Strength of Partial Penetration Welds

[magusinp]

The company I work for builds instrumentation for the oil & gas industry. The pressure containing parts of one of the products is built to B31.3 They are welding a 2-1/2" s/10 weld cap to S/10 pipe (316/316L). But instead of holding the root gap open and full pen. welding, they lay the cap directly on the pipe and weld. This is not a full pen weld! They don't wantto change so I am asked to determine what the strength of the gauge should be. I can determine this strength using engineering techniques of analysis but I would ask the forum what is the proper method to use. Especially since it is supposed to comply with B31.3

 

[metengr]

magusinp;
What exactly is the weld joint detail? In other words, are they simply butting the cap to the end of the pipe (with no weld root) and filling the groove that is exposed with weld metal?

 

[magusinp]

Yes, they are simply setting the weld cap on the pipe and filling the groove with weld metal. An alternative is offered wherein the welder fuses the lands together then makes filler passes over the fused lands. This seems better, is it acceptable?

 

[metengr]

Yes, the second option is more desirable because you have fused the root and will fill the joint resulting in full penetration. However, let me step back here and ask several fundamental questions;

1. Does the organization that is welding have a qualified welding procedure?

2. Qualified Welders?

Your first description of how the weld joint was made would be unacceptable for use in B31.1 piping applications. This is not a partial penetration weld, this is a weld that would be classified, in my mind, as inadequate penetration. Inadequate penetration is a rejectable weld defect.

 

[magusinp]

yes to both questions...the Qualified Welder offered the fusion weld as an alternative once he realized that this issue was coming to a head. His issue has to do with speed and fixturing. Our volume is not high enough to justify GMAW so we TIG. We are welding stainless steel. To do a full pen weld at present he sets the pipe and fitting on a table and holds the weld gap with a piece of wire and tack welds. Then he puts the tack welded assembly on the turntable and puts a purge at the end of the tube and then welds all around the 2-1/2" pipe. 1 root and 2 filler passes. Now if he doesn't have to hold a weld gap he tapes the cap to the pipe when making his tack welds and he doesn't have to purge the backside of the weld.