Maintaining the safety of aging pipeline systems depends on systematic condition assessment and timely intervention to mitigate failure risks during their service life. From an economic standpoint, maintenance planning should be guided by life-cycle performance rather than short-term criteria. However, existing life-cycle analysis used for decision frameworks of degradation pipelines still face important gaps. First, many studies estimate the failure cost by multiplying the probability of failure at each time step by a unit failure cost, which fails to capture the possible occurrence of multiple failures over the service life. Second, the repair actions are commonly modeled as fully restoring the affected segment to its original condition, overlooking the differing impacts of partial, or imperfect repairs on the subsequent degrading process and residual pipeline capacity. Finally, most prior work focuses on a single defect per pipeline or segment, with limited attention to a system that contains multiple defects within and across segments. This study proposes a life-cycle analysis framework that can be used to optimize reassessment intervals and repair criteria for corroded steel pipelines containing multiple corrosion defects across multiple segments (or joints). The pipeline is modeled as a series of segments exposed to potentially different corrosive environments. Defect growth is represented by using a power-law model, whose parameters are linked to segment-specific environmental characteristics. Segment reliability is assessed through burst capacity under operating pressure, explicitly incorporating relevant uncertainties. Periodic in-line inspections are scheduled over service life, and repairs are carried out once specified maintenance thresholds are met. Repair actions are triggered either when corrosion penetration exceeds a prescribed fraction of wall thickness (leading to small leak) or when burst capacity falls below an allowable level. Depending on the repair type, the defect may be fully removed (restoring the segment to a pristine condition) or partially mitigated. In the event of a burst failure, the entire segment is replaced. The probabilities of repair events and various numbers of failure events are analytically evaluated. The total life-cycle cost is then obtained by aggregating inspection, repair, and failure costs over the service life. The proposed framework is intended to support risk- and cost-informed corrosion management for steel pipelines with multiple corrosion defects.
