Electric Resistance Welded Seam Inspection Using Circumferential Flux

For conventional magnetic flux leakage (MFL) inspection where an excitation magnetic field is generated in the axial direction of a pipeline, axially oriented crack detection is impossible [1][2]. A new MFL tool design is presented that creates an excitation field in the circumferential or transverse direction, allowing for axial crack detection, as well as the more conventional metal loss detection. Design criteria that ensure detection include sufficient sensor density and magnetic field uniformity at sensor locations. The result is a new type of circumferential MFL inspection tool that can not only detect corrosion and other metal losses, but also axially oriented cracks. Based on the results of a series of inspection runs 22 crack-like features in the electric resistance weld (ERW) were investigated with 19 of those being verified as linear long seam features and were subsequently permanently repaired. Further information on the efficacy of this design is clarified in [2].