A closed relief valve system with a discharge pipe of 4", discharges gas into a 12" header. The header is anchored to the ground near the discharge point to the atmosphere. Therefore, thrust at the header/atmosphere inteaface is not transferred to the 4" discharge pipe. In this case, is it reasonable to assume that there is no load on the discharge pipe due to relief valve operation (relief valve opens in 10 milliseconds runs fully open for 1 second and closes in 10 millseconds)?

It is my understanding that acoustic shock due to sudden change in fluid momentum and associated travelling pressure wave as result of relief valve operation in gas systems does not generate forces large enough to be concerned of the pipe stresses. This phenomenon is important only in liquid systems. Therefore, for gas systems these forces can be ignored. Can some please comment.