Since this form of corrosion results from water invasion in a wet or humid atmosphere, selecting cellular insulation may be the only answer. Also, it might be best to use a plastic or synthetic-rubber jacket. Such jackets are factory applied and are fire and weather resistant. They offer protection from normal abuse and from easy penetration of water. Commercial plastic jacketings normally will not corrode. For example, Hypalon resists sodium chloride solutions to 260 degrees F.

Metal surfaces can, of course, be painted. Paints can inhibit cathodic and anodic reactions, and provide a highly resistive path to current flow. However, some pigments can promote corrosion, especially in the first coat of primers. Common ones are red oxides, gypsum, ochre, graphite and lamp black. Even in the normal corrosion process, alkali is formed at the cathode; this alkaline area grows, even under paint films pigmented with zinc or aluminum.

In selecting coatings to prevent galvanic corrosion, consider the following in regard to sacrificial materials: (a) as temperature increases, there is a chance of reversal in the polarity of galvanic couples; (b) salts carried into insulation and deposited onto surfaces interfere with, or destroy, the effectiveness of corrosion inhibitors; and (c) the insulation system is not freely ventilated and may have inadequate oxygen for sacrificial reactions to occur.