Leak Testing (hydro) w/o Considering Stress Ratios
Leak Testing (hydro) w/o Considering Stress Ratios
(OP)
Hello,
I've been inspecting local fabrication shops and i've noticed that at each one they do not factor the stress ratio [Stress Value of the metal at test temperature / Stress Value of the metal at design temperature].
E.g.:
Contact Tower
MAWP: 1360 psi @ 195 deg F
Leak test was done at 1768 psi @ ~85 deg F (cant remember the exact temperature).
So, they simply multiplied the MAWP by 1.3. I do not have any books with me to find the stress values but I am sure that for that ambient temperature, the test pressure should be much higher. Note, it has 600# flanges.
I did mention it to my superiors and their response was that the MAWP is not "high enough" to consider the stress ratios. The same thing happened with piping.
What are your opinions?
I've been inspecting local fabrication shops and i've noticed that at each one they do not factor the stress ratio [Stress Value of the metal at test temperature / Stress Value of the metal at design temperature].
E.g.:
Contact Tower
MAWP: 1360 psi @ 195 deg F
Leak test was done at 1768 psi @ ~85 deg F (cant remember the exact temperature).
So, they simply multiplied the MAWP by 1.3. I do not have any books with me to find the stress values but I am sure that for that ambient temperature, the test pressure should be much higher. Note, it has 600# flanges.
I did mention it to my superiors and their response was that the MAWP is not "high enough" to consider the stress ratios. The same thing happened with piping.
What are your opinions?





RE: Leak Testing (hydro) w/o Considering Stress Ratios
The calculation in UG-99(b) states that the minimum hydrostatic test pressure, at the top of the vessel, must equal 1.3*MAWP* the lowest stress ratio (LSR) for the materials of which the vessel is constructed. The stress ratio is the allowable stress value at the test temperature - St, divided by the allowable stress value at the design temperature - S. Hence, St/S.
For typical carbon steel vessels (e.g. SA-516-70), S=St up until (and including) 500°F. So, in your example temperatures of 195°F DT and ambient of 85°F, St/S=1.
It's certainly not an issue of the MAWP being "high enough". That's just wrong.
RE: Leak Testing (hydro) w/o Considering Stress Ratios
RE: Leak Testing (hydro) w/o Considering Stress Ratios
You are wrong with stress ratio
You are wrong with leak test. This is Hydrostatic test. Please see ASME V for leak test
Regards
r6155
RE: Leak Testing (hydro) w/o Considering Stress Ratios
By the way, the material is SA-516-70 and Sec VIII Div 1.
RE: Leak Testing (hydro) w/o Considering Stress Ratios