Magnetic flux leakage investigation of dents

The magnetic flux leakage (MFL) method is used to detect and characterize defects in steel pipelines. A MFL based detection systems is propelled through a pipeline by the pressure of fluid or gas behind it. It locally magnetizes the pipe wall as it travels through the pipe and detects the MFL from defects.; This research examines the ability of the MFL method to detect and characterize mechanical damage where severe metallurgical damage is absent.; This thesis examines three orthogonal components of the MFL signal from dents, including the effects of both dent geometry and residual stress on signal features. The effects of residual stress are examined by comparing the MFL signals from samples before and after stress relief annealing. Furthermore the experimental results are compared to results from a magnetic finite element model (FEM) in which residual stress and dent geometry causes of the MFL can be isolated.; The characteristic features of each MFL signal component are identified, along with their geometry and residual stress contributions. The effects of dent dimensions and dent depth on the MFL signal features are then examined.