Minimum Required inlet piping opening per ASME Section VIII Div 1 UG-135 (b)(1)

[0NE]

I was wondering if anyone had experience with ASME Section VIII Div 1 UG-135 (b)(1) and the minimum required pipe/fitting area between an ASME Section VIII Vessel and its thermal relief valve. UG-135 (b)(1) states:

The opening through all pipe, fittings and nonreclosing pressure relief device (if installed) between a pressure vessel and its pressure relief valve shall have at least the area of the pressure relief valve inlet.

The existing configuration that its being investigated is a short NPS 1/2 SCH 40 pipe (welded to the pressure vessel), 1/2"x3/4" NPT reducer and a 3/4"x1" NPT relief valve. The question around UG-135 (b)(1) is what the "area of the pressure relief valve inlet" refers to? Does this mean the relief valve should be no greater than a 1/2" inlet like NPS 1/2 SCH tank pipe? Or is this relief valve inlet area referring to the relief valve orifice diameter?

Thanks

 

[racookpe1978]

If your calculation required a 3/4 nominal diameter relief valve, you MUST connect that PV to the relief valve with a 3/4 nominal pipe. Outlet pipes from the relief valve to atmosphere (or a vented retention tank) must not be smaller than the relief valve outlet nominal diameter.

Extreme lengths (of either minimum diameter) pipe are not allowed either in suction or discharge of the relief valve. Intent being "Thou shalt never strangle flow to a closed Pressure Relief Valve, nor shalt thou ever prevent flow out of the an opened Pressure Relief Valve."

 

[0NE]

Thank you for the reply racookpe1978. In this case the vessel was supplied with a short NPS 1/2 connection for thermal over pressure protection. The required thermal relief capacity for this vessel was calculated to be ~10 USGPM, and both a 1/2" inlet or 3/4" inlet RV can handle this capacity. The as found state of the vessel was with a 3/4"x1" relief valve. I was wondering if the 3/4" inlet relief valve on the vessel should be changed to a 1/2" relief valve inlet to meet the code requirement of ASME Section VIII Div 1 UG-135 (b)(1), or whether it is acceptable for the 3/4"x1" relief valve to remain in service. The confusion is whether it is acceptable to have a relief valve with a larger nominal inlet size (3/4") than the piping (1/2") between the relief valve and the vessel.

Thanks again

 

[nickelkid]

One, I would try to not use a larger relief, it will only raise questions.

 

[GenB]

Required minimum is the orifice of the safety valve. Also required same or smaller of the fitting to which is attached. Never can be larger. Saying that the 1/2 in is the appropriate valve by the ASME B&PV Code.