SRV discharge piping - minimum wall thickness?

[kclim]

Is there any guidance in the codes (31.1 in particular) as to the minimum wall thickness for safety relief valve discharge piping, immediately downstream of the valve?

I assume that it will be more than a simple pd/2t calculation, and requires consideration of reaction forces when the valve is operating.

TIA

 

[MJCronin]

kclim..

In ASME B31.1, there is an APPENDIX 2 that addresses the desihn of safety relief valve systems and the pressures generated within the system upon actuation.

For most cases, you will find that Sch 40 piping is acceptable. I have never heard or encountered a system that was any thicker than schedule 40.

In my opinion, I would not use piping that was any less than Sch 40 because of the shock generated during SRV actuation. Having a "stiffer" system that is able to take the internal shock generated is advaiable.

Be sure that the pipe diamter is adequately sized for the service. A good rule of thumb is: Systems reliving steam or flashing fluids, make the tailpipe size two pipe sizes larger than the SRV outlet size by ; for all other services, one pipe size larger..

My opinion only.....

Anybody else have guidelines or websites to offer ?

-MJC

 

[davefitz]

The code appendix that MJCRONIN refernced is a good place to start. However, the curves in that appendix are only valid for short stacks with few elbows and no outlet restrictions ( ie, fL/D < 2.0).

If you have a longer pipe with many elbows ( ie, fL/d > 2.0), then you will need to use the compressible flow equations for adiabatic, perfect gas flow ( Fanno flow), to predict the pressure immeidately downstream of teh relif vale ( at the inlet to the exhasut pipe). Outlet restrictions such as silencers or manifold for joining other flows will add more pressure drop and increase the pressure.

 

[MJCronin]

I agree with davefitz....

kclim: what is the geometry of your discharge piping ?

-MJC