Corrosion-What is it?
Simply put corrosion is oxidation of the metal usually on the surface, but it can also occur as pitting, crevice or flaking.
Oxidation occurs on any metal surface when exposed to air & moisture
In the case of underwater camera equipment, there are a number of causes other than just air & moisture, the most common being galvanic corrosion, this is when two metals of different electrical potential are joined physically or by a conductive solution and are subjected to moisture, like salt water.
Each type of metal has a potential to conduct electrical energy, and the galvanic table list all metals in order of their potential rating. Any two metals joined with dissimilar ratings are likely to react with each other. The greater the potential difference between metals the faster the rate of corrosion.
Most metals react with with moisture & most metals The more noble metal will become the cathode while the less noble will become the anode, the greater the potential difference between the metals, the faster the anode will suffer corrosion.
As you can tell there are many variables with galvanic corrosion, and the best protection found so far to reduce the effect is the sacrificial anode. This works best when the anode is sized correctly to have the biggest effect.
So the physical size of the anode compared to the cathode, basically means the smaller the anode in relation to the cathode the higher the rate of corrosion of the anode.
This anode needs to give enough protection over a long enough period for our kit, preferably protecting between services. Obviously we all have different dive logs so most anodes overshoot the average divers experience, but they are always available as a spare for you to change.
However with worth noting that any sulfate’s or bacterial deposits left on your kit can also cause a continued cycle of attack even when out of the water.
This is another reason why metals corrode much faster in salty water than fresh water, but even faster when they are continually immersed & removed.
This is the most difficult environment to stop damage from occurring, which is why it’s so important to understand how to protect your valuable kit from corrosion or be resigned to renew it.
I have a routine of testing and replace failing surface sport kit that has been damaged by salt corrosion at least once a year!
The piece of kit I find most vulnerable and is critical to safety, is the carabineer this is not easy to dismantle or clean thoroughly and sometimes I am on the water for several days, getting wet/dried repeatedly, any surface wet sports will suffer the same problems with critical kit and often replacement is the only option.
Obviously most manufacturers try to limit this corrosion so it’s worth thinking about the efficiency and relevance of the presence of any protective coatings, barriers, inhibitors and of course the efficiency of the electrolytic, what contaminants the water has that you are diving in, is it fresh but in an area with harmful deposits e.g. iron ore, chemicals, acidic or alkaline and of course wether it is fresh water or salty.
I think you will agree understanding the problem is probably enough, finding out what contaminants are effecting your housing on any trip, is probably way beyond most mortals!