Borzki,

In addition to T.J.N's comments, other reasons often cited are:

(1) Utility piping usually has a greater number of large-diameter loops which are more easily located in the upper rack.

(2) The process level is more likely to contain corrosive liquids. If a leak occurred in such a system it could damage any piping below.

(3) Process piping in the rack is more likely to be subject to pump pressure than utility piping. Locating the pumped piping in the lower rack can result in lower pump head requirements.

(4) Some process lines may be expensive alloys. Where the line runs from one grade-mounted equipment item to another, the use of the lower rack reduces the total footage of the piping.

(5) Process lines that are to be run without low-point pockets can be more easily accommodated in the lower rack. This is particularly true at the unit battery limits where the upper rack piping must be looped vertically over the battery limit platform.