Root Cause Analysis of Girth Weld Cracking in a Mechanically Lined Pipeline

Failure analysis was conducted on a girth weld that cracked during pressure testing of a mechanically lined pipeline. A deep-hole flaw was found in the seal-weld region near the weld toe. Lack of fusion and small cracks were observed at the triple junction of the backing pipe, CRA liner, and seal weld, while martensitic microstructure and cold cracks were present in the filler and cover passes. The leakage crack consisted of multiple individual cracks: some initiated in the filler and cover passes and propagated toward the inner and outer surfaces, while others initiated at the triple junction and extended in both directions. The failure was attributed to improper welding procedures and non-compliant operations, which resulted in deep-hole flaws, lack of fusion, microcracks, and martensitic microstructure within the weld joint. The combined action of internal pressure and welding residual stresses promoted crack propagation and coalescence. The martensitic regions in the filler and cover passes likely provided preferential paths for crack propagation.