Shell test for PSV 4

[aizat.mzaki]

Dear All,

For PSV shell test as per ASME VIII Div 1, UG-136(d)(2) Hydrostatic Pressure Test specify to perform the test at 1.5 x design pressure of the part.

For PSV body, e.g. 900# inlet flange x 300# outlet flange, should we test it to the 900# or 300# rating for the shell test?
If we test it to 300# pressure, how do we prove the body can withstand 900# inlet pressure?
If we test it to 900# pressure, can the 300# outlet flange withstand the higher pressure?

Appreciate all the opinion and thanks a lot for the help.

Best Regards

 

[The Obturator]

Hi,

Generally speaking, most, if not all, SRV manufacturers comply with API-526.

API-526 Provides inlet and outlet pressure ratings. For larger sizes these are lower than the actual flange limit, due to the limitations of standard designs. In particular, having a balanced bellows design reduces the outlet pressure rating in early all cases, since the outlet is then limited by the bellows design pressure.

When we talk about a valve body and testing, then hydrostatic testing is done on the body component without bellows. Maufactureres will base their hydrostatic test pressure of the body at 1.5 X the OUTLET DESIGN RATING (manufacturers limit) OR the API-526 OUTLET PRESSURE LIMIT (Conventional valve type), whichever is the higher (same body used for conventional and bellows type).

You will note that outlet pressure ratings for large orifice SRV's is much lower than actual flage pressure limit.

For the inlet, following ASME VIII, It is the nozzle that is subjected to a hydrostatic pressure test. Some manufacturers take the set pressure as the design pressure for this. Generally, this is only applied to cast construction nozzles, though for EU PED, this is a primary pressure containing part and should be hydro tested to 1.5x inlet flange rating in all cases.

The SRV body you see, is not directly exposed to the primary pressure.

Do not confuse the above tests with Pneumatic Shell Testing - this is a pressure test performed on an assembled valve after set pressure and leakage testing. It requires a nominal 7 bar/100 PSIG of air fed into the valve outlet to test the integity of the valve joints (if bellows, same test pressure is fed into bonnet vent to prevent bellows damage).

Hydrostatic testing is done once ony at the manufaturer and certified. There is normally no need to do it as part of a maintenance or overhaul unless there is a specific issue.

Hope that helps.





Per ISO, only the term Safety Valve is used regardless of application or design.

 

[aizat.mzaki]

Thanks a lot avalveman for such a clear explanation. Really grateful for that.

I hope you may provide further clarification with regards to the hydrostatic testing.
As there are 2 type of nozzle for PSV i.e. full nozzle and semi-nozzle.

While the semi-nozzle design will exposed the valve body to inlet pressure (high pressure), can we still apply HT pressure of 1.5 x Outlet Design Rating for the body? The same also applies to pilot type PSV where it does not have a nozzle at the inlet, thus the body is subjected to the higher inlet pressure.

My concern is that, this lower test pressure may not be able to prove the body can withstand the higher inlet pressure in the case of semi nozzle and pilot type PSV design.

Appreciate your kind help and advise sir.

Best Regards

 

[The Obturator]

The first picture is the two spring operated design SRV's. I have covered the full nozzle in the earlier reply.

The other "Semi-Nozzle" design is effectively a non ASME/API design, though you can obtain ASME VIII "UV/NB" certification. These semi-nozzle valve types are more of a European DIN/TUV supply. They are also limied to lower pressure classes. I don't have too much information on the testing of the semi-nozzle design, but would believe that some form of hydro is performed with the nozzle seating area blocked off. This to also test the integrity of the weld of the nozzle to body internally (sometimes this design has the nozzle scrwed in or swaged in by force). The same principle, as before, using the body outlet rating would apply for the body bowl(shell) testing. You would need to contact the specific manufacturer on this since there a few varying designs of his set up.

The pilot operated SRV design depicted may have an inlet hydro done in a similar fashion as the semi nozzle spring operated SRV. Again, different manufacturers have different set ups. In this case the sensing tube and seating would need blanking off for hydro test. Full inlet rating applies to all pilot operated SRV sizes.

For the body bowl (shell), the outlet method is used again. For these designs. the outlet is fully rated for all sizes (D to T orifice).

Per ISO, only the term Safety Valve is used regardless of application or design.

 

[aizat.mzaki]

Huge Thanks avalveman for the clarification.

Really appreciate it sir.

Best Regards,