Query

One is a fraction of the other and the fraction used depends on the vessel and what it is being used for.

• A steam locomotive boiler might have a design pressure of, say 210lb/sq.in for cold hydraulic testing purposes, and a maximum operating pressure in steam of ²/₃ this at 140lb/sq.in, for example.

The design pressure is always higher than the maximum operating pressure so as to allow for the higher operating temperature, and to allow for corrosion between scheduled insurance inspections.

In all cases, the design pressure and the maximum operating pressure will be stated on the insurance company's surveyor-inspector's report for the pressure vessel in question, which will be found in the general register for the equipment concerned.

See this previous thread:

http://cr4.globalspec.com/thread/30865