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. Consult Electrical and Instrument Engineers.
Anchors and Anchor Bays
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 nit.
Future Growth Space
Any pipe rack design should provide for 20% future growth. Check client requirements. Some clients require 25% extra for racks widths upto 16m and 10% extra for width above 16m. EIL PDB : 25% Alternative Approach to Expansion is shown below.
Structural Considerations
Most lines require support when leaving or entering a pipe rack. Structural members called spandrels are the most common means of satisfying this requirement.
After all the lines have been run in the pipe rack, the plant layout designer must begin to locate the spandrels necessary to support all of these lines. Following figure shows how the requirement can be handled. If the structural engineers require additional spandrels for stability of the pipe rack, they should bring this requirement to the attention of the plant layout designer. Following figure shows some variations of spandrel design.
The plant layout designer should be aware that precast concrete pipe racks require structural members that are much larger than most designs. Following figure illustrates a precast column with an embedded steel member for the spandrel support.
The spandrel also has an embedded steel member that is bolted to the column and eventually grouted in.
An installation sequence for a precast pipe rack is also shown in following figure.
Equipments Above Pipe Rack
Such equipment as drums and deaerators is often located above pipe rack columns.
To avoid wasting valuable rack space with the large support columns, the inside face of the pipe rack column must line up with the inside face of the equipment support column, as shown following figure.
This approach also allows the feed-water outlet piping to run vertically down to the pump before the expansion loop is added.
Fire Proofing
Fireproofing of pipe rack columns is shown in following figure. If hydrocarbons are prevalent, it is common to fireproof the columns to a level just below the lower, rack support beam. If air coolers or other equipment is located above a pipe rack, the fireproofing is
extended to the equipment support beam. This issue must be reviewed with the client; allowances may need to be made for
as much as 4 in (100 mm) of fireproofing.
Flat Turn Pipe Rack
Occasionally, a situation arises in which a flat-turn pipe rack may be employed. This often happens near a dead-end area where the potential for problems is minimal.
As shown below, the line sequence on the left side of the rack must
remain constant as long as flat turns are used. A different elevation must be used at a 900 turn in the rack if the sequence must change, as shown on the right side of the diagram. This approach must be well thought out before it is used.