Pipe Rack 1

PIPE RACK & RACK PIPING

1.What 1. What is Pipe Rack & Rack Piping Pipe rack is the main artery of process unit. It connects all equipment with lines that cannot run through adjacent areas. Because it is located in the middle of the most plants, the pipe rack must be erected first, before it becomes obstructed by rows of equipment. This carries the pipes and cable trays from one equipment to another equipment within a process unit or carries the pipe and cable trays from one unit to another unit. It connects all equipment with lines that cannot run through adjacent areas. Pipe racks carry process, utility piping and also include instrument and electrical cable trays as well as equipment mounted over all of these. Routing of pipe the pipes on this pipe rack is called rack piping Pipe Rack is designed on the basis of:

Shapes

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Future Space

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Width of Pipe Rack

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Clearance

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Pipe Rack Loading

Rack Piping is done on the basis of:

Positions of Lines (Process & Utilities)

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Hot Lines & Cold Lines

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Bigger Size Lines

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Pipe Spacing

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Anchor Bay

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Unit Battery Limit

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Expansion Loops

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Pipe Route

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Trays

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The primary data required for detailed development of a pipe rack:     

Plot Plan P&ID’s Client Specification Construction Materials Fire proofing requirements Statutory requirements

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2.Pipe Rack Criteria 2.1 Shapes:There are various shapes of pipe rack like L/T/U/H/Z. These shapes shall be considered based on the area available.

DEAD END YARD LINES ENTER & LEAVE ONE END OF THE RACK

STRAIGHT THROUGH YARD LINES CAN CAN ENTER & LEAVE BOTH ENDS OF THE RACK

L-SHAPED YARD LINES CAN ENTER LEAVE NORTH & EAST OF THE RACK

T-SHAPED RACK PIPING CAN ENTER & LEAVE THREE SIDES OF THE RACK

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COMPBINATION OF I & T SHAPED RACK

U-SHAPED YARD LINE CAN ENTER & LEAVE ALL FOUR SIDES OF THE RACK

COMPLEX RACK PIPING ARRANGEMENT FOR VERY LARGE CHEMICAL PLANT

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2.2 Future space The total width of the pipe rack shall include 25% extra space for future expansion/modification in unit for rack-width upto 16m and 10% for rack-width above 16m. The future space %age is normally based on the client requirements.

2.3 Width of Pipe Rack The width of piperack is influenced by : 

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The number of lines Electrical/instrument cable trays. Space for future lines.

The width of a piperack may be calculated using the following method : First estimate number of lines as described. Add up the number of lines up to 18” diameter in the most dense section of the piperack. The total width in meters (W) will be : W = ( f x N x S ) + A meters Where f, safety factor = 1.5, if the lines have been laid out as described in initial evaluation. Where f, safety factor = 1.2, if the lines have been laid out as described under development.

N = number of lines below 18” diameter S = average estimated spacing between lines in millimeters. Usually - S = 300 mm Usually - S = 230 mm ( if lines in piperack are smaller than 10” ) A = additional width required meters for : 

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Lines larger than 18”. Future lines.

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Instrument and electrical cable trays. Any slot for pump discharge lines 500 mm - 1 meter.

The total width is thus obtained. If W is bigger than 9M usually two piperack levels will be required. Note : At the beginning of a job, `W` should usually include 30 - 40% of clear space for future lines. The width of the piperack may be increased or determined by the space requirement, and/or access to equipment arranged under the piperack.

Clearance 

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Clearance beneath pipe rack shall be 4m minimum both in longitudinal and transverse directions. For Offsite, clearance beneath pipe rack shall be 2.2m minimum both in longitudinal and transverse directions. Road clearance shall be 7m for main road and 5m for secondary road.

Pipe Rack Loadings Pipe rack loads shall be given by stress group to Civil & structural discipline for pipe rack design. 

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Sustain Load (Dead Load) o Weight of piping, valve and load insulation

Thermal Load o Load by thermal expansion of piping & Reaction force by internal pressure of expansion bellows Dynamic Load o Load by vibration of piping & by wind and earthquake

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Sustained Load (Live Load) o Liquid load for hydrostatic pressure test o Live load (L) on access platforms and walkways and on equipment platforms should be considered, as applicable. Wind Load (W): o Transverse wind load on structural members, piping, electrical trays,equipment, platforms, and ladders should be determined in accordance with project approved design code.

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Rack Piping Position of Lines Predominantly process lines are to be kept at lower tier and, utility & hot process lines on upper tier. Hot Lines & Cold Lines Generally hot lines & cold lines are to kept at different tiers or at different groups on a tier. Pipe Spacing Minimum spacing between adjacent lines shall be decided based on O.D. of bigger size flange (minimum rating 300# to be considered), O.D. of the smaller pipe, individual insulation thickness and additional 25mm clearance. Even if flange is not appearing the min. spacing shall be based on above basis only. Actual line spacing, especially at ‘L’ bend and loop locations, shall ta ke care thermal expansion/thermal contraction/non-expansion of adjacent line. Nonexpansion/thermal contraction may stop the free expansion of the adjacent line at ‘L’ bend location. Bigger Size Lines

Large size lines (14” and larger) shall be arranged clo se to the column in order to decrease the bending moment of beam. Water lines more than 30” shall not be routed over pipe rack, these shall be routed underground. Anchor Bay Anchors on the racks are to be provided on the anchor bay if the concept of anchor bay is adopted. Otherwise anchor shall be distributed over two to three consecutive bays.Anchors shall be provided within unit on all hot lines leaving the unit. Pipe Route Racks shall be designed to give the piping shortest possible run and to provide clear head rooms over main walkways, secondary walkways and platforms.

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Trays Generally top tier is to be kept for Electrical cable trays (if not provided in underground trench) and Instrument cable ducts/trays. Cable tray laying to take care of necessary clearances for the fire proofing of structure.

Battery Limit (ISBL) Process lines crossing units (within units or from unit to main pipeway) are normally provided with a block valve, spectacle blind and drain valve. Block valves are to be grouped and locations of block valves in vertical run of pipe are preffered. If the block valves have to be located in an overhead pipe-way, staircase access to a platform above the lines shall be provided. Expansion Loops Expansion loop is provided on the high temperature lines. This information shall be given by stress group. All the loops shall be located around one column only.

Make lines into group and install a large size piping and high temperature piping to the edge of the rack.

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When necessary to install an expansion loop on the condensate line, do it horizontally to prevent water hammering. But do as above if horizontal loop is impossible.

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SUPPORTS Supports are used to hold the pipes and pipe rack in position. A satisfactory design of the Piping System should therefore give a careful consideration to achieve the above requirement. This is generally accomplished by providing external attachments (known as pipe supports) at various locations of the piping profile. There are two types of supports:  

Primary Supports Secondary Supports

Primary Supports These are the supports which are attached to or are adjacent to the pipelines. Types of primary supports:U-Bolt It is used for non insulated piplines upto 4” NB maximum.

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Cleats

It is used for non insulated pipelines for 6” and above

Cleat

Shoe It is used for hot insulated CS and LAS pipe lines.It is also used for hot insulated SS or exotic pipelines with clamp.

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Clamps It is used for SS and exotic pipelines with the shoe welded to the clamp.

Trunnion Support It is used for non insulated and insulated CS and LAS pipelines

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Support for cold insulated pipes

Insulation

For plastic pipelines Continues supports are required for these pipelines

For small pipes

For large pipes

Cable Tray (like supporting tray for pipes)

For pipelines running together

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Secondary Supports These are the supports on which primary supports rests. Types of secondary supports:T support

Inverted T support

Goal Post

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Inverted Goal Post

L support

Inverted L support

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Piping GAD General Arrangement drawings for piping systems and equipments are developed by piping designers. These drawings indicate the locations of main equipments in the plant. The main piping items, valves, and fittings are also indicated in the General Arrangement or GA drawings. Most often the piping is indicated using a top-view. Sometimes a side view of the pipe rack is also presented on the GA drawing.

General arrangement drawings are also developed for individual equipments. These drawings present the main dimensions of that equipment using 2D views, top-view, side-view and sometimes front-view. All the nozzles for concerned equipment are indicated on the equipment General Arrangement or GA drawing.

For a green field engineering project, equipment location drawings are prepare at the proposal stage by piping designers. On commencing the project work, these drawings are used as first basis for development of piping layout. Depending on the feasibility of the piping layout arrangement, often the equipment locations are revised and updated. The changes to equipment location can sometimes be substantial in order to have the desired piping arrangement.

Thus piping layout arrangement and development of piping general arrangement or GA drawings is dependent on reference sources developed prior to the piping arrangement work and modifications required to those references to allow for the desired piping layout arrangement.

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Pipe Rack 1

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