The paper discusses the history and development of the Structural Integrity Management (SIM) process. A recap is provided of the significant industry initiatives and technological developments that have punctuated the passage towards the creation of the first stand-alone API recommended practice for the structural integrity management of existing offshore structures. The paper explores relevant SIM issues associated with the life cycle of an offshore structure. It looks at where risk-based SIM strategies have been applied, the benefits that have been delivered and where risk-based SIM strategies may lead in the future. Examples are provided of recent BP initiatives in the Gulf of Mexico and offshore Trinidad and Tobago.
Structural Integrity Management (SIM) is an ongoing lifecycle process for ensuring the continued fitness-for-purpose of offshore structures. The SIM process has evolved over the last 25 years to provide industry and regulatory authorities a means to ensure the continued safe and reliable operation of the aging fleet of offshore platforms around the world. The four phases of the SIM process: Data - Evaluation - Strategy - Program, as described in ISO (ISO/DIS/19902, 2004) are illustrated in Figure 1.
As new SIM data is collected it is evaluated to determine whether it increases operating risk, i.e. either the consequence or likelihood of platform failure. Data may emanate from inservice inspections, platform modifications or other sources such as new technology or industry learning. If the operating risk has increased significantly then some level of assessment engineering is required to determine whether the platform remains fit-for-purpose or whether risk reduction or mitigation measures are required. The role of assessment engineering within the SIM process is illustrated in Figure 2.
Risk reduction measures include options to decrease the likelihood of failure of the structure e.g. strengthening, modification or repair. Risk mitigation options include operational changes to reduce consequences of failure e.g. demanning or removal of storage facilities. Reduction and mitigation alternatives will have financial and operational implications. For that reason it is usually cost-effective to use appropriate assessment engineering techniques to determine the fitness-for-purpose of the facility. A clear distinction between design and assessment engineering is recognized in the SIM process.
The SIM strategy will define the planning of the inspection program. The plan for the inspection program includes the frequency of inspections and the scope of work. It also includes the survey tools/techniques to be used and the deployment method e.g. diver, ROV or combination of these and/or other alternative methods. In addition to the inspections, the program may include implementation of risk reduction or mitigation measures in accordance with the SIM strategy.
Increasingly, operators are adopting risk-based strategies for integrity management (Craig et. al. 1994 and DeFranco et. al. 1999) to optimize the focus of valuable resources whilst ensuring HSE risks are maintained as low as reasonably practical. Amoco, in the North Sea, had a risk-based underwater inspection program approved by the certifying authorities in the mid eighties.