Frequently, water injection pipelines do not last their design life due to corrosion problems. More often than not, the reason has been ‘channelling’ or ‘grooving’ corrosion at the bottom of the carbon steel pipeline. Once this mechanism does manifest itself within a pipeline, it may not be stopped, only slowed and the pipeline is doomed to either constant rupture/repair or enforced retirement as a consequence of corrosion rates proceeding in the order of approximately 1.0 – 2.5 mm/yr. This paper does not attempt to provide the reader with the electrochemical surface chemistry, but show the reader from several case histories how this mechanism manifests. This paper will address inadequate chemical housekeeping, the precursors necessary for initiation of ‘microbial induced erosion-corrosion’, why it can result in sudden unknown failure. Also discussed will be interpreting and identification of ‘channelling’ from different intelligent pigging technologies and ways to provide physical evidence to help determine if a Water Injection pipeline has succumbed to ‘channelling’ without employing an intelligent inspection.
The degradation pattern manifests as a continuous channel at the 6 o’clock position (Figure 1) with the location of damage depending on the profile of the pipeline. The physical-electrochemical attack of the pipeline has no suitable mitigation technique once channelling has begun resulting in corrosion rates on the order of 1.0 - 2.5 mm/yr. Channel corrosion is the result of debris at the bottom of the pipeline, loss of microbial control, and suitable flow dynamics. Water injection pipelines if mismanaged (process and chemical management of the topside deaeration system), perfectly fit into the risk category profile for channel corrosion to propagate and become active.
In the case of channel corrosion related to non-suspended solids, there is a characteristic thin black composite scale surrounding the circumference which is void in the groove (Fig 3).
