In-Line Stress Measurement by the Continuous Barkhausen Method

This paper describes a novel concept for measuring pipe wall stress. Southwest Research Institute^® (SwRI^®) pioneered the use of the Barkhausen effect for stress measurement in the 1960s, and the method is still in use today. University researchers in Canada are using the technique for determining stress magnitude and direction by making measurements at quite high resolution. Their technique, which follows from the early SwRI work, requires an alternating magnetic excitation field and an inductive sensor that responds to the Barkhausen magnetic transitions. In contrast, the Continuous Barkhausen concept does not require an alternating excitation field, relying instead on the field transition already present as a magnetic flux leakage (MFL) pig moves through a pipeline. All MFL pigs in use today create Barkhausen noise as they move through the pipeline. The only requirement for using those signals to reveal information about the pipe is to provide suitable sensors and amplifiers to develop a data interpretation procedure. This paper reports on work sponsored by the U.S. Department of Transportation in which SwRI and their commercializing partner, H. ROSEN Engineering, performed laboratory and pull-test experiments to validate the technique using MFL pig hardware in a test line having artificially induced stress anomalies. Details of the technique, laboratory experimental results, and pull-test results are presented, along with recommendations for the application of the method to operating pipelines.