PSI - Issue 70

Rajesh Dube et al. / Procedia Structural Integrity 70 (2025) 365–371

369

3. Case Study Following case study is based on review of 500 inspection reports covering topside structural inspection of 30 offshore platforms located in the North China Sea. All these platforms are experiencing similar environmental conditions. The data analyzed and exemplified numbers clearly illustrate the concepts driven by the author and the benefits of not adhering to a single approach for RBWS. Figure 5 below indicates the average distribution of structural component wise anomalies distribution.

Fig. 5 Average distribution of structural component wise anomalies on topside structure

It is clearly observed that about 33% of the total anomalies belong to primary and secondary structural members while the remaining 67% anomalies belong to access structures and miscellaneous components. After identifying the anomalies, the next stage was to risk screening the anomalies using RBWS method. At this stage of risk screening, engineers are required to take a judicious decision to select an appropriate approach viz. final failure or progressive failure approach to assign the risk. Before progressing further, it is important to note that as per conservative estimate, cost of repairing a primary and secondary structure in offshore field is approximate 10 times than repairing an access structure or miscellaneous support component (Sehgal, 2024). If at this stage all the primary and secondary anomalies are risk screened as per progressive failure approach, all these anomalies will have higher POF to reach to next stage of degradation. On the risk matrix, primary and secondary structure anomalies risk will cluster towards right hand side of tolerable risk level (towards Medium-High to High-risk zone) as shown in Figure 6 below.

Fig. 6 Risk Matrix generated using Progressive failure approach.