Corrosion is the deterioration of purified metals back to their oxide form through reaction with oxygen, sodium chloride and moisture in the environment. To ensure the longevity of your installations, you need to avoid it at all costs.
Oxidation of metals is an electrochemical reaction in which a natural battery is formed. The current that flows in this battery is central to an anodic process that sees metal disintegrate. The process can be accelerated when 2 metals with different nobilities are in contact with each other. During this process the metal with the least resistance to corrosion is always the one that corrodes first, and it does so much faster than it would if corroding on its own.
This anodic relationship applies to electronic security installations where cheapo metals are used in screws and mountings in contact with other metal parts. As a result, you need to ensure housings are properly prepared and painted or powder coated, with screws and bolts being marine grade stainless steel or galvanized steel. There are also coatings you can apply that will help parts resist corrosion. If you can’t find them at Bunnings, try a Marine Chandlery like Whitworths or BIAS.
The idea is to properly prepare and maintain external metal fittings, painting them and ensuring any nicks or scratches in the paintwork are retouched. You also need to ensure there’s no way moisture can build up on and around the metal conduit or its fittings. This most often happens when the conduit is mounted firmly against a wall and dust, dirt and plant matter build up in the wall side crack, retaining moisture that begins to break down the metal. It’s also important to keep fixings clean and lubricated using marine grease or a lanolin-based oil.
In terms of choice, we’d look at galvanised steel, stainless steel or copper conduits (galvanised steel and copper are cheapest), with galvanized or stainless-steel fittings. It’s also best practise to keep some metals apart – for instance, aluminium and stainless steel. You can do this with plastic spacers anywhere 2 incompatible metals will be in contact. If your installations are on the coast, you will need to be doubly vigilant when it comes to avoiding galvanic corrosion of housings, brackets and fixings.
Listed from lowest to highest resistance to corrosion are metals including zinc, untreated iron or steel, lead and tin solders; copper, brass and bronze; stainless steel (all SS grades ranging from lowest to highest in quality). Aluminium, which is used in many CCTV camera housings, has good corrosion resistance when not in contact with stainless fixings. But bring bare aluminium and stainless together in a coastal application and aluminium – even if painted – will bubble away to powder.
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