A Monte Carlo Model of Pitting Corrosion of Underground Power Transmission Cable

The life of underground power transmission cables is greatly reduced by pitting corrosion of the reinforcing tin-bronze tapes and this corrosion fatigue leads to cable failure. Since these cables are distributed in different places and can fail at different times, it is difficult to maintain and replace these cables until they fail. Hence, accurate prediction of pit growth in these tapes and plastic deformation analysis of these tapes with pits are crucial steps in cable maintenance. This thesis documents the findings from the probability distribution of corrosion pits on reinforcing tin-bronze tapes using deterministic Monte Carlo simulations. The findings were compared with the measured pit depth distribution of tapes that have been in service for over 40 years obtained from open literatures. Additionally, the finite element model (FEM) was used to analyse the relationships of applied stress and pit depth with a model of failure mechanisms. The input data for the FEM were based on the pit depth from the simulation and applied internal oil pressure from the experiment data. A Monte Carlo simulation was performed with every stable pit that had nucleated, propagated, and repassivated on the metal surface, and the model considered the interaction between individual pits in an explicit manner. The measured data were compared against previously published data from actual samples from different locations and with various service durations to investigate the complete distribution of pits. The studies showed that the simulated pit depth distribution is very similar to the experimental pit depth distribution on the tapes. This pit depth distribution model provides a powerful tool to determine the residual life of reinforcing tin-bronze tapes used in underground power transmission cables. The FEM was used to examine the failure condition of the reinforcing tapes under various applied stress and pit depths. The pit depth was gained from the Monte Carlo simulations, and the applied stress was based on UTS. Thus, the life of an underground power cable can be calculated. This FEM procedure provides an alternative method to determine the probability of failure of reinforcing tapes and a convenient way to identify the life of underground cables, dependent on the failure model.