Corrosion and Cathodic Protection

Our group was the first to develop finite-element and boundary-element calculations for cathodic protection of coated pipelines with coating holidays that expose bare steel. These calculations, developed for the Trans-Alaska pipeline, were validated by laboratory experiments on full-scale sections of the Trans-Alaska pipeline. The development of boundary-element models was generalized to account for interactions between multiple pipelines, to account for stray current between independent CP networks, and to allow calculations for very long sections of pipelines. The resulting software was used by Arco (now BP) for remediation of the Trans Alaska Pipeline and for design of a new gas field in the South China Sea.  Other related projects involve solution of the inverse problem, needed to determine underprotected regions of the pipeline from field measurements, and development of detailed models capable of predicting the rate of delamination for painted metals.

Storage facilities for petroleum products usually consist of a series of aboveground steel storage tanks. The tank bottom consists of a sheet of steel that is thin as compared to the wall thickness for transmission pipelines; thus, corrosion of the tank bottom can result in rapid perforation. Successful cathodic protection strategies must address several complicating factors. To ameliorate the threat of tank failures, tanks often have an underlying cache basin to prevent leakage into the aquifer. As the liner of the cache basin can block passage of current, CP anodes for such tanks are placed between the liner and the tank bottom. An additional complication is associated with the cyclic nature of oxygen concentration profiles underneath storage tanks, due to motion of the tank bottom when the tank is emptied and filled.  The calculation results demonstrate the influence of the insulating cache basin and show the limitations of analytic formulas.

Calculated potential distribution for a tank bottom protected by 21 Mg ribbon anodes placed directly underneath the tank with a uniform oxygen distribution: a) with no insulating barrier; and b) with an insulating barrier placed 0.61 m (2ft) below the tank bottom. The blue color indicates that the presence of an insulating barrier actually enhances the ability of the Mg ribbons to protect the tank bottom.