Metallurgical Failure Analysis of an Elbow Weld

An elbow component that was part of a component cooling water (CCW) line was found to exhibit a pin-hole leak at the weld. The elbow is welded to two pipes that form part of the CCW line; it is suspected that the leak was a result of a weld defect that had been sealed by a coating.

Computed tomography (CT) imaging of the elbow component confirmed a circumferential crack that initiated at the root of the weld and progressed to the surface at the centerline. Additionally, the fit between the butting ends of the elbow and pipe left a gap of 0.123 inch. For reference, a socket weld assembly per ASME B31.1 requires a 1/16 inch gap between the end of the pipe and the shoulder of the socket. The elbow component failed as a result of a stress-corrosion cracking at the weld. The crack initiated at the root of the weld at a sharp contour remnant from the poor weld geometry.