Repairing exterior rust on steel tanks

[FloridaMan1974]

Hey everyone,

I have done a lot of googling and reading and wanted to just hear your thoughts before I go ahead with my plan.

I recently purchased two LP 120s with a significant amount of rust under the boots, fortunately they both passed hydro & vip.

1. Remove rust with this
https://www.rustoleum.com/product-ca...rust-stripper/
2. Take it to a shop and have the paint stripped/shot-blasted
3. See if they can paint this on it, or do it myself
http://www.zrcworldwide.com/products...izing-compound

Thoughts?

Should I do anything else/not do anything of the above?

Thanks,
Max

 

[falcon125]

Evapo-Rust Rust Remover Evapo-Rust Rust Remover Store

This is what some Antique Motorcycle Restorers are using on gas tanks. Amazing product.

 

[claymore]

I am in the same boat with some OMS tanks so I am following this thread

 

[captain]

Hey everyone,

I have done a lot of googling and reading and wanted to just hear your thoughts before I go ahead with my plan.

I recently purchased two LP 120s with a significant amount of rust under the boots, fortunately they both passed hydro & vip.

1. Remove rust with this
https://www.rustoleum.com/product-ca...rust-stripper/
2. Take it to a shop and have the paint stripped/shot-blasted
3. See if they can paint this on it, or do it myself
http://www.zrcworldwide.com/products...izing-compound

Thoughts?

Should I do anything else/not do anything of the above?

Thanks,
Max

I would have it blasted first which will also remove most if not all rust, treat with Ospho, roll on 3 coats of Galvalite, let cure for 2 weeks, good to go.

Ospho Rust Treatment - Since 1947
ZRC Galvilite - Products - ZRC Worldwide

 

[Eric Sedletzky]

I know that if you have the inside of a tank shot blasted it automatically needs a hydro.
I'm assuming it would be the same on the outside. I would call a hydro facility just to make sure it's cool to do that without re-hydroing it.
The other solution is to use Rust-Mort which will kill the rust and turn it into black iron. The tank then should be coated with several coats of an 80% zinc dust cold galvanizing compound and that all it needs.
I would choose sand blasting first over phosphoric acid personally.

 

[captain]

Rust- Mort is phosphoric acid, same as Ospho. A phosphoric wash is pretty standard treatment on steel before painting.

https://www.semproducts.com/manage/html/public/content/techsheets/sem_tds_rust-mort.pdf

 

[Eric Sedletzky]

Rust- Mort is phosphoric acid, same as Ospho. A phosphoric wash is pretty standard treatment on steel before painting.

https://www.semproducts.com/manage/html/public/content/techsheets/sem_tds_rust-mort.pdf

Yes I know, I've been doing steel a long time. Auto body, marine-steel boats, steel fabrication, etc. and industrial painting, it's what I do.
Clean sandblasted steel is preferable over trested rust. If the coverted rust is left in place then an impervious waterproof epoxy coating is recommended since they do not breathe and neither water or oxygen can get back in. A product called Por-15 was actually a material that was dedigned as a quick fix on Navy ships out at sea to protect steel between scheduled maintenance. It's a black paint that both kills rust and provides a waterproof barrier from the elements. The only problem is it doesn't "heal" a chipped spot how cold galvinizing does. And if there's even one small pinhole water can penetrate and start invisible damage. Galvinizing is always telling.

 

[lowviz]

This is a nasty problem that I haven't yet put to rest. I remain convinced that a thin electroplate galvanizing coating is better than spray-can galvanizing, but spray paint galvanizing is rather good and stupidly simple. Good enough to keep your tank alive.

I have too much on my plate at the moment to give this the attention that it deserves. But it really is tops on my "B" list. http://www.galvanizeit.org/uploads/publications/Zinc_Coatings.pdf

Maybe later...

 

[Diving Dubai]

@lowviz

To help you out...

Hot dip galvanising gives a coating which is metallurgically bonded to the substrate (the steel tank) and thus is a very strong coating. It also acts as a sacrificial layer in that if you scratch to the steel gives cathodic protection (similar to an anode on a boat)

Zinc spray (cold galvanising) is just a coating. It attaches to the substrate by a mechanical bond (adhesion) if the zinc has a high enough particulate count (mixed thoroughly for instance) There is debate whether it gives cathodic protection, as it depends on the zinc particles not being encapsulated with a non conductive barrier.

For either to work the material needs to be chemically cleaned. Easy in a factory, less so otherwise. Ideally even if you sand blast you need to ensure all grease and contaminants are removed

The trouble with Hot dip, (apart from it being a factory process) is the need to dip the part in a tank of liquid which is 830F (440C). Looking at the Worthington video, they appear to hot dip as the final process after heat treatment and hydro testing. I'm having trouble reconciling this in my head - it could just be that they've shown the process out of order.

Certainly there is no way you would take a used tank and have it re dipped as it would no doubt change the metallurgical composition of the cylinder to an extent that could only be defined by taking test samples and confirming the strength on the material in theory.

 

[captain]

Yes I know, I've been doing steel a long time. Auto body, marine-steel boats, steel fabrication, etc. and industrial painting, it's what I do.
Clean sandblasted steel is preferable over trested rust. If the coverted rust is left in place then an impervious waterproof epoxy coating is recommended since they do not breathe and neither water or oxygen can get back in. A product called Por-15 was actually a material that was dedigned as a quick fix on Navy ships out at sea to protect steel between scheduled maintenance. It's a black paint that both kills rust and provides a waterproof barrier from the elements. The only problem is it doesn't "heal" a chipped spot how cold galvinizing does. And if there's even one small pinhole water can penetrate and start invisible damage. Galvinizing is always telling.

I did not advocate Ospho in place of blasting, I advocate it as a treatment after blasting but if blasting is not an option it is better than nothing.