ASK MTI - PUBLIC DISCUSSION

I have a section of piping that I am replacing with a 150# flange. This piping system has a PSV with a set pressure of 100psi. Is hydro testing the newly fabricated piping to 1.5 x 285psi the only option? Or is hydro testing to 1.5 x 100psi allowed? Thank you.

Jesse,

The design MAWP is usually designated through your piping specifications. These can refer to ASME 16.5 which then puts your design MAWP at the limitation of the flanges. If there is a listed design pressure and temp then you would use those values.  In turn, this will set your test pressure to the 285 @ 1.5 on based on a 150# CS flange. If you have heat and material balance sheets, these might contain design pressure and temps as well. 

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Brandon Stout
Reliability Engineer
Nouryon
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Hello all

Lets call 

- P_d  The design pressure (internal pressure)
- S_t The allowable stress of the prevalent piping material at Test temperature

- Sd The allowable stress of the prevalent piping material at Design temperature
 (x = multiplication)

Hydrostatic test for piping system                                          Pt=1.5xP_dx(S_t /S_d) 

or 1.5 times the design pressure multiplied by the stress ratio at test temperature to design temperature

As you write wrote that the set pressure for the PSV is 100 psi so the design pressure must  be less than 100 psi, so the 1.5x285 either contain the stress ratio (correction for temperature) or  the design temperature greater than the test temperature.

If you give us the prevalent construction material , design temperature , test temperature and design pressure, I will calculates for you the hydrostatic pressure (as given by B31.3)

For the ¨PSV  It must be blocked or removed during the hydrostatic test


Regards 

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Elhazel Aymen
Mechanical engineer
Groupe Chimique Tunisien
Tunisia
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Hi Jesse,

You would want to test the new piping at the recommended 1.5 x 285 psi. You should either remove the PSV, if possible, or blind it off from the piping being tested.

Jesse - as others have said it is wise to test to flange pressure test limit. An important rationale is that now you have to track this replacement piping system as having a lower design pressure from the rest of the piping system that exists (likely originally tested to flange rating). This means extra diligence in the long term to track this and in many cases gets lost in the usual industry practices of 1.5x flange design.