Dear All,

During internal pressure hydrotest we take advantage of allowable stress = 0.9 * yield stress.

I have one case wehrein jacket chamber MAP is limited by MAEP of inner shell.

now if we do Hydrotest pressure as per UG-99(c) = 1.3*MAEP that inner shell will fail.

Does any body having any reference to increase stress value B from external pressure chart(CS-2) to 0.9*Yield stress for the hydrotest.

Note : Code is silent about external pressure hydrotest.Refer code interpretation : VIII-82-57

Dear moderators please share your views.

As we know this external pressure chart is stress strain diagram.where factor B - stress,factor A - strain.

One of software programe is taking basis of UG-28(2)Step-3 & taking Yield stress as = 2 * B factor for hydrotest check.

But UG-28(2)step-3 is applicable for Do/t < 10 means thick cylinders.

As ASME Sec.VII Div.1 doesnot gives guideline to evaluate hydro test induced stress only div.2 says 0.95*yield but

0.9*Yield stress is generally followed when we are doing internal hydrotest but in above mentioned jacketed vessel case hydrotest pressure will be applied externally than what to do?

Any body having any basis of any reference book/code/specification please share.

Hi Mitul,
May be I have not understood your problem correctly. But I have few comments.
As you said, Code is silent about external pressure hydrotest:
1. Please refer to UG-99 (b). vessels designed for internal pressure shall be subjected to a hydrostatic test pressure. Your case is of external design pressure.

2. Ug 99(f) says that single-wall vessels designed for a vacuum or partial vacuum only, and chambers of multichamber vessels designed for a vacuum or partial vacuum only, shall be subjected to an internal hydrostatic test.