| April 30, 2007
( Houston, TX) A booming market for mobile offshore drilling rigs (MODU) is expected to keep many ageing rigs in employment for years to come. With an estimated 85 percent of the MODU fleet already 20 years of age or older, leading offshore classification society, ABS, has developed an Enhanced Monitoring System that gives owners, and the society’s own surveyors, a clearer assessment of the structure of the most common jackup and semisubmersible standard designs.
“It is the first time the offshore industry has had to deal with such a high percentage of aging equipment,” says Chris Serratella, Director of Operational Safety & Evaluation, ABS Corporate Technology. “With utilization rates the highest in decades, all available rigs are in service and we are looking to help operators extend the service life of their existing fleet in a rational and cost-effective manner,” he adds.
Serratella points out that many older rigs have been subject to on-going structural repairs and equipment changeouts over the years that have updated their capabilities and extended their lives. This is especially true in the semi fleet, where first or second generation floaters designed in the 1970s and 80s for service in 1,000 ft. water depths have been transformed to work in deep water of up to 10,000ft. “But even with major modifications, these rigs, like aging athletes, have old body parts that need age-specific maintenance and inspection regimes,” says Serratella.
ABS’ Enhanced Monitoring System provides a roadmap for taking these rigs forward. It offers operators a new way of looking at the maintenance of their older assets.
Detailed analysis of tears of accumulated data, coupled with the collective insights of a pool of the society’s veteran rig surveyors, have created a customized rig inspection planning tool for each type of rig. The analysis, led by Serratella, extracted data from ABS’ electronic survey report databases. A series of studies were run to examine systemic failures and structural damage on the most common 20 plus-year old jackup and semisubmersible designs. Serratella says ABS then conducted a pilot study focusing on the Sedco 700 semisubmersible and LeTourneau 116 jackup, workhorse rigs represented in the fleets of all major drillers.
The analysis categorized the rigs into “zones” - seven zones for a jackup (including upper leg, lower leg, deck attachments, upper hull) and ten zones for semis (such as upper braces, lower braces, pontoon base etc). ABS extracted the damage data and assembled an historical condition profile for each zone.
Groups of experienced rig surveyors then examined the data for each rig type, vetting the results and comparing this condition history with the current ABS rules and survey requirements governing each location or zone. Visual inspections and nondestructive examinations (NDE) were conducted on sample rigs. The surveyors described from experience the frequency with which each type of observed damage occurs and the criticality of its consequences. Then they further analyzed the current ABS Rules to determine if the present set of requirements were sufficient to take these aging rigs forward.
ABS technical staff examined the structure of each rig to see where the current criteria should be enhanced. For example, Serratella says the analysis indicated that, at the Special Survey for an aging semi, at least 25 percent of the connections at the upper columns should be subject to some surface NDE, while the brace-to-chord connection near the spud can of a jackup should be subject to a 100 percent NDE over the five-year survey cycle.
The enhanced monitoring gives a clear presentation of the current and enhanced inspection criteria for each rig design. It can also be integrated into an operator’s electronic work tracking system and used to develop asset maintenance plans.
Serratella says although the data is compelling and the inspection enhancements authoritative, the higher criteria are merely suggested and not mandated as a condition of class. “Even though enhanced monitoring is not a mandatory program,” he explained “ABS will likely find it most useful in guiding our surveyors toward a structure’s historical hot spots. It will help them zero-in on traditional, rig-specific problem areas.”
Founded in 1862, ABS is a leading international classification society devoted to promoting the security of life, property and the marine environment through the development and verification of standards for the design, construction and operational maintenance of marine-related facilities.
Editor’s Note: Downloadable photos illustrating inspection of aging rigs and computer screen shots from ABS’ Enhanced Monitoring System are available from newsroom of the ABS website at: http://www.eagle.org/news/press/otc2007/
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