Too Much Rust?

[spectrum]

I have a couple of PST 100's (Genesis branded with color overcoat) bought used that looked a lot worse than that on the bottom. The original boots left the butt of the tank hitting the floor and over time the galvanized finish wore away. I dusted them clean where damaged with the grit blaster, sprayed with cold galvanize compound and a top coat to similar to the original paint. Then I installed some good Underwater Kinetics self draining boots that have the spider to shield the bottom of the cylinder.

 

[Michael Guerrero]

The white dots are high points in the paint and primer. They signify that they have corrosion under them. I had similar

Personally I would remove the paint, treat with anti rust agent and take them for inspection prior to painting, so at least you are being transparent. After that as others have said a Zinc primer and re paint the area.

I thought the white dots were rust underneath too, but when I checked some of them out the steel had no rust.

Anyone have a good way to get all the paint off? Chipping it away didn't work well. Can I use a paint stripper chemical like you can use on aluminum tanks? I'm in the middle of nowhere so the likelihood of being able to take it to a place that won't damage them is low I think.

I wouldn't worry about that. Now, what's going on in the inside.. VIP them.

I think they were viz'd two years ago and got a sticker. Last time I looked in them they had some rust dust in them but I didn't see any large pitting or anything. It has probably been three years since I looked in them though. They have always been stored pressurized. Anyone have a good url I can look at for doing a viz? I'm more than 1.5 hrs from the nearest scuba shop and my Oxy Hacker's Companion hasn't arrived yet.

 

[Wookie]

First, why would you strip them? There is nothing wrong them from a usability standpoint the way they are, and there is not really anything you can do with them as a home painter/galvanizer to make them better. Second, if you look in them and see only rust dust, they are fine. Dump it/blow it out and replace the neck o-ring (214 buna or viton) and go back to work. If you see real rust in there, you have to send it for tumbling and hydro anyway.
If the inside isn't any worse than the outside, keep on trucking until next hydro. If the inside is worse than the outside, you (or your cylinders) need professional help anyway.

Worry about the right things. This is nothing to worry about.

 

[Michael Guerrero]

Mainly I'm concerned that rust has migrated up into areas I can't currently see because they are covered in the shell of the paint. The only way I noticed some of them was because the paint had a few hairline cracks and once chipped it away I found the rust. It was not readily apparent from the paint surface that rust was underneath.

I'll just keep an eye on them and take a look inside next time I empty them.

Thanks for all the help folks.

 

[Diving Dubai]

Sorry I'm going to disagree with Wookie, however pragmatic he's trying to be.

Leaving the pin prick corrosion points is a mistake because the corrosion will progress. Once the top coat of paint is damaged then capillary action allows moisture to contact other areas of the tank. Primer is porous.

I'll re-iterate my comments. remove paint (Sanding with no greater than 120-180 grit) treat corrosion. Subject tank to Visual inspection then re-paint

A hydro test won't prove the tank, unless the corrosion had caused a significant loss of the cross section of the sub strait.

for what it's worth I'm an ex materials scientist and metallurgist

 

[Remy B.]

If you want to do it right, go to a place where they SODA blast, pay attention that I mention SODA blasting NOT sand blasting, then have it coated to C5i or C5M classification coating, that is marine environment coating, this consist in 3 coats ( I believe maybe a bit more don't remember ) with a certain thickness, starting with a premier, the only people that can do this are industrial or marine coating specialist.

Cheap, no, is it good, yes, the best thing you can do I think.

Like everything in live you pay for what you get.

You may want to look to other options, but you shall soda blast your tanks now before the rust keeps digging in and spreading under the paint you have now.

 

[Michael Guerrero]

Insides have some speckles of rust around them, but nothing like what it looks like outside. There was also no rust dust this time. No significant looking pits either.

Just cleaned the valves and put everything back together. More diving...

 

[bamafan]

I have Faber's that were worse than that. I used a wire brush on a small side grimder to strip all the paint off to up above the boot. I wiped the tanks down with solvent then primed them with cold galvinizing paint. I then painted over that with truck bed liner paint.

 

[rjack321]

The grey OMS paint is crappy.
BUT:
You don't want to soda blast these tanks, it will take off most of the spray-on zinc primer which turns these into doorstops.
You don't want to strip the paint, its better than what you can apply at home.

Step 1 is to throw away whatever OMS boots you might have ever used on these tanks. They don't drain properly and are the likely source of the pits seen in picture #2. The isolated pits are not worrisome at all, the standards for line corrosion are 1/2 that for an isolated pit. Ignore the tiny paint bubbles, those do not extend into the underlying steel, that's how the paint fails, underneath that is the zinc and way under that is the structural steel. Messing with those pin bubbles is not necessary and will accelerate your corrosion problems. Just get rid of the boots!!!!

Lightly sand down the edges of the paint chips. You are trying to feather out the edges of the underlying spray galvanizing so you can determine the depth of pitting into the structural steel, which appears to be zero but might be 0.01" or something trivial. Once you finish that just use a brush to touch up the paint with rustoluem from a tiny can, it'll be thicker than spray on. You can also leave those patches bare if you diligently rinse the tanks.

 

[Carl_F]

All but the first three pictures just show cosmetic rust that does not affect the structural integrity and could be left alone. The first picture is harder to tell whether there is any depth to the corrosion. If no depth, then it's cosmetic and can be left alone. If there is any noticeable depth to the corrosion spot then that's not good.

I would not take a grinder to the metal as there will be a whole lot more material removed from the grinding than the cosmetic corrosion. Leaving the cosmetic corrosion won't affect performance one way or another so I'd just leave it and continue a quick external fresh water rinse after diving followed by air dry.