Clean outside of tank?

[Arkman]

I picked up a pile of used gear from someone. It game with a tank new in 2020. But looks like at some point the tank maybe say in water or something for an extended period of time? There is some discoloration around it. I tried scrubing it off witha sponge but that didnt do anything. It doesnt really hurt anything but it does look yucky, especially compared to the nice clean aluminum elsewhere. Anyone have any suggestions to clean it up?

 

[Waterwulf]

I'd try some Aluminum wheel cleaner from the auto parts store.

 

[Badger7]

I concur, you don't want to do anything abrasive on the outside of a tank, but it doesn't look like that tank is clear coated and that's an oxidation layer on the raw aluminum. Definitely try something like a Mother's aluminum polish, and if working it with a terrycloth towel and elbow grease gets you some good results on a test area, then maybe move up to a polishing ball (non abrasive) on a drill at low speed just to try to work some of the oxidation out of the low spots without actually removing material.

Most people would say ignore it, but I'd be trying to clean that up too.

 

[OTF]

First of all, get a good visual inspection / make sure the inside of the tank is clean. It's possible though unlikely that some ugly galvanic stuff was happening that affected the inside as well.

Try an aluminum cleaner/polish product first. Might need a reasonably aggressive one.

Try a mild abrasive like scotchbrite. You can get the pads in different coursenesses. Personally I wouldn't be afraid of more aggressive treatments like wire wheel or sandblasting a tank but I'm sure those suggestion would around here. With any abrasive you'll need to do the entire surface equally or it will look uneven. Ask me about the refrigerator I tried to clean once lol.

 

[happy-diver]

Considering it's a painted steel tank, grab some cream cleanser perhaps progress to dissolved washing powder

applied with a cloth type thingy by hand




or by buff?

 

[SlugLife]

As far as inspections, you can "pre-inspect" the tank yourself.

Depressurize it completely. Tap the handle of the valve with a rubber-mallet lightly in the counter-clockwise direction until you can unscrew by hand. Use a flashlight and look on the inside of the tank for any debris, corrosion, or pitting. A small dental mirror can be used to look at the threads for any cracks or damage. You also want to look for any pitting on the outside of the tank, especially since it was sitting in water.

This is not a substitute for an annual inspection of course, but is roughly 75% of what a tank inspection does. If you do find pitting, that's where the other 25% of the inspection comes in, because it hasn't necessarily failed yet, it really depends on the depth of the pitting, and area/length of the pitting. (I am of course massively over-simplifying what's actually in the pressurized-cylinder inspection class)

You don't have to inspect tanks yourself of course, but if you are somewhat of a DIYer, or grab tanks off the used market, these steps could help you avoid buying bad tanks, or even avoid scuba-shops which fail tanks for nonsense reasons or try to charge you for services you don't need.

 

[OMyMyOHellYes]

Green scotch brite pad and a solution of 1:1 water:white vinegar. If it's smooth aluminum, it will look like new. If it's brushed aluminum, it will come out like new. If it's shot-peened finish aluminum, it will probably never clean up like you want as you won't ever really get down into the tiny shot pocks.

I usually finish mine with aluminum polish and a couple coats of carnuba car wax because I like shiny.

One I did a few months ago:

 

[OMyMyOHellYes]

You don't have to inspect tanks yourself of course, but if you are somewhat of a DIYer, or grab tanks off the used market, these steps could help you avoid buying bad tanks, or even avoid scuba-shops which fail tanks for nonsense reasons or try to charge you for services you don't need.

C'mon! We BOTH know that would NEVER happen.

There's a place in East Texas that still claims that tanks over 20 years old cannot be filled as it's a "DOT recommendation". Yet the "proof" they offer actually says so long as they pass testing, they're OK. I was kinda doubting that DOT would put out a testing guideline and then say "but our required testing is not any good so don't use the tanks that just passed our test." Even when challenged they're too loopid (well, rhymes with 'loopid') to know what they don't know.... But they've been in the scooba shop business forever, they sure won't listen to anybody else because they're the only ones that know. Don't listen to others like DOT. Or Luxfer. Or PSI. Or anybody.

They did however offer to sell me new tanks to replace my "beat up" dangerous old bottles so I could dive safely. Sun don't shine inside a scuba bottle or where I suggested they stick said AL80....

More editorial saved for that place for another time. BTW, I note that they won't fill "unsafe" old tanks, tanks that are over 20 years old, but they'll damn sure offer to sell you "unsafe" 24-25 year old tanks -

Wanted - Al80 doubles (or O2 clean singles)

Hi All, I'm looking for some Al80 doubles in the North Texas area. I'd also be interested in singles if they are oxygen clean. I'd also be interested in an oxygen clean AL40. Thanks, D.

scubaboard.com

 

[OhioDivingDude]

C'mon! We BOOTH know that would NEVER happen.

There's a place in East Texas that still claims that tanks over 20 years old cannot be filled as it's a "DOT recommendation". Yet the "proof" they offer actually says so long as they pass testing, they'er OK. I was kinda doubting that DOT would put out a testing guideline and then say "but our required testing is not any good so don't use the tanks that just passed our test." Even when challenged they're too loopid (well, rhymes with 'loopid') to know what they don't know.... But they've been in the scooba shop business forever, they sure won't listen to anybody else because they're the only ones that know. Don't listen to others like DOT. Or Luxfer. Or PSI. Or anybody.

They did however offer to sell me new tanks to replace my "beat up" dangerous old bottles so I could dive safely. Sun don't shine inside a scuba bottle or where I suggested they stick said AL80....

More editorial saved for that place for another time. BTW, I note that they won't fill "unsafe" old tanks, tanks that are over 20 years old, but they'll damn sure offer to sell you "unsafe" 24-25 year old tanks -

Wanted - Al80 doubles (or O2 clean singles)

Hi All, I'm looking for some Al80 doubles in the North Texas area. I'd also be interested in singles if they are oxygen clean. I'd also be interested in an oxygen clean AL40. Thanks, D.

scubaboard.com

I think it comes down to the alloy. The tanks on that link look to be 3AL which is perfectly fine. Older tanks with an alloy of 6498 used to get the 3AL stamp and could be filled but now no one is filling them because of the alloy its made of. Id be willing to bet your "beat up" tanks have that or another similar alloy. Do you know if they were 3AL or not?

 

[OMyMyOHellYes]

I think it comes down to the alloy. The tanks on that link look to be 3AL which is perfectly fine. Older tanks with an alloy of 6498 used to get the 3AL stamp and could be filled but now no one is filling them because of the alloy its made of. Id be willing to bet your "beat up" tanks have that or another similar alloy. Do you know if they were 3AL or not?

"3AL" has nothing to do, per se, with the alloy. That is the DOT standard under which they're certified. Older 6351 tanks were not originally certified under DOT3 - they were usually special permit tanks, but at some point DOT converted those special permit tanks (some, maybe all - not gonna spend a ton of time researching the conversion) over to DOT3 classification. \

I think you are referring to use of 6351-T6 alloy. It had a higher lead content to the alloy mix than 6061-T6 alloy which Catalina always used - or even all Luxfer Al bottles manufactured since mid-1988.

Some of the 6351 bottles exhibited a tendency to crack/fracture in the shoulder/neck/thread area of bottles caused solely by the stress of being filled to pressure over time. This is called "Sustained Load (Stress) Cracking" or usually abbreviated SLC. That kind of cracking is usually considered a bad thing.

Yours is an intelligent question though - the concern IS in the alloy. Or should be. Not on the age. The shop in question, in my opinion, couldn't tell its theoretical ass from a hole in the top of a scuba bottle. Even when confronted by legitimate, authoritative information and documentation. This is because I don't believe they could even spell 6-3-5-1 or S-L-C, much less tell you who made them 6351 scuba bottles (Luxfer, Walter Kidde, Cliff Impact, mainly), when they were made, and what the concern with 6351 bottles is. They just say 20 years is too old to fill. Big signs posted at their facility (or were, back when I didn't know better to avoid them a couple of years ago) say as much. Then out of the other side of their mouth will try to sell 24-25 year old bottles on scooba bored.

Even the old 6351 bottles can still be used and filled to the owner's heart's content, legally, ethincally, and safely, provided they pass eddy-current testing at the 5 year hydro mark (DOT regs) and annual VIP of those tanks should also include the eddy-current test (not DOT mandated).

I have a couple of old Luxfer 6351 bottles I still use but not in a pressurized capacity because I don't want the hassle of the more expensive, I mean extensive, annual testing. One of my 6351 bottles is prettier than any new bottle on an LDS' showroom floor - that one I use for holding valves when torquing the packing nut or the over-pressure plug (burst disk) when I rebuild valves (or just change the burst disk for a different working pressure.)