Long-term development of pitting corrosion for steels in water injection and production pipelines

The longer term development of pit depth in water injection pipelines and in crude oil production pipelines is of interest for environmental as well as economic reasons. Herein data obtained from North Sea from intelligent pigging runs are used to show that such pitting progresses in steps, after some time of exposure typically each step being about 0.4mm deep, irrespective of whether the pipeline conveys water or the typical crude oil-water-sand mix extracted from crude oil wells. The multiple pit depth observations available allow the data to be plotted on Gumbel extreme value plots. These show the incremental behaviour very clearly. It also can be observed for pit depths measured by optical microscope for steel coupons exposed for several years in seawater. All show overall similar behaviour despite the considerable differences in exposure conditions. The reasons for these observations are discussed in terms of pitting potential and the factors that govern it.