Internal Corrosion of Seabed 'Parked' Steel Oil and Gas Pipelines

Seabed 'parking' of steel pipelines is a common practice in the oil and gas industry. However, despite the use of corrosion inhibitors and biocides internal corrosion remains an issue. So-called 'wet parking' may show severe pitting corrosion, often at the 6 o’clock position and usually attributed to microbiologically influenced corrosion, since high concentrations of various bacteria often are detected. The usual response, dosing with biocides, may not be not effective. It also can have environmental consequences if biocide is eventually or accidentally released. Current practices and options for parking of offshore pipelines are reviewed briefly. Recent findings for internal corrosion inside water injection pipelines are then considered as these have implications for 'wet' parked systems. After initial oxygen controlled corrosion longer term corrosion can occur under anaerobic conditions and this has implications for corrosion during periods of stagnant conditions and for corrosion under deposits of rusts and other debris. These corrosion mechanisms can be enhanced by microbiologically influenced corrosion but only if necessary nutrients are available. Acceptably low levels of corrosion can be achieved inside 'wet' parked pipelines with the use of seawater with low concentrations of particulate matter and low concentrations of microbiologically-critical nutrients.