Corrosion, types white rust

However, in this section emphasis is placed upon damp and wet atmospheric corrosion which are characterised by the presence of a thin, invisible film of electrolyte solution on the metal surface (damp type) or by visible deposits of dew, rain, sea-spray, etc. (wet type). In these categories may be placed the rusting of iron and steel (both types involved), white rusting of zinc (wet type) and the formation of patinae on copper and its alloys (both types). 

This type of corrosion can take place on any new surface of zinc and is best prevented by storing the metal in a dry, airy place until a protective layer has been formed. Zinc which has been properly aged in this way is safe against white-rust formation. Various methods are employed to prevent white rust. A chromate treatment is widely used for zinc-plated articles and for galvanised sheet, and occasionally for zinc die castings. Fatty substances, such as oils or lanolin, are sometimes used to protect larger items. 

FREEPORT, TEXAS TOTAL IMMERSION Base meal shows deep corrosion pin over 20 % of che panel surface, front and back. Sprared meal shows geneial red and white rust over che entire surface. CR seal coar is completely dissipated. Base metal shows deep corrosion piu over 4>o96 of che panel surface, froot and back. Sprayed metal shows geoerai red and white nut over the cficire surface. CR seal coat is completely dissipated. Base metal shows dem corrosion pits over 1 % of the panel surface front and back. Sprayed metal shows thin white rust and large red mil stains, froot and back. Same as Type 2. 

WRIGHTSVIUE BEACH. NORTH CAROLINA (below-low-dde) TOTAL IMMERSION Same u Type 1. Base metal shows no lots of tttei. Sprayed meal shows red rust staining over entire surface. Base metal shows a few corrosion pio and some loss steel at the edges. Sprayed mecal hosri rust stains. CR seal coat completely dissipated. Base metal oa attacked. Sprayed metal shows white rust over entire surface. CR seal coar completely dissipated. 

If patching is required due to chloride corrosion then the usual specification is to remove concrete to about 25 mm behind the rebar ensuring that all corroded steel is exposed around delaminated areas and the rebar is cleaned to a near white finish to remove all rust and chlorides. Figure 6.1 shows three types of repair. A bad repair, a good chloride repair and a patch for cathodic protection. The cut edges and faces of the concrete must be square and clean of all dust and debris. 

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