Pony bottle and Galvanic corrosion

[BobbyT22]

I dive a steel HP 119, and I want to mount a pony bottle as a independent air source. Can I mount an aluminum pony on a steel tank? I'm very familiar with galvanic corrosion on metal boats, and my gut tells me that the same thing would happen between 2 tanks of dissimilar metal, but I don't see it mentioned. Any thoughts?

 

[mark G]

I have some knowledge of corrosion control from the aircraft industry. I believe that the stainless steel bands will negate the dissimilar metal corrosion effect and being dry when not actually diving should also help, If you haven't already you might consider getting a steel pony instead of aluminum or removing aluminum tank while not actually in use.

 

[Jimmer]

The tanks themselves aren't going to be an issue. They won't be in contact. The pony mount could be an issue in salt water tho. I would suggest put something underneath it, such as a strip of the mesh tank wrap, or better yet, just sling the tank instead of back mounting it.

Jim

 

[texdiveguy]

Dude, SLING the bottle and don't mount it to the back gas tank!

 

[DA Aquamaster]

Slinging a pony does work really well.

But tankmounting the pony is not any different from a corroision standpoint than if you used stainless tank bands on an aluminum set of doubles or an aluminum single tank adapter on a steel tank.

Realisitically if the paint is intact on both tanks or if the steel tank is galavanized you have non issue. Practically speaking that is not always the case. But unless you leave them in contact for long periods of time with salt water present where ion exhange can occur, it will not be an issue. If you leave them assembled, just rinse thoroughly with fresh water and let them dry. If you use an aluminum mounting bracket permanantly attached to the steel tank, it's not a bad idea to have a piece of rubber from an innertube or something similar under the bracket and any metal straps to create what amounts to an insulator, although rinsing is still important.

 

[SmokinReefer]

I dive a steel HP 119, and I want to mount a pony bottle as a independent air source. Can I mount an aluminum pony on a steel tank? I'm very familiar with galvanic corrosion on metal boats, and my gut tells me that the same thing would happen between 2 tanks of dissimilar metal, but I don't see it mentioned. Any thoughts?

I may be talking out my arse here and feel free to correct me, but aren't you looking at dielectric corrosion due to contact of two dissimilar metals? My brother used to tell me something about dielectric corrosion when I helped him out on plumbing jobs over a decade ago. Apparently some combination of connecting copper/brass/iron pipes causes corrosion over time. I wouldn't think it would be a problem with your gear though if you just kept it clean.

 

[ClayJar]

I sling my pony with stainless steel "hose clamps" as part of the rigging. I took a length of small inner tube and wrapped it around the tank, with the hose clamps over it. It isolated the dissimilar metals and provides a very nice grip.

I imagine you could do something similar, if neccessary. (As long as there's not a conductive path between the metals, corrosion should be minimized.)

 

[Jimmer]

I may be talking out my arse here and feel free to correct me, but aren't you looking at dielectric corrosion due to contact of two dissimilar metals? My brother used to tell me something about dielectric corrosion when I helped him out on plumbing jobs over a decade ago. Apparently some combination of connecting copper/brass/iron pipes causes corrosion over time. I wouldn't think it would be a problem with your gear though if you just kept it clean.

Keeping everything clean of saltwater after a dive is the key. I personally like to sling those bottles which solves the issues, but for a tank mount, like several of us have said, put something between the mount and the tank, and rinse it every dive. As for the issue of the actual galvanic or dielectric corrosion, it can be a serious PTA. I've worked in the bicycle industry for 7 years, and have seen more than 1 frame scrapped, because an aluminum or steel part was installed in a frame of the other material, without proper grease, or the bike was used as a commuter in the winter up here, with all the salt on the roads. Never a fun thing to find out your bike frame is now being tossed out, because you can't get the seat post out of the frame when it broke.

 

[Jimmer]

Sorry for the double post

 

[texdiveguy]

http://www.corrosion-doctors.org/Forms-galvanic/galvanic-corrosion.htm