Using WRC-107 for pipe support bkt clips

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It is my understanding that WRC-107 analysis is used to evaluate shell stresses that result from loads on pipe support bkt clips. My question is how correct is it to do so? I think WRC-107 analyzes nozzle loads with the assumption that the nozzle is set in. That is not quite the way a bkt clip is typically welded to the vessel shell. Further if WRC-107 suggests a repad, the repad is welded the shell and the clip is welded on top of it. Well, the analysis assumes the pad to be welded around the clip and not the clip welded on top of the pad. I think, if you put the clip on top of the pad, the thickness of the pad does not quite matter as all the load is taken up by the pad welds - it would be weld size that would matter and not the pad thickness. Thus the pad is just helping distribute the total stress over a larger area, it is not alleviating the stress in the way WRC-107 assumes it is doing. Please correct me if I am wrong.

For example, if you do WRC-107 analysis for some loads on the clip. The analysis suggests a 1" thick pad with 4" width around the clip. Now if you weld clip on top of the pad, all that 1" thick plate is not doing anything but transfer all the load to the shell thru the welds. Well a 1/2" thick plate will also do the same. Thus in this case, are the actual stresses in the shell more than what WRC-107 calculates? (In other words are actual stresses in the shell more than the allowables)

 

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What is normally done with WRC107 or WRC297 is:
1)check the stresses at nozzle weld using the combined thickness vessel wall+pad
2)check the stresses at the periphery of the pad using vessel wall thickness alone (and this is often the controlling condition)
You can't do check 1 for a support clip, but check 2 remains valid: this is what I currently do.

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