MAWP vs Hydrostatic Test Pressure

mgeorgiadis · **Joined:** Mon Jul 04, 2011 3:58 pm **Posts:** 14

Hi
Please advise because I'm new in this field but require some pointers:
I am designing a vessel for 1000KPa int. pressure. The "code" calls for 1500KPa test pressure. But I would expect the vessel to burst if stressed to 1.5 x the design limit. Assume no reduction to yield strength used.
Am I missing something?
Michael

Javed Nasir · **Posted:** Mon Sep 05, 2011 2:54 pm

mgeorgiadis,

Would you like to tell us Code of construction?
If it is Section I then it is okay 1.5*MAWP, see also PG-99.
If it is Section VIII-1, then 1.3*MAWP*LSR, see also UG-99.
What is the design temperature? and Material of construction?
Greater is the design temperature, safer is the vessel when the vessel is tested at a higher test pressure.
You have to check overstressing during hydro if you want to perform hydro test at a greater test pressure than that Code requires.

mgeorgiadis · **Joined:** Mon Jul 04, 2011 3:58 pm **Posts:** 14

Thank you for the reply back. The code is ASME VIII Div. 1. So I will take from your reply the hydrotest pressure is 1.3 x the design pressure. I assume the LSR is a factor due to temperature. If the temperature is 100deg, it can be just 1.3 x design pressure. But I am still not understanding why test at the design pressure x 1.3? My intuition tells me to test at the design pressure and allow operating pressure be be less by some factor of safety?
Please explain this to me so I can understand the idea of testing above a design limit.

Javed Nasir · **Posted:** Mon Sep 05, 2011 5:28 pm

mgeorgiadis

Question: But I am still not understanding why test at the design pressure x 1.3?
Reply: Because it is written in the Code.

Why you are afraid of performing the test at 1.3*MAWP? You should know there is a factor of safety 3.5 on UTS and 1.5 of Yield strength (both yield and UTS are taken at design temperature). So 1.3 is not harmful if you understand these factor of safety. For further details of these factors of safety, please see Mandatory Appendix I of ASME Section II Part D. Test pressure is 1.5 times the MAWP in Section I and B31.1 as I already pointed out in my above message, the reason is safety factor on yield.

mgeorgiadis · **Joined:** Mon Jul 04, 2011 3:58 pm **Posts:** 14

Yes thank you Nasir, now it makes sense to me. Kind regards to you

MAWP vs Hydrostatic Test Pressure

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