Estimating the long-term reliability of steel and cast iron pipelines subject to pitting corrosion

Water-injection, oil production and water-supply pipelines are prone to pitting corrosion that may have a serious effect on their longer-term serviceability and sustainability. Typically, ob-served pit-depth data are handled for a reliability analysis using an extreme value distribution such as Gumbel. Available data do not always fit such monomodal probability distributions well, partic-ularly in the most extreme pit-depth region, irrespective of the type of pipeline. Examples of this are presented, the reasons for this phenomenon are discussed and a rationale is presented for the oth-erwise entirely empirical use of the 'domain of attraction' in extreme value applications. This per-mits a more rational estimation of the probability of pipe-wall perforation, which is necessary for asset management and for system-sustainability decisions.