Residual magnetic fields reduce pit depth

The influence of the magnetic field on pitting corrosion in pipeline steel has been studied on samples of APU 5L Grade 52 steel. The samples underwent pitting immediately after magnetization by immersion in a solution with dissolved Cl^- and SO^-₄ ions for 7 days. Investigation showed the magnetic field confined within the pipeline wall influencing the pitting corrosion process. Finite element simulations demonstrated the role of the leaked magnetic field in pit depth reduction caused by the forced movement of paramagnetic species toward zones of higher magnetic gradients. The soil properties having greatest influence on pit growth are soil pH, Cl^- content and SO^-₄ content. The maximum and mean values of pit depth in magnetized coupons are smaller than the values for the control coupons. The results suggest that following pit initiation, the magnetic flux leakage within and near nucleated pits reduces their growth.