Paint for corrosion

Refrigerated storage tanks are iasulated usiag great care to minimize heat loss and access of air and moisture to the iasulation or metal surface. In double-wak tanks, the annular space is usuaky fiked with perlite and the external surface of the outer tank is painted for corrosion protection. 

Painting for corrosion protection usually involves a thorough cleaning of the metal surface to remove any corrosion products followed by application of a primer containing a corrosion inhibitor such as zinc chromate or calcium plumbate next follows a heavily pigmented undercoat for the purpose of reducing the permeation of water to the metal surface elimination of the internal circuit— the electrolyte), finally a third decorative coat that is resistant to the atmosphere. 

Samui, A.B., et al. 2003. Study of polyaniline containing paint for corrosion prevention. Prog Org Coat 47 (1) 1. 

Zinc yellow became an important corrosion-inhibiting pigment for aircraft during World War II. However, the war production rate of 11,000 t/yr has not since been reached. Now, 2inc yellow is widely used for corrosion inhibition on auto bodies, light metals, and steel, and in combination with red lead and ferric oxide for stmctural steel painting. 

Fouling organisms attach themselves to the underwater portions of ships and have a severe impact on operating costs. They can increase fuel consumption and decrease ship speed by more than 20%. Warships are particularly concerned about the loss of speed and maneuverabiHty caused by fouling. Because fouling is controUed best by use of antifouHng paints, it is important that these paints be compatible with the system used for corrosion control and become a part of the total corrosion control strategy. 

Most steels when exposed to air will gradually rust. (This does not apply to all steels stainless steel for example was invented - in Sheffield - specifically to resist rust.) Steel has therefore always been covered - frequently painted for example - by its users in order to protect it. Nowadays the steelmaker can improve steel s corrosion resistance by coating it in the factory prior to delivery to the end-user. A wide range of different coatings is available, including ... 

Paint for structural steelwork is required mainly to prevent corrosion in the presence of moisture. In an industrial atmosphere this moisture may carry acids and in a marine atmosphere this moisture may carry chlorides. Paint is therefore required to prevent contact between steel and corrosive electrolytes, and to stifle corrosion, should it arise as a result of mechanical damage or breakdown of the coating through age and exposure. 

Paints used for protecting the bottoms of ships encounter conditions not met by structural steelwork. The corrosion of steel immersed in sea-water with an ample supply of dissolved oxygen proceeds by an electrochemical mechanism whereby excess hydroxyl ions are formed at the cathodic areas. Consequently, paints for use on steel immersed in sea-water (pH 8-0-8-2) must resist alkaline conditions, i.e. media such as linseed oil which are readily saponified must not be used. In addition, the paint films should have a high electrical resistance to impede the flow of corrosion currents between the metal and the water. Paints used on structural steelwork ashore do not meet these requirements. It should be particularly noted that the well-known structural steel priming paint, i.e. red lead in linseed oil, is not suitable for use on ships bottoms. Conventional protective paints are based on phenolic media, pitches and bitumens, but in recent years high performance paints based on the newer types of non-saponifiable resins such as epoxies. 

Chromates are very effective inhibitors of the corrosion of magnesium alloys by saline and other waters, and many treatments have been developed by means of which substantial hlms containing slightly soluble chromate are formed in the metal surface. Except on parts which are to be exposed only to a rural atmosphere, chromate treatment must be supplemented by paint, for which it provides a good base. 

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