Treating rust inside a fuel tank

[NFCN]

Hi all

Having finally bitten the bullet and emptied out my mild steel fuel tank, and cleaned it all out, I have found some limited internal rust patches. I obviously want to treat them before putting it all back together again - but fear that Fertan or Krust, or similar products, might (a) not grip due to the residual diesel on the metal (I also used paraffin to help clean the inside out) or (b) contaminate the new diesel.

Any thoughts? Or has anyone been caught hoovering out the inside of a fuel tank by their wives recently? !

Nick

 

[WoodyP]

Fill it up again. Its not going to rust under a coating of diesel....................or is it?

 

[pagoda]

One possibility is something like this treatment kit ..
I used it on a 48 year old car petrol tank and have been favourably impressed. The chemicals are fairly noxious - and the sealer is really a use ONCE only - since it will start curing once the tin is open!. Worth considering anyway?

http://www.frost.co.uk/item_Detail.asp?productID=8223&frostProductName=Car Tank Repair Kit

Not all that cheap either, but my replacement tank was >£400, and there wasn't a huge amount wrong with the old one.
You can buy the compounds individually if you want. Just follow the instructions to the letter, particularly the cleaning & drying out...

Graeme

 

[Ross D]

There are a number of tank paints available which I have used in ship repair they must be available from retail, try contacting International or Blakes paints. They will have advice on how to prep the surface to ensure the paint adheres, it will probably need steam cleaning and a hot and soapy scrub.

Steel tanks do rust even when they have diesel in them, any moisture in the fuel or condensation in the tank will gradually lead to a layer of water sitting on the bottom of the tank. This is why it is advisable to empty your tank and clean it regularly. There are several microbes which live on the water fuel interface (floating on the water and feeding on the dieso) some of these can attack the metal on the tank others simply clog your filters.

Before you represerve you need to ensure you don't have SRB (Sulphate Reducing bacteria) in the tank, these eat the steel causing localised deep pitting of the surface, if you paint you simply seal these in and they will eat your tank under the paint. If you have them you need to treat with a biocide before you represerve.

Ross

 

[Bosun Higgs]

Try the classic car and classic bike suppliers - they have just this problem.

 

[savageseadog]

I've cleaned small tanks by shaking around a quantity of ungraded small granite gravel around the tank together with some soapy water. Hydrochloric acid (brick cleaner) will clean it but you need to be careful. I would suggest a blowlamp (roofing torch for a big one) to dry and sterilise it.

 

[KREW2]

I have just taken out my fuel tank and cut a large inspection hole in the top. It's 20 years old and made of mild steel.
I used a degreasing powder and loads of boiling water to clean of all the diesel and crud, and the steel inside looks as good as new, and all the welded joints seem okay. What I conclude from this is, diesel is a good preservative of steel. If you refill your tank the diesel will do as good a job as any rust inhibitor. You just need to reduce the intake of moisture and air to a minimum, that means not leaving the tank half full for too long a period.

 

[Bav32]

rusty tank

Had this problem on my previous boat; rusting from the inside.
Simple solution if you have access to welding kit is " just replace the bottom" presuming the rust wil be confined pretty much to the bottom surface.

First steam clean or pressure wash the inside - this will save explosions later.
Scribe a line about 1/4 inch up from the bottom all round the outer (making a presumption here that the tank is square / rectangle shape)
With a sharp hachsaw cut in to this line at all the corners before using an angle grinder with a cutting blade to cut along the scribed linealong the sides.
Usual rules about gloves eye protection and ear defenders.
Take very accureate measurements of the base you have to replace and then find you local Metal Supermarket who willl be able to cut very accurately mild steel plate. You want to get this about 2 mm smaller that the outside measurements of the existing tank - just big enough so the new plate will not fall into the tank.
Very care fully make tack welds at a couple of places around the edge.
If satisfied that everything is lined up OK, start to weld all round the seam but do this in welds a few inches long and then weld at a different point until all done
Spacing out the welds like this reduces the distortion from the heat.
The idea about making the replacement plate a little smaller is that the welding that you have now applied should fill that space.
Now run round the weld with an angle grinder to buff off excess weld.
Weld all round the tank again this time which will almost certainly make it secure against leaks - pressure test to confirm.
Finally , couple of coats of paint; Hammerite or similar