Corrosion

Generally, copper itself is resistant to corrosion; however, rainwater run-off may cause staining on adjacent materials and severe corrosion to other metals. Zinc, galvanised steel and non-anodised aluminium should not be used under copper, although in this respect lead, stainless steel and brass are unaffected. Copper may cause corrosion to steel or anodised aluminium in direct contact, if moisture is present. Specifically, copper should not be installed below exposed bitumen, bitumen paint, or cedarwood shingles where leaching action producing acid solutions can cause localised attack on the metal. Additionally, some corrosion may arise from the acid produced by algae on tiled roofs. The accidental splashing of lime or cement mortar onto copper causes a blue-green discolouration; however, this can readily be removed with a soft brass brush. Some corrosion of copper pipework may be caused by soft water, particularly if high levels of dissolved carbon dioxide are present; hard waters generally produce a protective film of calcium compounds which inhibits corrosion. Pitting corrosion has been reported in rare cases associated with either hard deep-well waters or hot soft waters with a significant manganese content. Additionally, excessive acidic flux residues not removed by flushing the system may cause corrosion. Within heating systems in which oxygen in the primary circulating water is constantly being replenished through malfunction or poor design, bimetallic corrosion will occur between steel radiators and copper pipework. This will result in the build-up of iron oxide residues at the bottom of the radiators. The use of appropriate inhibitors will reduce this effect.

Fig. 5.21 Copper roof construction - Urbis Centre, Manchester. Architects: Ian Simpson Architects. Photograph: Courtesy of Chris Hodson
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