scope:

Description of Driving Event:

During dimensional inspection of orbital tube welds involving 316L tubing, it was found that 8 of 8 welds failed because of weld mismatch. The weld joints were located between two bends that formed a "S" bend. There was approximately 1 inch of straight tubing from each bend to the joint of the weld. The mismatch in this case is not to exceed 25% or 0.010 inch which ever is less.

Root cause: Tube bending / shaping typically causes the tube to take an oval shape, creating matching problems during weld fitting. Engineering drawings provided insufficient length for oval / runout to occur of the shaped / bent tube prior to welding of the joint.