SwRI's nonlinear harmonic technique senses changes in the magnetic properties of steel resulting from changes in applied stress or plastic deformation. A sensor design was developed that is compatible with the in-line inspection systems of the commercial partner. SwRI engineers successfully evaluated nonlinear harmonic technology for the detection and characterization of mechanical damage on pipelines. Excavation crews often unintentionally cause such damage to pipelines. GRI is funding the investigation of a new pipeline corrosion assessment procedure.
Current assessments make use of corrosion dimensions as inferred from in-line inspection data.
These assessments, though useful to the pipeline operator, do not take into account the local stress environment of the defect. They therefore must be especially conservative to tolerate potential elevated stress caused by bending or thermal effects. This project seeks to merge the MFL technology and the SAFE analysis procedure to determine pipeline strength using both defect dimensions and stress environment directly from the MFL signals. Data are being derived from MFL scans of instrumented test specimens in biaxial loading. Moisture can penetrate between the concrete and the pipe, and cracks and corrosion can occur where the pipe is in contact with the concrete support.