Failure of piping sockolet /weldolet

[Dlew]

What can the major causes of sudden failure of piping sockolet /weldolet other than piping vibrations and if they are even ruled out?
Piping itself could be heavy, unsupported even if the vibrations were not present?
Welding quality issues?
What else?

[arcpro]

I believe Even with no vibration that even when there is no vibration, excessive loading due to unsupported branch piping weight, valve weight hanging from the branch, instrument manifold weight, thermal expansion loads, settlement of supports, misalignment during installation can cause the o-let damage.
The o-let acts as a stress concentration point. A small branch connected to a large header may look strong, but if the branch is carrying significant bending moment, the weld toe becomes highly stressed.

[irish]

Existence of thermal stresses is normally overlooked.
Examples include steam tracing، cyclic startup/shutdown, hot process line connected to colder branch, differential expansion between header and branch.
Repeated thermal cycles can cause thermal fatigue cracking, low-cycle fatigue, crack initiation at weld toe. Check if you can identify any of these.
Indicators are multiple fatigue crack origins, beach marks under microscopy, and cracks perpendicular to principal stress.

[mechcolor]

Even in the complete absence of vibration, a heavily loaded or poorly supported branch connection can accumulate high bending stresses and fail at the sockolet/weldolet weld region. Thermal fatigue and fabrication defects are the next most frequent contributors.

[Dlew]

What about an inherent weld defect or design deficiency itself?

[arcpro]

Inherent weld defect obviously could have contributed to this failure.
Some failure analysis should actually take you to that conclusion.
However, at the start of all this investigation, keep all the causes in front.
Design deficiency sure can contribute very well as these connections upon certain loading may give away like what happened in your case.

[Dlew]

Should we be running some sort of an inspection plan on similar welds in similar piping system installed at the same time, if a design deficiency is picked?

[irish]

yes Dlew, you might want to extend inspection to welds in similar service /material /system to look for welding defects.
Have you already identified that there was some design /construction /welding deficiency?