This is my opinion!
When RPad is required only to reduce local stress generated by external piping on a vessel (WRC 107) or piping, the width of Rpad should be enough so that the local stress generated at edge of the pad are within stress allowable limit.
Above check is done while doing WRC 107 hence width of the Pad is iterated to a standard value and finalised.
In case of pipe, I am a not sure that we can proceed with WRC calc. (Even if geometric parameters may be within limits as specified by WRC107, the boundary condition is different- here we have just support/guide rather than an anchor). You may go back to Prof. Bijlaard's paper can come to a conclusion.
Presuming d/D>0.15, Having a Rpad dia greater than 2*d might not be effective for analysis purpose (which means stress generated is no longer a local stress) and taking practicality of welding it.
Hence, above thumb rule of " 2*d and thickness of T" should be good.
Edited by stressguy81 (02/16/11 01:15 AM)