Steel Fuel Tank renovation

[Andy]

I'm currently working on a friends boat and as part of a survey recommendation, we have removed the diesel tank. The exterior of the tank is in ok condition. When we got the inspection hatch off we found about an inch and a half of 'sludge' at the bottom of the tank, and after cleaning that out, some fairly heavy surface rusting on the bottom only. The walls of the tank have only mild rusting evident. We'd like to keep the tank if possible (to save some money), but what is the best way to go about refurbishing it? We originally thought of doing a pressure test with water (although it wasnt leaking before we removed it), degreasing with a selection of solvents, steam cleaning using a carpet and walpaper steamer, then shot blasting (dangerous?) inside and out before an immediate coating of Interprotect on the outside and the International tank paint on the inside. Would this work, or is there a better way?

[PAR]

There are a number of products that will remove much of what is inside your tank.

I prefer to remove the tank, chemical treat, physically remove scale and loose rust. I then place a slurry of kerosene, small river rocks and sand inside the tank and use this to scour the bottom (shake the crap out of it), where water in the fuel has left some rust.

After another inspection there is an acrylic product you can use or my preference is epoxy, which is poured in, then the tank tumbled to completely coat the inside. I'll do this at least twice with the epoxy, which seals the tank very well.

Pressure testing before the sealer goes in is a good idea.

[Andy]

Thanks PAR. What chemical treatment do you use before removing the scale and rust? Is this to degrease the tank? Also, do you know if its safe to grit blast the outside of the tank, assuming we have degreased it and steam cleaned it? The painter at the yard said that it would need to be spotless before we put any epoxy on it or the rust would pop through in time... Id also be interested to hear how to pressure test the tank. We were thinking of using a large tank of water above the fuel tank connected to it using the filler hose, or alternatively a manual car tyre pump with a pressure gauge. I read that 4 to 5psi is a good range to aim for?

[PAR]

There are a number of products, some leave a zinc phosphate coating behind, which acts as a primer for an additional coating, others don't. For your application, use a "system" like what's offered from "KBS" or "POR-15". These systems have a prep, cleaner, primer and coating, with instructions.

I wouldn't be aggressive with blasting the outside of the tank (unless using a soft medium), particularly the bottom, you've lost enough metal.

I don't get too scientific about pressure testing, I drop the tank in a tub of water, after plugging all the outlets. I use a filler neck hose with a hose clamped stopper in it and an in line air gauge/quick disconnect fitting, I toss several pounds at it and look for bubbles. No bubbles, no worries.