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With the offshore oil and gas sector paying record day rates for MODUs, operators are pressing all available rigs into service and are looking to extend the service life of their existing fleets in a rational and cost-effective manner. Of the more than 500 mobile offshore drilling units in the ABS fleet and in service around the world, over 85 percent of the rigs are age 20 years or older.

Chris Serratella, ABS Director of Operational Safety & Evaluation, says these statistics drove the initiative within ABS to develop a comprehensive, enhanced asset integrity management (AIM) program for the aging rig fleet.

According to Serretella, many owners of rigs 20 years or older approached ABS seeking guidance in terms of structural inspection and evaluation. Serratella conducted a pilot program that drew upon ABS’ survey experience with aging rigs. “Pulling from historical data we did a series of studies examining systemic failures and damages found within the structures of typical jackups and semisubmersibles that are common to many rig operators’ fleets,” he explained.

“Once those studies were performed, we pre-populated a simple risk assessment worksheet which broke out each rig into zones – for a semi, the zones included braces, pontoons, the upper and lower columns, the underdeck structures and so on. We did the same for the jackups.”

The study team then placed the functional failures that were identified from the queries for each zone into a spreadsheet so that reviewers could see what had been identified from a historical perspective. This was followed by a sequence of interviews conducted with experienced surveyors and engineers within ABS to confirm that the failures identified were truly representative of the historical record. Regional effects were also taking into consideration. For example, rigs operating in a fairly benign region in terms of wave height and wind, corrosion at the water line will be a factor. A similar rig in the North Sea might have a greater prevalence of stress-related cracking.

Each type of rig in each zone was discussed by a panel of experienced offshore engineers and surveyors.

The results indicated the structural areas that could benefit from an enhanced survey program.

Serratella is currently working with owners to develop programs to meet their specific needs. The study also indicated that an asset integrity management program such as this could be of comparable benefit if applied to machinery, such as drilling and jacking systems.

“The study has been very rewarding,” said Serratella. “It has provided us with the information we needed to evaluate our survey processes and that better prepares our surveyors so that they are more aware of those areas within a rig’s structure that may experience higher rates of corrosion or incidences of stress, depending upon the type of familiarity and its operating location.”