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High-performance anticorrosion coatings are applied to steel and concrete structures to provide protection from corrosive environments. Generally, the coatings are separated into two major markets:
- Industrial maintenance or protective coatings applied to structures in the oil and gas, petrochemical, paper mill, and power generation industries, as well as to bridges and water and waste treatment plants. Most of these coatings are applied to structures that are “on shore,” but some are applied to offshore oil and gas rigs.
- Marine coatings applied to commercial ships, including freight carriers, tows, cruise ships and others.
The same types of coatings tend to be used in each market, and tend to be based mainly on epoxy, urethane and ethyl silicate, and to a lesser extent, acrylic, vinyl and chlorinated rubber binders. Epoxies account for around 40% of the global market; these coatings are noted for very good chemical and abrasion resistance and for excellent adhesion. Urethanes, accounting for 15–20% of consumption, display excellent color and gloss retention, and good abrasion resistance and flexibility. Ethyl silicates are used mainly as binders for zinc dust; these inorganic zinc coatings form excellent primers, providing superior corrosion resistance to the surface. Vinyls and chlorinated rubber coatings provide good corrosion protection and are easily applied. Often, combinations of coatings are used. As an example, the primer may consist of an inorganic zinc coating, while the intermediate coat is epoxy and the topcoat is urethane. Alkyds, which are polyesters modified with fatty acids or oils, are used in environments that are subject to little, if any, corrosive elements. Alkyds are still favored by many contractors because of their easy applicability, and are sometimes used on structures that have limited remaining service lives. Good growth is expected for coatings that are based on waterborne acrylics, especially in the United States, as environmental regulations become more stringent.
Heavy-duty coatings, applied to substrates subject to highly corrosive environments, account for about two-thirds of the total market. The other one-third consists of lighter-duty coatings applied to such areas as the interiors of industrial buildings and structures located in dry rural environments. However, architectural coatings, applied to residences, office buildings and the like, are not included. The value of the industry is much higher if one includes the value of surface preparation (cleaning the steel substrate to enhance adhesion prior to coating) and application operations. The cost of the coating material itself often amounts to only 10–20% of the installed cost of the coating. Coatings manufacturers have been stressing the life cycle concept to users over the past 20–25 years, pointing out that it is less expensive in the long term to use high-quality (and usually more expensive) coatings that have relatively long service lives; thus, savings in touch-up, repair and downtime costs can be realized over the lifetime of the structure. Unfortunately for the coatings industry, this message is becoming more difficult to sell; with the downsizing in the corporate world, many facilities have eliminated corrosion engineers and other coatings personnel who understand the value of maintenance painting. |
