Experience in the offshore industry demonstrates that while vessels such as mobile offshore units are designed to provide watertight integrity (WTI), incidents continue to test their WTI from time to time. Owner investigations sometimes show flooding has progressed to hull compartments beyond the original breach. With the worldwide fleet of mobile offshore drilling units (MODUs) increasing to nearly 1,000 units in the next few years, the industry is seeking a greater understanding of the threat of progressive flooding during an incident and the benefits of available control measures. One such control measure to be discussed in this paper is a program of comprehensive, owner-driven audits to verify the crew's maintenance performance.On MODUs, maintenance attention naturally focuses on the drilling process. In day-to-day operations, drilling equipment is susceptible to wear and tear, which can occasionally lead to downtime and an immediate need for repair and maintenance. Safety-critical marine equipment might only show flaws on those rare occasions when it must function as intended, without failure, such as in a marine safety drill or emergency. A natural tendency for "complacency" and "errors in risk perception" can affect the timely maintenance of marine equipment differently than drilling equipment. WTI audits address the need to properly assess the maintenance requirements of the hull structure as well as specific marine equipment on board the vessel. These vessel-specific, owner-driven audits would supplement periodic class surveys to verify how well the crew is performing this maintenance. Whenever possible, the owner would conduct this maintenance while afloat and without significant downtime. The benefits that can be realized from owner-driven audits would be to avoid major flooding incidents across all types of mobile offshore units; improving industry safety performance on MODUs (especially aging units, non-self-propelled units, and newbuilds which have experienced the most problems) and production installations; reducing unexpected downtime during out-of-service periods; and increasing the crew's awareness, which can lead to improved competence, quality, and safety culture. Ideally, best practices and lessons learned from the WTI audits would be shared with the industry to improve maintenance of watertight integrity and owner inspection practices.

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