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Removing rust from petrol tank

The little BSA I'm restoring has quite a bit of rust in the bottom of the petrol tank, although it seems solid enough, there are flakes of rust coming out. This looked like it would need a bit more than a bit of gravel shaken inside. I wasn't sure if it would need a resin sealer, but I didn't want to do this and I couldn't have poured it onto loose rust. There are 2 methods I've known about but have never got round to trying.

The first, I got an old 1 litre measuring jug and put about 150ml of salt in it and filled with boiling water. Stirred the salt until it was dissolved. I put 2 very rusty 5" coach bolts into the jug making sure they were submerged, and left them over night. The next day all the rust had turned black. A quick wipe with a cloth and a lot of the black came straight off to bare metal. This worked very well.

The second is when you get a bucket filled with water and salt, put steel electrodes all the way round it, then suspend the item you are de-rusting from a rod over the top of the bucket. Put the positive to the electrodes and the negative to the rusty item and with a battery charger or similar current source the current flows from neg to pos taking the rust off as it goes. ( that's how it works as far as I know). This works well but I can't fit a petrol tank in a bucket and it's the inside that wants de-rusting. The electricity will only flow in a straight line from neg to pos.

So I dissolved salt into water again but used a couple of jugs and more salt. Poured it into my petrol tank and filled to the top with water. I'd already screwed in some old petrol taps into the tap holes. I then wired 4 long bolts together and made rubber feet for each end of the bolts so when I put them in the tank they wouldn't touch the metal and short out, then put 2 each side of the tank. I used a battery charger on 6v that flicked up to about 15amps when turned on. As it was the tank that was rusty, that needed to have the neg terminal attached and the pos to the electrodes (long bolts). Don't get this round the wrong was as the pos electrodes are eroded away and you don't want this to happen to your tank. A way to check is the part that's rusty is the part that fizzes. I held one of the bolts in the water at the top of the tank to see if the bolt fizzed, it didn't so I had it right. Make sure you turn off the electricity ever time to lift the bolts in or out of the tank or it will short out. 12volts bubbled a lot more but I left it on 6v to see how it did.

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You need to do with outside or a very well ventilated place as the gases produced are Hydrogen and Oxygen and probably some other nasty stuff. As soon as the electric is turned on the water starts to rise and bubbles appear, then a rust coloured foam. I topped up the water regularly and left this for 4 hours. When I returned the flour was covered in rusty foam.

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I washed the tank out, cleaned the electrodes which had eroded quite badly, and repeated the process. This time the foam was green and grey with out any rust colour. I only left it for an hour this time as the rust looked to have gone.

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I washed the tank out again in clean water and got an LED torch on a rod to have a good look inside. I could see patches of clean metal, the bottom was obviously pitted but looks to be solid. The rust that was remaining was now black and no flakes. I could have probably left it a bit longer the second time but it seems to be just a black residue left that will wash out with petrol.

It was a messy job that has stained the patio with rust but it seems to to have worked well

email (option): horror@blueyonder.co.uk

Re: Removing rust from petrol tank

Thanks for taking the time to put this up on the forum. Very helpful and relatively
Simple to do

Re: Removing rust from petrol tank

I'd be careful with that...I'm sure I've seen that foam before in a 1950s SciFi film and it was eating a bloke.. ...

Interesting process though and not one I've tried before...Ian

email (option): ian@wright52.plus.com

Re: Removing rust from petrol tank

Quatermass! Who would have thought of using salt to remove rust? Ron

email (option): ronpier@talk21.com

Re: Removing rust from petrol tank

Thanks for posting this.

I've done this kind of electrolysis in exactly the way as described except I used washing soda (the stuff that is a main component of dish washer powder). I bought a whole lot of it from a swimming pool maintenance company up the road and have hardly used it. You don't need much. Anyway, the idea is exactly the same. It worked extremely well, but was slow. Perhaps salt is faster?

Best wishes, Allan

email (option): allanmatchless@yahoo.com

Re: Removing rust from petrol tank

I've never heard of this method being used to de-rust the inside of a tank, but I couldn't see why it wouldn't work. The problem was getting the electrodes inside the tank without touching the sides. I was thinking of a stiff wire like a coat hanger, pushed inside some tubing. But I wouldn't have been able to get it right inside the tank. The 4 bolts worked well with the rubber feet, I was surprised it didn't short out at all.

email (option): horror@blueyonder.co.uk

Re: Removing rust from petrol tank

See if you'd had a fibreglass tank like my Starfire had, you wouldn't have had this problem .........You would have had a different problem Ron

email (option): ronpier@talk21.com

Re: Removing rust from petrol tank

yeah, I've got a Commando like that Ron. Melting fibreglass doesn't do your carbs much good.

email (option): horror@blueyonder.co.uk

Re: Removing rust from petrol tanknaval jelly, etc.)

killing rust by electrolysis is a well establish commercial process, some oil rigs Ive worked on have an 'active' system using batteries and even a small generator on one.

Other rig + boats i have had, simply use a sacrificial electrode using - galvanic erosion/corrosion - to protect ferrous metals.

I suspect the addition of salt is simply to allow the water to become more conductive and the electrodes are the bits actually doing the work.

I've tried several techniques - the most effective/cheapest is Phosphoric Acid (same as naval jelly) bought 43% concentrated from Ebay (dilute 1:4 with water for best effect).

I've also recently found another product which works very well and is cheap; Fortress Rust Eradicator - from B&Q - a liter of slightly gell Phos. acid, for ~£10 which can be sloshed around inside the tank, to good effect.
A much cheaper alternative to Naval Jelly and similar such.

Re: Removing rust from petrol tanknaval jelly, etc.)

I have used the electrolisis method but using washing soda as the medium and it works ok but takes a lot of time.
A quicker method is to use spirit of salts( acid so be carefull!) swill it round for 5 mins,then empty and neutralise using soda,then fresh water,it comes out like new! dont forget to coat inside with an oily mixture if not using for a while otherwise rust will be back....

Re: Removing rust from petrol tanknaval jelly, etc.)

Thanks for the tips and pics Horror,

Useful to know .... I'm thinking or cleaning my tank too ,

Cheers,

Mark

email (option): towersmark84@yahoo.co.uk

Re: Removing rust from petrol tank

Gents, I use electrolysis all the time. As an anode I use stainless steel as it lasts many repeats uses. Washing soda crystals as the electrolyte, washing soda is Calcium Carbonate. Small items can be submerged in either vinegar or citric acid, sold at supermarkets with the herbs and spices.
Note don't get caught pilfering the misses pots or citric acid.

Re: Removing rust from petrol tank

Washing soda is sodium hydroxide

email (option): bsansw1@tpg.com.au

Re: Removing rust from petrol tank

Yes, great info, thanks a lot.

Has anyone tried one of the above on the earlier tinned / solderd tanks?

Cheers, Michiel

Re: Removing rust from petrol tank

washing soda = caustic soda = drain cleaner = Sodium hydroxide = very alkali

careful when mixing with any acid - such as vinegar/citric/acetic/etc - expect a reaction like foaming .......

Generally any electrolysis process will cause some 'fizzing' as gas's are released from the metals - different from the foam caused by acid+alkyd reaction.

Gases released can be flammable - best to do outside (think exploding batteries....).

Oh yes - a lead acid battery if 'pushed' too hard (asked to give a LOT of AMPS) can also explode.

Enjoy yourself guys experimenting, but please wear glasses of some form - skin burns, more or less heal - eyes don't.

Never stopped me, but then again i have so much metal in one eye (die grinding) i cannot have an MRI ......

Re: Removing rust from petrol tank

I know there's nothing new in using electricity to remove rust, the experiment was to see if I could remove it from the inside of a petrol tank. The salt is there to conduct electricity better, but as with the first method, it seems to kill rust as well. No chemicals, acids or alkalines, so the water is quite harmless.

So I'm trying the salt de-rusting method to see how good it is. 150ml salt in a litre of boiling water, then I found the rustiest thing I could (no it wasn't one of my bikes) and it's been in there for 48 hours. I would say the rust is no longer rust..?

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I don't know if it will do any good leaving it longer but I'll see. I think a wire brush and the black would come off.
So with hind sight, I think I should have filled the tank with salty water and left it for a day or 2 which seems to kill any rust. Then use electricity to remove the black residue. I may do it again to see if this works.

email (option): horror@blueyonder.co.uk

Re: Removing rust from petrol tank

H

You're getting sucked in .... i spent days messing on this subject, not certain what the end result was though .... ?

It looks as if there's been some transformation of the ferrous oxides to the black material - most of the chemical treatments do that, though electrolysis may/should be better on flaky stuff which the chemical treatments tend not to get to (hence mechanical 'abrasion' nuts/bolt etc.).

My test pieces were something left in a bomb-fire then left to rust - heavily.
Almost all the chemicals i tried, produced the black deposit.

HOWEVER - high concentrations of the phosphoric acid ~20% by volume, did clean the metal back to bare steel.
It was also evident though it attacked the FeO2 first, it then started on the steel, itself.
In other words its aggressive and you need to keep an eye on it.



Slightly different subject - i'm thinking of stripping chrome, firstly from the h/bars then having a go at the plating on the brass levers.
As usual, lots of bollox on the internet - anyone with real experience?

I reckon cheap chrome on steel, will be no problem, minimal if any nickel and no copper.
What about the brass?
Would need to be nickel plated to get the Chrome to bond, what about the zinc in the brass?

Re: Removing rust from petrol tank

trevor
Washing soda is sodium hydroxide

Sorry Trevor washing soda is sodium carbonate, that is it comes from limestone. My Typo.
However sodium hydroxide is caustic soda, not the same.

Re: Removing rust from petrol tank

here is my method. 1 block off tank outlets etc
2 go to supermarket buy 15-20 lts of cheapest white vinegar
3 fill tank right to the top with vinegar
4 leave for three days
5 get a big container and large funnel,empty contents of
tank into container
6 rinse with high pressure water hose.
7 repeat as many times as necessary, may take upto three weeks
just keep using the same vinegar
8 when your happy with the last rinse before it dries pour
one or two litres of the cheapest engine degreasers you can
get (one of the ones that mixes with water)and give it a
good swish around and drain
9 finished.

email (option): daavem20@gmail.com

Re: Removing rust from petrol tank

nigP
washing soda = caustic soda = drain cleaner = Sodium hydroxide = very alkali

careful when mixing with any acid - such as vinegar/citric/acetic/etc - expect a reaction like foaming .......

Generally any electrolysis process will cause some 'fizzing' as gas's are released from the metals - different from the foam caused by acid+alkyd reaction.

Gases released can be flammable - best to do outside (think exploding batteries....).

Oh yes - a lead acid battery if 'pushed' too hard (asked to give a LOT of AMPS) can also explode.

Enjoy yourself guys experimenting, but please wear glasses of some form - skin burns, more or less heal - eyes don't.

Never stopped me, but then again i have so much metal in one eye (die grinding) i cannot have an MRI ......


Washing soda and caustic soda are not the same chemical, another use for washing soda is to relax muscles. You can bathe in washing soda. Sodium carbonate
However vinegar is acetic acid, I drink it. It is safe, keeps scurvy away as well. As well as pickling foods.Including Rollmops.
Citric acid is used in cooking and again is safe.

Re: Removing rust from petrol tank

Washing Soda - sorry, you are correct - reading one thing, thinking another.

You still get a reaction with an acid, be it a Carbonate or Hydroxide, only difference is the gas given off - one explosive the other, not.

Tried acetic and citric acid ...... sorry but life's too short for me to wait on something happening - even after chucking a fish-tank heater in to warm things up.
3-4 weeks, i expect the rust killed, the paint applied and the tank fitted and filled with petrol, within that time scale!
Acetic acid fumes get to my asthma so i don't consider it that benign (nice on F & C's though).

The expensive Rust Killer - 5L of EVAPORE or something was bloody slow reacting - i say expensive because it seems to be nothing more than citric acid - see previous thread on the subject.

As for keeping scurvy away - i think Cpt Cook would disagree with you, it had a very limited effect - however it was an excellent disinfectant and used right into the late 19th century by the navy.

Anyway good luck finding a the ultimate solution ... do like idea of electrolysis though - just fitted an old sacrificial anode to my trailer in an attempt to stop it rusting.

Re: Removing rust from petrol tank

nigP
H

You're getting sucked in .... i spent days messing on this subject, not certain what the end result was though .... ?


Yes you're probably right Nig, but it's keeping me out of trouble

The other methods sound good, I don't thing I'll be trying them all.... but saying that I have got a couple of other tanks that will need cleaning out

My shed will look like Dr Jekyll's lab by the time I've finished..!!

I don't think messing about with this stuff is doing me or my family and friends any good...!!

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email (option): horror@blueyonder.co.uk

Re: Removing rust from petrol tank



i used to be Lab/R&D Manager for a Centrifuge company and did all the 'dodgy' jobs - mainly cos i've no sense of smell.
I was once dragged out our 'fume-room' after collapsing on Hexane fumes - I think my eyes were like your family ....

Re: Removing rust from petrol tank

Whatever you do using electrolysis don't use stainless steel. A by product is hexachrome which is highly carcinogenic.

email (option): leonhop3_at_planet_dot_nl

Re: Removing rust from petrol tank

Leon I sent you an email. But as usual you didn't reply Ron

email (option): ronpier@talk21.com

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