2 replies to this topic

[libn999]

Hello, 

I am looking for some guidance with ASME hydro test pressure.

 

ASME code specifies the minimum test pressure as 1.3 times the MAWP at test temperature.

 

I have seen in general practice, engineers using 1.5 times the MAWP at the design temperature, claiming it will be satisfying the ASME requirement (mentioned above) at the same time it wont let the stress go above the yield limit.

 

But is it true? there could be some cases when this general practice pressure values going less than the ASME minimum limit?

 

 

Libin

[Art Montemayor]

Libin:

 

The following are my opinions on this subject and the basics of how I ran my projects for over 50 years during which time I functioned as a process engineer, project engineer, Production Manager, Project Manager, and Project Director.

 

It is basically the process engineer that dictates the characteristics and scope of the operations of the process vessel in question.  On some occasions a mechanical engineer has the capability of doing this also, assuming he has a strong process background.  The engineer coordinates the fundamental and basic design with a mechanical engineer who usually does the mechanical vessel design and it is during this design phase that the ultimate hydrotest pressure required is identified.  In all the projects that I was involved in, I always employed the traditional 1.5 ASME hydrotest formula.  This was the level of design hydrotest used by all engineers that I worked with at that time and the level of the hydrotest pressure was not lowered until recently (about 10 years ago, if I remember correctly).

 

If you fix the ASME Section VIII-1, UG-99, 1.5 rule at the outset, it is the mechanical engineer designing the vessel that allows for the safe test pressure that will not exceed the material’s (steel?) yield limit.  Therefore, you should not have any concerns regarding this issue.

 

If you employ the 1.5 Rule, then I don’t understand how your concern for having a vessel tested at a pressure below that level.  What, specifically, are your concerns?  Is it the safety of the test?  Or is it the safety of the ultimate pressure imposed on the vessel in the event of a process upset or other high pressure?

[Technical Bard]

Art - in 1999 ASME changed the safety margin in Sec VIII Div 1 from 4 to 3.5, and therefore also lowered the test pressure margin from 1.5 to 1.3 such that test stays below yield.  Vessels designed to the code prior to 1999 will have test pressures of 150% of MAWP.  Newer vessels will have test pressures of 130% of MAWP because the allowable stresses in the code tables were increased.