hydrostatic test

[ali119]

hi
I have a quesion 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

 

[cloa]

That's a composites or piping question not a metals question. Probably Piping forum prefered.

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[tamal1475]

PN 20 means pressure rating of 20, ie. maximum working pressure not test pressure.