A harsh environment we call home
It is often said that the ocean is one of the most corrosive places on earth. This is primarily due to the fact that sea water is an extremely good conductor that promotes a number of electrochemical reactions between sea-going structures and the body of water.
And with different materials prompting different types of reactions, the degree of corrosiveness varies accordingly. Where steel experiences generalised corrosion throughout its material structure, stainless steel on the other hand experiences a very localised form of corrosion, as does aluminium. And therefore, every material calls for its very own form of anti-corrosion.
Precious metals worth protecting
The two most common and widespread anti-corrosion methods in use today are the application of paint, in its numerous compositions, and the installation of cathodic protection which is a technique that involves creating an electrochemical cell where the protected metal acts as a cathode and a more easily corroded ‘sacrificial’ metal acts as the anode that wears down in place of the protected metal.
The cost of durability
With various materials and various anti-corrosion methods performing better than others in terms of corrosion resistance, one might think that material selection simply involves selecting the most resistant and durable materials. However cost is and always will be an important factor in design, especially when designing marine renewable energy (MRE) structures such as tidal turbines, wind turbines and heat exchangers as they are intended to produce electricity at a ‘below the market’ price and must therefore keep a competitive price tag.
Today, cost is also becoming an increasingly crucial design constraint in the naval defence sector. One must therefore consider the initial cost of the materials as well as their associated maintenance cost throughout the product’s lifespan. The design process therefore involves making calculated ‘material vs. cost’ compromises and finding innovative solutions to optimise anti-corrosion methods and produce durable yet economical vessels and MRE structures.
Anti-corrosion: Another form of defence
Designing for anti-corrosion implies acknowledging the various forms and mechanisms of corrosion and taking them into consideration through a project’s lifecycle, from design through to decommissioning. Be it research and development, the identification of innovative materials and systems, material selection, construction standards, design review or testing, every piece of relevant data or knowledge contributes towards what can be considered a ‘holistic’ long-term design procedure.
Wear and tear: our most valuable indicator
Whatever the discipline, engineering design calls for reliable entry data. When it comes to anti-corrosion design for sea-going structures, this entry data may originate from a number of internal sources. They include in-service monitoring via sensors, in-situ observations and research and development. These are precisely the activities that DCNS Research’s marine corrosion centre in Cherbourg carries out on a daily basis. As an integral part of DCNS group, the marine corrosion centre in Cherbourg benefits from invaluable ‘field’ data as well as complementary data resulting from their in-house research and testing facility. With the use of advanced laboratory equipment, the marine corrosion centre is capable of recreating sea-going conditions thus producing relevant data used to develop and optimise the design of the various types of structures.
An additional and more recent design constraint is that of environmental sustainability. With the introduction of the European Union regulation REACH, a number of products are no longer on the market and DCNS is obliged to abide by more stringent regulation on the use of polluting substances, especially those used in various types of paints designed for anti-corrosion. Such non-polluting paints are the focus of extensive research.
Historically the field data used in design originates from the naval defence industry, however with DCNS group diversifying into the MRE industry, its research efforts are also being diversified. Though the two primary anti-corrosion methods used in both industries are the same, real maintenance opportunities on naval vessels and MRE structures differ significantly. This is why there is a real need to adapt the anti-corrosion design depending on the type of structure. The two industries serve vastly different purposes, however it is safe to say that their technologies are 100% compatible and complementary, and breakthroughs made in the MRE industry are generally applicable to the naval defence sector, and in some cases even reveal more economical solutions and scenarios.
Ultimately, research and development in the MRE sector leads DCNS experts to approach anti-corrosion problematic in a different light, which can only be beneficial for both industries.