Bechtel Engineering-Pipe rack

O:\WINWORD\3DG\P22\009-01.DOC PAGE 1 OF 1

BECHTELPLANT DESIGN & PIPING

ENGINEERING DESIGN GUIDE FORPIPE RACKS3DG P22 009, Rev. 01, 12/94Prepared by: A. DominguezApproved by: E.F. Bausbacher

TABLE OF CONTENTS

Page No.

LIST OF TABLES 4

LIST OF FIGURES 5

1.0 PURPOSE 7

2.0 INTRODUCTION 7

3.0 PIPE RACK WIDTH 7

4.0 PIPE BENTS 14

5.0 LINE SPACING 14

6.0 PIPE RACK ELEVATIONS 14

7.0 LARGE DIAMETER LINES 15

8.0 SETTING LINE LOCATIONS 24

8.1 Line Locations 248.2 Relief Header Location 248.3 Vertical Drops 24

Page No.


9.0 METER RUNS 24

10.0 VALVE LOCATIONS 28

10.1 Header Block Valves 2810.2 Operating Valves 2810.3 Battery Limit Valves 28

11.0 UTILITY STATIONS 28

12.0 PIPE FLEXIBILITY 28

12.1 Thermal Expansion or Contraction 3512.2 Cold Spring 3512.3 Determining Line Growth 3512.4 Determining Anchor Points 3512.5 Expansion Loops 35

13.0 PIPE SUPPORTS 38

14.0 PIPE RACK STRUCTURE 38

14.1 Steel Structures 3814.2 Precast Concrete Pipe Racks 39

15.0 EQUIPMENT OVER PIPE RACKS 43

16.0 FLAT TURNS 43

17.0 PIPE RACK INTERSECTION 43

18.0 PIPE RACK EXPANSION OR ADDITIONS 43

19.0 ELECTRICAL AND WELDING RECEPTACLES 49


Page No.

20.0 BRANCHES 49

21.0 VENTS AND DRAINS 49

22.0 SENSITIVE LINES 49

23.0 FIELD WELDS 49

24.0 SLOPED LINES ON PIPE RACKS 49

25.0 PLASTIC PIPE 50

26.0 OPERATOR ACCESS 50


LIST OF TABLES

Table 1 Basic Allowable Maximum Spans

Table 2.1 Expansion Coefficients

Table 3 CPVC Allowable Maximum Spans


LIST OF FIGURES

Figure 1 Line Routing Diagram

Figure 2 Pipe Rack Cross Section

Figure 3 Pipe Rack Composite Cross Section

Figure 4 Line Spacing Chart

Figure 5 Pipe Rack Bent Spacing

Figure 6 Flanged Line Spacing

Figure 7 Cold Spring

Figure 8 Line Movement

Figure 9 Large Lines Elevation Changes

Figure 10 Pipe Rack Layout

Figure 11 Relief Header Location

Figure 12 Alternate Pipe Rack Expansion

Figure 13 Pipe Rack Meter Runs

Figure 14 Meter Run Clearance Box

Figure 15 Header Block Valve Location

Figure 16 Utility Station Piping at a Column

Figure 17 Battery Limit at Single Level Rack


Figure 18 Alternate Battery Limit for Single Level Rack

Figure 19 Battery Limit at Two Level Rack

Figure 20 Flexibility Procedure Check List

Figure 21 Pipe Rack Anchor Bent

Figure 22 Steam Line Drip Legs

Figure 23 Line Support

Figure 24 Intermediate Pipe Support

Figure 25 Longitudinal Beam Location

Figure 26 Longitudinal Beam Variations

Figure 27 Precast Concrete Pipe Rack

Figure 28 Equipment on top of Pipe Rack

Figure 29 Fireproofing Requirements

Figure 30 90 Degree Pipe Rack Turns

Figure 31 Pipe Rack Intersection Layout

Figure 32 Pipe Rack Intersection Detail

Figure 33 Pipe Rack Additions

Figure 34 Lighting Panels and Welding Receptacles

Figure 35 Operator Access

Figure 36 Weld and Pipe Shoe Clearance


1.0 PURPOSE

This standard establishes the minimum requirements for Refinery andChemical plants piperack design.

2.0 INTRODUCTION

A pipeway is a space that has been allocated for routing parallel adjacentlines and connects equipment with lines that cannot run through adjacentareas. A pipe rack is a structure in the pipeway for carrying pipes and isusually made of steel, or concrete and steel. In addition, pipe racks maycarry electrical cable and instrument trays, as well as equipment mountedon top of the structure, e.g. air coolers.

It is important to coordinate all design with other disciplines since piperacksare a costly plant item. Overall pipe rack design must meet the currentrequirements of a client as well as any plant expansion plans withoutmaking major modifications to existing facilities. Available space in the piperack must be considered valuable and used to the utmost advantage forpresent and future needs.

The primary information required for the detailed development of a pipe rackincludes the following:

• Plot Plan• Piping and instrumentation diagrams• Plant layout specifications / standards• Client specifications• Construction materials• Fireproofing requirements• Equipment details and loading

3.0 PIPE RACK WIDTH

3.1 Establishing the width of a pipe rack is generated by a line routing diagram,shown in Figure 1. A line routing diagram is a schematic drawing of allprocess or utility piping systems drawn on a copy of the plot plan. Itprovides preliminary locations of pipe lines and identifies the most


congested piping bent in the pipe rack. The early issue of P&ID diagramshave information on commodities, line numbers and preliminary sizes.



3.2 Process Flow Diagrams and preliminary line designation tables provideoperating temperatures and identify the requirements for insulation.

3.3 The pipe rack width, bent spacing and number of levels can be determinedonce the line routing diagram is complete.

3.4 With the use of the line routing diagram, a dimensioned cross section of thebent that will carry the most piping is shown in Fig. 2.

3.5 The most common arrangement for a refinery process unit pipe rack is tohave process lines on the lower level or levels and the utility lines on the toplevel. Instrument and electrical cable trays are placed on the top level withutility lines or on a separate level above all pipe levels (Fig. 3). Theapproximate size of all trays must be obtained from the instrument andelectrical engineers to ensure that ample space is provided. The pipe racklayout designer must review the tray space requirements with electrical andinstrument engineers early in the pipe rack layout to establish theserequirements. It is suggested, the initial design of the pipe rack should allowfor a 10-20% growth in number of lines, throughout the engineering phase ofa project. Client requirements for clear unused space in a pipe rack, uponcompletion of the engineering phase, should be addressed on a case bycase basis.

Line spacing must be set with the line spacing chart (Fig. 4) before futuregrowth space can be determined. Once future rack growth, conduit andinstrument tubing drop areas have been considered for in the plan the laststep is to add up all the dimensions and round off to the next whole number-for example, 20 ft. (6,100 mm) rather than 19 ft. 5 in. Depending on thenumber of lines in the rack a larger width greater than a 20 ft. wide rackcould be required. For instance, two 30-ft. (9,150-mm) wide levels or three20-ft (6,100-mm) wide levels. This is a significant decision that requiresconsultation with civil/structural and project management for total costimplications.

A pipe rack composite is shown in Figure 3. This cross section shows itemsmentioned previously and indicates additional considerations. The accessway width is determined by the space necessary to service equipmentlocated at grade below the pipe rack.





4.0 PIPE BENTS

4.1 A pipe bent consists of vertical columns and a horizontal structural memberor members that support piping systems, usually above headroom. Thedifferent line sizes that are installed in the pipe rack establish the bentspacing. Generally 2" is the smallest line size we use in the pipe rack toavoid intermediate supports.

Table 1 illustrates a typical pipe span chart and shows how far a particularline can span based on size, schedule, liquid or vapor, and insulated or barepipe. Pipe racks are unique to a specific plant. Pipe sizes are larger inrefinery units than those found in chemical plants. If a plant requires a piperack to have 20 ft. bent spacing, the variation shown in Figure 5 allows for a40 ft. spacing by adding intermediate supports. This type of bent spacing,also called pipe bridge, may be used to cross roads, accessways or avoidunderground obstructions. Consult with civil or structural engineers on thisapproach since it could be costly.

5.0 FLANGED LINES

When flanges or flanged valves are required on adjacent lines, the flangesare staggered as indicated on Figure 6. Maintain a 12-inch minimumclearance from supporting steel on flanges taking pipe shoe length intoconsideration.

6.0 PIPE RACK ELEVATIONS

After establishing bent spacing, rack width and number of levels, theelevation of the levels must be set. The pipe rack designer must know theminimum clearances required to set the elevations. Clients may be able toprovide what their road clearances are and the type of mobile equipmentused at their plant.

If equipment is located beneath the pipe rack it can influence the pipe rackelevation. Usually, space is allowed below the pipe rack for equipment, witha minimum height clearance of 12 ft (3,660 mm).


7.0 LARGE DIAMETER LINES

The next factor to is to determine the dimension between the bottom of aline in the rack and the bottom of a branch as it leaves the rack. Review thelayout for largest lines in the entire pipe rack, for example, it shows there aretwo or three large-diameter lines (e.g., 18, 20, or 24 in) and the remaininglines are 10 inches and smaller, the exit level above and below the rack canbe 3 ft (915 mm).

Figure 9 depicts how to route the large-diameter lines by using a 45o elbowor trimming an elbow to a more shallow angle. The pipe rack design is nowcomplete with the exception of installing equipment over the rack.










8.0 SETTING LINE LOCATIONS

Many factors must be taken into account when locating piping, valves, andinstruments in the pipe rack. Figure 10 is an example of a typical layout.

8.1 Line Locations

When the pipe rack designer is locating lines in the rack, he should run thelargest lines near the outside where possible to reduce the overall loads onsupport beams. Hot lines should be located near the outside to allow forexpansion loops.

Piping must be routed to avoid dead spaces because space in the pipe rackis limited once the design is set. The designer should ask area designers toidentify which lines can run within their areas in order to minimize pipe runsin the pipe rack. During the early stages of pipe rack development it cansubjected to multiple line location changes for which consideration isnecessary prior to firming up the rack design.

8.2 Relief Header Location

Relief headers are located on or above the top level of the rack and aresloped to allow the line to drain to the blowdown drum. Locating the reliefline over the centerline of the column for support should be avoided topermit columns to be extended for future rack expansion. Figure 11 showsa suggested location for the relief header that does not impose on futureexpansion of the pipe rack.

8.3 Vertical Drops

Vertical drop of lines outside the rack is set by the average line size in theunit, usually a clearance of 2 ft (610 mm) is sufficient. If the average linesize is 2 in., an 18 in (450 mm) drop may be more appropriate.

9.0 METER RUNS

Locate meter runs in the pipe rack only when absolutely necessary andother alternatives don't exist. Meter runs or venturis that have to be installedon the pipe rack they should be placed directly next to the columns so that


access is available by portable ladder or mobile platform, as shown inFigure 12. Locate meter runs in the pipe rack only when absolutelynecessary.

Meter runs require a maintenance area and in order to accomplish this ameter run clearance box should be indicated on the orthographic, as shownon Figure 13. Instrumentation should be consulted for the acceptablelocation of the orifice flange taps.




10.0 VALVE LOCATIONS

10.1 Header Block Valves

Header block valves at utility headers are located inside the rack area in thehorizontal position, directly above the header if room permits, see Figure 15.

10.2 Operating Valves

Operating valves in the rack area must be accessible from platforms or bychain operators as shown on Figure 10. Valves must be set in an area thatwould permit the chain to fall free from obstructions that would impairoperation, but not be an obstruction itself.

10.3 Battery Limit Valves

Battery limit valves for a single-level pipe rack are shown in Figure 17.Valves are staggered on either side of the battery limit platform, andhandwheel extension stems are furnished for the ease of operation whennecessary. If a single level rack elevation change is required between theprocess and off-site units see Figure 18. This design has the block valvesinstalled in the vertical portion of the line.

A battery limit platform for a two-level process unit pipe rack is illustrated onFigure 19. The elevation change to the Off-site area is either below or abovethe process unit pipe rack.

11.0 UTILITY STATIONS

Figure 16 shows a typical arrangement for utility station piping avoiding thecolumn for future expansion. Refer to the Bechtel or client Utility Stationstandard for the proper details.

12.0 PIPE FLEXIBILITY

Although conducting the final stress analysis is the responsibility of thestress engineer, the pipe rack designer calculates preliminary line expansionusing relevant data. Figure 20 highlights the steps required in making a


preliminary flexibility check. Refer to the pipe stress analyst design guidesection on layout aids for pipeways.

After the preliminary pipe rack design is completed, submit a copy to thestress engineer for review to ensure that the design will not require majorrework during the formal stress check.







12.1 Thermal Expansion or Contraction

A problem that is often overlooked is header growth. The line spacing tablemay have been used to set distances between lines, but lines may havebeen set close to a column. Figure 8 shows that an adjacent line or columnmust not restrict the movement of a line because it will act as an anchor andcould create a problem. A line should move its maximum distance and stillretain a minimum clearance of 2 in (50 mm) from any obstruction.Accommodation for thermal expansion or contraction must be reviewed withthe stress group.

12.2 Cold Spring

If an alternate method can be used, avoid cold springing of lines. A line maybe cold sprung to reduce the movement from thermal expansion orcontraction in order to prevent interference. Figure 7 illustrates the use ofcold springing.

12.3 Determining Line Growth

The growth of headers must be determined by multiplying the coefficient ofexpansion by the length of the line. The coefficient of expansion is based ona certain type of material operating at a specific temperature. Upsetcondition temperatures take precedence over operating temperatures. SeeTable 2.1.

12.4 Anchor Points

Let us assume that an anchor is located in the center of the header, thedesigner should calculate and determine whether the growth of variousbranches have enough flexibility to absorb the header growth. Using theapplicable nomograms, the designer can calculate the amount of expansionleg required to satisfy all flexibility requirements.

12.5 Expansion Loops

The line requiring the largest expansion loop must be located outside ofother loops with less growth. Locating the headers that require loops alongone side of the pipe rack allows the expansion loops to sit with a slight


overhang along the adjacent side of the pipe rack. This arrangement forexpansion loops is seen in Figure 21.

Steam headers require a means of removing condensate build-up on eitherside of the expansion loop. The practice that is most commonly used toaccomplish this is to add drip legs and traps, as shown in Figure 22.



Allow room for loops and other pipe arrangements to cope with expansionby early consultation with the pipe stress group. Notify structural engineersof any additional steel required to support such loops.

As a result of adding anchor loads on a particular bent, bracing may berequired to grade, restricting the location of any equipment in that particularbay.

13.0 PIPE SUPPORTS

Figure 23 shows the use of a dummy leg welded to the elbow for a line thathas exceeded its allowable span.

Figure 24 shows how large bore lines in a pipe rack are used to support agroup of small lines that may have exceeded allowable pipe spans becauseof bent spacing. The uninsulated large bore lines are U-bolted to thesupporting steel and the smaller lines then rest on the steel. Insulated linesmust not used to support other lines. Refer to Bechtel or client pipe supportstandards for proper use.

14.0 PIPE RACK STRUCTURE

14.1 Steel Structures

Support is required by most lines when leaving or entering a pipe rack.Structural members called longitudinal beams are the most common meansof meeting this requirement. After all the lines have been run in the piperack, the designer must begin to locate the support beams necessary tosupport all of these lines. Figure 25 illustrates how the requirement can bedealt with. Structural engineers will add additional longitudinal beams forstability of the pipe rack when required, they should bring this requirement tothe attention of the pipe rack designer. Figure 26 shows some variation oflongitudinal beam design. The pipe support member on the bent is called atransverse beam.

14.2 Precast Concrete Pipe Racks

The designer should keep in mind that precast concrete pipe racks requirestructural members that are much larger than most designs. Figure 27 illustrates


how an embedded steel member is placed into a precast column for the supportmember. The support member also has an embedded steel member that isbolted to the column and eventually grouted in.





15.0 EQUIPMENT OVER PIPE RACKS

Equipment such as drums, deaerators, and air coolers are often locatedabove the pipe rack as shown in Figure 28 and 29.

Pipe racks that require fireproofing of columns are shown in Figure 29.Fireproofing of columns to a level just below the lower rack support beamwill be required if hydrocarbons are prevalent in the unit. If air coolers orother equipment is located above a pipe rack, the fireproofing is extended tothe equipment support beam. This issue must be reviewed with the clientand safety group.

16.0 FLAT TURNS

Use of flat turns are to be avoided. Every now and then, a situation arises inwhich a flat-turn pipe rack may be used. This often occurs near a dead-endarea where the possibility for problems is minimal. As shown in Figure 30,the sequence of lines on the left side of the rack must remain constant aslong as flat turns are used. A difference in elevation must be used at a 90o

turn in the pipe rack if the sequence must change, as shown on the rightside of the diagram. This design approach must be well thought out beforeit is used.

17.0 PIPE RACK INTERSECTION

A primary pipe rack that has a secondary pipe rack intersection is shown inFigure 31. There is a right and wrong approach to set this location. Duringthe development phase it may appear more uniform to locate the secondaryrack directly south of the main north/south rack. Figure 32 also clearlyillustrates why this should be avoided. The lines heading north off the maineast/west rack prevent the lines from the south from entering this commonarea. In order to eliminate any problems the secondary rack should beshifted east one bay.

18.0 PIPE RACK EXPANSION OR ADDITIONS

Pipe rack expansion of the individual levels can be achieved by addingcantilever beams as needed on the outside of the column. Vertical riserscommonly found outside the pipe rack use a considerable amount of space


and the only problem with this design is, if not planned for, it can limit theamount of the space of the extension, as indicated in Figure 12.

Pipe rack additions are shown in Figure 33. Area 1 shows a two-level piperack, as planned. Because of the possibility that the pipe rack can beexpanded in the future, the area over the columns must be kept clear ofpiping and conduit. The future expansion may include another pipe racklevel (2), an air cooler (3), or a series of shell and tube exchangers (4).






19.0 ELECTRICAL AND WELDING RECEPTACLES

Welding receptacles and lighting panels should be planned for during theearly stages of the pipe rack design. They are attached directly to the piperack columns; Electrical engineers designate the location of regular andemergency panels. Client personnel select the preferred location forwelding receptacles (see Figure 34).

20.0 BRANCHES

Gas, steam, and vapor branch lines must be taken from top of headers.Liquid lines may branch from of the top or bottom.

21.0 VENTS AND DRAINS

Vent all high points and drain all low points on rack piping.

22.0 SENSITIVE LINES

Ensure very hot lines are not run adjacent to lines carrying temperaturesensitive fluids, or elsewhere, where heat might be undesirable.

23.0 FIELD WELDS

Keep field welds and other joints at least 3 inches (75mm) clear fromsupporting steel or other obstruction. Allow room for the joint to be welded(Fig 36).

24.0 SLOPED LINES ON PIPE RACKS

Sloped lines can be carried on cantilevers attached to pipe rack columns.To obtain the required change in elevation at each bent, cantilevers may beattached at the required elevation. Alternately, a series of cantilevers canbe attached at the same elevation and the slope obtained by using shoes ofdifferent sizes. This method leads to fewer construction problems.


25.0 PLASTIC PIPE

Pipe made either from flexible or rigid plastics cannot maintain the samespan loads as metal pipe and requires a greater number of support points.One way of providing support is to lay the pipe upon lengths of steel channelsections or by suspending it from other steel piping. The choice of steelsection depends on the span loads, size and type of plastic pipe. See Table3 for preliminary allowable pipe spans.

26.0 OPERATOR ACCESS

When locating piping manifolds, control stations, instruments, and pullboxes along the pipe rack columns, the designer should avoid blockingaccess from under the pipe rack to adjacent equipment areas by leavingclear space, as illustrated in Figure 35.



Documents

Bechtel Engineering-Pipe rack