Many of the mobile offshore drilling units (MODUs) constructed in the late 1970s to early 1980s were designed to operation in cold and harsh environments. Today, many of these MODUs now operate in warmer, less benign and more humid environments and are more likely to suffer a significant structural failure due to corrosion than fatigue.

Corrosion rates are difficult to predict, but increased the temperature, salinity or bacteria are known to greatly accelerate corrosion. Additionally, due to the difficulty to access ballast tanks, owners of ageing MODU fleets are becoming increasing concerned as sudden corrosion failures have led to downtime and, in some cases, contract cancellations.

DNV's new Recommended Practice for Corrosion Management will assist owners to develop a rigorous corrosion management strategy for units of any age or condition. Briefly, the RP is based upon a five step process:

• Pre-assessment. Determine mechanisms for coating breakdown, collect historic information and model the structure to determine "hot spot locations."

• Indirect examination and risk ranking. Consider the probability and consequences of failure.

• Detailed examination. Inspect the high risk locations.

• Remediation. Repair the high risk locations.

• Life cycle management. Continuously assess effectiveness of remedial actions.

DNV's five step approach, combined with specialized analysis performed by our corrosion engineering experts, provide the basis for sound, risk informed decisions for life cycle management. The five step process can easily be tied into the owner's overall asset strategy.

Blaine E. Collins

Director of External Affairs, DNV

Above article was initially published at DNV website.