Piping Design Basis for Pipe Racks

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Piping Design Basis mentions various aspects of Pipe Rack Design requirements in a particular project. Here are sample requirements for pipe rack design.

Pipe Rack Layout

In general, equipment layout shall be prepared considering straight pipe rack, however other shapes like L / T / U / H / Z etc. can also be considered based on area available.

The total width of pipe rack shall include 25% extra space for future expansion / modifications in unit.

The width of the rack shall be 6M, 8M or 10M for single bay and 12M, 16M or 20M for double bay having 4 tiers maximum. The spacing between pipe rack portals shall be taken as 6M in general. However it can be increased to 8M depending on the size of the pumps to be housed below pipe rack, in which case an intermediate structural member may be provided in pipe rack for tier depending on line size.

  1. For units, clearance beneath pipe rack shall be 3.0M minimum both in longitudinal and transverse directions.
  2. For offisites, clearance beneath pipe rack shall be 2.2M minimum both in longitudinal and transverse directions.
  3. Road clearance shall be 7M minimum for main road and 6M for secondary road.
  4. Water lines more than 30″ shall not be routed over pipe rack, these shall be routed underground.

Rack Piping

Racks shall be designed to give the piping shortest possible run and to provide clear head rooms over main walkways, secondary  walkways and platforms. Predominantly process lines are to be kept at lower tier. Utility & hot process lines on upper tier.

Cable Trays

Generally the 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.

Lines Grouping

Hot lines and cold lines shall be kept apart in different groups on a tier. Bigger size lines shall be kept nearer to the rack column.

Spacing Between Pipes

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 25 mm clearance, even if flange is not appearing. Actual line spacing, especially at ‘L’ bend and loop locations, shall take care of 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.

Pipe Anchors

Anchors on the racks are to be provided on the anchor bay if the concept of anchor bay is adopted. Otherwise anchors shall be distributed over two to three consecutive bays. Anchors shall be provided within unit on all hot lines leaving the unit.

Battery Limit Valves

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 preferred. If the block valves have to be located in an overhead pipe-way, staircase access to a platform above the lines shall be provided.

Branches in Headers

Stubs in sea water shall be from top of main header.

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