Materials characterization challenges for MFL pipeline inspection

Magnetic flux leakage tools are widely used for the inspection of large diameter, transmission, gas pipeline where the pipe condition, with regard to outside diameter corrosion, is of interest. In seeking to extend the inspection capability of such tools to the detection and characterization of other pipe conditions such as mechanical damage and stress corrosion cracking, it has become clear that much more needs to be known about both the magnetic characteristics of the materials constituting the inspection tool, as well as the specific pipeline material condition to be determined. This paper gives an overview of magnetic flux leakage inspection tools and describes recent developments in tool modeling and signal processing which are aimed at extending the detection limits of existing equipment and which highlight the need for improved knowledge of material behavior in the vicinity of stress corrosion cracking and mechanical damage.