standardization purposes. These minimumthicknesses are summarized in Work Aid 3.

Note that the required tube thickness varies with the tube material. This variation is due todifferences 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 thetubes of air-cooled heat exchangers because the thickness that is required for pressure issmall, and the tubes are considered to be replaceable parts.

Selection of Tube Fins - The tubes of air-cooled heat exchangers normally have external fins inorder to increase their external heat transfer area. API-661 describes the various types of tubefins that are available. 32-SAMSS-011 specifies temperature limits and restrictions on the useof the various fin types and attachment methods based on Saudi Aramco experience. Theselimits 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 ofthe fins. Meshing of the fins limits their effectiveness from a heat transfer standpoint andcould also result in mechanical damage to the tubes. API-661 specifies a maximum center-to-center distance between tube supports in order to minimize the possibility that these problemswill occur. API-661 requires that structural hold-downs be provided at each tube support inorder 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 peripheryof the fin for bearing in order to not damage the fins. The spacers must also prevent the finsfrom 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 individualcomponents and procedures to calculate the required wall thicknesses of the flat plates that areused to fabricate the header.




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 isgreater than 200°F (111°C), split headers, U-tubes, or other means must be used toaccommodate the differential thermal expansion that will occur between the tube passes. Thisaccommodation is required in order to avoid excessive stress in the tubes that could cause thetubes to fail and to avoid excessive forces at the tube-to-tubesheet joints that could result inleakage.

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 nominalcorrosion allowance of 3.2 mm (1/8 in.) for carbon and low-alloy steel components. SAMSS-011 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 strengthand rigidity of the header box structure, to accommodate typical tube-to-tubesheet and plug-to-plug sheet design details, and to better resist the loads that are applied by the connectedpiping system.

Header Type

32-SAMSS-011 requires that plug-type headers be used for process-type coolers and thatremovable 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 oilcooler applications because plug-type headers are less prone to leakage and are preferred formore severe process applications.

Plug-Type Header - Requirements for plug-type headers are specified in API-661. The tubeplug holes are specified to be slightly larger than the tube diameter in order to providesufficient 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 designrequirements for removable cover plate-type and removable bonnet-type headers. Animportant consideration in the design of the flat cover or bonnet cover of these header types isthe spacing of the bolts that attach the cover or bonnet to the header. If the bolts are spacedtoo far apart, insufficient compressive load may be exerted on the portion of the gasket that isbetween the bolts. Insufficient gasket compression will make the cover prone to leakage.API-661 provides an equation to determine the maximum permitted bolt spacing. Becausethe bolts must be tightened with a wrench, the bolts must also be spaced a minimum distanceapart in order to provide sufficient space for the wrench. API-661 also specifies minimumbolt spacing requirements in Table 1.




Gasket Requirements

The gasket surface of the tubesheet plug hole must be spot-faced in order to provide a smoothand confined seating surface for the gasket. Gaskets that are used for tube plugs should beeither the solid metal or double-metal-jacketed type and be of the same material classificationas the plug. The use of these gasket types ensures that the gasket is of relatively strongconstruction 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, non-asbestos filled type, except that synthetic fiber gaskets can be used in water, lube oil, and sealoil service if the pressure does not exceed 2 100 kPa (300 psig) and a parting agent is used onboth sides of the gasket. The minimum width of cover plate gaskets must be 9 mm (3/8 in.) inorder 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. 32-SAMSS-011 specifies additional requirements that relate to nozzle strength, type ofconnection, 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 nozzlesby the attached piping. Each nozzle must be designed by the manufacturer to withstand acertain 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 designthe header itself to withstand a certain amount of total load from all the nozzles. If there ismore than one bundle per heat exchanger bay, the total of all nozzle loads should not exceedthree times the loading for one header. The piping designer uses these permissible loads asadditional design criteria when he is designing the associated piping systems. Themanufacturer must ensure that the nozzle is not overstressed when these permitted loads areapplied.

Note that neither API-661 nor the ASME Code specifies how the manufacturer must designthe nozzles and headers for these loads. These load limits were set by a consensus agreementbetween the manufacturers and the users, and these limits have historically proven to beacceptable. Therefore, the use of standard nozzle and header design details is usuallyconsidered to be sufficient.




ASME Code Requirements

Tubesheets, plug sheets, and covers must also be designed in accordance with the ASMECode Section VIII, Div. 1, Par. UG-34 and Appendix 13. The rules of Par. UG-34 can beapplied to the design of the flat rectangular plates that make up the header box, a bonnet-typecover, and a removable flat cover. The equations in UG-34 are explicit and can be used tocalculate 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 ofrectangular 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 bonnetcovers of air-cooled heat exchangers. The design procedures that are in Appendix 13 usuallyyield 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 thethickness of a single component in terms of other quantities).

Appendix 13 treats the header box as a complete structure, and the internal pressure loadcauses 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 bendingstresses in the plates are a function of the moment distribution factors that are in turn afunction of the thickness and the dimensions of all of the plates that make up the box. This isa relatively complicated design procedure to apply.

Typical Header Box Details

Figure 16




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

Ligament Efficiency =

p − dp

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 adesign has been developed, a trial-and-error method must be used for the initial design. In thetrial-and-error method, an initial estimate of the component thicknesses is made based onassuming that the end of each side of the box is rigidly supported. The thickness of the platesis then incremented until all of the components that make up the box are below the allowablestress. The design of such components is therefore easily programmed into a computer.




Sample Problem 4: Evaluate Contractor-Specified Dimensions for the Inlet/OutletHeader Box of an Air-Cooled Heat Exchanger

You must evaluate the contractor-specified dimensions for the inlet/outlet header box of anair-cooled heat exchanger. All the information that is needed to solve this problem is inContractor Design Package 5 in Course Handout 4. This information includes thespecification sheet for the air-cooled heat exchanger, the dimensions of the inlet/outlet headerbox, and the CODECALC computer program output. Work Aid 3 is used to solve thisproblem.

The first step in evaluating the manufacturer's design is to compare the dimensions that arespecified in the drawings of the inlet/outlet header with the computer program input. Thesedimensions include the length, width, and depth of the header box, the componentthicknesses, and the tube hole and plug hole dimensions. Additional design information thatmay 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 beenverified, it is concluded that the dimensions specified by the manufacturer for the header boxplates are correct based on stress analysis considerations because the CODECALC outputshows 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 requiredby API-661. Therefore, the stay plate thickness must be increased to 0.5 in. Because thestresses are acceptable and the component dimensions are consistent between the programand the detailed drawings, the header box design is acceptable once the stay plate thickness isincreased.




COMPLETING A SAFETY INSTRUCTION SHEET FOR A SHELL-AND-TUBEHEAT EXCHANGER

As discussed in MEX 202, the purpose of a Safety Instruction Sheet is to ensure thatoperations, maintenance, and inspection personnel have adequate information in a consistentformat. This information concerns safe operating limits, protective devices, and any specialsafety precautions that may be required.

SAES-E-001 requires that a Safety Instruction Sheet be completed for every new process heatexchanger. In most cases, a contractor who is working for Saudi Aramco is responsible forcompleting the Safety Instruction Sheet. The Saudi Aramco Engineer is then responsible forchecking the contractor's work. In all cases, the Safety Instruction Sheet is completed basedon the final, certified, as-built, manufacturer’s data for the heat exchanger, not the data that ison the heat exchanger specification sheet.

The Safety Instruction Sheet must also be revised whenever the heat exchanger is rerated ormodified. The Saudi Aramco engineer may be responsible for revising the Safety InstructionSheet when heat exchangers are rerated or modified.

Saudi Aramco has Safety Instruction Sheets for both shell-and-tube and air-cooled heatexchangers. This module only discusses the Safety Instruction Sheet for shell-and-tube heatexchangers. SAES-A-005, Preparation of Safety Instruction Sheets, outlines the proceduresfor preparing Safety Instruction Sheets. These procedures are referenced in Work Aid 4. Acopy 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, isshown in Figure 18, and additional copies are provided in Course Handout 3. Form 2713includes general information, basic process design information, mechanical designinformation, and operating limits, The following paragraphs highlight several of the primarytypes of information that are required on Form 2713. Refer to Figure 18 or Course Handout3.




Safety Instruction Sheet Form 2713

Figure 18




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

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

- 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 theshell 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




• 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 drawinginformation, and the left side contains revision record and approvalinformation.

Form 2713 provides much information about a shell-and-tube heat exchanger. It makes itpossible for operations, maintenance, and inspection personnel to get needed informationfrom one source without reviewing many drawings. There will be situations when thedetailed 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 focusesthe 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 fromthe 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 thatmight have to be obtained from other sources:

• Any special design considerations or unusual construction features that shouldbe highlighted would have been developed either during the initial specificationof the exchanger or during its detailed engineering. Pertinent informationcould be obtained from the process and mechanical engineers who wereassigned to the work.

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

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




WORK AID 1: PROCEDURE FOR EVALUATING CONTRACTOR-SPECIFIEDDESIGN CONDITIONS FOR TEMA-TYPE AND AIR-COOLED HEATEXCHANGER COMPONENTS

The procedures in this Work Aid may be used to evaluate whether design conditions that arespecified in a Contractor Design Package for a heat exchanger meet the Saudi Aramcorequirements that are specified in SAES-E-001. A copy of SAES-E-001 is included in CourseHandout 2. Part 1 of this Work Aid is used for TEMA-type heat exchangers, and Part 2 isused 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 theprocess operating conditions in Figure 19 under Operating Conditions. Operatingconditions are specified in Section A of Form 2714.

2. Determine the mechanical design conditions specified by the contractor for the shellside 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 SAES-E-001. These requirements are summarized as follows:

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

• The design temperature must be at least the maximum operating temperatureplus 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 thatis coincident with any pressure greater than 25 percent of the design pressure.The possibility of auto-refrigeration during start-up, shutdown, or upset must beconsidered in determining the minimum design temperature.




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

DESCRIPTION OperatingConditions

DesignConditions

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 underOperating Conditions. Process operating conditions are indicated on Lines 16 and 23of Form 2716.

2. Determine the design air inlet, outlet, and ambient temperatures. List these in Figure20 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 thesein Figure 20 under Design Conditions. Process-side design conditions are indicated onLine 42 of Form 2716.

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

5. Determine if the air-side design inlet, outlet, and ambient temperatures meet therequirements 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.




Description OperatingConditions

DesignConditions

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




WORK AID 2: PROCEDURE FOR EVALUATING CONTRACTOR-SPECIFIEDDIMENSIONS FOR SHELL-AND-TUBE HEAT EXCHANGER COMPONENTS

The procedures in this Work Aid may be used to evaluate whether the dimensions that arespecified in a Contractor Design Package for a shell-and-tube heat exchanger meet SaudiAramco, TEMA, API-660, and ASME requirements. This Work Aid is divided into fourmajor parts as follows:

• Part 1 provides a general procedural-type checklist that should be used in allcases.

• 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 bedone while checking the design details and dimensions in accordance with Parts 2through 4 of this Work Aid.

2. Confirm that the dimensions and design details are in accordance with requirementsspecified in 32-SAMSS-007, API-660, and the ASME Code. Further details on thischeck 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 exchangermanufacturer. For the purposes of this course, it may be assumed that theCODECALC computer program that is being used has been verified.




Part 2: Girth Flanges and Flat Channel Covers

Use the following procedure to check computer calculations that have been made to verify thedesign of a girth flange or a channel cover. This procedure is generic in that it may be appliedto calculations that have been done using most computer programs. However, because theCODECALC program is used for all calculations that are done in this course, the parameternames that are used in the CODECALC program are identified in parentheses whereappropriate.

The program input must be checked to ensure that it conforms to the flange designrequirements. The program output must be checked to ensure that it verifies the design thathas 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




1. Verify that the correct flange type is specified. Heat exchanger girth flanges aretypically the integral weld neck flange. Permissible flange types are specified inAppendix 2 of the ASME Code.

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

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

4. For the girth flange, verify that the corrosion allowance (FCOR) is equal to thecorrosion allowance that is listed on the specification sheet.

For the flat channel cover, verify that the corrosion allowance is equal to the depth ofthe pass partition groove in the channel cover.

5. Verify that the flange material is the same as the material listed on the specificationsheet.

6. Verify that the allowable stress for the flange or flat cover material conforms to theallowable stress specified in the ASME Code. Note that many programs such asCODECALC have the ASME allowable stress tables built into them and automaticallyuse the correct allowable stress.

7. Verify that the bolt material is the same as the material listed on the specificationsheet.

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

9. Verify that the flange inside diameter (B) is equal to the uncorroded (new) diametershown 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) diametershown on the detailed drawing.

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




12. Verify that the hub thickness at the back of the flange (large end, G1) is equalto the uncorroded (new) thickness shown on the detailed drawing. This is notapplicable for the flat channel cover.

13. Verify that the flange thickness (T) is equal to the uncorroded (new) thickness shownon 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 thedetailed drawing.

16. Verify that the bolt diameter (DB) is equal to the diameter shown on the detaileddrawing.

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 thefollowing bolt loads have been specified based on calculations that have been madefor 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 preliminarycalculations that are done for the flanges.

20. Verify that the gasket outside diameter is equal to the diameter shown on the detaileddrawing.

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

22. Verify that the gasket inside diameter is equal to the diameter shown on the detaileddrawing.




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

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

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

26. Verify that the sketch number that is specified for the flange facing agrees with thesketch number listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the typeof 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 columnnumber listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the specifiedgasket type.

28. Verify that the gasket thickness is equal to the dimension shown on the detaileddrawing.

29. Verify that the nubbin width (when a nubbin flange face is specified) is equal to thedimension 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 gasketand Ng is the width of the girth flange gasket. This only applies for channel coverswhen 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 permittedbolt spacings. The permitted spacings should have been determined based on TEMArequirements.

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




• 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 orequal to the specified thickness (T) and the thickness that is shown on the detaileddrawing.

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




Part 3: Stationary and Floating Head Tubesheets

Use the following procedure to check computer calculations that have been made to verify thedesign of a tubesheet that is either stationary or at a floating head. This procedure is genericin 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 thiscourse, the parameter names that are used in the CODECALC program are identified inparentheses where appropriate.

The program input must be checked to ensure that it conforms to the tubesheet designrequirements. The program output must be checked to ensure that it verifies the design thathas been used for the tubesheet.

In using this procedure, refer to Figure 22 for tubesheet geometry and nomenclature.

Tubesheet Geometry and Nomenclature

Figure 22




1. Verify that the correct tubesheet type is specified and is consistent with informationthat is contained in the detailed drawing. Several common tubesheets options are asfollows:

• 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 temperaturelisted on the specification sheet.

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

5. Verify that the allowable stresses for the shell, tubesheet, and channel conform to theallowable stresses specified in the ASME Code. Note that many programs such asCODECALC have the ASME allowable stress tables built into them and automaticallyuse the correct allowable stress.

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

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




8. For gasketed tubesheets:

a. Verify that the gasket inside diameter and outside diameter equal the diametersindicated 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 indicatedin the ASME Code, Section VIII, Division 1, Appendix 2, Table 2-5.1, for thespecified gasket type.

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

e. Verify that the sketch number that is specified for the flange facing agrees withthe sketch number listed in ASME Code, Section VIII, Division 1, Table 2-5.2for 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 thecolumn number listed in ASME Code, Section VIII, Division 1, Table2-5.2 for the specified gasket type.

g. Verify that the gasket thickness is equal to the dimension shown on the detaileddrawing.

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

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

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




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

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

14. If the tubesheet is extended as a flange, verify that the outside diameter of the flangedportion (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 thedetailed drawing.

17. Verify that the bolt diameter (DBOLT) is equal to the diameter shown on the detaileddrawing.

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 thedetailed drawing.

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




Part 4: Floating Heads With and Without Backing Rings

Use the following procedure to check computer calculations that have been made to verify thedesign of a floating head. This procedure is generic in that it may be applied to calculationsthat have been done using most computer programs. However, because the CODECALCprogram is used for all calculations that are done in this course, the parameter names that areused 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 designrequirements. The program output must be checked to ensure that it verifies the design thathas 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 thedetailed drawing. The most common type is Type (d) as described in Appendix 1-6 inthe ASME Code.

2. Verify that the specified design temperature (TEMP) is equal to the temperature listedon the specification sheet.




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

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

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

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

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

8. Verify that the allowable stresses for the head, flange, bolts, and backing ring conformto the allowable stresses specified in the ASME Code. Note that many programs suchas CODECALC have the ASME allowable stress tables built into them andautomatically use the correct allowable stress.

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

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

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

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

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

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

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




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

17. Verify that the distance between the centroid of the flange and the attachment point atthe 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 andverify that the appropriate detail is specified in the calculations. The flange willnormally not be slotted.

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

20. Verify that the bolt diameter (DBOLT) is equal to the diameter shown on the detaileddrawing.

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 shownon the detailed drawing.

24. Verify that the gasket outside diameter is equal to the diameter shown on the detaileddrawing.

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

26. Verify that the gasket inside diameter is equal to the diameter shown on the detaileddrawing.

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

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




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

30. Verify that the sketch number that is specified for the flange facing agrees with thesketch number listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the typeof 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 columnnumber listed in ASME Code, Section VIII, Division 1, Table 2-5.2 for the specifiedgasket type.

32. Verify that the gasket thickness is equal to the dimension shown on the detaileddrawing.

33. Verify that the nubbin width (when a nubbin flange face is specified) is equal to thedimension 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 gasketand Ng is the width of the girth flange gasket. This only applies for channel coverswhen 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 requiredthickness (considering the corrosion allowances) and is consistent with what is shownon the detailed drawing.

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

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




WORK AID 3: PROCEDURE FOR EVALUATING CONTRACTOR-SPECIFIEDDESIGNS FOR AIR-COOLED HEAT EXCHANGER TUBE BUNDLES ANDHEADERS

The procedures in this Work Aid may be used to evaluate whether the tube bundle and headerdesigns that are specified in a Contractor Design Package for an air-cooled heat exchangermeet Saudi Aramco, API-661, and ASME requirements. This Work Aid is divided into threemajor parts as follows:

• Part 1 provides a general procedural-type checklist that should be used in allcases.

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

• Part 3 provides a procedure for evaluating whether the mechanical designcalculations are in accordance with the ASME Code. It is assumed that acomputer 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 bedone while checking the design details and dimensions in accordance with Parts 2 and3 of this Work Aid.

2. Confirm that the dimensions and design details are in accordance with requirementsspecified in 32-SAMSS-011, API-661, and the ASME Code. Further details on thischeck 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 exchangermanufacturer. For the purposes of this course, it may be assumed that theCODECALC computer program that is being used has been verified.




Part 2: 32-SAMSS-011 and API-661 Requirements

Use the procedure that follows to determine whether the requirements that are specified in 32-SAMSS-011 and API-661 have been met. The paragraph references that are indicated are inAPI-661 unless otherwise noted. For each requirement, circle “Yes” or “No” depending onwhether 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 completeassembly? Yes/No.

2. Par. 5.1.1.3. Has provision for at least 6 mm (1/4 in.) of lateral movement in bothdirections 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 thermalexpansion of the tubes? Yes/No.

4. 32-SAMSS-011, Par. 5.1.1.4. Do the bundle and the structural mounting have Teflonslide 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 slopeddownward 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 sealconstruction? Yes/No.

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




11. 32-SAMSS-011, Par. 5.1.1.11. Do the tube ends extend beyond the tubesheet3 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 onthe outer periphery of the fins for bearing, and do the spacers prevent the fins frommeshing? Yes/No.

Tube Wall Minimum Thickness

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

14. Par. 5.1.12.3. Does the minimum tube wall thickness meet the requirements shown inFigure 24? Yes/No.

Tube Material Minimum RequiredThickness, 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 requirementsspecified in Figure 25? Yes/No.




Fin Type Use Limitations

Tensionwound

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 over111°C (200°F), is a split header design, U-tube design, or other means used toaccommodate 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 accordancewith Figure 26 ? Yes/No.




Component Carbon or Low-Alloy Steel High-Alloy Steel orOther Materials

Tubesheet 20 mm (3/4 in.)* 16 mm (5/8 in. )*

Plug sheet 20 mm (3/4 in.) 16 mm (5/8 in.)

Top, bottom, and endplates

12 mm (1/2 in.) 10 mm (3/8 in.)

Removable coverplates

25 mm (1 in.) 25 mm (1 in.)

* 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 inFigure 27? Yes/No.

Pass Partition PlateMaterial

Minimum RequiredThickness, 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 inFigure 28? Yes/No.




Exchanger Service Header Box Type

Process Cooler Plug Type Header

Lube Oil Cooler or Seal Oil Cooler Removable Cover or Cover Plate if less than1 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 coverperiphery 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 theminimum 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 toAPI-661 directly)? Yes/No.

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

24. Par 5.1.6.11. For bolts that straddle the corners, does the diagonal distance meet themaximum 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 outsidediameter 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 UnifiedFine 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 12thread series per ANSI B1.1? Yes/No.




Gasket Requirements

29. Par 5.1.9.1. Are gaskets for tube access plugs solid metal or double-metal-jacketedtype 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, non-asbestos filled type? Yes/No. Per 32-SAMSS-011, if the pressure does not exceed 2100 kPa (300 psig), a synthetic gasket with parting agent on both sides of the gasketmay 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 (3/8in.), 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 pipeused? Yes/No.

If the connections are 50 mm (2 in.) or smaller, is the thickness Schedule 80minimum? Yes/No.

33. 32-SAMSS-011, Par 5.1.10.15. For small diameter connections, are bosses used perSaudi 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 theheader? 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 resistantmaterial, are the nozzles also lined in the same manner? Yes/No.




Part 3: ASME Code Calculations for Header Box Plate Thicknesses

Use the procedure that is summarized in Figure 29 to check computer calculations that havebeen made to verify the design of a header box for an air-cooled heat exchanger. Thisprocedure is generic in that it may be applied to calculations that have been done using mostcomputer programs. However, because the CODECALC program is used for all calculationsthat are done in this course, the parameter names that are used in the CODECALC programare identified in parentheses where appropriate.

The program input must be checked to ensure that it conforms to the header box designrequirements. The program output must be checked to ensure that it verifies the design thathas been used for the header box.

In using this procedure, refer to Figure 30 for header box geometry and nomenclature.

Step Item to Verify InformationSource

1 Correct Header Box Type Has Been Selected forAnalysis. Several common options are as follows:

• Equal or unequal thicknesses of the long-side plates.

• One or two internal stay plates.

• External reinforcement.

Detailed Drawing

2 Design Pressure (P) Form 2716

3 Design Temperature (TEMP) Form 2716

4 Material Specifications for the Header Box Componentsand Stay Plates

Form 2716

Header Box Calculation Verification Procedure

Figure 29





5 Allowable Stresses and Minimum Yield Stresses forHeader Box Components and Stay Plates Conform toASME Code.

Note: Many programs such as CODECALC have theASME allowable stress tables built into them andautomatically use the correct allowable stress.

ASME Code

6 Short-Side Length Dimension (H). The new, uncorrodedlength should be input.

Detailed Drawing

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

Detailed Drawing

8 Mid-side joint efficiency on the short side (E) inaccordance with the ASME Code and consistent with theradiographic inspection specified on the detaileddrawing.

• 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.

ASME Code

Detailed Drawing

9 Corner joint efficiency on the short side (EC) inaccordance with the ASME Code and consistent with theradiographic inspection specified on the detaileddrawing. See Step 8.

ASME Code

Detailed Drawing

10 Long-Side Length Dimension (h). Detailed Drawing

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

Detailed Drawing

Header Box Calculation Verification Procedure, cont'd

Figure 29





12 Mid-side joint efficiency on the long side (E) is inaccordance with the ASME Code and consistent with theradiographic inspection specified on the detaileddrawing. 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 Form 2716

15 Tube Hole Pitch Distance (p) Detailed Drawing

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

Detailed Drawing

17 Depth of the Holes. Each hole diameter will have aspecific 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 Form 2716

22 Membrane Stress, Bending Stress, and Total Stress inthe Short-Side Plates, Long-Side Plates, End Plates, andat the Corner Sections. Check that actual stresses arebelow the corresponding allowable stresses.

Computer Output

23 MAWP based on Membrane Stress, Bending Stress, andTotal Stress. MAWP for the exchanger is the lowest ofthe calculated values, and should be above the designpressure.

Computer Output

Header Box Calculation Verification Procedure, cont'd

Figure 29




Header Box Geometry and Nomenclature

Figure 30




PLATE WITH MULTIDIAMETER HOLES

Header Box Geometry and Nomenclature, cont'd

Figure 30, cont'd




WORK AID 4: PROCEDURE FOR COMPLETING A SHELL-AND-TUBE HEATEXCHANGER SAFETY INSTRUCTION SHEET

Use the procedural steps that are contained in SAES-A-005, Preparation of Safety InstructionSheets, 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 inFigure 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 notrequire further explanation. The following additional procedural information is provided toassist 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 AllowablePressure 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




The basis for calculated test pressure on the shell side is the minimum of the MAPNCslisted above. Use the shell-side design pressure if the MAPNCs for the componentsare 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 componentsin 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 MAPNCslisted above. Use the tube-side design pressure if the MAPNCs for the componentsare not provided in the contractor calculations.

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




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 nominalcorrosion allowance, this is the tm for the component.

• If the minimum required thickness includes a corrosion allowance, subtract thenominal corrosion allowance from the minimum thickness that was determinedby the manufacturer. This is the tm.

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




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

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

Figure 33




GLOSSARY

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

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

footed fin An L-shaped aluminum fin that is wrapped under tension overthe outside surface of a tube with the tube fully covered bythe feet between the fins. The fin ends are secured to preventloosening or unraveling of the fins under the designconditions.

integral fin An aluminum outer tube from which fins have been formedby extrusion and then mechanically bonded to an inner tube.

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

Documents

Specifying Design Requirements for Heat Ex Changers