An Optimal Approach for Semiquantitative Risk-Based Inspection of Pipelines

Abstract

Risk-based inspection (RBI) analysis and recommendations provide an optimal strategy for inspection planning in the oil, gas, and petrochemical industries. The RBI analysis and recommendations are performed based on qualitative, semiquantitative, and quantitative approaches. The suggested approach complements the qualitative RBI analysis approaches, as the existing techniques result in suboptimal inspection intervals. Although quantitative RBI methods have been well-developed for above-ground (and topside) piping and equipment, there is a significant need for developing quantitative or semiquantitative approaches for underground (or subsea) hazardous liquid pipelines. This manuscript presents a new approach to assess risk for liquid pipelines. The proposed method encompasses both time-dependent and time-independent damage types. In a proposed approach, for risk analysis of time-independent damages, an improved Kent Muhlbauer method is suggested. The improved Kent Muhlbauer method uses logical weight factors and modification factors which help to obtain repeatable results. In addition, the general failure frequency method as proposed in API-RP 581 is suggested for time-dependent damage types. The combination of these two methods constitutes the core of the proposed risk assessment algorithm of this study. The proposed method was implemented in a pipeline integrity assessment project. The overall study findings revealed that the results are satisfactory and reasonable and have a practical significance for inspection planning engineers.