Hydrotest of 3000# fitting

[mehdiza]

Hi

I'm not a piping engineer. I mostly worked on static equipments but a problem happened to me that I will appreciate if piping specialists could help me about.

We have a forged fitting (A182 F321, 3/4" SW tee type joint with 3000#). The end user has requested that hydrotest to be done as per B16.34. while the design temperature is 5 barg (@85 C) they requested a very high pressure around 150 barg for testing. I have tried to read piping standards in this regard but it is still confusing for me. Is really such test pressure needed? If yes, what is the philosophy of such pressure?

I will appreciate if you reply.

Best regards,

 

[Shmulik]

A forged fitting is rated according to ASME B16.11 (Forged Fittings, Socket-Welding and Threaded), while ASME B16.34 is a standard for valves (Valves – Flanged, Threaded, and Welding End).

You are not able to test a Socket Weld fitting when it stands on its own. You may do it only when it is a part of piping system.

Test Pressure requirement is according to the design code and it is limited by material's yield strength.

#3000 SW Fitting is correlated by ASME B16.11 Table 7 to Schedule 80 seamless pipe.

Take the OD of NPS 3/4" pipe: 26.67 mm
Take Sch. 80 wall thickness: 3.912 mm Minus 12.5% pipe's under tolerance = 3.423 mm
First, make sure that thickness is sufficient for systems design conditions acc. to design code requirements.
Follow design code requirements and calculate system's pressure test, considering:
1. Design conditions (pressure and temperature).
2. Material's allowable stress at design temperature and at test temperature.
3. Material's yield strength at test temperature.
4. Test medium (hydrostatic / pneumatic).

 

[mehdiza]

Thanks Shmulik

I used your instruction. The fitting could withstand in such pressures.
But it is still a question for me why applying such pressure for hydrotest. I asked some piping colleagues and they said that in plants - in reality- tests pressures will be 1.5 * design pressure for a line which will be much much less than this value. Also in real operational cases it doesn't seem that we may have an over pressure (If it was the case it shall be considered in design pressure). I still don't understand the philosophy of considering such high test pressure.

 

[Shmulik]

Hi,
ASME B31.3 (Process Piping) requires a test pressure of not less than 1.5 times the design pressure (for hydrostatic test).
Additional important consideration is the allowable stress ratio I've mentioned at no. 2 above. Please see ASME B31.3 ; 345.4.2(b)
If the design temperature is high - the stress ratio is high accordingly, and so the required test pressure.
If your system has nothing to do with high temperature – so, I don’t see a reason to raise the test pressure above 1.5 times the design pressure.

I hope this helps.