A bracket is joined with a fillet weld (GTAW process) all round to a pipe surface and when subjected to great force, the bracket broke off and the fracture is along the centre of the fillet weld.
Part of the weld is attached to both the bracket and the pipe.
I understand the HAZ is the weakest link and from PQT records we know that most fractures are at the base metals.
In the above case, is the weld likely to be too small or due to some other reasons?
Regards
Boon
It sounds like the fillet failed through the throat. That makes sense because that is the shortest failure path through the weld.
Unlike a complete joint penetration groove weld, a fillet weld has a built in failure mechanism, i.e., a crack initiator at the joint root where the butting and non-butting members meet.
The allowable stress for fillet welds in steel is typically 0.3 times the tensile strength of the filler metal (AWS D1.1), whereas the allowable for the CJP groove weld it is the same as the base metal.
You could increase the size of the fillet weld to increase the load capacity, but something has got to fail when the connection is overloaded. Is it better to have the bracket fail or the pipe wall? I would have to imagine the answer depends on what the pipe is carrying.
Best regards - Al
Al has hit the nail right on the head.
id wonder if the weld large enough to support "great force".
The root is suspect in this case, but perhaps someone needs to run the calcs on the design find out if it makes sense.
MDK
AL explained it well
It should be noted that for shrinkkage strain cracks (probably the most common type of crack) on a single pass bead the crack will almost always be in the center of the weld.
for example low melt point inclusions such as lead, zinc, manganese etc will always migrate to the center of the bead, likewise a concave weld profile will put high internal stress on the centre of the weld.
While this doesn't sound like a weld crack due to internal issues, if a fillet weld has been weakened by things like concave craters, contamination etc. A crack will almost always propogate from the middle (on a single pass bead)
Also as mentioned in fillet welds, the weld will almost always fail by means of shear stress across the throat which is by nature the weakest area. By code, fillet weld expected strength is generally equal to shear strength across the throat regardless of what type loading the joint is likely to be under. The only time I would expect a crack at the toes due to loading (in your scenario) would be due to poor fusion or undercut with the base material.
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