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Tank coatings

Discussion in 'Technical Discussion' started by Northwind, Jan 15, 2017.

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  1. Northwind

    Northwind Member

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    I am restoring an old USCG boat (there are several posts on this project).

    The existing tanks are mild steel. They don't leak but we have to be nearing the end of their usual lifespan.

    What is the best way to preserve the tanks? Is there a coating system that will protect the metal and the integrity of the system? What needs to be done to prepare the internal surfaces for diesel and oil tanks? Steam cleaning?
  2. K1W1

    K1W1 Senior Member

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    Diesel and Oil tanks can be steam cleaned, they should be treated after drying by wiping over with the fluid they will carry once full.
  3. Lepke

    Lepke Member

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    I have 1942 steel tanks. If you keep a good conditioner in the fuel and circulate the fuel often, you can keep the water and bugs out of the tanks. When I opened mine, I had some deep pits in the bottom. After cleaning I welded the pits. There are epoxy paints for tank coating, but they require clean, sand blasted metal.
    My tanks were built w/o entry ports so hadn't been entered since built. I used them for a couple years before I got to that project. I always use diesel additives are biocides and help separate the water from fuel so your primary filter can catch it. When I opened the tanks they were clean, no sludge, no noticeable water. Pumps left about 2" of fuel that had to be removed with a portable pump.
    If some of the tanks aren't used for long periods, they should be completely empty and the metal treated. I've seen tanks in mothballed ships that disappeared with sand blasting.
  4. Northwind

    Northwind Member

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    Thanks. That is very helpful.

    Can you elaborate on your last sentence? Are you saying that sandblasting an old steel tank may blow a hole in the tank?
  5. K1W1

    K1W1 Senior Member

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    In my experience the answer to that is a big yes, I would not paint fuel or oil tanks myself and can't remember being on a ship where they were painted.
  6. Marmot

    Marmot Senior Member

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    Most of the fuel tanks on ships I have been on have been painted internally. A good reference for the prep and paint specs can be found in US Navy NavSea publications. Likely the same paint specs used by the CG.

    Like the internals of larger engines, painting provides a smooth surface so that contaminants are less likely to adhere to the tank sides and bottom as well as provides corrosion protection. Many of the large slow speed engines are painted white internally to make inspection easier and make it a little less like a coal mine when working inside them, fuel tanks are usually painted in that red/brown color that already looks like rust.
    Last edited: Jan 21, 2017
  7. Capt J

    Capt J Senior Member

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    Diesel in and of itself is a lubricant. So, the tank is not going to corrode on the inside with diesel in it, if the tank is empty and exposed to the air, the steel can rust big time and it could just crumble as big flakes of rusty steel.
  8. Bill106

    Bill106 Senior Member

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    That may be changing Capt J, I've replaced a couple sets of aluminum diesel tanks in the last two years on boats that were less than ten years old. These tanks were all coated on the outside and properly installed but the corrosion and pitting that led to failure was on the inside bottom surfaces. Apparently what happened is microbes grew in the water collected in the very bottom of the tanks and their excrement is acidic and eats into the aluminum eventually resulting in failure. Our local tank cleaning service tells me he's been seeing an increasing amount of these problems. An internal coating should help if not eliminate this problem on all types of fuel tanks.
  9. Lepke

    Lepke Member

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    I have seen tanks in long mothballed naval ships being returned to service that have rust so bad that when sandblasting the tank wall you suddenly are looking into the next compartment with each sweep of the gun. In most cases the navy closed that one up and picked another ship.
  10. Capt J

    Capt J Senior Member

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    This is/was common in the 63' Ocean SF's if they had water in the fuel. Those boats had 2 big saddle tanks that gravity fed to a 250 gallon tank in the center bilge and everything drew off of that tank. So all water would settle in the 250 gallon tank and the bottom would get eaten out. Sounds like more of a water issue though than fuel. I love fiberglass fuel tanks!