Cracking failure analysis on a high-frequency electric resistance welding pipe in buried fire water pipeline

Abstract

Leakage of a buried fire water pipeline occurred after in service of 15 years. It was manufactured from a Q235B carbon structural steel plate by high-frequency electric resistance welding. The water pressure increased from 0.8 MPa at a normal operating condition to 1.2 MPa at the tube burst moment. Cracks propagate along the weld and incomplete fusion defects are observed. This paper aims to explore the cracking failure through a combination method of experimental tests and theoretical analysis. The metallographic analysis clearly shows that the crack is located in the fusion zone and grains are coarse in that zone. Mechanical property tests indicate tensile properties of the anti-corrosion layer meet requirements. Finite element analysis reveals that the pipeline with an incomplete fusion can safely operate under a pressure of 0.8 MPa, while fracture occurs under the pressure of 1.2 ∼ 1.3 MPa. The results indicated that the deep unfused defect of the welded joint was the root cause of cracking, and selective seam weld corrosion also played an important role. The failure progress and mechanism were discussed in details.