ASME B31.3 Hydrotest limit considering Yield

[PSSC]

I have been in the process of revamping several process piping systems that need to be hydro tested.
I have the original drawings with the hydro test pressures.
They do not seem to take into account the prevision of not exceeding the yield strength of the material at the test temperature.
I have always used the values from Table A-1.
Specifically the value of "Min Temp to 100", for the test temperature strength.
This is usually lower than the "Specified Min. Strength".
Am I using the correct value?
If I used the higher value I think the original hydro test values would be acceptable.
If not I am guessing no one paid attention to this part of the code.
What is the customary value to use?
Thanks in advance.

 

[ijzer]

For checking the stress during hydrotesting you should compair the calculated stress with the yield , also to be found in table A-1 . You should stay below that value ( usully one uses max. 90% of this yield value). The value "Min Temp to 100" shall not be used for that purpose because it comtains a safety factor of at least 1.5 to the yield and as such wpuld limit the test pressure to much.

 

[PSSC]

Thank you for your reply.
I had started to figure out by reading other threads here, that the Min to 100 value was not the correct value to use.
But it's always nice for someone to confirm it!

Thank you again.

 

[pennpiper]

PSSC,
Here is something you might want to consider.

You wrote that you were "revamping several process piping systems." Revamping means that they are existing systems.

What are these systems?
When were they designed, fabricated and installed?
What Design Code was used and what was the Date of issue in effect at the time?
Are you designing to the same Code and Issue?

 

[Duwe6]

Unless this is a 100% welded pipe system, the flanges will limit the max hydro pressure *far* short of the pipe yield stress. Per the ASME B16 flange spec, max hydro for P-1 carbon steel flanges is 420 psi and 1080 psi for Class 150# and Class 300# flanges, respectively.
For P-8 stainless steels [304, 316, 347, etc.] the max pressure is 345 psi and 900 psi, for 150# and 300#.
These are derived by taking 1.5 times the max allowable room-temperature flange design pressure.

FYI, A-53 GrB pipe is hydroed in the pipe mill MUCH higher than the above [as are all other ASME pipes]. 2"NPS Sch 40 at 23500 psi, 4"NPS Sch 40 at 2210 psi, 4" Sch 80 at 2800 psi. This is why the hydro of a pipe system is only to test the welds. The pipe has already passed a VERY heavy hydro in the pipe mill.