vessel head crack

[yonderboy226]

Hello all,

We have a vessel that has formed a crack in the head while in service. I am looking for some suggestions of where to start the root cause analysis. The crack is near the top of the head and runs between the surface welds of a nozzle support and a lifting lug. The welds (mig) are close enough so that there is likely an overlap in the HAZ. The vessel is 316 SST., approx. 12" diameter, with a formed head (seamless) about 1/4" thick operating around 150psi (gas). I was thinking maybe the heat treat of the head or proximatey of the welds? Thanks for your ideas.

 

[metengr]

It is possible the crack was either a weld defect that propagated in service or was a service-induced crack (no pre-existing flaw) from fatigue crack intiation and propagation. To determine the probable cause would require the crack or portion of the crack to be removed for follow-up metallurgical lab analysis. What I would do, is try to excavate the crack with the intent of removing a portion of the crack and surrounding base material for metallurgical analysis. The excavation remaining can be weld repaired after surface NDT is performed to ensure complete removal of the crack, and after weld repair.