Pipe Racks Arrangement.ppt

7/22/2019 Pipe Racks Arrangement.ppt

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Pipe Racks (PipeWay)

Arrangement Design

G. N. Kotwal

V.I.T. Pune.


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Introduction Pipe-Rack Considered as Main Artery of a process

plant. Basically Overhead piping supported on steel orconcrete bents.

Located in the central part with branches to the sides.

To be Designed, Layed out & Erected first alongwith

electrical cable trays, drainage trenches, sewers, &roads. After which the equipments are to be placed.

Pipe racks carry process & utility pipings and mayinclude instruments & cable trays also.

Piperack structure is a major item and is often fireproofed. It is also an important cost factor.

Lot of care, planning & coordination with other groups

needed as mistakes can be very costly.


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Types Pipetracks areAbove ground piping supported on concrete

sleepers at grade level. (Off site areas where equipment is wellspaced out)

Trenched Piping are Below ground piping laid in connectiontrenches.

Costly and usually undesirable; unless trenches are wide,

shallow and well vented, heavy gases may settle and create afire hazard through the length of the trench.

For these reasons, only pump out lines, chemical sewers orchemical drain collection systems are sometimes placed intrenches and routed to a pit or underground collection tank.

Underground Piping : Piping direct buried below ground level.Due to costly maintenance and the usually corrosive nature ofsoil, this method of routing is generally reserved for sewer anddrain lines.

In some plants, especially in cold climates, cooling water linesare buried below the frostline. This should be determined at thebeginning of a job, is generally a Client request.


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Pipe Rack : Concrete Fireproofed steel structure with

piping attached for oilfield project.


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Primary Inputs & OutputsInputs : Plot / Site plan

Process Flow, Utility Flow, Engineering flow diagramsandP & I Diagrams

Plant layout Specifications

Client specs

Construction materials Fireproofing requirements

Battery limit, valving requirements.

Catwalk, platform and ladder access to valves and relief valvesin piperack.

Minimum headroom and clearances under overhead piping orsupporting steel within areas and for equipment positionedunder piperacks .

Operating and safety requirements affecting piperack andstructure design.


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Outputs :

Pipe rack width No. of levels & elevations

Bent spacing

Pipe flexibility, access & maintrnanceconsiderations


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Special ConsiderationsCertain types of piping require special consideration:

4.1 Process Lines

Lines interconnecting nozzles on process equipment more than 6M apart

Products lines which run from vessels, exchangers or pump to battery / unitlimits

Crude or other charge lines entering the unit which run along piperackbefore connecting to process equipment, furnaces, exchangers, holdingdrums or booster pumps.

4.2 Relief Headers

Individual relief lines, blowdown lines and flare lines should be self drainingfrom all relief valve outlets to knock-out drum, flare stack or to a point at theplant limit.

To achieve this, lines will connect into the top of the header and at 45degrees in direction of flow. To eliminate pockets, and obtain required slopeto knock-out drum relief headers must be placed above the main piperack.

4.3 Instrument and Electrical Cable Trays Often instrument and electrical cable trays are supported on the piperack

track. Space must be allocated to accommodate them from the outset. Dueto the possibility of induced current interference instrument andcommunication cable trays must be located away from electrical and powercable trays. Consult with Instrument /Electrical Department for separation

requirements.


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PipeRack Bent spacing Pipe bent includes the vertical columns & the horizontal

structural members carrying pipes.

Normal spacing between piperack bents varies between 4.6Mto 6M. May be increased to a maximum of 8M.

Pipe sizes & weights decide the bent spacing.

Spacing may be increased (To cross roadways or provide forconstruction below it.) by adding intermediate bents supportedfrom spandrels ( horizontal cross beams for stability & support).

Special consideration must be given to :

Smaller lines which must be supported more frequently .

Liquid filled lines requiring shorter span than gas filled lines.

Hot lines which span shorter distances than cold lines of thesame size and wall thickness

Insulated lines; small bore, cold - insulated lines due to weightof insulation must be supported at relatively short intervals.

Space requirements of equipment at grade can sometimes

influence piperack bent spacing.


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Piperack ElevationPiperack elevation is determined by the highest requirement of the following :

Headroom over main road

Headroom for access to equipment under the piperack

Headroom under lines interconnecting the piperack and equipment located outside.

The size of steel or concrete beam supporting overhead piping must be taken intoconsideration.

Elevation at Piperack Intersection Where two two-tier piperacks meet, it is essential that elevations of lateral piperacks

slot between elevations of main piperack.

Generally, lines running at right angles to main piperack are assigned elevations 500mm to 1 meter higher or lower (depending on headroom requirements) than linesrunning in main piperack. 500 mm differential between pipe runs is the absolute

minimum. a piperack intersection where the respective main and lateral piperack

elevations do not slot between each other is to be avoided at all costs.

Where a single tier piperack turns through 90, and all lines can be kept in the samesequence in both directions, no elevation difference is necessary. When linessequence changes, introduce an elevation change at the turn.


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Elevation at Piperack Intersection


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No. of levels (Tiers)& LocationsOne Tier Piperacks:

Heavy lines (very large diameter lines, large bore lines full ofliquid) regardless of service are placed over or near thepiperack columns. This simplifies steelwork or concretepiperack design. Centrally loaded column and reduced bendingmoment on the beam will result in a lighter overall design.

Place process and relief lines next to these. Lines serving lefthand areas of plant on left, lines serving right hand areas on theright.

The central piperack portion is reserved for utility lines whichmay serve both right and left hand areas on the plant.

The position of product lines is influenced by their routing afterleaving the unit, right, (left) turning lines should be on the right(left) hand side of the piperack.

If possible, a centrally placed section of the piperack isreserved for future lines. This section should run the wholelength of the piperack.


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Other Guidelines (related to Fig. on next slide)


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Locating Lines. Valves & Instruments

Two Tier Piperacks

Where the number of lines dictate the use of a twolevel piperack, utility lines are placed on the top leveland process lines on the bottom level.

Instrument & electrical trays are either with utility levelor on a separate topmost level, decided in consultationwith the respective groups.

Largest lines be run near the outside to reduce theoverall load on beams.

Relief headers be located above top level of the rack

to allow for drain line. Space should be kept for Columnsexpansion in

vertical direction.

Utility Shut-off and operating valves be in horizontal

position & accessible from platforms or chains.


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Position of Hot Lines

It is advantageous for pipesupports to group hot linesrequiring expansion loopstogether, preferably onside of the piperack.

Horizontally elevated loopsover the piperack arecommonly used tominimize the effects ofexpansion on hot lines, thehottest and largest linebeing on the outside.


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Piperack Layout Piping economy depends

primarily on the length of linesrouted in the piperack. Fig.shows critical dimensionswhich influence overall cost.

Dimension A, is the totallength of piperack and is

governed by the number andsize of equipment, structuresand buildings arranged alongboth sides of the piperack. Onaverage, 3 meters of piperacklength are required per item of

process equipment, good lay-out can reduce piperacklength. (Thereby costs).

Equipment in pairs, stacked exchangers supported from towers, two vesselsbi d i t l l l t d t ith l tf


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combined into one, closely located towers with common platforms, processequipment located - under piperack - are examples which help shorten piperacklength. In a well arranged plant, average length of piperack per item of processequipment can be reduced to 2.1 meters to 2.4 meters.

Careful selection of dimensions B and C, below figure will minimize interconnectionequipment on opposite sides of piperack. C is normally no more than 1.8 meters to 3meters.

Dimensions D and E, (see below figure), minimize. Overgenerous dimensioning herewill increase vertical pipe lengths. Maximize use of available platforms for access tovalves.


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Plant layoutdetermines the

main piperackpiping runs.The shape ofpiperack is theresult of plantarrangements,site conditions,Clientsrequirementsand overallplant economy.(Fig.)

Plant layout


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ydeterminesthe mainpiperackpiping runs.The shape of

piperack isthe result ofplantarrangement,siteconditions,Clients

requirementsand overallplanteconomy.(Fig.)


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Flexibility & Supports

Considerations Pipe rack designer needs to do elementary designs so

as not to require major rework later.

Find potential flexibility problems in lines , e.g. steamheaders

Estimate the amount of expansion. And provide enoughspace for it and even some additional clearance.

No. of anchor points be decided.

Drip legs, steam traps be provided on either side ofexpansion loop.

Dummy legs / supports may be used. Larger lines may be used to support smaller lines.

Uninsulated lines are U-Bolted to the supports whileInsulated lines shoes are welded to the supports.

Insulated lines should not be used for supports. If used,

expansion be allowed.


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Structural Considerations

Supports are needed when line is enteringor leaving rack. Spandrels (cross beams)are used for this.

Inside face of pipe rack column should lineup with that of equipment support column.

Fireproofing is needed in most racks.

Either upto the lower rack or if equipmentsare located, upto its support beams.

Upto 4in. Thickness.


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Other Considerations

Expansion of the pipe rack can be done by

adding a cantilever beam on the outside of

the column.


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Pipetracks (Laid on Grade level)

Generally associated with offsite areas whereequipment is well spaced out, and land space isnot a premium.

Generally single tier

Pipetrack Width, Spacing of PipetrackSleepers, Pipetrack Elevation, Line Location(Line routing is all important. ), Line Spacing ,Road Crossings (The standard method is toprovide culverts under access roads.), AccessWays , Valves, Expansion Loops all similar toPiperacks, but simpler & less expensive.


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Underground Piping Keep buried piping to a minimum. Generally only sewer drain

lines and fire mains are located below ground. In some casesdue to Client or climate requirements, cooling water lines arealso buried below the frost line.

With future maintenance in mind, buried lines should be locatedwell clear of foundations, and if running side by side, wellspaced out. A minimum of 300 mm clearance is necessarybetween foundations and lines and between the lines

themselves. All buried steel pipes should have applied a corrosion resistant

coating and wrapping.

Deep valve boxes for buried lines should be designed withample room inside the box for a maintenance man to bend overand use wrenches for tightening flanges of re-packing valves.Consideration should be given to the use of concrete pipe inlieu of square boxes.

The criteria for a good underground piping design should beease of maintenance. Piping should be so spaced as to allow

Pipe Racks Arrangement.ppt

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