Microbiologically influenced corrosion: A review focused on hydrotest fluids in subsea pipelines

Abstract

The selection of an appropriate seawater treatment for preservation of subsea pipelines during hydrotesting and subsequent wet lay-up poses a significant dilemma for offshore engineers. Seawater, which is routinely used in the hydrotesting of offshore pipelines, contains oxygen and microorganisms which are known aggressive species towards metallic materials. Particularly, microbiologically influenced corrosion (MIC) represents a serious threat to the extended preservation of wet-parked pipelines where degradation of treatment chemicals and the increase in microbial activity are expected. Despite the best efforts of corrosion researchers, mechanistic aspects of MIC in wet-parked pipelines remain elusive mainly because of the intricacies of biofilm-steel interactions and the diversity and variable nature of microbial life. In addition, there is limited experience and experimental data available on the long-term performance of hydrotest fluids and as a result, key misconceptions, biases and knowledge gaps continue to persist in the understanding and control of MIC in wet-parked assets. This article reviews the literature on MIC of offshore pipeline steels in seawater, in particular, MIC associated with hydrotesting and wet parking of pipelines to appraise methods, challenges and advances in the field. The impact of physico-chemical parameters and substratum properties on microbes and biofilms are discussed in an attempt to provide an update on the critical factors influencing MIC.