Failure analysis of external thread insulated live joint for metering in gas transmission station

An insulating joint is an important accessory of a cathodic protection system and plays an important role in the safe operation of a pipeline. In this paper, failure analysis is carried out on the fracture cause of an insulated live joint with an external thread. This type of insulated joint is an assembly and the middle part is connected by the butt welding method. The failed insulated live joint with external thread breaks at the welded joint, and the failure cause is closely related to the incomplete welding of the whole circle at the root and the poor fusion quality of the weld. In addition, the welded root of the intact external thread-insulated live joint submitted for inspection is not welded through. Relevant standards are used to evaluate the service capability of the insulated joint with defects, and the suitability evaluation results are unacceptable under operating pressure and design pressure. At the same time, considering the poor fusion quality of the weld, it is recommended to choose the machine for equipment replacement.