Pipe

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First, it has to be safe.....ie it has to support the pipe, with no risk of it falling with enough safety factor built in..

Second, the pipe will have to drain......completely

these guys may have something for you? order some literture it may help?

Phoenix911 stated:

"Second, the pipe will have to drain......completely"

This is NOT a true statement for all services or for all plant types. It is very difficult and very expensive to make ALL pipes drain completely.

The original poster should give more information about the specific plant type and commodities.

Most plants that I have worked on (Refineries, Chemical Plants, Power plants etc.) tried to the the Pipe Support spacing to limit pipe deflection (sag) to 1" maximum.

The pipe sag is, I presume, due to incorrect/ insufficient supports.

This is the one which will guide you in determining the sag.

a) The maximum stress created due to the unsupported pipe (hence the sag)

b) The stresses at the end joints, - the threaded joints, rotating equipment flanges etc should not have stress. The mid pipe flanges stress will be decided by the design and the codes.

c) And also ensure these at the hot/cold conditions.

Depends upon the required industrial standards in your area.