Polyethylene (PE) and its composite pipes have been widely used in the transportation of energy

such as natural gas and petroleum.Pipe welding joints have been proven to be a weak link of the whole pipeline.This means that non-destructive testing (NDT) and safety assessment of these joints are key technologies to guarantee safety of pipeline.In this paper

the theory and method of NDT technology on welding joint of PE pipes

inspection technique of cold welding and safety assessment of welding joints containing defects are introduced.Ultrasonic phased array and coupling focusing technology are applied in the inspection of electrofusion and butt-fusion joints of PE pipes respectively.Figures with inspecting image and cross section of practical joint are given.A cold welding inspection method based on ultrasonic phased array technology was invented

which has clear physics concept and is convenient in application.The defects in the electrofusion joints of PE pipe are classified into four categories:poor fusion interface

over welding

voids and structural deformity.Mechanical tests of joints with different kind of defects show that there are three main failure modes of EF joint under inner pressure

that is

cracking through the fusion interface

cracking through the fitting

and cracking through copper wire interface.A safety assessment method was proposed based on the experimental and analytical results.The proposed method can greatly improve intrinsical safety of such pipeline.