This paper provides a review of a pipeline crevice corrosion model (PCCM) previously developed to investigate the crevice corrosion of coated pipelines under cathodic protection (CP). The crevice is a channel, formed between a pipe surface and a disbonded high-density polyethylene (HDPE) coating. Oxygen (O2) is the cause of the crevice corrosion; it reaches into the crevice by migration through coating defects (holidays) and by diffusion through the coating. An induced current caused by an O2 concentration cell has been quantified flowing through the crevice solution layer from within the deaerated area to the aerated holiday. This induced current results from polarization at the pipe surface. The polarization was considered in this model and the crevice corrosion levels off within the crevice. The earlier models did not consider the pipe polarization and the corrosion rate decreases sharply from the holiday into the crevice. External CP current reduces crevice corrosion by consuming O2 near the holiday area. The CP cannot penetrate sufficiently deep into the crevice and the corrosion there is determined by O2 transport through the coating and the local pH. Lower crevice solution resistivity increases the CP penetration into the crevice significantly. The key for a sufficient protection of the pipelines is an appropriate CP that reduces all O2 diffusing from holidays and a good coating that minimizes the permeation of O2.
Keywords" model, corrosion, pipeline, coating, cathodic protection (CP), oxygen, crevice