Baldpate Integrity Management Plan: A Continued Service Case Study

Abstract

An effective Structural Integrity Management (SIM) program allows operators to manage structural risks and reduce the need for hazardous and costly underwater interventions. Inspection and operating decisions and costs are significantly affected by the SIM program definition and execution. This is particularly true for unique, deepwater assets like the Baldpate compliant tower, which features an innovative structural system and is among the tallest structures ever built. This valuable deepwater asset requires a well-executed SIM program to provide confidence that continued service and potentially expanded operations can be safely achieved. Earlier studies had shown that fatigue sensitivities at critical locations could potentially limit Baldpate's useful life beyond the original 20 year target. In order to better understand the characteristics of this unique structure, a series of reassessment analyses were performed. These showed that fatigue sensitivities are not limiting factors for continued service of Baldpate, and the areas of fatigue sensitivity were incorporated into a long term SIM plan to focus future inspections and monitoring efforts. This paper provides details on the challenges facing the execution of the SIM plan, including benchmarking and verification performed for the Baldpate structure using field measurements, implementation of a real-time monitoring system, and targeted underwater inspections. The dynamic behavior of axial tube guides, modeled using gap elements and surface friction, was identified as one of the more critical objectives to be addressed in the SIM plan. This posed a challenge since previous design and assessment efforts did not consider these components critical for global response. SIM options for these components were included in the plan, such as underwater inspections and on-site dynamic motion recording to examine the potentially undesirable behavior of these components. Undertaking these tasks led to affirmation of the structural reassessment results and facilitated development of new SIM resources. In particular, benchmarking the monitoring system provided Baldpate with constant surveillance of its condition. This real-time monitoring plan measures the dynamic characteristics of the tower under different load conditions to indicate when certain unique structural characteristics (e.g., axial tube motion within the guides) would affect the fatigue life of critical joints in the Baldpate tower.