hi every body
in the project I'm following, the hydrostatic test for onshore section is 1.5*98 +10 barg.
according ASME B31.8, the test pressure is 1.5 times OP. why do they add 10 barg? please explain me. thanhk.

It could be simply a client preference, however in your particular case it is especially unfortunate because that puts your 157 barg test pressure higher than the ANSI#600 test pressure allowable (156 Barg) by just 1 bar. Dropping that seemingly arbitrary 10 Bar addition and strictly follow the code reqirement would allow you to use ANSI#600 flanges, whereas now technically you would have to go and upgrade to 900# just to legally reach that bloody 157 Barg test pressure. The +10 Bar seems to be an exceedingly blind-sided requirement in this case. I'd duke it out with the client before I went to 900# class just to make some seemingly arbitrary test pressure. There is no techical justification for it that I can see from here. Ask your client why, then explain to them what I just told you above.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

I see a lot of arbitrary nonsense added by clients to test requirements. I've had good luck with going to clients and explaining the problems that their arbitrary and capricious rules cause. I'm with BigInch in his excellent recommendation.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.