4.2　Layout of Piping

4.2.1　Layout of the piping on piperacks should comply with the following requirements：

a）Piping with large diameter should be routed close to piperack columns，and piping with small diameter，piping for gas service and piping for utilities service should be routed in the middle of piperacks.

b）Piping requiring thermal compensation should be routed on one side of piperacks to facilitate installation of -shaped compensator.

c）Piping for fluid service at operating temperature equal to or higher than 250℃should be routed in the upper layer of piperacks.If the piping for fluid service at operating temperature equal to or higher than 250℃is routed in the lower layer of piperacks，it may be routed on the outside of piperacks，however，it shall not be adjacent to any piping for liquefied hydrocarbon service.

d）Piping for utilities service，such as steam，plant air，nitrogen and instrument air，and process piping for gas service should be routed in the upper layer of piperacks.

e）Piping for liquefied hydrocarbon and corrosive fluid services should be routed in the lower layer of piperacks，however，piping for corrosive fluid service shall not be located just above electric motors.

f）Piping for cryogenic fluid service should be routed in the lower layer of piperacks.

g）Piping for cryogenic fluid service，piping for liquefied hydrocarbon service and other piping requiring avoidance of heat radiation shall not be routed just above the piping for hot fluid service or shall not be routed adjacent to the uninsulated piping for hot fluid service.

h）Process piping may be routed in the upper layer or lower layer of piperacks based on the elevations of equipment nozzles to be connected at both ends of the piping to avoid pocket.

i）If the piping for hydrogen service is routed with the piping for other services in the same piperacks，the piping for hydrogen service should be routed on the outside of piperacks and in the upper layer of piperacks.

j）Electrical cable tray and instrument cable tray should be installed in the upper layer of piperacks，and any piping releasing heat shall not be routed near or just below the cable tray.

4.2.2　If the piping for oxygen service is routed with the piping for flammable gas or flammable/combustible liquid service on the same piperacks，the piping for oxygen service shall be routed on one side of piperacks，and should not be routed just above or just below the piping for flammable gas or flammable/combustible liquid service.The clearance between piping arranged in parallel shall not be less than 500mm，and the clearance for line crossing shall not be less than 250mm.

If welded joint is used for the piping for oxygen service and no valves are installed，the clearance between piping arranged in parallel may be taken as 250mm.

The piping for oxygen service and piping for flammable gas or flammable/combustible liquid service should be separated by the piping for utilities service.

4.2.3　Valves，flanges or unions in piping shall be arranged close to piperack beams.

4.2.4　If slope is required in piping on piperacks，such measures may be taken as to change the height of pipe shoe，put section steel beneath the pipe shoe or plate shims on the beam.

4.2.5　Layout of disposal system headers on piperacks should comply with the following requirements：

a）Headers should be routed in the top layer or above the column of piperacks.

b）Headers slope should not be less than 0.003，and shall be sloped towards to knockout drum.

c）Headers should use natural compensation.

d）Laterals with nominal diameter equal to or larger than 50mm shall be an entry at 45° to the top of headers axis along flow direction.