On an increasingly frequent basis, pipeline operators are using risk-based decision making to prioritize cross-company expenditures. Due to the long-term mitigation benefits of Cathodic Protection (CP), when planning external corrosion mitigation activities, pipeline operators typically prioritize mitigation of deeper anomalies for integrity expenditures due to their higher Probability of Failure (PoF). However, anomalies that are not receiving adequate CP or those experiencing electrical interference may remain unaddressed using this rationale. This paper presents both a qualitative and semi-quantitative approach to support the quantification of the risk reduction benefits gained from external corrosion prevention on pipelines. This can help in the efficient prioritization of both pro-active and re-active integrity repair activities. Supporting examples are also discussed to help explain the intended use of the methodology and the interpretation of the results.
Various aspects of the mechanism of C02 corrosion are reviewed, together with a discussion about the validity of a number of simplifications which can be used with models for predicting the corrosion rate. A "worst case" rate can often be predicted. To this end a number of parameters has been identified, the
influence of which has to be accounted for. The effects of protective corrosion product layers and of dissolved corrosion product on pH needs to be included in the prediction. More quantitative information about the effect of flowpattern and flowrate is needed. For wet gas pipelines, the prediction of the effect of injection of glycol as a measure against corrosion is of special interest. Predictive models consisting of a system of rules and equations can be conveniently developed in computer spreadsheets.