hi!
I can't find any description about stress under hydro. test pressure in ASME VIII-1, but the software (pvelite) supply two option for it: one is the stress under hydro. test less than 1.3 allowable stress under room temperature, the other is less than 0.9 yield stress, I want to know why. so please help me for my confusion.

During hydro test, the general memberane stress should not exceed 0.9 times the yield or 0.2% proof stress....It is good engineering practice that is normally followed.
ASME Section I(PG-99) mandates the over stress during hydro not be greater than that stated above.

_________________
Thanks & Regards,
Nasir
Welding Engineer
DESCON Engineering Limited.
Lahore, Pakistan.
Mobile # 0092-336-4145402

gd_juan,

You may also refer Clause 4.1.6.2(a) of ASME-VIII-2-07ed., which says that general primary membrane stress during hyrotest shall not exeed 0.95Sy.
Although ASME-V111-1 is silent on allowable stress for hydrotest conditions, the Div. 2 philosophy is often extended to vessels designed and tested in accordance with Div. 1 of Code.
Please note that pre-2007 Div. 2 edition allowed general primary membrane stress during hyrotest to 0.9Sy only(refer AD-151.1 of Div. 2 code), which has been revised to 0.95Sy in the 2007 edition.

Thank for you answer.