Hi All,

Sometimes we receive jobs where we have to rerate the piping at higher temperature or pressure. In some situations the required code hydrotest pressure becomes higher than previous hydrotest pressure and a rehydrotest is needed.

In such situations we check if pipe is Ok for new hydrotest pressure. We check the thickness of pipe for hydrotest pressure using the equation given in B31.3 but using 90% of yield stress as allowable. We also use the same equation to calculate the required thickness for design conditions.

In one such situation we have Wc less than 1 due to very high temperature. We checked the thickness for the design pressure and temperature using Wc less than 1 as required by the code. While checking the pipe thickness for hydrotest I am not sure whether we should use Wc or not. One argument is that since piping has been in operation for many years, the weld strength may have gone down and therefore we should use Wc in our calculations.

To summarise should the Wc factor be used when checking the suitability of a pipe in the hydrotest case?

Could any senior member comment on this please?

Thanks and regards

MW