Some Aspects of Application Magnetic Scanners

The method of magnetic flux leakage (MFL) is widely used for examination of pipeline wall to detect the presence of internal and external stress-corrosion. Magnetic scanner in which the MFL method is realized provides the pipe wall material magnetization, after magnetization the MFL is registered by magnetic field sensors. The stress-corrosion defects present in the pipeline wall are detected based on information picked up by the sensors. The main problem of defects parameters estimation is the fact that basic measured parameter is subjected to influence of numerous factors including: pipe material respond on magnetization, type of sensor, their placement scheme, pipe wall thickness and gap between measuring elements and pipe surface, etc. The scheme of examination implemented in the magnetic scanners comprises magnetic module which create the magnetic field in the pipeline wall. Between magnets located are sensors mounted with preset step. To solve the task of stress-corrosion damage depth evaluation it is required to determine the number of required sensors and distance at which they should be positioned between magnets. In the paper described is the problem and approaches for determination of necessary and sufficient number of sensors to register the peak amplitude of signal that further on is correlated to the depth of stress-corrosion crack. There are mention different models of magnetic scanner in the paper.