Marine anti-corrosion

16.10.2014

Combating corrosion is an ever greater concern for both navies and offshore and civilian maritime industries. In the defence sector, this is part of the capital conditions guaranteeing the availability of the resources to ensure State sovereignty at sea. Nicolas Bocca, specialist engineer in anti-corrosion coatings/protection at DCNS tells us more.

Marine corrosion has always existed in naval construction. How do we deal with this problem today?

article-anticorrosionA ship is composed of 90% steel. We estimate that approximately 25% of the world’s steel production is destroyed by corrosion, in other words, 5 tons per second. The costs arising from corrosion are calculated to be several tens of millions of euro per year for leading navies such as the French or American navies. As an expert in the naval sector, we are constantly looking for the best cost effectiveness for our clients in addition to the environmental priority.

Today, our activity meant that we had to respond to a strict environmental protection requirement. Since 2003, we no longer use tributyltin to protect the skin of French navy ships following its prohibition by the IMO directive in 1998.

“Combating corrosion requires both knowledge of the marine environment and materials, and expertise in coatings”

How is an anti-corrosion action successfully carried out on a ship?

An anti-corrosion policy must be taken into account right from the design phase. Designing a ship with a high-performance, anti-corrosion protection and with a low life cycle cost has consequences for the design, structure and construction process. Knowledge of the environment in which the ship will operate and its operating profile is essential for making the right choice of materials, protective means and coatings, including paints.

The paint and architecture of a paint system is chosen according to its function (anti-corrosion, anti-static, non-slip, conductive, radar reflective, etc.), its targeted durability and its implementation characteristics.

As for all special processes, the application of paint requires compliance with the complete procedure with specific attention paid from the surface preparation stage, i.e. cleaning the surface of its contaminants (salt, oxides, dust, etc.) using specific tools in order to enhance the adherence and service life of the coating.

For the submerged parts and if necessary, there is another means of protection in addition to the coatings: cathodic protection, which aims to bring the corrosion potential of the steel structure into its stability domain.

 

How does the coating participate in ship performance levels?

Certain paint systems have specifically military functions: radar reflection or absorption, conductive, anti-static or even non-slip on the flight decks. The coating of an aircraft carrier flight deck must, in addition to its stringent anti-corrosion characteristics, absorb particularly significant impacts without being abrasive so as not to damage the aircraft arresting cables. The arresting cable area is maintained each year. Other paint systems applied inside the ships contribute to the vessel’s fire safety, such as the intumescent paints. However, the most widely known function on a boat, and perhaps the oldest, is the anti-fouling function which ensures the cleanliness of the skin and consequently its hydrodynamic performances.

 

What is the future for coatings in naval defence?

The systems which are the subject of the most R&D studies by laboratories and companies are the anti-fouling systems where efforts are being concentrated on reducing their environmental impact, i.e. reducing the biocides used to combat biofouling of the hulls.

At DCNS, in close cooperation with our DCNS Research centre, we have and are carrying out studies which aim to improve and/or replace systems specific to whole warships in order to comply with the European directive, REACH.

A constant watch is also carried out with respect to new surface preparation means which are more environmentally friendly.

Another area of particular interest is the ship assessment and instrumentation means in order to anticipate maintenance operations.

 

Concepts

Paint system: In the majority of cases paint is applied in several coats, these coats are more often than not, composed of different products with different roles. Under the mat or gloss finish and its colour, there is an anti-corrosion protection provided by a barrier effect or by the presence of pigments in the primer in contact with the steel which also guarantees adhesion to the support. We use around thirty different paints for a surface ship or submarine.

Biofouling: incrustation of marine organisms on a solid material submerged in an aquatic environment.

REACH: Registration, Evaluation, Authorisation of Chemicals, (European regulation No. 1907/2006) which came into force in 2007 to safety the manufacture and use of chemical substances in the European industry. It lists, assesses and monitors the chemical substances manufactured, imported and made available on the European market. Between now and 2018, more than 30,000 chemical substances will be known and their potential risk established.

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