A Monte Carlo Model for Pitting Corrosion in Phosphor Bronze Tape Used in Underground Power Transmission Cables

Abstract

Life of underground oil-filled power transmission cables used with phosphor bronze tapes is greatly reduced by pitting corrosion and hence accurate prediction of the pit growth in these tapes becomes essential. In the present work, the probability distribution of corrosion pit depth on phosphor bronze tapes is calculated using probabilistic Monte Carlo simulations and compared with the measured pit depth distribution on samples of broken tapes which have been in service for about 50 y. This Monte Carlo simulation is performed on every stable pit that nucleates, propagates, and repassivates on the metal surface. Due to the random nature of pitting corrosion, the probability of failure of this class of cables can be simulated based on the Monte Carlo model. This paper shows that the simulated pit depth distribution is very similar to the experimental data. The results demonstrate that the Monte Carlo model by Engelhardt and Macdonald can be effectively applied to long-term field data of phosphor bronze tapes, even over 50 y. In addition, the probability of failure due to pitting corrosion can be evaluated analytically, without need of conducting expensive and time-consuming experimental campaigns. Therefore, this probabilistic pit depth distribution model will be a powerful tool in the decision-making strategy for the replacement of underground power transmission cables near their end of life.