^ Application of Anti-Fouling Paint on a New Hull
Image Courtesy of Hein Muck at https://en.wikipedia.org/wiki/File:Nordseewerke-Stapelllauf-Frisia-Br%C3%BCssel-Helling.JPG
Prospects for the Marine Coating Industry
Research firm MarketsandMarkets estimates the marine coatings market to hit $10.4 billion by 2019. The need to protect marine assets over longer durations, continued growth of the oil-gas sector, and enforcement of the IMO ballast tank coating rules will drive this expansion.
Innovation will rise as regulators implement progressively stringent environmental laws and customers demand greener coatings that slash the ecological footprint of ships, the report added. Researchers are focusing more on developing eco-friendly coatings.
Asia-Pacific consumed over 75% of the marine coatings in 2013 and is expected to be the main market in the future. China leads the way with South Korea at second place. Possible decline in shipbuilding activity and consolidation of shipping companies pose challenges for the industry.
Most ship owner-operators ask for anti-corrosive coatings that have a 60% market share followed by anti-fouling coatings at 34%. Based on chemistry, epoxy-based marine coatings are the most popular.
Importance of Marine Coatings
Seawater is among the most corrosive of environments. It contains common salt or sodium chloride (NaCl) that lends it greater electrical conductivity and penetration ability vis-à-vis freshwater.
Corrosion, fouling, and osmotic blistering are the main issues affecting ship hulls and other marine assets. Mechanical damage, extreme temperatures, and ice promote corrosion. Fouling is more of a challenge in tropical and temperate waters.
A staggering 30% of marine assets fail due to marine corrosion. Severe fouling escalates a ship’s fuel use by as much as 40% while moderate fouling can cause 10-18% loss of speed. For every 25 micron increase in hull roughness, the engine has to pump 2-3% more power.
This transforms into more fuel use and emissions while lowering the useful life and maneuverability of ships. By cutting down fuel use and lowering maintenance hassles, marine coatings slash expenses sizably. They also save you from the wrath of environmental regulators.
Cutting friction can lower fuel use by up to 5%. Considering that ships transport over 90% of the globally traded merchandise and emit about 3.3% of all the carbon dioxide, this 5% becomes a mammoth statistic.
Threats to Marine Assets
Ships in open water have to overcome hydrodynamic friction that depends on the shape and smoothness of the hull. Plying in ice is a completely different ballgame.
In order to move through ice, hulls have to break ice, move it aside, and overcome hull-ice friction. The hull along the waterline faces maximum friction and impact. The area of this zone depends on ice thickness, hull form, and ship speed.
There was no coating system for protecting hulls from very low temperatures right up to the mid-1970s. Operators either did not coat icebreakers at all or coated them for temporary corrosion protection only because the paint wore off within the first few hours or days.
Furthermore, it is difficult to determine the extent to which various factors influence hull-ice friction. At very low temperatures, for example, snow is almost as hard as sand and adds greatly to hull-ice friction.
Such complexity means that hull smoothness becomes a very important factor for icebreakers. Operators therefore prefer coatings that are better able to maintain hull smoothness.
Hull roughness rises by around 25 microns per annum for well-maintained ships and by about 80 microns for poorly-maintained ships. The average rise is approximately 40 microns.
Mechanical damage and large temperature variations aggravate the following hazards that marine assets face:
- Osmotic Blistering
Prevention of corrosion and fouling without impacting the environment negatively is the main objective of marine coatings. Good coatings prevent these three hazards by shielding marine assets against mechanical damage, temperature variations, and stray electrical currents.
Corrosion can be:
- Rusting: corrosion of metals in the presence of oxygen and moisture
- Pitting Corrosion: formation of small holes on the metal surface. Changes in temperature, water flow, and oxygen supply over metal surface expose it to the environment
The exposed part becomes anode (positive terminal of an electrochemical cell) and the area around becomes the cathode (negative terminal) while seawater becoming the electrolyte. Anodes corrode faster
- Galvanic Corrosion: results when two different metals are connected through an electrolyte (seawater in this case). The less noble (more reactive) metal becomes the anode and corrodes
- Electrolytic Corrosion: similar to galvanic corrosion but needs an external stray current
- Cavitation Corrosion: flow imperfections create a pressure spike that removes metal
Cathodic Protection places a less noble, sacrificial anode near the to-be-protected metal. The anode corrodes faster and thereby shields the metal against pitting, galvanic, and electrolytic corrosion.
Quality coatings guard against rusting. Correct installation of electrical equipment eliminates stray currents. Harder materials better withstand cavitation. Materials such as stainless steel are naturally resistant to pitting.
Fouling is the colonization of marine assets by organisms such as algae, mussels, barnacles, seaweed, polyzoans, and tubeworms. Fouling increases with water salinity. Stationary ships are more prone to fouling because microbes cannot attach to ship hulls moving at over 1 knot.
Ships plying in tropical and sub-tropical waters (temperatures over 200C) are most prone to fouling. Hulls in temperate (5-200C) waters are moderately vulnerable while those in polar waters (below 50C) are least exposed.
Osmotic Blistering results from certain elements in coatings – glycol, polypropylene, and heavy alcohol – absorbing water inside the coated layer. This forms blisters on the outer layers of coatings.
Of all ship types, cruise ships present a unique challenge. One, they sail in diverse waters ranging from the warm Caribbean ones to the freezing Arctic waters. They sail for one day and drop anchor on the very next day, something that complicates the job of the coating designer.
Then again, different areas need separate kinds of protection. And, builders have to combine coating operations with other shipbuilding operations such as welding, cutting, assembly and the like. This makes the process complicated.
Ballast Tanks: corrosion damage to ballast tanks is usually the main reason for ships migrating to scrap yards. Presence of nobler metals, irregular and poorly coated areas, and mechanical damage expose ballast tanks to pitting corrosion.
Coatings for ballast tanks must withstand corrosion, polluted seawater, and the side effects of cathodic protection. They must also be free from pores while providing fine edge coverage and having low soluble salt concentration.
Underwater Areas: of the ship determine its safety and efficiency but are particularly vulnerable to corrosion and fouling. Coatings on these parts must resist corrosion, fouling, and abrasion while being cathodic-protection-friendly.
Cargo Tank: coatings must be compatible with diverse cargoes. They must neither contaminate any cargo nor cross-contaminate different cargoes.
Resistant to ballast water and corrosion, they must be easy-to-clean, and free from pores. Cargoes with methanol soften coatings and promote corrosion, osmotic blistering, and cracking.
Topside and Superstructure: need anti-corrosive coats that look good.
Deck Coatings: must be anti-slip even when wet. And they must stand up to weather, cleaning agents, water, cargo spills, abrasion, corrosion, oils, greases, fuels, scratching, and impacts.
After examining the threats to hulls and other marine assets that marine coatings keep at bay, literally and figuratively, it is not very difficult to see why the market for these coatings looks reasonably bright even when the global economy continues its sluggish trot.
In the second part of this series, we will take a look at some of the top marine coating companies and their products.
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