The maintenance of structural integrity is a significant consideration in the safety management of offshore installations. This paper presents an integrated approach for fitness-for-service evaluation of a deteriorating offshore radio tower structure. The approach is intended to assist engineers in assessing the overall fitness and survivability of aged offshore structures. A 43 m tall radio tower on an oil and gas platform located offshore Australia was reported with areas of heavy and medium corrosion of structural members. Severe corrosion in one leg of the radio tower had caused an obvious hole (extensive damage) through the leg at approximately 36m above the main deck and raised structural integrity concerns with the tower. The platform had been shut down due to concerns of a possible collapse of the tower. An assessment/repair program was developed to assure the short term integrity of the tower with minimal repair works. The integrity of the critically damaged leg had been temporarily restored using a clamped sleeve repair to allow progress with the inspection / thickness measurement of the corroded areas of the tower. As part of the fitness-for-service assessment, the minimum thickness acceptance criteria for the suspected corroded structural members were developed to enable initial assessment of the measured remaining wall thicknesses of the corroded member. Fitness for service integrity assessment requirements were developed to assess the locations that did not meet the minimum thickness criteria. The integrity requirements were adopted based on the average measured wall thickness, sensitivity structural analyses for reduced wind speeds for shorter life spans, and stability/survival assessment of the tower. An inspection program was carried out for the suspected locations and any additional locations identified during the inspection process. The inspection measurements were assessed against the fitness-for-service criteria. Where the measurements indicated that members did not meet the acceptance criteria temporary repairs were specified. Consequently, the tower fitness-for-service was found sustainable for up to 12 months until a more permanent repair or replacement of the tower could be completed, thus enabling the platform to resume normal operations.

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