PSI - Issue 70

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

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Fig. 2 Typical corrosion damage event tree

The figure clearly demonstrates the differences between the two approaches.

2.1. Final failure approach In the final failure approach, the intermediate damage stages are not considered, and the probability & consequence directly relates to final failure of structural member. This approach is typically applied to primary and secondary structural members, which are not on the critical load path and have sufficient redundancy, for example a wind brace member. Sound engineering judgement and experience tells us that a small percentage of metal/section loss on such members does not lead to global structural collapse & repairs can be deferred to next shutdown/repair campaign after inspection. However, if the design assessment report suggests that the structural member under consideration is on critical global structure load path, for example, a knee brace member, a progressive failure approach can be utilized. In the final failure approach, the selected structural members are allowed to degrade till the last stage of failure before repairs are taken up. For such members, based on the condition of degrading members, low-cost temporary measures, for example, securing or netting the member to prevent local corrosion debris drop object hazard on personnel & equipment, sealing the holes in the members to prevent accelerated corrosion due to water ingress etc. are employed based on the immediate threat associated and permanent repairs are planned for future opportunities, leading to work optimization. The probability of failure of all such structural members, whose repairs are deferred till next shutdown/ repair campaign, are on lower side of risk matrix for current cycle. However, the financial consequence of failure of such members always remains high due to major repairs or in some case complete replacement of the member & associated scaffolding cost. Figure 3 below shows the typical risk scatter on risk matrix of structural member anomalies selected under final failure approach.

Fig. 3 Typical risk scatter of structural member anomalies selected under final failure approach