Cause Analysis on Bursting of X65 High Frequency Welded Steel Pipe

Bursting reasons for the 457 mm×7.1 mm X65 grade high frequency welded (HFW) pipeline was analyzed by means of chemical compositions analysis, mechanical properties test, metallographic examination and scanning electron microscope analysis. The results show that existing cold welding defects in the welding line and disqualification of impact ductility of the welding line were main reasons for the bursting. The effective bearing area reduced because of the cold welding defects and the original cracks initiated and expanded in the welding line. At the same time the ability of resistance the crack spreading was worsened because of low impact ductility of the welding line. So the X65 grade pipeline burst at the welding line under the force of hydraulic pressure test.