Estimation of Maximum In-Service Inspection Intervals Based on Risk: A Fuzzy Logic Based Approach

Risk based inspection analysis (RBIA) on offshore topsides static mechanical pressure systems aid the optimum performance of in-service inspection. Risk based inservice inspection analysis (RBISIA) essentially considers failures by loss of containment of the pressure envelope and supports decision making in inspection planning. This is based on the potential failure risk of a system, a sub-system or a thickness measurement location (TML): comprising the consequence of failure (CoF) and probability of failure (PoF). The RBISIA process is designed to aid the development of optimized inspection and recommendations for monitoring and testing plans for production systems. In this context, a tailor-made risk matrix supports the estimation of maximum inspection intervals (MIIs). When the MIIs are calculated using a risk matrix, suboptimal classification tends to occur as there are no means to incorporate actual circumstances at the boundary of the input ranges or at the levels of linguistic data and risk categories. This manuscript suggests fuzzy logic based approach via a fuzzy inference system (FIS) to overcome the aforementioned. Membership functions (MFs) and the rule base development have been carried out in alignment with a tailor-made risk matrix which has been utilized by a plant operator organization. A rule view and a calculation result have been demonstrated to illustrate the methodology.