Stochastic modeling of pitting corrosion and its coupled effect on burst pressure degradation in steel pipelines

Among all the degradation modes, pitting corrosion is among the most severe with its very localized and nonlinear behavior, especially for pipeline integrity in oil and gas transportation systems. A complete numerical model developed in MATLAB to simulate the pitting corrosion evolution and impact on pipeline burst pressure is presented. The pit growth was simulated with a stochastic power-law model, and the localized pit geometry was simulated using a Gaussian distribution to be applied over a service life of 20 years. This was done through developing nonlinear formulations that were coupled with a modified Barlow burst pressure model, with the aim of assessing the stress concentration effects and degradation in structural integrity. The results of the simulations show that, the pit depth has a non-linear increase with time, and reaches values of about 3.58 mm at 5 years, 10.05 mm at 10 years and up to 26.93 mm at 20 years, which suggests higher degradation after mid-life. The stress concentration factor rises from 1.6 – 2.4 (early stage) all the way to 7.2 at 20 years, a factor of four times the increase in local stress intensity. Similarly, the burst pressure drops from 25.6MPa to 15.1MPa at 10 years (41.02% reduction) and to 15.1MPa at 0.11 years (≈99.33% reduction). Comparative analysis revealed that the pitting corrosion is more severe than uniform corrosion with ~12.5% lower burst pressure capacity at end of life. In addition, the protective coating increases the burst pressure to 40 MPa and the high strength material increases the resistance to ~33.2 MPa for 20 years. The results show that the risk of structural failure is greatly influenced by localized corrosion, and the pipeline vulnerability may be underestimated by the conventional uniform corrosion models. The proposed framework gives a realistic prediction technique for integrity assessment and maintenance planning of corrosion prone pipeline systems.