exchanger piping

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BECHTEL CORPORATIONENGINEERING – PLANT DESIGN

DESIGN GUIDEEXCHANGER PIPING3DG-P22-00004, Revision 002, 2002 July 23Reason for Issue: Issued for UsePrepared by: B. TarrChecked by: P.R.WoodApproved by: R. Fox

INTRODUCTION

This Engineering Design Guide explains the different types of heat exchangers that are mostcommonly used in facilities.

It addresses locations, elevation requirements, nozzle locations, exchanger supporting, associatedpiping supports, maintenance and operation access.


Bechtel Confidential © Bechtel Corporation 1995, 2002. All rights reserved.Engineering Design Guide – Exchanger Piping3DG-P22-00004-002 of 52

TABLE OF CONTENTS

INTRODUCTION ......................................................................................................................1

LIST OF FIGURES ...................................................................................................................5

1.0 PURPOSE .......................................................................................................................7

2.0 EXCLUSIONS..................................................................................................................7

3.0 DISCUSSION...................................................................................................................7

3.1 SAFETY...........................................................................................................................7

3.2 OPERATION....................................................................................................................7

3.3 MAINTENANCE ...............................................................................................................7

4.0 TERMINOLOGY ..............................................................................................................7

5.0 BASICS OF HEAT TRANSFER ......................................................................................9

6.0 TYPES OF EXCHANGERS ...........................................................................................10

6.1 SHELL & TUBE .............................................................................................................10

6.2 DOUBLE PIPE EXCHANGERS .....................................................................................18

6.3 AIR COOLERS .............................................................................................................18

6.4 OTHER EXCHANGER TYPES .....................................................................................20

7.0 EXCHANGER PLOT LOCATION AND ELEVATION OF EXCHANGERS ....................24

7.1 SHELL & TUBE ARRANGEMENTS .............................................................................24

7.2 LOCATION BY ASSOCIATION .....................................................................................24

7.3 EXCHANGER BATTERY ARRANGEMENTS ...............................................................27

7.4 ELBOW NOZZLES TO REDUCE SHELL ELEVATION ................................................28

7.5 EXCHANGERS WITH CONDENSATE POTS ...............................................................28

7.6 REBOILERS WITH CONDENSATE POTS ...................................................................30



7.7 DOUBLE PIPE EXCHANGERS .....................................................................................30

7.8 RACK MOUNTED AIR COOLERS ................................................................................30

8.0 SHELL AND TUBE NOZZLE LOCATION & NOZZLE TYPE .......................................33

8.1 SHELL & TUBE NOZZLE LOCATION OPTIONS .........................................................33

8.2 SHELL & TUBE NOZZLE ORIENTATION OPTIONS ...................................................34

8.3 NOZZLE LOCATION WITH R ESPECT TO FLOW .......................................................35

8.4 AIR COOLERS ..............................................................................................................35

9.0 SUPPORTS ...................................................................................................................37

9.1 SHELL & TUBE .............................................................................................................37

9.2 SPACE FRAMES OR SPACERS ..................................................................................38

9.3 SADDLE / FOUNDATION CLEARANCES ....................................................................39

9.4 SHELL & TUBE PIPE SUPPORT LOCATIONS ...........................................................40

9.5 VERTICAL REBOILER SUPPORTS .............................................................................41

9.6 AIR COOLER SUPPORTS ............................................................................................42

10.0 MAINTENANCE AND OPERATIONAL ACCESS .........................................................43

10.1 SHELL & TUBE .............................................................................................................43

10.2 BUNDLE EXTRACTOR .................................................................................................46

10.3 CLEARANCES ..............................................................................................................47

10.4 STACKED EXCHANGERS ............................................................................................47

10.5 CRANE ACCESS...........................................................................................................47

10.6 AIR COOLERS ..............................................................................................................47

10.7 AIR COOLER HEADER BOX ACCESS ........................................................................48

10.8 PLATFORM OPTIONS FOR AIR COOLER MOTOR ACCESS ....................................49

11.0 PIPE STRESS.............................................................................................................50



11.1 EXCHANGER ANCHOR LOCATION ............................................................................50

11.2 SHELL & TUBE NOZZLE LOADS ................................................................................51

11.3 AIR COOLER NOZZLE LOADS ....................................................................................51

12.0 REFERENCES............................................................................................................52



LIST OF FIGURES

Figure 1 Standard Counterflow Patterns for Shell & Tube .................................................9Figure 2 Exchanger Nomenclature...................................................................................12Figure 3 Shell & Tube Fabrication Tolerances.................................................................14Figure 4 Shell & Tube Fabrication Tolerances.................................................................15Figure 5 Vertical Vessel Mounted Reboilers ....................................................................16Figure 6 Condensate Pot Effect on Tower .......................................................................17Figure 7 Vertical Direct Mount Condenser .......................................................................17Figure 8 Double Pipe Exchanger Components ................................................................18Figure 9 Air Cooler Header Box Types ............................................................................19Figure 10 Air Cooler Components......................................................................................20Figure 11 Stab-in Reboiler .................................................................................................21Figure 12 Spiral Exchanger................................................................................................21Figure 13 Plate Exchanger.................................................................................................22Figure 14 Aluminum Core Exchanger ................................................................................23Figure 15 Core Exchanger Insulation.................................................................................23Figure 16 Standard Piping Arrangements for Shell & Tube Exchangers ...........................24Figure 17 Exchanger Placement ........................................................................................27Figure 18 Arrangement of Exchanger Batteries .................................................................28Figure 19 Elbow Nozzles ...................................................................................................28Figure 20 Alternative to Vertical Condensate Pot ..............................................................29Figure 21 Condensate Pot Piping Arrangement ................................................................29Figure 22 Double Pipe Exchanger – Method of Support....................................................30Figure 23 Conventional Platform Design for Air Coolers ...................................................31Figure 24 Air Cooler Supports ...........................................................................................32Figure 25 Nozzle Adjustments to Standard Exchangers....................................................33Figure 26 Possible Nozzle Arrangements for Shell & Tubes .............................................34Figure 27 Change Nozzles to Improve Routing .................................................................35Figure 28 Change Flow to Improve Routing ......................................................................35Figure 29 Odd or Even Pass Air Coolers ...........................................................................36Figure 30 Standard Air Cooler Piping Arrangements.........................................................36Figure 31 Inserts for Air Coolers ........................................................................................37Figure 32 Shell & Tubes at Grade with Same U/G Cooling Water Supply ........................38Figure 33 Shell & Tubes on Elevated Platform ..................................................................38Figure 34 Space Framing...................................................................................................39Figure 35 Clearances for Shell & Tube Exchangers ..........................................................40Figure 36 Support Design for Piping at Shell & Tube ........................................................41Figure 37 Vertical Reboilers...............................................................................................42Figure 38 Air Cooler Supports ...........................................................................................43Figure 39 Shell & Tube Exchanger Access........................................................................44Figure 40 Tube Pulling Requirements ...............................................................................45Figure 41 Tube Bundle Extractor .......................................................................................46Figure 42 Crane Access.....................................................................................................47



Figure 43 Plugged Header Box..........................................................................................48

LIST OF FIGURES (contd.)

Figure 44 Air Cooler Platforming Alternatives....................................................................50Figure 45 Slotted Holes for Shell & Tubes.........................................................................51Figure 46 Lateral Stresses on Air Cooler Nozzles .............................................................52Figure 47 Spring Supports for Air Coolers .........................................................................52



1.0 PURPOSE

To provide the layout designer with guidelines for the development of piping design for non-fired heat transfer exchangers.

2.0 EXCLUSIONS

All or part of this guide may be superseded by client mandatory standards or by the codes andregulations imposed by governmental jurisdictions covering the location where the piping isinstalled.

3.0 DISCUSSION

3.1 SAFETY

Proper consideration for personnel safety around exchangers requires arranging piping andvalves in a manner that does not obstruct access for operation, maintenance or egress.

3.2 OPERATION

Exchangers normally require minimal attention during operation. Valves however, must be locatedfor easy access. Where valves cannot be operated from grade, chain operators shall be used. Ifchain operators are not allowed per client specifications, platform access to valves shall beconsidered.

3.3 MAINTENANCE

Piping shall be arranged in a manner to allow adequate access to removable channel coverswithout requiring excessive dismantling of the piping system. The bolting connecting the channelcover to the shell must be easily accessed in order to pull the tube bundle. Consideration shall begiven for clearances in all directions for the use of bundle extractors (10.2).

4.0 TERMINOLOGY

Baffles: Partial interior walls set within the shell of an exchanger to redirect the flow in theexchanger to maximize contact time and thereby increase heat transfer (Fig. 1).

Bundle: A group of tubes connected to common inlet and outlet head/heads. Bundles are usuallyassociated with shell and tube type exchangers (Fig. 1), though at times they may be usedindependent of a shell (as in the case of stab-in heaters) (Fig. 11).

Cell: A grouping of tubes connected to common inlet and outlet manifold boxes. Cells areusually associated with air coolers.



Conduction: The ability of an object to pass (conduct) heat through its molecular structure; thedistribution or transfer of heat (energy) from one end of an object or from one object to anotherthrough physical contact.

Convection: The mixing action that occurs in any heated fluid (heated fluid rises displacing cool fluid which falls replacing heated fluid); the transfer of heat within a fluid or from one fluid toanother by means of the thermal mixing action.

Fins: Appendages affixed to the outer skin of tubes to augment their surface area to increasecontact time and thereby heat transfer.

Forced draft: A method of tube cooling in which fan driven air is blown directly through a tube cell(Fig. 10).

Induced draft: A method of tube cooling in which fan drawn air is pulled (induced) through atube cell (Fig. 10).

Parallel: A method of interconnection of exchangers in which the flow stream is split betweentwo or more exchangers capable of operating independently either simultaneously or in back-upof each other. Exchangers in parallel usually can be isolated from the flow stream to allow formaintenance or for temperature or output control (Fig. 16).

Series: A method of interconnection of exchangers in which the flow stream must past througheach exchanger in sequence. Exchangers operating in series are treated as one system component and usually cannot be isolated without shutdown of the system (Fig. 16).

Shell: Closed conduit used to convey a medium around a set of tubes for the purpose of heattransfer between that medium and one being conveyed by the tubes (Fig. 1).

TEMA: The Tubular Exchanger Manufacturers Association, an industrial association which haspublished standards for the design and manufacture of tubular exchangers (Fig. 2).

Thermosiphon : A method of circulation based on a heated fluid's tendency to rise. This methodof circulation is used most often in boiler and reboiler systems.

Tubes: Closed conduit for a single heating/cooling media most often used in conjunction with asealed outer conduit (shell), but may also be used in open contact with atmosphericcooling/heating media. They are also often referred to as channels (Fig. 1).



5.0 BASICS OF HEAT TRANSFER

The most common method of heat transfer from one fluid to another in a process environmentis by the use of exchangers. Exchangers, while varying greatly in design, all operate on thesame principle. The principle that heat (energy) tends to equalize by dissipation. That is thatheated objects try to equalize their temperature by transmitting their heat to surroundingcooler objects. This is similar to a liquid seeking its own level. Hot objects try to transmit theirheat to any cooler objects around them, which in turn tend to absorb that heat. All exchangersemploy this principle by using one or more of three heat transfer methods; conduction,convection and radiation.

The tendency of the heated portions of a fluid to rise dictates the most common pattern of flow inexchanger piping. That pattern is for the fluid receiving heat to flow up through the exchanger andthe fluid expending heat to flow down (Fig. 1).

Figure 1 Standard Counterflow Patterns for Shell & Tube



6.0 TYPES OF EXCHANGERS

While often referred to by their design and construction characteristics, exchangers are mostfrequently identified by their process function. The following is a listing of process names oftenassigned exchangers relative to their function:

Exchanger: Heats one stream while cooling another (Very efficient in that there is no waste heatloss).

Cooler: Cools liquids or gases without condensation.

Subcooler: Condenses vapor and further cools the condensate using water as a cooling medium.

Condenser: Cools a vapor to its dew point in order to extract condensate from it.

Chiller: Uses refrigerants to cool a stream below the standard temperature of available coolingwater streams.

Heater: Heats process stream (generally to its boiling point) with no appreciable vaporization(often uses steam as heating medium).

Reboiler: Reboils (vaporizes) the bottom stream of a fractionating tower prior to its return to thetower. Often employs thermosiphon phenomenon rather than any mechanical flow enhancement.

Waste Heat Boiler: Uses waste heat (i.e., gas-turbine exhaust) as a heating medium.

Steam Generator: Uses process liquids or gases to produce steam (usually from boiler feedwater).

Vaporizer: Vaporizes part of a process stream (also called an evaporator).

6.1 SHELL & TUBE

The most common heat exchanger encountered in any process or power plant is the shell andtube exchanger. These exchangers, because of their reliability, low maintenance, and durability,generally offer the most economical method of heat control and transfer, while their "no movingparts" simple means of operation can be very efficient.

They operate by conducting one fluid stream through the channel (tube) head of the exchangerinto a set of tubes (the bundle) that is encased within the exchanger shell. A second fluid issimultaneously directed through the shell (usually in the opposite direction) while maintainingcontact with the tubes. The heat transfer is effected through the tube walls without the fluidscoming in direct contact with each other.



6.1.1 Conventional TEMA Exchangers

Of shell and tube exchangers the most common are those designed to meet TEMA standards ofdesign and construction (Fig. 2).



Figure 2 Exchanger Nomenclature

TEMA exchangers offer the following:



Economy: they can be varied in size in accordance with the heat transfer required thereby utilizingthe minimal material for the maximum result; they can handle large flow rates with a large range ofpressure ratings; they can often reduce waste heat by heating one flow stream while coolinganother.

Maintenance: standardization allows standardized maintenance procedures with more readilyobtainable parts; few parts subject to failure; minimal assembly/disassembly requirements.

Efficiency: by “multiple pass series flow” these exchangers offer an almost unlimited range oftransfer rates.

Reliability and Consistency: design is made simpler and reliability increased by thestandardization of design and construction tolerances set by TEMA.

6.1.2 Fabrication Tolerances



Figure 3

Shell & Tube Fabrication Tolerances



Figure 4 Shell & Tube Fabrication Tolerances



6.1.3 Reboilers

A variation of the conventional shell and tube, still incorporating TEMA standardized components,is the reboiler (Figs. 5 and 6).

Figure 5 Vertical Vessel Mounted Reboilers



Figure 6 Condensate Pot Effect on Tower6.1.4 Direct Mount Condensers

Occasionally condensers associated with separators, knockout drums, or accumulators aremounted directly on the vessel. Such configuration can be very cost effective in that they eliminatesome of the components required for a stand alone condenser, the interconnecting piping betweenthe equipment as well as the supports for said piping. (Fig. 7)

Figure 7 Vertical Direct Mount Condenser



6.2 DOUBLE PIPE EXCHANGERS

Double pipe are probably the most economical exchangers available. They consist of a singletube enclosed within another. As with conventional shell and tube exchangers, double pipes relyon the cross flow of two fluid streams to affect a heat transfer.

In an effort to increase the contact time of fluids in double pipe exchangers, most manufacturesattach fins to the inner tube. This practice has resulted in this type of exchanger being referred toas fin-tubes or G-fins. (Fig. 8)

Figure 8 Double Pipe Exchanger Components

6.3 AIR COOLERS

Air coolers make up the second largest family of process and power plant exchangers. While notas efficient, compact or precise as shell and tubes, air coolers are often the answer when suppliesof cooling fluids (cooling water, refrigerant, cool process fluids...) are limited. Their purchase costis often lower than that of shell and tubes, which can also make them preferable for services whereprecise temperature control is less of a concern.



Air coolers operate by flowing a fluid through a set of tubes (cell) while air is passed through thecell around the tubes. The passing air absorbs and carries away the heat.

Header boxes for air coolers may be specified plugged or with cover plate. Plugged boxesallow the maintenance of damaged tubes without the disassembly of the box but are generallyheavier and more prone to leakage. (Fig. 9)

Figure 9 Air Cooler Header Box Types



6.3.1 Forced Draft

Forced draft coolers operate by pushing air through the tube cells from fans mounted below them. This method of fan and motor mounting make them easily accessible from below the exchanger. These coolers are more efficient than induced draft because the cool air they move is denser(more air is moved), however, because the fans tend to channel the air, distribution may beuneven. This may result in the formation of hot spots in the cells and cause uneven tube wear. The cells of these coolers are exposed to the elements, also contributing to wear (Fig. 10).

6.3.2 Induced Draft

Induced draft coolers draw air up through the tube cells with fans mounted above them. Thisarrangement reduces the formation of hot spots by flowing air more evenly across the tubes anddo protect the cells from the elements by covering them with the fan cowlings. The air they move,however, is warm and less dense (having already passed through the cells), reducing theirefficiency. The over head fan and motor mounting make these coolers more difficult to maintain(Fig. 10).

Figure 10 Air Cooler Components6.4 OTHER EXCHANGER TYPES



6.4.1 Stab-In Exchangers Also referred to as bayonet exchangers, they are often used where pressure loss through piping,space limitations or other circumstances preclude the use of more conventional exchangers. Theyare usually constructed of a TEMA standardized head and tube bundle. Often used as heatingelements for tanks and occasionally in lieu of reboilers for fractionating towers. These exchangers, because of the way they are integrally connected to the equipment theyservice, usually cannot be worked on without shut down of that equipment. This limits theirmaintainability and often makes them a last choice method of heat control (Fig. 11)

Figure 11 Stab-in Reboiler

6.4.2 Spiral Exchangers These consist of a tube or set of tubes, twisted into a helical coil, contained in a barrel likeshell or casing. The casing is usually split (most often vertically) and can be opened formaintenance. One fluid enters and exits the tubes through nozzles penetrating one side of thecasing while the second fluid passes through the casing from nozzles on either end (Fig. 12).

Figure 12 Spiral Exchanger



6.4.3 Plate Exchangers

While not having true tubes, the plate exchanger operates on the same mechanical principles asthe shell and tube. Instead of tubes the plate exchanger uses sets of tightly arranged thin, flat,hollow plates. The fluids flows through alternate contacting opposite walls of each plate,transferring their heat in the process. These exchangers can be very efficient in their ability totransfer heat attaining as low as a 2% heat differential between exiting fluids. Plates can also beadded or removed to vary the performance or for maintenance and repair (Fig. 13).

Figure 13 Plate Exchanger

6.4.4 Core Exchanger

Core exchangers (or core chillers) are a unique variation of plate exchangers. These exchangersuse plates alternately set within a shell through which the flow media pass, as do plateexchangers. The plates in a core, however, are sealed together, in a process called brazing, tocreate a single monolithic unit. Materials used in these types of exchangers are often aluminum oraluminum alloys, which are great for heat transfer, but notoriously bad in terms of tinsel strengthand stress durability. For that reason cores are used for low temperature or chilling servicesexclusively. Piping serving these exchangers is usually S.S., requiring a transition piece betweenthe piping and exchanger. These are often supplied by a third party vendor specializing in suchitems. (Fig. 14 & 15)



Figure 14 Aluminum Core ExchangerFigure 15 Core Exchanger Insulation



7.0 EXCHANGER PLOT LOCATION AND ELEVATION OF EXCHANGERS

7.1 SHELL & TUBE ARRANGEMENTS

With exchanger piping, as with most piping systems, the less piping required, the better the design. The designer shall investigate strategies such as stacking and banking exchangers in like service to minimize the piping required (Fig. 16)

Figure 16 Standard Piping Arrangements for Shell & Tube Exchangers

7.2 LOCATION BY ASSOCIATION

In setting locations for exchangers, attention shall be paid to the placement of associatedequipment. (Fig. 17) Locations will be chosen with a view toward reducing the amount of



piping required to connect the system. The overall system flow will be reviewed and studiesdone to determine the optimal placement for exchangers.



POORLOCATION

PREFEREDLOCATION

PREFEREDLOCATION

POORLOCATION

Example 1

Example 2

EXCHANGER PLACEMENTFig. 17

Figure 17 Exchanger Placement

7.3 EXCHANGER BATTERY ARRANGEMENTS

Exchanger battery arrangements for maintenance and operational access and also serve asunobstructed escape routes from the area in case of emergency (Fig. 18).



Figure 18 Arrangement of Exchanger Batteries 7.4 ELBOW NOZZLES TO REDUCE SHELL ELEVATION

The elevation of exchangers is frequently set by the requirements of the process they are trying tomaintain. The designer shall be aware, however, of the opportunities for reducing piping runs thatlowering or raising some exchangers may present (Fig. 19). It should be noted that elbow nozzleswill, to a certain extent, “fix” the pipe routing local to the exchanger due to nozzle orientations. Thecustomer shall be consulted prior to any decision to use elbow nozzles.

Figure 19 Elbow Nozzles7.5 EXCHANGERS WITH CONDENSATE POTS

The elevation of exchangers operating on steam is often set by the resident time of thedownstream condensate pot, i.e. the time the condensate must remain in the pot prior to being



returned to the condensate header, and is critical to maintaining upstream and downstreampressure and temperature. If process conditions allow, use of a horizontal pot rather than avertical one, it can significantly lower the elevation requirements of the exchanger (Figs.20 & 21).

Figure 20 Alternative to Vertical Condensate Pot

Figure 21 Condensate Pot Piping Arrangement



7.6 REBOILERS WITH CONDENSATE POTS

With vertical reboilers the condensate pot is commonly at grade and once again backpressure iscritical to maintaining temperature in the reboiler. The pot elevation in this case is often set by thepump or downstream condensate system requirements. Every effort must be made to keep theelevation of this pot as low as possible. The higher the pot has to be, the higher the reboiler mustbe and consequently the higher the tower liquid level must be. As the tower goes up so do allcosts associated with it (additional skirt steel, additional piping, stronger foundation...) (Fig. 6).

7.7 DOUBLE PIPE EXCHANGERS

These exchangers are usually stacked in large banks and operated in series because of theirrelatively low heat transfer rates. Occasionally, when only one double pipe is required, it is goodto keep in mind that there are options on mounting the exchanger that can result in significant costsavings. The standard method of support for such items is an independent two-pier foundation,but the light weight of the double pipe lends it to mounting on piers for other required equipment(such as drums) or even nearby structural columns by side bolting (Fig. 22). Such mountingeliminates the need for the foundation.

Figure 22 Double Pipe Exchanger – Method of Support

7.8 RACK MOUNTED AIR COOLERS

Air cooler elevations (whether at grade or elevated on racks or structures) are generally set bytheir air drawing capabilities, therefore a certain amount of clear space must be maintained toensure the performance of the cooler. It is necessary to provide maintenance platforming foraccess to the motors and header boxes (Fig. 23 & 24). Note that this platforming, because ofits relative elevation when air coolers are rack mounted, makes a good place for locating reliefvalves.



HEADER BOXES PLATFORMS MOTORS

HEADER LEVEL MOTOR / FAN LEVEL

CONVENTIONAL PLATFORM DESIGN FOR AIR COOLERS

Fig. 23

Area can be used forequipment relief valves to flare

PLATFORMING

Figure 23 Conventional Platform Design for Air Coolers



PLAN

ELEVATION

BY VENDOR BY ENG. CONTRACTOR

AT GRADE ORON RACK

ACCESSWAY

ACCESSWAY

BY VENDOR BY ENG. CONTRACTOR

WHEN ENGINEERING CONTRACTORPROVIDES SUPPORTING STEEL,INTERMEDIATE PIPE SUPPORTS CANBE LOCATED MORE EASILY

AIR COOLER SUPPORTS Fig. 24

Figure 24 Air Cooler Supports



8.0 SHELL AND TUBE NOZZLE LOCATION & NOZZLE TYPE

8.1 SHELL & TUBE NOZZLE LOCATION OPTIONS

The designer shall be aware of the allowable variations to shell and tube exchanger nozzlelocations (Fig. 25).

Figure 25 Nozzle Adjustments to Standard Exchangers



8.2 SHELL & TUBE NOZZLE ORIENTATION OPTIONS

A rearrangement of nozzles, can in some cases, reduce the required piping for a system.While such relocation is something that must be discussed with and approved by theResponsible Engineer (RE), significant cost savings can be attained by such rearrangement.(Fig. 26 and 27)

Figure 26 Possible Nozzle Arrangements for Shell & Tubes



Figure 27 Change Nozzles to Improve Routing8.3 NOZZLE LOCATION WITH R ESPECT TO FLOW

As with relocation of nozzles, a change in the flow direction of an exchanger can at timesresult in an improved design (Fig. 28). As with nozzle relocation, any changes in the flowdirection must be discussed with and approved by the RE prior to implementation in thedesign.

Figure 28 Change Flow to Improve Routing8.4 AIR COOLERS

8.4.1 Nozzle Locations

The locations of nozzles are based on the number of tube bundle cells manifolded together andthe number of passes the tubes make between the inlet and outlet manifold boxes. An evennumber of passes place the inlet and outlet nozzles on the same side of the cooler, while an oddnumber of passes results in the nozzles being on opposite sides. This can be particularlyimportant when the coolers are rack mounted. If the upstream and downstream equipment are onthe same side of the rack an even pass arrangement is preferable, while if they are on oppositesides of the rack an odd number of passes could reduce piping runs (Fig. 29).



Figure 29 Odd or Even Pass Air Coolers8.4.2 Air Cooler Piping Arrangements

The piping arrangements called for at air coolers can also greatly affect their placement andelevation. In cases where true symmetrical (cascaded) piping is required to stabilize two-phaseflow, the required elevations of supports for the piping can become prohibitive. In such cases theuse of header box inserts may reduce the need for symmetry to the point that a rake stylearrangement may be used (Fig. 30 and 31). The RE shall be consulted about such possibilities.

Figure 30 Standard Air Cooler Piping Arrangements



Figure 31 Inserts for Air Coolers

9.0 SUPPORTS

9.1 SHELL & TUBE

Shell & Tube exchangers at grade operating off of the same underground cooling watersupply line shall be aligned by the channel head nozzle (Fig. 32). The offset of the supportswill have little cost effect at grade. Exchangers in upper levels of structures, however, shall bealigned by supports to minimize the requirement for structural steel (Fig. 33).



Figure 32 Shell & Tubes at Grade with Same U/G Cooling Water SupplyFigure 33 Shell & Tubes on Elevated Platform

9.2 SPACE FRAMES OR SPACERS

As a standard, shell and tube exchangers come with saddle supports. When ordered for astacked application, the lower exchanger is generally ordered with opposed top and bottomsaddles to support the upper exchanger. However, there are occasions when it is desirable toset the upper exchanger at a greater height than normally achievable with saddles (i.e.,exchangers in different services that are stacked to save plot space or expansion of an



existing unit requiring the placement of a new exchanger on an existing one). In these cases,space frames (or spacers) will be required (Fig. 34).

Figure 34 Space Framing

9.3 SADDLE / FOUNDATION CLEARANCES

Clearances for piping, valves, insulation, maintenance equipment and instrumentation shallalways be checked (Fig. 35).



Figure 35 Clearances for Shell & Tube Exchangers

9.4 SHELL & TUBE PIPE SUPPORT LOCATIONS

Often pipe supports at shell and tube exchangers can be incorporated with the exchangers support foundations or can be set upon the same foundation. This can save the expense of



separate support foundations (Fig. 36). Anchors set on such supports allow the pipe to growwith the exchanger instead of against it.

Figure 36 Support Design for Piping at Shell & Tube

9.5 VERTICAL REBOILER SUPPORTS



In setting vertical reboilers, a number of options for method of support are possible. The bestchoice for any given application will depend on the process requirements as well as the availabilityof space, type and weight of the equipment being used. The maintenance requirements for thesereboilers shall also be reviewed in deciding how best to support them in that bundle pulling for avertical exchanger can require some unconventional clearances (Figs. 5, 37 & 40)

Figure 37 Vertical Reboilers

9.6 AIR COOLER SUPPORTS



Air coolers can be ordered with two different types of supporting structures, with or withoutlegs provided (Fig. 38). The latter of these two options can help reduce costs and increaseflexibility of the exchanger's supports especially when the coolers are to set above a piperack. Coolers provided with legs can reduce costs for grade mounted air coolers and can alsobe mounted with air controlling louvers or walls to protect against freezing or reduce motornoise levels. The types of supporting structures for these coolers can affect the piping runsserving them.

Figure 38 Air Cooler Supports

10.0 MAINTENANCE AND OPERATIONAL ACCESS

10.1 SHELL & TUBE



Exchangers shall be piped with a view toward maximizing access to the tube bundle and othermaintainable components (Figs. 39 & 40). Break out flanges at the channel end, however, areoften an unnecessary added expense. Even at exchangers with fixed tube bundles (wherebundle pulling is not a concern), sufficient room shall be allowed at the heads to allow roddingout of tubes. Usually an area equal to the length of the tubes will do.Clear accessways should be provided to allow operator access to valves. If chain operatorsare used for elevated valves, care should be taken to avoid chains obstructing the walkways.

TUBE LENGTH + 30" (750mm)

18" (450mm) MIN. BETWEENFLANGES OR INSULATION

OPERATING VALVES(SUGGESTED LOCATIONS)

WALKWAY 30" (750mm) min.

9" (230mm) min. (ALL BODY FLANGES)

HEAD + 30" (750mm)

18" (450mm) min.(TYPICAL)

HEAD SWING (IFFITTED WITH A DAVIT)

HE

AD

RE

MO

VA

L A

RE

A

SHELL AND TUBE EXCHANGER ACCESSFIG. 39

Figure 39 Shell & Tube Exchanger Access



Figure 40 Tube Pulling Requirements



10.2 BUNDLE EXTRACTOR

Most tube bundle pulling equipment can operate with a minimum of space allowance (Fig. 41). Check the client's clearance requirements for his particular bundle extractor.

Figure 41 Tube Bundle Extractor



10.3 CLEARANCES

Clearances for maintenance, such as wrench clearance at flanges shall be provided in all cases. Often 12" (300mm) from bottom of pipe to grade is an adequate elevation for piping, however if adrain is provided in the line, a minimum of 4" (100mm) below the plug shall be provided for theremoval of that plug. Knuckle clearance shall also be provided around spectacle blinds (whereprovided) (Fig. 36). As stated earlier, access ways shall be provided for the maintenance of all exchangers requiringmaintenance. These access ways shall provide a minimum of 2’-6" (750mm) of unobstructedwalkway with a minimum of 7’-0" (2200mm) headroom. The designer shall review thearrangement of exchangers and the placement of access ways as an overall scheme instead of interms of individual components. Each access can be used to service more than one set ofexchangers, optimizing the space allocated to their placement (Figs. 39, 40 & 42).

10.4 STACKED EXCHANGERS

Shell & Tube exchangers may be stacked up to a maximum of three shells high if approved by thecustomer.

10.5 CRANE ACCESS

For exchangers requiring the movement of large heavy components for maintenance, road andheavy equipment access must be a consideration. Clear unobstructed lift and laydown areas, andcarry-out routes must be designated and kept clear of equipment, platforming and structures. Asingle crane lift area can service several pieces of equipment if properly located (Fig. 42).

Figure 42 Crane Access 10.6 AIR COOLERS

As well as platforming for header box maintenance, most air coolers (especially those mounted onracks) require platforming for motor access (Fig. 44). If the cooler is at grade and the motors arewithin the reach of and are accessible by mobile equipment, the platforms might be eliminated.



10.7 AIR COOLER HEADER BOX ACCESS

Platform access at air cooler header boxes is often required. Such platforming shall provideenough access to allow the blinding of cells or the plugging of damaged tubes without interferingwith the support and routing of manifold piping (Fig. 43)

Figure 43 Plugged Header Box



10.8 PLATFORM OPTIONS FOR AIR COOLER MOTOR ACCESS

In cases where large platforms are needed to service several bays of coolers, use a solid patternfor platforming. Reducing the details required for design, and simplified construction, outweigh thesavings in material (Fig. 44).Finger style platforming shall be used only after consulting with Civil/Structural engineer.



FOR LONG AIR COOLERS

CONVENTIONAL APPROACH TO FAN MOTOR MAINT. PLATFORM

CONVENTIONAL APPROACH PROVIDESMORE PLATFORMING, W HILE HAVINGLITTLE COST IMPACT VS. ALTERNATE

FAN MOTORS

FAN MOTORS

ALTERNATE APPROACH

AIR COOLER PLATFORMING ALTERNATIVESFIG. 44 Fi

gure 44 Air Cooler Platforming Alternatives

11.0 PIPE STRESS

11.1 EXCHANGER ANCHOR LOCATION

Anchors play a large role in determining the piping configurations for exchangers. In many casesthe location of anchors can be adjusted to accommodate a better piping design. This is applicable



to both pipe anchors and exchanger support anchors. With shell and tubes, anchors are generallyplaced to allow the piping to grow parallel to the growth of the exchanger. This minimizes thestress loads on the nozzles (Fig. 36).

Anchor points of the exchangers themselves can often be manipulated to provide the best design. Slots can be cut into the exchanger support bolt holes to allow movement in a desired direction(Fig. 45). If friction forces created by the weight of the exchanger are excessive, slide plates canbe introduced to allow greater ease of movement.

Figure 45 Slotted Holes for Shell & Tubes

11.2 SHELL & TUBE NOZZLE LOADS

The allowable loads at nozzles for shell & tube exchangers are not usually a problem. However,when exchangers in like service are banked, it shall be kept in mind that tight fitting-to-fittingconfigurations for the piping may generate unacceptable loads. Changes to the pipingconfiguration or the addition of springs to piping supports can be used to reduce these loads. Adding springs to piping supports can also aid in vertical thermal load reduction when exchangerlocations require lengthy vertical piping runs.

11.3 AIR COOLER NOZZLE LOADS

Air cooler piping anchors shall be placed close to the exchanger to minimize the growth toward thenozzles. Anchors on distribution headers shall be centered to equalize, as much as possible, thelateral growth parallel to the header boxes.

Air coolers are notorious for the low limits of allowable stress at the points of piping connection.The header boxes for these exchangers are usually made of gage steel and configured in afashion that affords little if any structural strength. When these conditions are applied to evenmoderately hot services the result is often stress loads at the nozzles that far exceed acceptable. Lengthening the piping riser between the piping header and the manifold box can help to reduce



the lateral stresses (Fig. 46) and the addition of spring supports can reduce the load forces in thevertical (Fig. 47)

Figure 46 Lateral Stresses on Air Cooler Nozzles

Figure 47 Spring Supports for Air Coolers

12.0 REFERENCES

Tubular Exchanger Manufacturers Association Standards (8th Edition)3DI-P21-00001 ISBL Equipment Layout3GS-P34-00002 Piping Design and Layout

exchanger piping

Documents

tube fabrication tolerances

fan moto rs

significant cost savings

exchanger battery arrangements

outlet manifold boxes

plugged header box

motor mounting make

double pipe exchangers