Flexible coatings for marine structures

All maritime structures, such as platforms, offshore installations and ocean-going ships, are strongly and constantly affected by abrasion and corrosion. This translates into important investments for the companies that manage them.

The marine environment is hostile to surface coatings, both in terms of wear and application methods. Some of the most affected areas are bridges, superstructures, ballast tanks and anchor or chain wells. These areas are exposed to extreme exposure to salt water, chemicals and abrasion.

One way to minimize and mitigate the effect of some types of corrosion is through the use of surface coatings that are flexible, waterproof and resistant to chemical attack from salt and petroleum products.

The coverings used must also have anti-slip properties to provide safety for personnel while moving on floors and walkways.

Abrasion protection

These coatings are specially developed for the oil and gas industry which performs drilling operations using core drills and pipes. If the latter were not protected by a coating, they would be subject to a strong abrasive force which would expose the bare metal to direct and rapid corrosion.

To prepare surfaces for the coating treatment, it is necessary to sandblast to clean any existing coatings and profile the surface thus creating optimal adhesion of the primer and protective coating.

A zinc-rich primer is first applied to the prepared metal surface, onto which a second spray primer is quickly sprayed. The best primers for this type of application contain no volatile organic compound (VOC) and can be applied quickly by spray.

For maximum protection, a thick layer of polyurea is finally applied for a thickness of 3000 microns (3 mm). This final coating is chosen for its resistance to extreme weathering, excellent flexibility and impact resistance. Polyurea has the ability to cure quickly, allowing crew to walk on the surface in minutes, making it easy to walk on the structure, and minimizing downtime and drying time (a fast-setting coating can cure in just 6 seconds).

Unlike all other coatings, pure polyureas are not adversely affected by ambient humidity or temperature during application, making them ideal for offshore operations.

Polyurea characteristics

Polyurea is an elastomer that forms when a liquid isocyanate is mixed at high pressure with an amine. Isocyanates are reactive because the covalent double bond connecting the carbon atom to the nitrogen and oxygen atoms easily breaks to form single bonds in the more stable tetrahedral configuration around the carbon atom.

Some types of polyureas come as a two-part solution that is mixed at high temperature and pressure (3000 psi at 65ºC) in a specially designed spray equipment. Once applied, the excellent chemical cross-linking produces a dense yet flexible surface. The high density makes the coating almost impervious to abrasion, water and chemicals.

Another advantage is polyurea's ability to be sprayed up to 6000 microns thick (and beyond) onto an inclined or vertical surface without sagging or running. The surface of a thick polyurea coating is easy to maintain, clean and, if necessary, repaint.

While epoxy resins and paints form a solid, rigid shell, the flexibility of pure polyurea coatings allows them to move with the expansion and contraction of the underlying structure as temperatures change.