Meg Aluminium can "decaying"?

Outlaw · 17th October 2007, 14:17

ok, suppose i put some rubber tube, specially the ones they put inside the old car weels....then how about the clips that hold the head? aren't they made from a different metal connecting to the Aluminium?

i would like to see pics if possible guys.

Thanks. i dont think everyone knew about this issue, at least i did not...

Joe · 17th October 2007, 14:56

The Meg is shipped with webbing around the bands. Did you remove it? Or did you buy it stripped without the tiger gear? Tiger gear it is aluminum so disimilar metals is not an issue. Other brands are steel so you need to use a barrier. Also the can is anodized.

Like others said, put some inner tube under anything touching the can that is not aluminum and you will solve the problem. (Also thoroughly hose down the unit with fresh water asap when diving in sea water.)

PSquared · 17th October 2007, 15:26

Just to get the paranoia going .....

Chrome plated brass pillar valve, aluminium neck ......... admittedly no exposure to sea water except the interface where the pillar valve "flange" meets the cylinder neck.

If I was going to get worried, which I am not, this would give me more sleepless nights than some unsightly marks on my stack.

HMP · 17th October 2007, 15:41

The best way to completely stop the damage getting worse would be to put an anode some were on your rig. Anodes are frequently (frequently? I mean always) used on aluminium camera housings to prevent just this kind of problem and I have just installed one to prevent some corrosion on some new electronics pods in my 15.5
Anodes work and they can be pretty small. The dont have to be touching the corroded area just vaguely near so just one will probably do.
You can get them in all sorts of shapes and sizes from a boat chandlers as almost every boat and boat engine in existence uses them. You could thread one on to an existing jubilee clip or put a band around your scrubber and put one either side or the scrubber near the cylinders between the cylinders and your back. You wouldn't even know they were there, and it would look after all your metal.
Or you could get a plastic housing (sorry bad joke)

Hugh

UKSteve · 17th October 2007, 16:12

Quote: (Originally Posted by Meng_Tze)

Galvanic corrosion does happen yes, but will it corrode through the material (Al)? In 200 years maybe (or whatever big number, point is; not in our lifetime under normal diving circumstances). It is not pretty on tanks or the meg can, but not a mechanical problem. If you want to make sure it does not happen, put a barrier between the dissimilar metals.

Not through .... but it does not require much corrosion for a cylinder to fail the visual inspection that goes along with a hydro test. I don't have access to the British Standard for dive cylinder inspections... anyone in the business able to recall how much of a wormhole will result in failure of the cylinder?

Steve

**diver1369** · 17th October 2007, 16:48

"Not through .... but it does not require much corrosion for a cylinder to fail the visual inspection that goes along with a hydro test. I don't have access to the British Standard for dive cylinder inspections... anyone in the business able to recall how much of a wormhole will result in failure of the cylinder?
Steve"

Not a professional, but:

CGA C6.1 Std (AL): if wall thickness is .2" (5.08mm) or greater (most SCUBA 3AL cyls), general corrosion may remove up to 0.030" (0.76mm) and individual pits may be up to .060" before the cylinder should be removed from service.

Line corrosion of 6 inches or more in AL, regardless of depth, should render the cylinder unserviceable (per Luxfer).

In steel cylinders, line corrosion 6" or greater, and over .020" (.51mm) deep will be reason for failure of the cylinder. Individual pits in steel are generally left to the inspector's judgement becasue they may result in a leak, but not a rupture (per PSI and CGA). The pit inspection disc that PSI sells only goes up to 0.10 inch, which suggests that is at or over the maximum pit depth that requires such 'judgement'.

Personally, I'm a bit more picky than the stds for any tank I dive (or inspect for others).

BTW, dielectric thread compound will remove the concern of AL tank threads and non-AL valve stems.

john

scubadan · 18th October 2007, 03:00

Quote: (Originally Posted by Outlaw)

...then how about the clips that hold the head? aren't they made from a different metal connecting to the Aluminium?

The stainless steel clips are insulated from the aluminum can with a silicone grease such as Dow 111. I searched online and found a free sample. Probably more than I will ever need.

Dan

Outlaw · 18th October 2007, 06:03

Quote: (Originally Posted by HMP)

The best way to completely stop the damage getting worse would be to put an anode some were on your rig. Anodes are frequently (frequently? I mean always) used on aluminium camera housings to prevent just this kind of problem and I have just installed one to prevent some corrosion on some new electronics pods in my 15.5
Anodes work and they can be pretty small. The dont have to be touching the corroded area just vaguely near so just one will probably do.
You can get them in all sorts of shapes and sizes from a boat chandlers as almost every boat and boat engine in existence uses them. You could thread one on to an existing jubilee clip or put a band around your scrubber and put one either side or the scrubber near the cylinders between the cylinders and your back. You wouldn't even know they were there, and it would look after all your metal.
Or you could get a plastic housing (sorry bad joke)

Hugh

hi mate,

call me stupid, but i was never good with chemistry. do you have any pictures or any links as to the parts that you are using?

Thanks to you and to all who contributed.

Spyros

17th October 2007, 14:17	#11 (permalink)
Outlaw In search of Law breaking Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Cyprus, Nicosia Posts: 626	Re: Meg Aluminium can "decaying"? ok, suppose i put some rubber tube, specially the ones they put inside the old car weels....then how about the clips that hold the head? aren't they made from a different metal connecting to the Aluminium? i would like to see pics if possible guys. Thanks. i dont think everyone knew about this issue, at least i did not... __________________ CMAS - IANTD - TDI Kamikazi Instrustor Trainer DIRRebreather Team Member ---------------------------- "Once an Outlaw, always an Outlaw"
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17th October 2007, 14:56	#12 (permalink)
Joe Custom Title Allowed! Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Oct 2005 Location: Florida, USA Posts: 237	Re: Meg Aluminium can "decaying"? The Meg is shipped with webbing around the bands. Did you remove it? Or did you buy it stripped without the tiger gear? Tiger gear it is aluminum so disimilar metals is not an issue. Other brands are steel so you need to use a barrier. Also the can is anodized. Like others said, put some inner tube under anything touching the can that is not aluminum and you will solve the problem. (Also thoroughly hose down the unit with fresh water asap when diving in sea water.)
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17th October 2007, 15:26	#13 (permalink)
PSquared New Member Current Rebreather/s: Megalodon Other Rebreather/s: Inspiration Classic Join Date: Apr 2007 Location: South Africa Posts: 29	Re: Meg Aluminium can "decaying"? Just to get the paranoia going ..... Chrome plated brass pillar valve, aluminium neck ......... admittedly no exposure to sea water except the interface where the pillar valve "flange" meets the cylinder neck. If I was going to get worried, which I am not, this would give me more sleepless nights than some unsightly marks on my stack. __________________ P2 The voices say I wasn't really diving solo
(Online)

17th October 2007, 15:41	#14 (permalink)
HMP New Member Current Rebreather/s: MK 15.X Dolphin Other Rebreather/s: Inspiration Vision Dolphin Join Date: Aug 2006 Location: Plymouth, U.K. Posts: 93	Re: Meg Aluminium can "decaying"? The best way to completely stop the damage getting worse would be to put an anode some were on your rig. Anodes are frequently (frequently? I mean always) used on aluminium camera housings to prevent just this kind of problem and I have just installed one to prevent some corrosion on some new electronics pods in my 15.5 Anodes work and they can be pretty small. The dont have to be touching the corroded area just vaguely near so just one will probably do. You can get them in all sorts of shapes and sizes from a boat chandlers as almost every boat and boat engine in existence uses them. You could thread one on to an existing jubilee clip or put a band around your scrubber and put one either side or the scrubber near the cylinders between the cylinders and your back. You wouldn't even know they were there, and it would look after all your metal. Or you could get a plastic housing (sorry bad joke) Hugh
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17th October 2007, 16:12	#15 (permalink)
UKSteve Still a novice... Current Rebreather/s: Inspiration Vision Other Rebreather/s: Join Date: Jul 2005 Location: Weymouth, UK Posts: 557	Re: Meg Aluminium can "decaying"? Quote: (Originally Posted by Meng_Tze) Galvanic corrosion does happen yes, but will it corrode through the material (Al)? In 200 years maybe (or whatever big number, point is; not in our lifetime under normal diving circumstances). It is not pretty on tanks or the meg can, but not a mechanical problem. If you want to make sure it does not happen, put a barrier between the dissimilar metals. Not through .... but it does not require much corrosion for a cylinder to fail the visual inspection that goes along with a hydro test. I don't have access to the British Standard for dive cylinder inspections... anyone in the business able to recall how much of a wormhole will result in failure of the cylinder? Steve
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17th October 2007, 16:48	#16 (permalink)
diver1369 Supporting Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Sep 2005 Location: Maryland, USA Posts: 68	Re: Meg Aluminium can "decaying"? "Not through .... but it does not require much corrosion for a cylinder to fail the visual inspection that goes along with a hydro test. I don't have access to the British Standard for dive cylinder inspections... anyone in the business able to recall how much of a wormhole will result in failure of the cylinder? Steve" Not a professional, but: CGA C6.1 Std (AL): if wall thickness is .2" (5.08mm) or greater (most SCUBA 3AL cyls), general corrosion may remove up to 0.030" (0.76mm) and individual pits may be up to .060" before the cylinder should be removed from service. Line corrosion of 6 inches or more in AL, regardless of depth, should render the cylinder unserviceable (per Luxfer). In steel cylinders, line corrosion 6" or greater, and over .020" (.51mm) deep will be reason for failure of the cylinder. Individual pits in steel are generally left to the inspector's judgement becasue they may result in a leak, but not a rupture (per PSI and CGA). The pit inspection disc that PSI sells only goes up to 0.10 inch, which suggests that is at or over the maximum pit depth that requires such 'judgement'. Personally, I'm a bit more picky than the stds for any tank I dive (or inspect for others). BTW, dielectric thread compound will remove the concern of AL tank threads and non-AL valve stems. john
(Offline)

18th October 2007, 03:00	#17 (permalink)
scubadan New Member Current Rebreather/s: Megalodon Dolphin Other Rebreather/s: Dolphin Join Date: Jun 2006 Location: Richmond, Va Posts: 35	Re: Meg Aluminium can "decaying"? Quote: (Originally Posted by Outlaw) ...then how about the clips that hold the head? aren't they made from a different metal connecting to the Aluminium? The stainless steel clips are insulated from the aluminum can with a silicone grease such as Dow 111. I searched online and found a free sample. Probably more than I will ever need. Dan
(Offline)

18th October 2007, 06:03	#18 (permalink)
Outlaw In search of Law breaking Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Cyprus, Nicosia Posts: 626	Re: Meg Aluminium can "decaying"? Quote: (Originally Posted by HMP) The best way to completely stop the damage getting worse would be to put an anode some were on your rig. Anodes are frequently (frequently? I mean always) used on aluminium camera housings to prevent just this kind of problem and I have just installed one to prevent some corrosion on some new electronics pods in my 15.5 Anodes work and they can be pretty small. The dont have to be touching the corroded area just vaguely near so just one will probably do. You can get them in all sorts of shapes and sizes from a boat chandlers as almost every boat and boat engine in existence uses them. You could thread one on to an existing jubilee clip or put a band around your scrubber and put one either side or the scrubber near the cylinders between the cylinders and your back. You wouldn't even know they were there, and it would look after all your metal. Or you could get a plastic housing (sorry bad joke) Hugh hi mate, call me stupid, but i was never good with chemistry. do you have any pictures or any links as to the parts that you are using? Thanks to you and to all who contributed. Spyros __________________ CMAS - IANTD - TDI Kamikazi Instrustor Trainer DIRRebreather Team Member ---------------------------- "Once an Outlaw, always an Outlaw"
(Offline)

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