Study On The Metal Magnetism Memory Characterisic Of Welding Crack

Weld is the most important and widely used material-connecting method. However, the weld joint produced by welding process experiences the extremely welding heat cycle, and is different from the body material in physical and chemic performance. Then, these differences incur that the weld components rupture, fatigue, and corrupt at the weld joint during used. Therefore, the weld joint is the most significant point in the weld-quality-controlling. Metal magnetic memory is a nondestructive testing method, which is invented by Russian expert in 1997. The method use the ferromagnetic leakage magnetic field to detect the stress concentration position because the leakage magnetic field is produced by the magnetic domain orient irreversible change due to operating strain and stress in earth magnetic field. In order to apply the metal magnetic memory method to test the welding quality, the metal magnetic memory characteristic of the welding crack is studied, which is the most badly factor tampering with the weld joint quality. Firstly, the detection parameter is studied when the TSC-1M-4 metal magnetic memory device is used in the weld detection. It is the best detection parameter group that Ho set as ON, S set as 1mm and b set as 15mm. Secondly, the main aspects of the research are thought as the three relationships of the crack, stress field of the crack and leakage field of the stress concentration. As the subject investigated, X70 line-pipe steel has been researched on the stress field around the crack tip, the relationship between the stress field and the leakage field, and the relationship between the stress and the metal magnetic memory signal. Thirdly, the time and space availability of weld crack's metal magnetic memory testing is researched by the self-layout experiment. The detection result is available when the weld joint is cooled below 100℃, and the doubtful weld crack area include the positions from which the distance to the metal magnetic memory characteristic signal position is no more than 70mm. Fourthly, such self layout experiments has been carried out as tension, one-factor rotate weld pipeline standard sample cracks, and quadratic rotation-orthogonal combination design weld pipeline standard sample cracks, and these are detected by metal magnetic memory method. From the detection results, it is concluded that there are four metal magnetic memory signal characteristic of weld crack-Deta, △Hp/△Lx, △Hp and Fourier analysis phase saltation of metal magnetic memory signal. Comprehensive analysis of all the four signal characters above can reflect the existence and geometry shape of weld crack. Finally, the regression equations has arrived between such the signal characteristic variances as Deta, △Hp/△Lx and △Hp and such weld crack geometry shape parameter as length, angle and depth.