Study On Mechanical Properties Of Fused Joints With Defective Polyethylene Gas Pipeline

City gas pipeline has a rapid development scale as the speed of gas production and consumption growth, and town gas pipeline total mileage will reach60×104km at the "twelfth five-year" final. Polyethylene pipe is widely used in city gas network because it can effectively solve the problems of corrosion and leaks, and has good overall performance. The polyethylene pipe welding methods mainly include hot melt welding and electric fusion welding, and hot melt welding operation is simple, practical, so widely used in engineering. But due to the welding process are influenced by technology, environment and so on, prone to defects in welding tapping; Practice shows that polyethylene pipe welding joint is the weak link of the pipeline. Therefore, this thesis mainly study hot melt welded joint mechanical properties and nondestructive testing, etc, providing theoretical basis for the safe operation of city gas pipeline and technical support.First of all, the thesis analyzes the factors that influence the welding quality in different stages of the hot melt welding and precast large quantities of hot melt welded joint containing defects, and sums up the process of the defects, and other forms of three kinds of defects such as weld defects though dissecting and observing the surface morphology, and analyzes its causes.Secondly, the design of polyethylene pipe hot melt welded joint mechanical properties test, heat stability test and flanging size determination of performance evaluation, such as orthogonal test, the welding process is studied in the main process parameters affect the performance of hot melt connection rule and degree, and eventually clear is significantly influenced on the welding performance of three process parameters are:welding temperature, welding pressure and heat absorption time. In addition, it is concluded that the best welding technology parameters combination, in conformity with the relevant standard recommended value or range. As the focus of the polyethylene pipe hot melt welding process parameter control to provide the basis.Then, in view of containing hot melt process defects joint mechanical properties tests, mainly tensile test, impact test and high temperature and pressure test, tensile curve was analyzed through tensile test results and the way of sample fracture of correlation, and studied different hot melt process defects joint effect on the properties of tensile strength, elongation at break, etc. In impact fracture morphology specimen, on the basis of macroscopic analysis, observing the microstructure of the electron microscope scanning, finally determine the four typical fracture morphology. Against defects in containing process at the same time, the high temperature and high pressure resistance of hot melt joint were studied.Finally, X-ray digital imaging detection method using metal pipe, analyzes the influential elements of the polyethylene pipe hot melt joint detection effect, main detection parameters calculation. in the process of testing according to the specific specifications of polyethylene pipe hot melt welding joint for parameter adjustment, constructs the testing parameter combination, and can eventually melt joint defect effectively.