ANTIFOULING PROTECTIVE COATINGS
- 28 April 2017
- Posted by: Stm Coatech
- Category: Educational Articles
Antifouling kaplama, teknede organizmanın büyümesini önlemek için genellikle gemi veya tekne gövdelerinde uygulanan özel kaplamanın bir türüdür. Geminin bu bölümünde bulunan organizmalar dayanıklılığını ve performansını önemli ölçüde etkileyebilir.
ANTIFOULING PROTECTIVE COATINGS
What does Antifouling Coating mean?
Antifouling coating is a type of specialized coating that is usually applied on ship or boat hulls to inhibit organism growth on the hull. The presence of organisms in this part of the vessel could greatly affect its durability and performance.
Other than fighting the growth of microorganisms, this paint also serves as a corrosion barrier for hulls, which improves performance and water flow across the vessel hull.
Antifouling coating is also known as bottom paint.
Antifouling coating prevents fouling growth through the production of ingredients that prevent organisms from settling. Its use plays a huge role in decreasing not only the commercial costs of vessels, but the total operational expenses of maritime industries and others.
For instance, fuel constitutes more than half of the entire operating costs of vessels. If antifouling coatings are not used, the consumption of fuel as well as the emission of carbon dioxide could raise significantly. This can be the same in other industrial machinery.
Moreover, most high-quality antifouling coatings could deliver lifetime benefits like extended intervals of dry dock or decreased dry dock, which in turn lowers maintenance expenses as well as harmful emissions. Additionally, this type of coating prevents hull and other metal structures from undergoing corrosion. Antifouling coating can improve the corrosion resistance of steel structures other than stopping the growth of microorganisms.
There are various types of antifouling coatings ranging from linear-polishing polymer (LPP) as well as the more advanced self-polishing copolymers (SPCs). With this type of product, operators can effectively extend the life of vessels and other structures, reducing the entire operation’s costs.
Advances in Antifouling Coatings Technology
Marine coating systems are applied to ships and offshore structures both in sea and fresh water environments. They serve the dual purpose of protecting the structure from deterioration and keeping the ships looking good. The world merchant fleet is comprised of bulk carriers, tankers, container ships, cargo ships, and passenger and cruise ships, among others.
Marine coatings have specific functional properties that provide superior corrosion protection to the surfaces on which they are applied. The coatings protect submerged materials such as vessels, ships, or yachts from sea water. Marine coatings also protect materials from corrosion and abrasion. The application of such coatings improves the durability and overall performance of the vessel.
The latest survey report on the global antifouling paint market, published by Markets and Markets, projects the market to grow from U.S. $5.61 billion in 2015 to U.S. $9.22 billion by 2021 at a CAGR (Compound Annual Growth Rate) of 8.6 percent between 2016 and 2021. High demand for antifouling coatings from the shipping industry is expected to drive the growth of the market in the near future, the report states.
Asia-Pacific dominates the global distribution of marine coatings for both new shipbuilding and repairs. China is fast becoming the world’s largest shipbuilding nation and has set a goal of becoming number one in the industry by 2017.
As per record from ‘The Shipbuilders Association of Japan’ the New Shipbuilding share for 2015 is: Japan 19.2%, South Korea 34.4%, China 37.2%, Europe 1.4%, and the rest of the world 7.7%.
High demand for marine coatings in Asia-Pacific, especially due to the emergence of China as a major player in the shipbuilding industry, is driving the marine coatings market in the region.
Need for fuel-saving and low emission coatings are factors that have driven the growth of the marine coatings market over the past few years. Growth in the shipbuilding industry in India, Vietnam and the Philippines is expected to provide large opportunities for players in the marine coatings market during the forecast period.
The global marine coatings market is heavily consolidated, with 80% of the market shared by five companies—AkzoNobel (through its International Paint business), Chugoku Marine Paints, Hempel’s Marine Paints, Jotun and PPG.
There are three main types of antifouling coatings; they differ in the chemistry used to control bio-fouling.
The binder in an Ablative AF slowly dissolves in seawater,so it constantly presents a fresh layer of copper on the surface.Coating inspectors should know that during a repainting project, a leach layer of loose binder remains on the surface and must be removed by waterjetting or sweep blasting prior to over-coating.
Self smoothing AFs are similar to ablative Afs; however the rate of ablation is controlled and the surface of the coating system becomes smoother during use. They may each have a leach layer, but it is very thin and does not cause the same over-coating issues of a straight ablative. A tin-free version of this material is fairly new on world markets and several different chemistries are available. It’s up to each coating inspector to learn from AF manufacturers the over-coating specifics of each product.
Foul release Afs do not contain certain biocides and work on the principle of a non-stick surface. Bio-fouling attaches to ship surfaces while it is in dock or traveling very slowly. As soon as the vessel reaches about 14 knots, the bio-fouling slides off. The negative aspect of this type of AF is that it damages easily. Also, micro-fouling in the form of slime can stay attached, leaving the hull with a rough finish and increasing drag. Coating manufacturers are working on newer versions of this type of material to reduce both of these negatives.
These systems require very specific primers and intermediate coats and application is a little more complicated than typical coating application. Ensure that workers follow all recommended products and steps during surface preparation and application.
The film thickness of each coat of AF is very important to the life of the coating system,more so than with most typical coatings. Coating inspectors need to carefully measure the primer coats to ensure each coat of AF is applied at the specified thickness. In addition, any roughness in the applied coating will add drag and reduce the ship’s efficiency. Watch for correct application techniques and any over spray on the finish coat.
Traditional AF coatings are single package materials that generally cure by solvent evaporation. They do not adhere well to a cured epoxy coating, which is usually an undercoat. Application must be done in a very narrow time frame,commonly within 12 hours of the final coat of epoxy. An informal test to determine if the epoxy is cured enough to overcoat, is to push your thumbnail into the coating. If this indents the surface and it is not sticky with wet paint,it may be the right time to overcoat. If the surface does not indent,then the undercoat may have cured too much,so a thin tie coat needs to be applied. If the surface is still “sticky” to the touch, it has not cured enough. Ensure the applicator waits until cure is complete before AF application.Refer to the technical data sheets for specific recoat information.
A few of the major AF manufacturers have a special modified epoxy that has a narrower overcoat window to use as the intermediate coat in AF systems. Read the data sheet for each coat and never assume that the “rule of thumb” of coating while the epoxy is still soft is always true.
b-Recoating Existing Afs
It is fairly common for a commercial vessel to dry dock needing a %20 spot blast to a commercial finish, a full sweep blast, two spot coast of epoxy on the commercially-blasted finish, and one or two full coats of AF applied. It is necessary to ensure that the spot-blasted areas are feathered in.
Corosion Pedia,Antifouling Coating,Erişim Tarihi:27 Nisan 2017, https://www.corrosionpedia.com/definition/1451/antifouling-coating