Hydrostatic test 1

[m144]

hi
I have a question about hydrostatic test of GRP PIPES, (Glass Reinforced plastic piping materials).
when PN number of a GRP pipe is (for example) 20, means maximum test pressure is 20 bars.
but these pipes test by hydrostatic test at 28 bars in the factory that is more than 20 bars. Why do these pipes hydrostatic test at the test pressure more than PN number?
thanks

 

[LittleInch]

Please see this thread which asks a remarkably simialr question. Are you both working on the same question or project?..

http://www.eng-tips.com/viewthread.cfm?qid=347074

Tip no 1 - before posting do a search on this site for previous answers.

The PN ratings are the maximum long term pressure rating of the pipe which incorporates a safety margin below yield / cracking. A pressure test is permitted once to below this yield / cracking limit to prove the strength of the pipe.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way