Effect of Type B Steel Sleeve Rehabilitate Girth Weld Defect on the Microstructure and Property of X80 Pipeline

Abstract

In recent years, accident caused by girth weld defects is relatively common. The failure mode of girth weld is mostly fracture. It is an effective way to avoid the failure accident of girth weld to find the hidden trouble of girth weld and repair it in time before the failure. The type B steel sleeve is an effective method to repair the girth weld defects. However, quite few works have been carried out on the reliability verification and engineering practice of repairing the X80 pipeline girth welds. Therefore, it is necessary to carry out full-size physical test for engineering and obtain the influence law of welding operation on main pipeline performance, with the aim of reliability of repair quality and service after repair. In the present work, the reliability study of repairing with type B steel sleeve on X80 pipe girth weld defects was verified. The results show that the bearing capacity of the type B sleeve can effectively guarantee the safe operation of the pipeline in the case of leakage from the girth weld. But there are obvious influence on the material properties of the outer surface of the main pipe due to the welding heat. Effects from longitudinal weld seam is smaller than effects from fillet weld. Grain roughening occurred in heat affected zone of fillet weld which results in that the hardness of the main pipe under the fillet weld increased and the yield strength was reduced by 5.5%. Surface cracking occurs during bending test. There is a certain service risk and it should be used under more frequent monitoring than usual.