In-Field Applicable Coatings for Corrosion and Biofouling Control in Marine Environments

Abstract

Corrosion and biofouling control is an important consideration for offshore oil structures. Corrosion rates for steel exposed to seawater immersion and brine air can easily exceed 10 mils per year if left unprotected in the splash zone, while barnacles which attach in shallow tidal zones can similarly induce heavy, accelerated microbiological pitting corrosion. The subsequent deterioration of the ferrous substrates leave these structures at risk for mechanical failure, as the effects of particle impact, abrasion, wear, and erosion combine with the weakened surface structure to accelerate the loss of material. Maintenance of these critical assets often proves a logistical nightmare, when considering the limited accessibility, remote locations, and the huge expense of any interruptions in rig production. Attempts to contain the effects of corrosion are widespread, including strategies such as the introduction of chemical inhibitors to change the environment, sacrificial anodic and cathodic protection, and utilization of new highly alloyed materials. However, by far the most widely used technique is the application of specially engineered surface coatings to provide a physical and chemical barrier between the substrate and the surrounding corrosive media. Coatings can range between extremely simple hot-melted tar and liquid epoxy, which inherently have no chemical bonding to the substrate, and some slightly innate hydrophobicity, to engineered advanced systems including polytetrafluoroethylene (PTFE) and zinc silicates with specially paired primers for maximum surface adherence and broad chemical compatibility. None of the existing coating solutions practiced to date has been able to a key fundamental: coatings cannot be used as part of a refurbishment strategy to restore performance and production to existing structures after fouling. The purpose of this project was to develop a multifunctional, omniphobic coating with superior substrate adhesion such that it could fill in and plug surface crevices and pits stemming from corrosion. Additionally, unlike most other coatings, this surface adhesion could be attained through in-field application, either on exposed surfaces through aerosolized spray, or on the interior of transport pipelines via an in-line coating method. This paper will highlight various applications of the coating system on platform fixtures and supporting infrastructure, and how it can improve operational efficiency and extend the usable lifetimes of the selected assets. Offering abrasion resistance and an extremely low surface roughness finish, the coating has been demonstrated to actively repel both water and oil-based mixtures, as well as prevent the attachment and growth of typical marine biologicals such as barnacles and microbial algae. Suitable for nearly any substrate, this paper shall describe multiple ways in which the coating was deployed to combat not only corrosion on the platform itself, but also reduce drag in inspection underwater unmanned vehicles (UUV), and in offering flow assurance when used to refurbish a transport pipeline.