LACK OF FUSION ON SOCKET WELDS

By ROLAND RUSCA Date 02-21-2008 17:00

Hello again gentlleman, this is the Data,
Soxket welds with Superduplex 1/2" OD tubing, welded Tig, inspected VT, PT and hydrotested all acceptable per code.
We sampled some of the welds and did destructive testing ( macro, micro, hardness test and feriite content )
on the macro pictures in all of them we have LOF showing at the root, on the cut out pieces you actually can see it with the naked eye.
RT was performed before the destructive testing and the film also shows LOF.
Any comments on this issue will be of great help, previos history , similar cases anything, .. Thanks

By Kix

Date 02-21-2008 20:40

Is it only in the root area or does it extend all the way to the toes of the weld? More LOF on one side then the other? What position was the test done in?

By aaronshermer Date 02-25-2008 14:54

It has been my experience that L.O.F on socket welds are greatly in part to filler metal size selection. For the record, use the smallest filler metal wire you WPS will allow on all passes. Off the record, make a first pass "autogenous" (without filler metal) and there will be no L.O.F. in that weld joint.

By js55

Date 02-25-2008 15:11

My thought would be that an autogeneous root with superduplex would be a mistake. It is critical that you minimize time at temperature to avoid element segregation (predominantly Mo) and nitride formation, as well as destroying phase balance in a base material with a chemistry not balanced for welding regimes. Even given that too little heat input can be just as damaging.
My guess would be that undergoing the typical SDSS testing regimes wuold fail if too much heat has been imposed on the base metal and I believe the autogenous pass would impost too much heat. This is the same logic that prohibits autogenous passes(dry washes) for repairs or appearance sake.
Fillers for these alloys will be sluggish inany case. I think the smaller filler size is good advice. But you have to keep the heat input within the acceptable window.
If SDSS has been chosen it is generally for a reason.