B31.1 piping overpressure
B31.1 piping overpressure
(OP)
A steam desuperheater on our project is designed to B31.1 piping code. B31.1 allows a short term overpressure up to 20%. However, according to the vendor of the desuperheater the B31.3 short term overpressure allowance of up to 33% can be utilized, even though the desuperheater is designed to B31.1. Is it acceptable to use the B31.3 overpressure allowance for an item designed B31.1? The obvious answer is "No" as these are different codes, but wondering if anyone has a different interpetation of the codes.
Thanks.
Thanks.





RE: B31.1 piping overpressure
RE: B31.1 piping overpressure
In particular ,for components operating at low temperatures where UTS or YS define the allowable stress, there might not be sufficient safety margin in the B31.1 allowable stress values to permit a 33% sustained overpressure- the allowable stresses were recently increased to be more competitive with european codes, and the 33% overpressure is equivalent to a continuous hydrotest for low temperature components.
Also, the valve design codes only allow a 10% overpressure, and that is only permitted during safety valve lift events. Which birngs up another good point- what exactly are teh safety releif valves doing during this 33% overpressure event?
RE: B31.1 piping overpressure
Yes, the purchase order/datasheet for the item states that it is to be designed to B31.1 (there is no mention of B31.3).
The reason for using the short term overpressure is that the water side of the desuperheater has a higher (~30% higher) design pressure than the steam side. There is no safety relief valve protection on the steam side. There is a possibility that the steam side may be blocked in and see the water side design pressure.
RE: B31.1 piping overpressure
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
www.waterhammer.bigblog.com.au