Application Of Ultrasonic Phased Array Technology In Quality Inspection Of Gas-fired Polyethylene Pipe Electrofusion Welding

With the continuous development of urbanization,the gas penetration rate is rising,and the proportion of polyethylene pipeline in city gas transmission and distribution system is increasing.Due to its excellent corrosion resistance,PE pipes have been widely used in mediumlow pressure and some sub-high pressure transmission and distribution pipelines except highpressure sub-high pressure gas pipelines.As a way of connecting branch pipes on in use pipelines,electrofused saddle fitting has the advantages of no stopping gas,less leakage,less risk and less influence on downstream users,so it is widely used.However,it is also found that saddle type welding requires better welding quality than socket type welding.In addition to appearance testing and pressure testing before ventilation,a reliable non-destructive testing method is needed to detect welding quality.With the rapid development of city gas in China in the past 30 years,rich experience has been accumulated in controlling the welding quality of steel pipes in the construction field,especially in the aspect of non-destructive testing.Various testing techniques have been perfected.The defects of metal welding can be found in time during the inspection and acceptance stage by means of ultrasonic,radiographic and magnetic powder non-destructive testing..Polyethylene is a kind of non-metallic material.Although the welding principle is as same as the metal material,that is,it is melted and integrated by heating,it is not as widely used as metal tube in welding quality testing,especially in non-destructive testing.With the development of ultrasonic phased array technology,the welding defects of polyethylene can be clearly displayed on the instrument.Non-destructive testing methods will be more and more used in the detection of polyethylene pipe welding.In recent years,due to the characteristics of polyethylene materials,ultrasonic phased array testing technology is more reliable in electrofusion than in butt fusion joint detection.Polyethylene pipe used in gas pipeline,due to the rigorous consideration only using butt fusion or electrofusion.Under normal conditions,the joint strength of the two types of connections can be greater than that of the base metal,but in the course of application,many joint strength failures occur.The existence of these defective joints in city gas transmission and distribution system seriously affects the normal operation of social economy.Previous studies in electrofusion welding are biased towards the quality detection of socket welded joints.In this paper,the non-destructive testing of electrofusion saddle welding and the "cold welding characteristic line" in electrofusion welding are studied.Based on the analysis of the application of phased array technology in the existing projects,this paper summarizes the phased array technology at this stage,analyzes the shortcomings and puts forward the practical testing standards and the main problems to be solved in the future.