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Scuba_SI

Strobe Arm Electrolysis

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On a trip to the red sea over christmas i started to get major pitting on my hotshoe adaptor on my nexus D200 housing, on it's first trip.

 

Into that hotshoe adapter i had an ULCS ball adapter (part number AD-HS) connected to an ultralight spotting light adapter (Part number AD-USL) by an INON clamp. This INON clamp was sold to me by Ocean optics as being 'the same' as an Ultralight clamp, could this be the cause of the electrolysis?

 

In 9 dives i got quite deep pitting on the hotshoe adapter (not the housing) when i had no problems in thousands of dives with my D70 rig.

 

Is the AD-HS made of two very different metals? Is it the stainless steel spring in the hotshoe?

 

Can anyone help me find the root cause of the problem?

 

Thanks!

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Dis similar metals in a conduction solution usually results in electrolysis (pitting)

 

I have always screwed a small zinc anode on the bottom of our aluminum housings and have never had a problem.

post-6133-1173414704_thumb.jpg

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Yeah,

 

I can add an anode, but i've never had one before, and if i can replace the INON clamp for an Ultralight (for example) t to stop it then i will.

 

Im just a little confused as to why products that were all ordered at the same time from the same shop and their potential use discussed are causing damage to themselves.

 

I don't think its the stainless steel spring in the hotshoe itself, i mean that would be really dumb for them to make a housing that is also a battery! So i want to find the misbehaving piece!

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Do you use Sea&Sea TTL converter ? than, pls, read this;

 

http://wetpixel.com/forums/index.php?showtopic=17021

 

if not, I have been using mixture of Inon & ULCS arms+ball joints

but, never has problem.

 

One thing you can try is isolate Camera from housing by changing base plate of housing to plastic and/or change the camera mount screw to plastic.

 

Sam

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SCUBA-SI,

 

It is difficult to impossible to do a root cause failure analysis without looking at and evaluating the failed component(s) directly. Having said that I will attempt to provide some comments that may help with this problem and others of a similar nature involving marine corrosion. I apologize in advanced for the long post but corrosion is a very difficult and misunderstood subject:

 

1. Localized corrosion in the form of pitting is often the result of "crevice corrosion". This corrosion mechanism often occurs when a passive film former (e.g. aluminum alloys, stainless steels), are "covered" by a crevice former (e.g. barnacle attached to metal, gasket at a metal joint, adapter over a metal seat). Typically, tight, deep crevices are much more of a problem than loose, shallow crevices. For example, if you take an aluminum tube and stretch a tygon tube over its end (inner diameter of the Tygon the same or less than the outer diameter of the aluminum tube) and fully immerse it in natural seawater for a few weeks. Then remove the assembly from the water and take the Tygon from the end of the aluminum. You will notice significant pitting and etching on the outer diameter of the aluminum outer diameter surface. The tighter the crevice (Tygon fit over aluminum) and the deeper the crevice (distance the Tygon is placed over the end) and the longer the assembly is in seawater the greater the depth of attack.

 

2. Dissimilar Metal Corrosion (a.k.a. Galvanic Corrosion, etc.) occurs when dissimilar metals are in direct contact with another (although a metal wire can connect two metal components that are fairly remote from other). The active metal (the anode) will corrode preferentially to the noble metal (the cathode). This is the basis for cathodic protection which is purposefully placing an active metal in contact with another more noble component in order to preclude corrosion of the more noble component.

 

Dissimilar Metal Corrosion is often erroneously cited as the reason for numerous corrosion related failures mainly because it is easy to observe that two different metals are in contact with one another and draw the conclusion. Take the same assembly cited in paragraph 1 but slide a stainless steel sleeve tightly over the aluminum tube (specific alloys are important as is anodization but for simplicity sake let's not worry about it). All else being the same, pitting on the Tygon/aluminum assembly will be as significant if not worse than the Stainless/aluminum assembly.

 

Dissimilar Metal Corrosion becomes much more significant with unfavorable anode/cathode ratios. For example, if you place an aluminum rivet in a copper plate you will get much more attack than if you place a copper rivet in an aluminum plate (all else equal of coarse: size of plate, size of rivet, method of fastening, etc.).

 

Dissimilar Metal Corrosion is most problematic in full immersion conditions (assembly immersed in seawater for "long" periods of time). In alternate immersion conditions typically encountered with underwater camera systems, the dissimilar metals only see an electrolyte (seawater) for short periods of time. In the absence of seawater electrolyte, corrosion is nil/negligible. So if you rinse your system you will see little/no attack while in atmospheric conditions. If your system is not rinsed, a consistent salt mist is present, etc. then you can see some degradation above water but damage is limited to ~6mm (1/4") from the dissimilar metal juncture (interface). This limitation is due to the thin film electrolyte on the metal surfaces which results in high ohmic resistance and thus lower current density (corrosion damage is typically directly proportional to current density).

 

3. Electrolysis is a misnomer relative to corrosion. Corrosion is degradation by electrochemical reaction(s); Electrolysis is the dissociation of water.

 

4. Stray Current corrosion can be a problem when DC currents (and/or rarely with AC currents) enter and leave a metal component. Damage is seen where the current leaves the metal component. These types of failure tend to be very difficult to evaluate and mitigate. I am not qualified to comment much on stray current corrosion.

 

Now, on to your specific problem… I would guess that the primary mechanism for pitting is crevice corrosion. There may be some aggravation by dissimilar metal contact particularly if the aluminum adapter has a small nick(s) in its surface that damaged the hard anodized protective "film" (I assume that your hot-shoe is stainless steel?). Again, very small areas of exposed, bare aluminum are much more of a problem than if the entire surface was bare. This is the result of large current density (current densities on the order of pico amps per square centimeter are significant).

 

Since you experienced significant pitting in a very short period of time, it is also possible that stray-currents were contributing. I have little/no expertise in this area and it is difficult to imagine a source. Certainly the hot-shoe directly on the camera sees currents when the strobe is fired; however, most if not all housing hot-shoes are not "live" and are simply used to attach components such as spotting lights. Any one else think of a way that stray-currents may have entered and discharged through the adapter??? Keep in mind that a salt bridge can carry significant currents from one metal to another.

 

Camera housings are generally cast aluminum with small stainless steel “inserts/attachmentsâ€. Generally, this is an acceptable materials combination; however, design, workmanship, specific alloys, etc. are important to preclude corrosion issues.

 

Lastly, I believe the folks at ULCS use hard-anodized 6061 aluminum alloy. This material is successfully used in many components subject to marine “atmospheric†conditions (seawater mist, above waterline). A good example is window frames in oceanfront homes. The material generally does pretty well in alternate-immersion service but is marginal in full-immersion service (not regarded as marine grade where high-reliability components are concerned).

 

So, I would recommend that (a) you avoid a very tightly fitting adapter (this may not be possible with your specific parts), (B) make sure the housing hot-shoe/adapter juncture is rinsed topside, © somehow verify that there is not a stray current problem and (d) minimize relative motion between the hot-shoe and the adapter. Relative motion can be the result of (a) differential thermal expansion of the hot-shoe and the adapter, (B) galling type wear when sliding the adapter onto the hot-shoe, © abrasive wear if salt and or corrosion products develop in the crevice between the hot-shoe and the adapter, (d) handling the system by anything attached to the hot-shoe, etc.

 

Again, sorry for the long post. Hope this helps in some way.

 

 

Oh and bye the way, sacrificial anodes (typically zinc alloy) on the housing are of ZERO use at the surface. Furthermore, the system spends so little time in immersion conditions (perhaps 5 hours a day for 100 days a year even for the most prolific underwater photographers) that, in my opinion, they are of little value.

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Hi H2O Planet,

 

I think you may be the person to help! My pitting is no where near as bad as that on shchaes rig, but i think his is probably caused by electrical discharge rather than galvanic corrosion.

 

I have taken some shots of the rig, in the hope that someone (you!!) might be able to find the offending item!

 

dsc_0008.jpg

 

The image above shows where i got a deposit, white and powdery, it rubbed off fairly easily. and the arrow points to where i got the pitting.

 

This shows the components of the mount for the hotshoe, im 99% sure its all aluminium except for the stainless steel washer.

 

dsc_0010.jpg

 

Then this shows the hotshoe:

 

dsc_0013.jpg

 

 

Could it be that the black surround fro the hotshoe is of an inferior quality aluminium?

 

I know its hard to tell (impossible even) but im hoping for a push in the correct direction!

 

Thanks,

 

Simon

 

EDIT:

 

I guess cold-shoe might be more accurate!

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Are you sure that this damage is not of mechanical origin? Perhaps a ding, wear, etc... Perhaps the corrosion product developed after bare metal was exposed (mechanical damaged initiation)? After now having seen photos, it doesn't look like a crevice corrosion or dissimilar metal problem. For passive film formers (stainless and aluminum) crevice corrosion manifests itself under the crevice former but the damage you show is on a "boldly†exposed surface slightly remote from any obvious crevice. If dissimilar metal contact were a problem it typically would be most significant at a stainless/aluminum interface, which is not what I am seeing in your photo. I see two dings on the aluminum "cold shoe" base somewhat remote from the stainless steel "cold shoe" rail (for lack of a better term). Again, based upon location (corner and edge), it looks like mechanical damage??? Conversely, if this aluminum base is machined from a small piece of cast aluminum then it is possible that you have surface defects that have been exposed in a very short period of time (e.g. a non-metallic inclusion, shrinkage porosity, gas porosity, etc.). However, I believe that the aluminum base is probably a wrought aluminum alloy in the 5000 or 6000 series for which you rarely experience significant surface defects during processing.

 

Lastly, regarding your question of "inferior quality aluminum" that is doubtful. Without any evidence that your problem is common for your specific equipment, it is doubtful that the original materials specifications were "inferior". Furthermore, inadequate materials substitutions (using materials other than those specified) for high reliability parts are fairly unusual. My staff and I have performed several thousand failure investigations and improper materials substitution was implicated in only a handful of instances. Conversely, poor materials selection is fairly common because most designers rarely consult with materials scientists (metallurgists, etc.) and even more rarely consider input from corrosion engineers. If this is a poor materials selection then more people should start to experience similar damage.

 

There are just so many possibilities and without looking at the components I am probably just confusing matters for you?!?! Have you spoken with the housing distributor? The OEM??

 

Just a few more points-of-information for those interested in marine corrosion:

 

For copper based alloys, crevice corrosion typically manifests itself just outside the crevice former. Conventional wisdom is that crevice corrosion of copper alloys is due to a “metal ion concentration cell†while stainless steel (and some other passive film formers) exhibit crevice corrosion damage under the crevice former due to a “differential oxygen cellâ€. So, crevice corrosion of passive film formers is particularly dangerous considering you cannot see damage unless components are disassembled (this is why non-user serviceable o-rings scare me particularly with my old Nikonus systems).

 

Conversely, even user-serviceable o-rings can be a problem particularly if you don’t do a good job of cleaning and drying equipment. I do not maintain my equipment well and have experienced damage to systems that I believe was, in part, due to crevice corrosion. For example: (1) pitting on Nikonus RS cameras where the lens o-ring (crevice former) seats at the cameras stainless steel lens opening, (2) Under clamp o-rings with ULCS arm clamps, (3) metal-to-metal crevices where sync cords mate with housing or camera bulkheads (again many attribute this to dissimilar metal corrosion but I believe it is more of a crevice corrosion problem particularly when the oxide layer (anodized layer) of a female socket (bulkhead fitting) within the camera or housing has experienced mechanical damage such as cracking, abrasion or galling). Regarding non-metallic (e.g. Delrin) male connectors for sync-cords, I believe they generally work better than metal connectors but not because this removes a dissimilar metal but rather it presents a situation where mechanic damage (a pre curser to further, more serious, crevice attack) is much less likely. However, unless you are careful the weakness of the Delrin connectors in my opinion is that they can more easily “cross-thread†…such was the case with my Ikelite cords mating Nikonus RS cameras to Substrobe 200’s.

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In 9 dives i got quite deep pitting on the hotshoe adapter (not the housing) when i had no problems in thousands of dives with my D70 rig.

 

Is the AD-HS made of two very different metals? Is it the stainless steel spring in the hotshoe?

 

Can anyone help me find the root cause of the problem?

 

Thanks!

 

Hi Scuba_SI,

 

I started a thread on that at http://wetpixel.com/forums/index.php?showtopic=17425. Various reasons have been listed above, but the solution is the zinc anode described in the thread.

Works like a charm, good luck.

Barry

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Scuba-SI,

My current Nexus housing (one I just got replaced) is my 5th Nexus housing(F4,F100,D70,D200 & D200new) & To ME, what you show is normal wear/tear/corrosion on Nexus housing. I think your housing is still cleaner/newer than my last housing (only used for 3 days diving so far). I think Nexus is using powder-coating technic & is not perfectly covering the surface of housing.

 

Sam

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Quote"

Oh and bye the way, sacrificial anodes (typically zinc alloy) on the housing are of ZERO use at the surface. Furthermore, the system spends so little time in immersion conditions (perhaps 5 hours a day for 100 days a year even for the most prolific underwater photographers) that, in my opinion, they are of little value. " Unquote

 

 

On the ship, every ship/boat has zinc anodes & it protect the ship from electricity generated by current when ship is moving/sailing. When ship was moored at dock for a year, I've seen zinc anodes were almost new.

 

Sam

Edited by shchae

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Hi guys,

 

I spent 2 years on an aluminium hulled boat so i am reasonably familiar with the replacement of anodes on a large scale, my point is though, with the exact same equipment (bar the hotshoe and hotshoe adapter, i got 0 pitting on my Nexus D70 housing, diving 4 dives every day for years.

 

If i was to go back to working in the diving industry (highly likely), this pitting would destroy that piece in a few weeks. To me this is not acceptable, and i think if you have experienced it in several nexus housings you should really contemplate changing brand! Is this the norm for other nexus users?

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Hi guys,

 

I spent 2 years on an aluminium hulled boat so i am reasonably familiar with the replacement of anodes on a large scale, my point is though, with the exact same equipment (bar the hotshoe and hotshoe adapter, i got 0 pitting on my Nexus D70 housing, diving 4 dives every day for years.

 

If i was to go back to working in the diving industry (highly likely), this pitting would destroy that piece in a few weeks. To me this is not acceptable, and i think if you have experienced it in several nexus housings you should really contemplate changing brand! Is this the norm for other nexus users?

 

"assuming" everything you say is true, it's a bad part. Either they blew the alloy and or the coating/ anodizing process, not really that uncommon.

 

Rick

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