SAFETY ASSESSMENT OF COLD WELDING DEFECT IN ELECTRO-FUSION JOINT OF POLYETHYLENE PIPE

摘要

Cold welding defect is the most common defect in electro-fusion (EF) joint for connecting polyethylene (PE) pipe. In our previous study[l], the cold welding defect is successfully inspected by an Eigen-line method based on phased array ultrasonic testing technology. However, small amount of research has been reported on the acceptance criterion of cold welding defect in EF joint. In this paper, the bonding strength of EF joint is measured using a peeling test. The bonding energy of welding interface is calculated both by phenomenological model and deformation energy analysis method. EF joints with different degrees of cold welding are made and used for peeling tests. The results show that the bonding energy of fused interface rises rapidly after bonding and then goes through a plateau region. The starting point of the plateau region in the bonding energy vs. welding time curve is regarded as the minimum required welding time of EF joint. Based on bilinear fitting, the acceptable criterion of cold welding defect is proposed.