Relief Valve Discharge Pipework loads 1

[DSB123]

Hi All,
I have a general question regarding Relief Valves. Does anybody know what limits there are as regards the allowable loading generated from thermal and weight effects (plus seismic) which is allowed on a relief valve from the connected discharge pipework such that the performance of the Relief valve is not compromised?

 

[RVAmeche]

As far as I know that isn't a typical value provided; you should ask the manufacturer if you expect the force from the system to be significant.

As a starting point, I would use whatever guideline your company follows for the class flanges to be used. Another option would be to do a stress analysis, especially if you think seismic is significant.

 

[DSB123]

RVAmeche,
A stress analysis would be undertaken to establish the RV loads from thermal/weight and RV discharge reaction as well as Seismic. What I am after is the Forum's thoughts on allowable loading since using the flange leakage approach could be such that some damage to the RV's seat/body is caused. What do other members of the Forum uses as an allowable.

 

[MJCronin]

I agree with the recommendations for a detailed stress analysis as noted above.

As I recall, the CAESAR-II reference manual also shows an example of exactly this type. The purpose of this sample analysis is to show how a dynamic analysis can be used to qualify the piping system and design the discharge vent pipe supports.

Also see the Non-Mandatory Appendix-II of ASME B31.1 Power Piping Code ....

MJCronin
Sr. Process Engineer

 

[davefitz]

The valve mfr should be able to provide a statement regarding allowable nozzle loads. Performance or relief capacity is also affected by the exhaust piping backpressure.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[DSB123]

Thanks for the responses so far but none are really addressing my question. I appreciate the performance is affected by the backpressure and that a stress analysis is required. However I was trying to solicit the forum members experiences with allowable loads on relief valves from the discharge pipework. The Code say to keep the loads from the discharge pipework to a minimum and the discharge pipework should be supported which is all well and good and I have done this in the past, however, at present there is a stress engineer here who is running the discharge pipework 3.5m from the RV outlet (16" pipe) before turning vertical - support on bend. The RV has a vertical downward displacement of 8mm. This set-up will create a vertical force and moment at the RV connection. My feeling is that this could cause bending of the body of the RV and deformation of the seat.
Rather than responding with advice about other aspects of RV design i would be grateful if the actual question was addressed.

 

[curtis2004]

DSB123,

What is service, and code of construction?
You have to design your discharge pipe to be able to move 8 mm without significantly stressing RV and pipe nozzle.
I have seen steam service PSV which has a gap between PSV discharge pipe and Vent pipe. This will allow some flexibility and lets PSV discharge nozzle movements. Although the gap shall be checked for back blow from leaking.

Thanks,
Curtis

 

[hacksaw]

You definitely need a layot drawing to get proper response.