Misalignment of abutting edges of a pressure vessel during fabrication 1

[raajitha]

Hai gents,

During the process of fabrication of a pressure vessel, consider if a steel plate of any thickness has been rolled to any diameter, what is the maximum allowable offset of the abutting edges after the joint fit up has completed before proceeding to the longitudinal welding?( as per ASME sec Vlll standard)
Hope my querry is clear to you !!

 

[bmoorthy]

Hello Rajitha

The permissible offset is dependednt on the category of joint. For category A joint, the off set permitted is less as compared to Category B or Category C joint. For joint categorization you may refer to UW 3.

For the permissible limits of allowable offsets of (completed joints) you may check UW 33 of ASME sec VIII div 1. You may note that ASME specifies the offset of the completed joints. As regards how much you can permit at the time of fit up, it is common to keep closer tolerance for fitup stage than final acceptance so that you do not land up in problem after completion of joint. Low thickness joints can get distorted during welding and or during back chip and back welding due to improper restraints/supports/improper weld sequence.

You as a QC engineer/Inspector may face a situation where in the fit up was ok and after completion offset is observed. In this case it is the responsibility of your welding engineer.

How much can be tolerated at the time of fitup? Refer to your QC manual, if you already have one. If you do not have one, then in consultation with good welding engineer decide upon and incorporate in your Manual or creat a Manual.

What to do after completing the joint and observe that the offset is more? Use UW 40 (Consult your AI for special material)

Good Luck