Development And Application Of MFL Outside Testing System For Overhead Pipelines

MFL testing has the advantage of non-contact, fast speed, high efficiency, it has become a widely used detection method. In this dissertation, the problems due to various specifications and complex conditions of overhead pipelines(Φ57~Φ219mm) have been studied, a MFL outside testing system for overhead pipelines has been developed, and it is used for field application.Firstly, based on the analysis of the working conditions of overhead pipelines, a MFL testing model is established using the 3D finite element method. Authentic signals of magnetic leakage field are obtained by subtracting magnetic field signals of no defect from defective field signals. The signal to noise ratio(SNR) of MFL signals are obtained by dividing magnetic field signals of no defect from defective field signals. The influence of geometric sizes of the magnetizer on pipe magnetization and magnetic leakage field signals is analyzed through ANSYS simulation. According to ANSYS calculation, we get the optimal solution of geometric sizes of the magnetizer and how many magnetizers are needed to detect pipelines of different specifications.Secondly, based on the calculation results of magnetic field, MFL outside testing system for overhead pipelines is designed, which consists of crawling mechanism, testing probe, wireless controlling and signal processing unit. The motor driver is used to reduce the labor intensity. In order to ensure the accuracy and stability of MFL signals, the combined rigid and flexible structures are employed in the MFL testing probe mechanism. The wireless data transmission and motion control are realized by WI-FI and 2.4GHz wireless technology, which have improved the ease of operation.Finally, according to the demands of non-destructive testing, a series of sample pipelines with through hole, blind hole and notch are designed, they are used in the experiment for the MFL outside testing system, in order to obtain signals of standard samples, based on that, further field applications have been developed. The results indicate the MFL outside testing system is very suitable for field application and easy to operate, it has high testing efficiency and stable signal.The research of this dissertation has supported the formulation of national standard ‘GB/T 31212-2014 Non-destructive testing—Magnetic Flux Leakage Testing—General Principles’.