The dreaded C word (corrosion)

The last time I removed the strobe cables from the camera bulkhead feed-throughs I noticed some white power inside the connectors. The pins were perfectly dry, so I know that there was no leakage. After a through cleaning, it seems clear it was the dreaded C word (corrosion).

I did a little poking about and think I know what is going on. My Aquatica housing is nicely anodized and coated to prevent the seawater from contacting bare aluminum as much as possible. Both the housing and the door are protected by a small zinc sacrificial anode bolted to the bottom.

The bulkheads are also nicely anodized for the same reason. However, the problem is that anodize is a good insulator so the bulkhead is electrically insulated from the housing. This means that the housing zinc doesn’t project the bulkheads. I checked with an ohm meter and found that they are isolated, as expected. Where the strobe cables screw into the bulkhead, the stainless steel nut has worn away through the ano in a few places. The stainless in contact with the bare aluminum is making a battery in the sea water.

So far I have been dealing with this problem by being diligent about removing the strobe cable and cleaning the bulkhead after each day of diving, but it seems clear to me that the design is flawed. Of course this is just cleaning up the corrosion products.

A better solution would be to have a contact on the inside of the housing that electrically connects the body of the bulkhead to the housing. Alternatively I can make a ring that mounts onto the strobe cable and electrically tie them to one of the stainless steel bolts holding on the handles.

Has anyone else had this problem and come up with a solution?

Hi Steve!

I'm not sure if there is a solution of this problem that does it once for all (except of having a non-metallic housing).

Contact corrosion, as it is called, is a very local effect. I'm not sure if you can prevent it by having a good electrical connection. Also, this would mean to expose some other parts unprotected to the environment. It might be possible that you spend some "electrical shortcuts" that will dissolve in time and will have to be replaced in certain intervals to keep the expensive parts of the housing free of corrosion.

I'll try to get some infos from people dealing with that topic in detail.

Helge ;-)=)

Electrolytic corrosion is a well known problem and can be problematic in strobe connection sockets. Its severity depends on the interaction between the strobe cable end connector and the socket - some combinations are worse than others - and whether seawater enters the treads - some cables have a sealing 'O' ring to prevent this. Solutions that will help reduce the problem include lightly greasing the treads with silicone grease and regular cleaning of them, and not leaving the cable attached to the housing after use (I recommend removal after a day's diving or a weekend. I have had to use big grips to remove some cables from housings - inculding one which had been left assembled for many months - and have had to replace many connection sockets upon failure - which may have been exacerbated by slight leakage due to this sort of corrosion. The good news is that if you clean the threads regularly and disassemble cables from housing to prevent problems then the socket will be fine until it need replacing due to other problems (sockets are one of the main problems on many housings - Nikonos 5 types often rely on sprung contacts which eventually corrode or become greasy and fail - they are rarely servicable so need to be replaced if unreliable.

I too have experienced this from time to time over the years. My solution from the Nikonos days was to use a touch of WD-40 on the sync cord threads (also threaded attachments for housing handles and arms), applied with a swab so as not to touch any o-ring. This has preserved some of my cords for over a decade and also prevents any "lock-on". Electrolysis will always occur to some degree. A bit of lube or silicone grease can slow things down . . .

I am amazed at how conservative UW photographers are considering how rapidly the technology is changing. So far the responces are basically, "be careful and live with it." Maybe I'm a perfectionist. Maybe it is just that I design scientific instruments for a living, but this sort of thing tends to drive me nuts. It looks and smells to me like a design flaw that is easily remedied, resulting in a product that is more robust.

Let me clarify what I think possible improvements are>

1. Make the bulkhead body out of plastic. This eliminates the problem. Since the bulkhead is pretty beefy, there would be no issue with the pressure. The connector on my Inon stobes has a plastic body and works just fine and might actually be cheaper than that AL bulkhead

2. Make the bulkhead body out of stainless. This is probably expensive.

3. Add a ground lug to the AL connector body. This is basically free.

Since I already have an AL connector, I am going to try option 3 and see how it goes. Of course I also plan to clean and lube the connector after each dave of diving.

Lastly, I think that one reason something like this wasn't solved years ago is that either the housing vendors don't dive with their own products, or that they have plausible deniability. If the bulkhead corrodes, they can always say that it was inadequate maintenance, even if a simple grounding wire could have prevented the problem in the first place!

I think option 2 might be more expensive then you think. It might eat away you aluminium housing if exposed only a bit.. Better dont youe your whole housing as sacrificing metal......

I think option 2 might be more expensive then you think. It might eat away you aluminium housing if exposed only a bit.. Better dont youe your whole housing as sacrificing metal......

Option 2 won't cause the housing to corrode since the sacrificial zinc anode protects it. Besides the housing already has a bunch of stainless steel bolts in it. They hold on the handles and the focus light. The lock screws for the strobe cables are SS. The point of the sacrificial zinc anode is that it will corrode before ANY of the aluminum, but it only works for aluminum that is in electrical contact with it. Any aluminum that is isolated from the zinc, such as the bulkhead feedtroughs, isn't protected.

Not all stainless is equal! You MUST use the correct grade if fitting to an alloy housing AND some stainless fittings are fitted post anodisation or other coating method and using a thread locking compound which also helps to isolate them from the alloy and prevent corrosion.

The S6 connector (as fitted to some Seacam and other housings) suffers from less problems as its component parts are better matched metalwise and is a far better connector all round - the same is true for some Nik 5 type connectors - if they are from the same manufacturer. The problems really occur if a manufacturer hasn't thought this through or when mix and matching manufacturers (some are better than others but I'm not prepared to produce a list for very obvious reasons - suffice it to say that I think that this problem is being addressed slowly but surely as time goes on and awareness increase of both problem and solutions).

Lastly, although the problem could no doubt be fully addressed, there are economic factors as well as backward compatibility concerns that prevent connectors such as the S6 being adopted on a larger scale than they are!