temporary fit up attachments 1

[matschka]

We are fitting & welding a large vessel. Plate thk.
is 1.625 in.The weld joints are being fitted & temporary
steel fit up attachments with a 'rat hole' or weld access hemi hole in the attachment are being welded to the two plates on each side of the weld joint to maintain the alignment. The plates are then being tack welded & then the root, 2nd, & 3rd pass is deposited. Then the joint is being back gouged & welded on the opposite side.Then the opposite side is welded to completion. My question is when should the welded clamps be removed?

 

[unclesyd]

As per your OP the clamps should come off after the back welding is completed. I like to get the alignment fixtures out the way after the hot pass is completed.
If the metal moves on your vessel at this point you have some constraint problems that need to be corrected.