Study of pitting corrosion in line-pipe steel under the influence of remanent magnetization

The influence of remanent magnetization on pitting corrosion in line-pipe steels is studied. Pitting corrosion experiments were conducted on samples of an API 5L grade 52 steel under a magnetization level of the same order of magnitude as the remanent magnetization in the pipeline wall after in-line inspection based on magnetic flux leakage (MFL). The samples were magnetized using rings of the same grade as the investigated steel. Immediately after magnetization, the investigated samples were subjected to pitting by immersing them in a solution containing dissolved ions. The pitting experiments were conducted during a seven-day period. The pit depth distribution and the maximum pit depth in each sample were recorded and used to conduct extreme value analyses of the pitting process in magnetized and nonmagnetized control samples. The statistical assessment of the pitting corrosion data collected shows that the magnetic field reduces the average depth of the pit population and also the extreme pit depth values that can be predicted from the maximum values observed in the magnetized samples in comparison with to the non-magnetized control samples. Scanning electron microscopy observations show that the magnetic field alters pit morphology by increasing the pit mouth opening.