Surveying coatings in the offshore environment
Offshore oil and gas exploration and production platforms, which must operate in some of the harshest environments found on earth, are protected by high-performance coatings that must be routinely surveyed to check that they are performing effectively.
The oil and gas industry has adopted various materials to construct its offshore structures. These include carbon steel, stainless steel, aluminium, plastic composites and concrete. These are often protected with high-performance coatings to ensure the structures can effectively resist the impact of saltwater, erosion and fluctuations in temperature among other factors.
Steel jacket rigs, which generally comprise several decks supported by legs connected to the top of the piles, account for more than 90% of global offshore platforms and feature a space framed structure with tubular members supported on piled foundations. To protect these areas from the highly corrosive elements, thermal spray aluminium, glass flake epoxies, solvent free epoxy coatings and polyurethane are applied. Rubber among other specialist coatings and materials can also be used for the protection of conductor guides.
Other offshore structure types that will have protective coatings applied also include concrete gravity, compliant tower, tension leg platform, spar platform and FPSO (Floating Production, Storage and Offloading), semi-submersible platforms and jack-up drilling rigs.
A coating survey, which must be done in co-operation with the structure operator, is required to establish the condition of a coating on an offshore platform. Coating surveys may also be necessary for a maintenance painting specification and to ensure compliance with guarantees. Evaluation of coating performance can also aid the specification for future projects.
Various criteria for evaluation may be specified by the offshore operator. These include the employment of the European Scale of Degree of Rusting for Anti-corrosive Paints to define the maximum amount of rust – for example, Re 6 – and the use of ISO 4628 for evaluation of blistering, flaking, rusting, cracking and chalking.
It’s worth noting that access to the substrate can be a significant issue when surveying. Unless there is scaffold or permanent access (or rope access is used), the coating surveyor will have to rely on visual assessment rather than physically checking the adhesion and thickness in many areas.
