PSI - Issue 70

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

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Considering that only “Medium High risk” and “High - risk” anomalies will qualify for repairs in the upcoming opportunity, the number of work orders generated will be 159 (6+4+22+14+48+24+41). To optimize the number of repair work orders, a combination of the final failure approach for primary and secondary structural members and the progressive failure approach for access structures and miscellaneous support was adopted. Figure 7 below shows the risk matrix generated using hybrid approach, with following few observations – A few primary and secondary structure anomalies were still in high-risk zones, as these anomalies have reached a higher stage of degradation and could not be deferred. There is an overall reduction in the risk count (A, B, C-III risk cells), due to shifting of primary and secondary risk on left side of tolerable risk (towards Medium to Low-risk zone).

Fig. 7 Risk Matrix generated using combination approach

On the risk matrix in Figure 7, a shift of majority of primary and secondary structure anomalies risk towards left side of tolerable risk level (towards Medium to Low-risk zone) was clearly noticeable. In the hybrid approach risk matrix, the total number of work orders generated for repairs are 110 (11+4+1+8+1+28+16+41), resulting in about 30% reduction in volume of repair work order generated for current cycle. Moreover, out of 30% overall work reduction, about 75% of work orders are related to high-cost repairs of primary and secondary structures. 4. Discussion and Conclusions In this paper, we discussed the final failure and progressive failure RBWS approach for risk assessment of structural anomalies. The aim of this paper is to emphasize that a combination of final failure and progressive failure approaches in RBWS provides a consistent, practical and cost-effective repair strategy. The main conclusions drawn from this paper are as follows: • Final failure approach is best suited for primary and secondary structural members while the progressive failure approach is best suited for access structures. • The case study demonstrated that by adopting this hybrid RBWS approach at the anomaly risk screening stage, there is a 30% reduction in overall repair work orders, of which 75% of work orders are related to high-cost repairs of primary and secondary structures resulting in significant maintenance cost savings • Except for the few high risk structural anomalies, which need immediate mitigation, the methodology used in both the approaches is to keep the risk at ALARP level i.e. below tolerance risk level. ALARP stands for As Low as Reasonably Practicable, a safety risk management approach that balances risk reduction and cost effectiveness (American Petroleum Institute [API], 2023). • Both approaches help in optimizing the RBI planning. Progressive failure approach may require CVI to track the progressive degradation of access structure anomalies while final failure approach may require only GVI to observe any noticeable change in primary and secondary member degradation. • Provide guidance to structural engineers for making consistent judgements related to work selection and priority.