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Old 20th July 2013, 14:51   #1
RedSeaDiver
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Bubbling of coating?

Has anyone else had this problem? The black coating on the can of my Mark VI has developed raised bubbles or something similar under the coating right where the o-rings on the bottom cover are supposed to seal. It is on the inside of the can right where one of the bolts screw into the thread on the outside. The bubbling is so bad that I have my doubts that the o-rings are going to seal adequately so I'm concerned that it is going to leak at that point.
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Old 20th July 2013, 17:15   #2
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Re: Bubbling of coating?

Bummer! Sounds like Aluminium corrosion?

It's so tight around that bottom seal I bet you could sand it all off
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Old 20th July 2013, 18:27   #3
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Re: Bubbling of coating?

+ 1 on the corrosion

if the unit is not that old I'd try and see what your local Poseidon Centre say about it.


Of its old you you may find there not interested. Most likely there is pitting under the coating you would need to clean that out and then fill the pits with an epoxy before blending it in with the rest of the surface so the o rings seal.
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Old 21st July 2013, 02:05   #4
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Re: Bubbling of coating?

You have crevice corrosion IMHO caused by salt water getting between the coating and aluminum almost certainly from the transition to the threads themselves. Its aggressive but mainly cosmetic and I know as I have an aluminum boat.

Normally AL/SS bolts are treated with something like tefgel but if its a breathing hose, that not going to work.

If it was mine, I would strip it down and have it repainted or anodized and any aluminum/stainless steel interface needs special attention. Doing nothing is not an option.
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Old 21st July 2013, 12:11   #5
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Re: Bubbling of coating?

Quote: (Originally Posted by DwayneJ) View Original Post
You have crevice corrosion IMHO caused by salt water
I had that once, too much ocean diving in the Florida heat. A cool water spray and then application of a topical cream like savlon helped tremendously.
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Old 21st July 2013, 12:31   #6
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Re: Bubbling of coating?

Quote: (Originally Posted by DwayneJ) View Original Post
You have crevice corrosion IMHO caused by salt water getting between the coating and aluminum almost certainly from the transition to the threads themselves. Its aggressive but mainly cosmetic and I know as I have an aluminum boat.

Normally AL/SS bolts are treated with something like tefgel but if its a breathing hose, that not going to work.

If it was mine, I would strip it down and have it repainted or anodized and any aluminum/stainless steel interface needs special attention. Doing nothing is not an option.
I think this may be an issue for a few Discos Poseidon used SS helicoils for the threads in quite a few places on the scrubber case. But I think the issue that is being described is on the inside sealing face so unless the corrosion has gone all the way through the case it sounds localised. If its gone all the way through it could be a bigger problem.
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Old 21st July 2013, 16:22   #7
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Re: Bubbling of coating?

Quote: (Originally Posted by Diveratt) View Original Post
I think this may be an issue for a few Discos Poseidon used SS helicoils for the threads in quite a few places on the scrubber case. But I think the issue that is being described is on the inside sealing face so unless the corrosion has gone all the way through the case it sounds localised. If its gone all the way through it could be a bigger problem.
I don't think that it is all the way through, just a localised problem on the inside sealing face as you described. It's just a pain in the butt that it has happened right where the two o-rings seal against the inside of the can.
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Old 21st July 2013, 16:26   #8
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Re: Bubbling of coating?

Quote: (Originally Posted by Diveratt) View Original Post
I think this may be an issue for a few Discos Poseidon used SS helicoils for the threads in quite a few places on the scrubber case.
This is one of the reasons why I have a Titanium rebreather. I still have to deal with Ti-SS interfaces but its not as bad as SS-Al.
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Old 22nd July 2013, 13:11   #9
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Re: Bubbling of coating?

Quote: (Originally Posted by DwayneJ) View Original Post
This is one of the reasons why I have a Titanium rebreather. I still have to deal with Ti-SS interfaces but its not as bad as SS-Al.
agreed.for you guys who put ss bolts into helicoils , they will corrode quickly , if you wrap your ss bolt threads in teflon tape first , they will not corrode trust me , ,placing anodes on your kit will alleviate many of the problems even between ss and ti , although it is less of a prob. i use titanium bolts on my titanium so have no issues with that
mike
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Old 22nd July 2013, 15:07   #10
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Re: Bubbling of coating?

Quote: (Originally Posted by michael hearn) View Original Post
agreed.for you guys who put ss bolts into helicoils , they will corrode quickly , if you wrap your ss bolt threads in teflon tape first , they will not corrode trust me , ,placing anodes on your kit will alleviate many of the problems even between ss and ti...
Check out Tefgel or its equivilent - Its purpose is mitigate issues with dissimilar metals Just to clarify, galvanic corrosion will jump start crevice corrosion.

Quote: (Originally Posted by michael hearn) View Original Post
... although it is less of a prob. i use titanium bolts on my titanium so have no issues with that
mike
Thanks... What is your source for Ti Bolts?

Last edited by DwayneJ; 22nd July 2013 at 15:18..
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