Regulators around the world are taking ever increasing interest in the integrity assurance activities adopted by operators as they strive to ensure increased offshore safety and reduced environmental impact. In the past, prescriptive measures were typically accepted. However, following, and possibly as a result of, recent offshore incidents, there is a drive towards implementing a goal-setting regime where the operator is required to demonstrate it is operating safely. As a result, risk-based integrity assurance is finding greater acceptance, as it targets critical components providing justification for each inspection, monitoring, or mitigation activity based on the probability of failure and the consequence for not only personal safety and the environment but also asset availability.
The term “integrity management” (IM) is often misquoted or misunderstood. In industry terminology, IM usually refers to the program of surveillance during operation with typical integrity programs revolving around inspection management. Such an inspection management strategy may be well suited for static equipments/structures with good accessibility to conduct visual inspection, CP surveys, and UT testing. However, subsea systems such as jacket structure, riser-caissons, conductors, templates, risers, and umbilicals experience highly dynamic loading due to environment combined with internal and external corrosion issues. Therefore, inspection alone cannot ensure the integrity of these structures. A suitable IM program should employ simulation, monitoring, mitigation, and testing in addition to regular inspection.
Legislation, Class (if adopted), and operator procedure specifications determine a level of prescriptive requirements. However, most inspection, mitigation, and monitoring requirements are defined by criticality, or risk level, to system components. A risk-based approach typically forms the basis for the IM program, as specified in various recommended codes of practice. IM does not interfere with the subsea systems performance but it implements measures to monitor the ongoing deterioration of the component and predicts the likelihood of the component failure.
The risk assessment should be conducted for each subsea component for all possible failure modes. The failure modes can be classified in two major categories: age related (e.g. corrosion or fatigue) or non age related (e.g. impact). The probability of each failure mode should be based on evaluation of the design, fabrication, and installation of the system, along with operational practice. The consequences should be evaluated based on personnel safety, environmental impact, reputation, and commercial loss. Probability and consequence are combined to obtain a risk ranking for each component.
It is vital to preserve and use the knowledge created during asset design with proper documentation, along with data gathered during operation through inspection and monitoring, and with the management of change in order to feed into the integrity assurance process.
Confidence is important in the RBI process and the integrity review methodology, and, therefore, needs to be accurately assessed. Confidence is a measure an operator has in the component to satisfy its intended service life based on available data, such as the number of previous inspections, ability to measure/inspect any component degradation, quality of inspection and/or monitoring data to date, ability of inspection/monitoring technique to highlight an anomaly in sufficient time to avoid failure, etc. Overall criticality is calculated by combining the confidence grading and the risk ranking.
Based on the overall criticality, an informed engineer is able to assess and recommend the most suitable inspection technology and/or monitoring in order to detect the target failure mode. The extent of inspection and prescribed intervals, or the level of monitoring, are prescribed by this process.
In cases where there is no previous history of performance, “confidence” will be low, and, consequently, the frequency of initial inspections will be high. However, following a series of inspections showing good performance, “confidence” will increase, justifying an increase in time between inspections. Similarly, monitoring data interpretation showing good performance also can warrant increasing the gap between inspections, resulting in significant cost savings.
The risk levels change continuously during an asset life. Therefore, IM should be perceived as a continuous process rather than a one-time activity. If the IM process is conducted only once during the early stages of the asset life, the operator will only get a snapshot of the system status and will not be able to justifiably determine the overall performance. Only with continuous assessment, monitoring, and inspection, can the probability of failure be predicted and; therefore, avert the potentially disastrous consequence of a catastrophic failure.
Effective IM includes monitoring both long-term and extreme event loading response, as subsea system performance is driven typically by environmental and operational conditions. IM relies on timely interpretation of the data gathered.
Design, inspection, and monitoring records are managed from a central location to assess the subsea system performance and to effectively manage repair and maintenance requirements. This ensures informed decisions on integrity matters based on a complete dossier of background information.
Quality of the personnel conducting risk assessments is important. IM engineers should understand the subsea systems involved so all potential failure modes can be captured and recommendations made regarding ongoing inspection, mitigation, and monitoring. Competence is required at all stages in the process, including simulation data processing and inspection. An untrained or unsupervised technician can undermine the the entire program.
Global Subsea IM Business Manager, 2H Offshore
Technical Manager, 2H Offshore
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