Research On Polyethylene Pipe Butt Fusion Joints Based On Ultrasound Phased Array And Nonlinear Ultrasound Technology

High density PE pipeline is widely used in city gas pipeline for its excellent performance.In the field construction,due to the influence of welding process,welding environment and welder technology,some defects such as holes,inclusions and lack of fusion will be produced in the butt joint of polyethylene pipe.At the same time,due to the diversity of the long-term service environment of the pipeline,it will cause the aging of polyethylene pipes,which all will bring great safety risks to the safe operation of polyethylene pipes.In this paper,based on ultrasonic phased array and non-linear ultrasonic testing technology to study the detection method of polyethylene pipe hot melt joint defects and aging problems.The main work is as follows:(1)A custom-made water wedge with an angle of 35 ° was used to replace the traditional plexiglass wedge.Ultrasonic phased array detection technology was used to detect the customized polyethylene test block with different sizes(1 mm,2 mm,3mm in diameter)and depths(10 mm-50 mm)cross-hole defects.And through the defects on the actual polyethylene pipe to conduct a verification study,the results show that the defect detection effect on the test block and the actual pipe is similar.(2)The detection probability(POD)was introduced to analyze the influence of different factors on the detection rate of PE pipe butt fusion joint.The results show that the depth of defects can be detected under the condition of 95% confidence and90% detection rate.The 2.25 MHz probe is 26.21 mm and the 5 MHz probe is 14.98mm;The 2.25 MHz probe is used to detect 2 mm and 3 mm defects.As above,the depth of defects that can be detected is 27.78 and 28.88 mm,respectively.(3)Polyethylene samples for non-linear ultrasonic testing were prepared,including polyethylene cold-welded butt fusion joint,and polyethylene aging samples obtained by artificial accelerated aging methods of compression creep,etc.A non-linear ultrasonic transmission detection system based on RAM-5000 SNAP was established for experimental research..(4)A non-linear ultrasonic test study on polyethylene samples showed that:Non-linear parameters ? can effectively characterize the presence or absence of aging polyethylene pipe samples and joint samples,and the measured at the butt fusion joint is larger than the pipe;When the artificial accelerated aging test is performed without loading pressure,the more severe the cold welding(less heat absorption time)of the joint,the higher the measured nonlinear parameters ?,The 40%,60%,and 80% cold welded joints are 0.0237,0.0223,and 0.0214,respectively.After loading,the non-linear parameters ? of the hot-melt joint decrease from 0.0248 to 0.0229 and then increase to 0.0254 as the degree of cold welding decreases,with a trend of decreasing first and then increasing.