Features and Advantages of Applying Anisotropic Magnetoresistive Field Sensors to Testing the Full Volume of Small- and Medium-Diameter Pipes

The work is devoted to a comparative study of magnetoresistive and Hall magnetic field sensors used as primary transducers in multichannel magnetic flaw-detection systems. The principle of operation and application features of anisotropic magnetoresistive (AMR) field sensors are considered. Comparative tests of AMR and Hall sensors were carried out. The main objective of these studies was to select optimum measuring transducers necessary to achieve the required metrological and operational characteristics. We have developed and investigated a multichannel magnetoresistive system for measuring fields due to defects and processing the results of nondestructive testing using a magnetic (MFL—magnetic flux leakage) method. Based on this method, a new small-sized flaw-detection facility has been created and introduced in the industry for automated continuous in-process magnetic inspection and identification of defects in electric-welded small- and medium-diameter pipes over the entire wall thickness, i.e., over the entire product volume. It is shown that the use of computer technologies and high-resolution thin-film matrix transducers made using advanced technology for manufacturing AMR sensors significantly increases the capabilities of the flaw detector and makes it possible to detect not only defects such as violations of metal continuity and edge displacements, but also defects caused by violation of welding conditions such as cracks, fistulas, arc freezings, and sticking edges in the weld area. The system based on new-generation single-chip thin-film matrix transducers is highly sensitive and allows detecting both surface and bulk defects in a noncontact manner with a large gap and at a high speed.