Numerical Simulation Of PCCP Pipes Broken Wires Eddy Current Detection

Prestressed concrete cylinder pipe(PCCP)is one of the structures commonly used in long-distance pressure water conveyance projects.The pipe wall structure includes pipe core concrete,thin-wall steel cylinder,prestressed steel wire and mortar protective layer.Under the corrosion effect of groundwater in the long-term operation state,the prestressed steel wire in the pipe wall will break,which will lead to the crack of the pipe core concrete,and then lead to the pipe explosion accident,which will threaten the safety of water supply and public safety.Therefore,it is of great significance to detect the broken wire in the PCCP pipe,make prevention and repair in advance.Electromagnetic nondestructive testing techniques commonly used in PCCP pipelines include far-field eddy current and p-wave.Far-field eddy current is widely used in the detection of defects and cracks in ferromagnetic pipelines.Now this technology has been applied to the detection of broken wires in PCCP pipes.Subsequently,p-wave detection technology has emerged by improving the arrangement of excitation sources.The two detection technologies have just started in China,and the research on detection principle and broken wire is far from enough.In this paper,the mechanism of the two detection technologies and the signal characteristics and influencing factors of broken wire are simulated by using finite element method.The research contents of this paper are as follows:(1)The axisymmetric finite element method is applied to simulate the propagation of extremely low frequency electromagnetic field from inside to outside of PCCP pipes,to explore the far field eddy current phenomenon of PCCP pipes,analysis of prestressed steel wire around the formation of the inductive effect and eddy current field in the thin steel cylinder coupling effect.The effects of the number of prestressed steel wire fractures on the magnetic induction intensity and phase distribution near the inner wall of the pipe are summarized.The traditional far field eddy current shielding is improved,and the position change and influencing factors of the far field are analyzed.(2)The three-dimensional finite element eddy current field is applied to simulate the P-wave detection.To distinguish the detection signal characteristics of the PCCP pipes at different positions and with different amounts of broken wires,and reveal the variation rules of the amplitude and phase of magnetic induction intensity.The electromagnetic field distribution inside and outside the PCCP pipe and the eddy current effect inside the steel cylinder and steel wire are analyzed.And the principe of P-wave detection is explained.(3)To simulate P-wave detection of steel wire corrosion in PCCP pipes,and study the signal characteristics of steel wire when corrosion occurs.To distinguish different types of corrosion and different corrosion rates,and analyze the difference between steel wire corrosion signal and broken wire signal.At the same time,the broken wire and corrosion of PCCP pipes of double-layer steel wire are simulated,and the broken and corrosion characteristics of inner and outer steel wire are further determined.