Removing an epoxy lining

[COVCI]

Not sure how you hand make a hydro test stamp. Most testers do a pretty good job of getting the numbers lined up. but if they did not, it would not make it any less vailid just less neat and less professional looking.

The critical stamp will be the small one between the month and year that would consist of the code for the test facility (normally a pair of letters above a pair of numbers). That code is on a single stamp, so any oddity in their relationship would suggest a forgery. If the code looks valid and you are still suspisious, you could contact the facility and provide them with the date and serial number of the tank and they should be able to confirm if the hydro was really done there. It would be a PITA for them to pull the test record, but they should still have it on file somewhere.

But more importantly, if the DOT numbers are not stamped out and the tank passes a new hydro test it should be legal and serviceable. One thing I saw recently on a tank was a set of numbers stamped on the side of the tank as someone apparently thought that was ok if there was not a convenient spot on the shoulder. Another tank had a name stamped in the side as a means of permanantly identifying their now totally useless tank as anything stamped in the wall of the tank is treated like any other gouge or damage and the tank is condemned if it is too deep.

Hydrostatic Retester Stamps are refered to as RIN-Retester Idetification Numbers.

The "number" or code consists of not two letters and two numbers, but 1 letter and 3 numbers. Two on top and two on bottom. We read the RIN by starting at the top left corner which is the letter and reading clockwise.

EX.

A1
23

Would be RIN A132.

The US DOT has a database of valid RINs listed on their website. This database includes what the retester is authorized to test and also contact information.

Hope this helps.

Chris

 

[Inspector]

At the risk of sounding self serving, I invite you to attend on of my PSI Visual Cylinder Inspector training workshops. I would be glad to share with you my personal experience about the scores of cylinders that I have done this to. I will share with you my favorite recipe, the type of media I think is best suited for this task, where to get it, how long to tumble and how fast, the pros and cons of removing liners depending on your application ect... Also covered; how to interpret cylinder stamping, what's legit and what's suspect, sidewall stamping, O2 cleaning recommendations and so on. The only comment I would like to make here is addressing the proposed used of chemical strippers to remove internal epoxy liners. The technically best answer to post in writing is “contact the cylinder manufacturer” for their recommendation. Sure, you say, then there’s the real world. That’s why one of the underlying themes of the training program focuses on making yourself more defensible in practice and in a court of law. While it is possible that there may be such chemical agents available that are safe to use for this purpose, I personally am not familiar with any, have never used them, and as such, would not recommend the use of "Um... something from Home Depot." jeffadams@psicylinders.com PSI Instructor.

 

[oxyhacker]

Once upon a time hydro shops didn't have to have a proper ID stamp made up, and could stamp their RIN using indivdual stamps. Some of the old ones can look pretty homemade! The only way to tell if they are genuine (not that it really matters, if you are having the tank rehydroed) would be to look up the shop using the RIN and see if they really did the tank.

Old linings can look pretty sketchy, and flaking is common, so that's not proof that it's homemade. Someone more experienced with scuba tanks should be able to tell pretty easily.

Note that it isn't necessary to remove every last bit of the old lining (unless it's really is Rustoleum!). If you tumble it long enough to remove all the flaking and bubbling stuff, what is left will be solidly affixed to the tank wall, and can be left, at least, until next time.

72's are great tanks. It's well worth the effort to save them.

 

[Creed]

Once upon a time hydro shops didn't have to have a proper ID stamp made up, and could stamp their RIN using indivdual stamps. Some of the old ones can look pretty homemade! The only way to tell if they are genuine (not that it really matters, if you are having the tank rehydroed) would be to look up the shop using the RIN and see if they really did the tank.

Interesting. I didn't know that.

Note that it isn't necessary to remove every last bit of the old lining (unless it's really is Rustoleum!). If you tumble it long enough to remove all the flaking and bubbling stuff, what is left will be solidly affixed to the tank wall, and can be left, at least, until next time.

OK, I will keep that in mind.

72's are great tanks. It's well worth the effort to save them.

Well, I am certainly going to give it the good old college try. I decided to build a tumbler based on a variation of a theme I found here on scubaboard, from a gentleman with the handle Stone: http://www.magnificentrelief.com/Tumbler.htm.

I am presently hunting for a motor.

 

[Goose75]

I don't know the rules on scuba tanks but I work with epoxy all the time in aircraft. The epoxy liner in those tanks is probably a room temp cured low grade epoxy. It won't require high heat to soften it up. As long as you don't add enough heat to anneal the aluminum, it should be fine.

Maybe this is a dumb question, but why not re-coat it?

 

[oxyhacker]

Because when the factory was doing it, it didn't work. So not much chance a DIYer is going to do any better.

But mainly because it turned out it wasn't necessary. At the time coatings were being tried, air quality was not up to current standards, and moist enough that rust was common, so the coatings seemed like a good idea. They did not work out in practice, as it was found they tended to hide and concentrate rust, so deep pitting was a problem, so the industry went back to bare steel interiors. Today's air is good enough that, if a tank is properly cared for, corrosion isn't ordinarily a problem, and when it does occur, it is usually an indicator of other problems, like bad air, or bad fill station practices. With a bare steel interior, what rust does occur is spread out, easily spotted, and easily treated.

 

[Creed]

I don't know the rules on scuba tanks but I work with epoxy all the time in aircraft. The epoxy liner in those tanks is probably a room temp cured low grade epoxy. It won't require high heat to soften it up. As long as you don't add enough heat to anneal the aluminum, it should be fine.

Maybe this is a dumb question, but why not re-coat it?

Most places around here(here being Kansas, in my case) won't even look at an epoxy lined tank. So, my choices are remove the lining or junk the tank.

 

[FredT]

DEARMAN,
I've never seen an aluminum tank with a liner! Lined tanks are generally steel 72s, with nearly perfect buoyancy characteristics. BTW ANY Heat above boiling point applied to a tank voids the DOT rules and is cause to condem the tank.

Creed,
If you just have just one or 2 tanks to do and can find a trashed dryer with a working drum and motor (generally it's the control that dies) a few pieces of 2X, deck screws and a light switch will allow you to make a single tank tumbler.

Wire the motor through the light switch, remove the door and use the 2x and deck screws to put a spacer in it so the tank runs at about centerline. A couple of tarp bungees off the 2xs will retain the tanks while it runs. Your investment in the rig is going to be under $10, and you'll need to add another $5 for the "crushed decorative quartz" tumbling media. If you're close to the flint hills a bucket and a short walk upstream on a creek to a gravel bar will give you enough suitably sized gravel to do tanks for years.

The dryer trick isn't anywhere near elegant, but it works.

FT

 

[Creed]

I tumbled the tank, figuring that it would take a few days at least. After a few hours, I opened it up, and couldn't see anything because of this grey dust. So, I dumped the media and cleaned it out. The walls were nice and shiny again. I think it was some sort of paint.

FWIW, I used small rocks, sand and brass shell casings(22's mostly) for the media. It seemed to take off the coating quickly, without any visible effect on the steel. Just a pain in the tookas to get back out

I will have it hyro'd and vip'd this week, and let you guys know what happens. I also found a 72 at the dive shop for $50, so I am a happy camper.

 

[Creed]

The tank passed hydro and vip just fine. Not bad for a $5.00 tank.