Cutting up diesel tanks

Seagreen

Seagreen

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Oh joy! As part of my cockpit rebuild, I have to remove two steel diesel tanks. The fun part is that they were bolted by brackets on the top to the underside of the deck beams before the side decks were laid over them. So I have to rip up the decks, or cut the tanks to bits in situ. What's the best way to do this without setting fire to the boat or blowing myself up? I'm going to empty the tanks first, naturally.
 
I've got a very simular job to do as well, so I look forward to seeing how others have tackled this. Some years ago I was cutting up an old diesel storage tank ashore and it caught alight it took about 5 fire extinguishers to put it out. I am much more careful nowadays. /forums/images/graemlins/laugh.gif
 
I have seen 45 Gallon barrels sucked flat ! We used to run diesel engines with the air inlet via a barrel, flat out a 6ltr engine uses a huge amount of air and the practical jokers used to nip in the back door of the test room and hold a piece of ply over the open end,
flattened the barrel,and stopped engine in no time, so what about a big vacuum pump ?
P.S wear ear protection !
 
I had to cut up two onboard in the saloon. Used a reciprocating saw

One tip is to fit a pipe onto another source of exhaust, heater for example and feed it into the tanks, to fill them with exert gas and flush fumes. Although I think that tip is more appropriate to petrol tanks.

They should not ignite if the saw is slow and the right type. A cutting disk is probably too hot and furious. We had to cut each tank into three pieces to fit up the stairs.

Watch out for the filings, the cutting leaves tiny rust spots on your grp. Viakal or Limelite should get rid of them though.
 
Purge the tanks with carbon monoxide by fitting a tube from a suitable car exhaust,
cutting with a disc grinder will then be safe /forums/images/graemlins/blush.gif.
a friend had his bike Ali fuel tank rewelded by this method /forums/images/graemlins/shocked.gif
 
I had to cut a mild steel tank out of my fishing vessel. I drained it and then cut an inspection hole with a mini grinder to check out the interior. I was initially going to weld in a new section. The corrosion was too bad so I used the mini grinder and a few discs and cut it into sections I could manoeuvre out the hatch. Diesel is hard to ignite.
 
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Diesel is hard to ignite.

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Well so it is, its just the sparks, vibration and lots of fresh air may just give it the chance to burst into flames. I have some cheap Lidl extinguishers handy. As I can't flush out the tanks, maybe just draining them and leaving them to settle for a few hours before taking a grinder to them would help?
 
When I have used old gas containers to make other things, I have filled them with water before cutting/welding.
This may in your case, if left, raise the remaining diesel to the surface where you could skim or aqua vac it away. You will probably only have a problem if you use oxy!

Sabre saw good idea.
 
I reckon there would be less chance of a fire with a reciprocating type saw, or depending on the thickness of the steel maybe an air chisel or one of those falcon nibblers the car restorers use?

I suspect that a grinder will be fine, just have an extinguisher handy.
 
I was thinking of draining and them filling with CO2 from an old Liferaft cylinder. I've a mate who runs a pub, if I could get it off him. They use CO2 in the shandy, don't they?

Mind you, draining, venting and wafting it all out seems best. I once cut up an oil drum (barbie) and it was only the tar residue that caught fire, and little of that too. If only people would build stuff with a view to the eventual demolition? That's another rant.

BTW, in demolishing the cockpit, I discovered another classic - wait for it...

Gas bottle locker with hose vent which drains into the bilge. Think about that for a moment. <u>Thats why I fitted a Taylors.</u>
 
I presume the gas installation is down to a previous owner , very dangerous but so many people don't think about the potential bang
As for the fuel tank , get a couple of out of date CO2 extinguishers and empty the contents into the tank ( presuming you're aware of the chill ) then keep another handy just in case and use a nibbler or disc cutter
 
burgundyben is right. Air hammer and chisel, or better, the tool that looks like a gouge and cuts out a kerf about 3 mil across, will rip the tanks to bits in literally minutes, assuming we're talking sheet steel rather than plate. A good pistol-type air hammer and the right tool will just demolish anything up to 1/8 inch thick. You could use an electric hammer instead but they're really bulky and heavy, sods to use in a tight space, plus the motors produce sparks, not good if we have fuel vapour. Air hammers are a dream to use in comparison anyway. If you have the right tool on all you have to do is steer-- the hammer does all the work.

If the tanks are thicker metal and an air chisel is not going to work (and the metal will have to be pretty thick to defeat one) I'd use a reciprocating air saw. Believe me it's just night and day using air tools against electric for this sort of thing and as I said, no sparks.

I would never use a gas axe anywhere near a wooden boat, fond though I am of them. Even if the tanks don't catch you are just about guaranteed to blow some red-hot slag somewhere flammable.

BTW I remember one calloused old welder telling me he was quite relaxed about welding fuel tanks because the fumes inside were so concentrated they excluded all the oxygen-- and so would not burn. Never had the guts to try it myself.....
 
Steam clean it out. If you have a residue you can't get rid of, it could be worth throwing some dry sand into the tank.
 
I'v e done it with a disc cutter and I also set the bloo%y thing alight, once the flame caught it was a total conflagration. fortunately this was ashore too but it burnt for hours, use something that doesn't make sparks because fuel seems to soak into all the joints, (where welding was external originally) plus all the sludge on the bottom holds a fair bit. Don't think your Insurance Co would be too thrilled if you incinerated the entire boat. Also, in the confined space of the tank, purged/inert-gas-filled or not there is still a risk of hot vapours rising up above the purge level and going "whoof", taking off your eyebrows or toasting any other part of your anatomy in the way. Ask yourself, "do I still need my b%ll%cks or not?" If the answer is "Yes" then hire the air tools like the man says.
 
As for not using a cutting disc, I've actually got an SDS hammer Drill which cuts through concrete like the proverbial hot knife. Apart from being en electric tool ( I can wrap tights round the venting) will this be ok? Chuffing noisy but it may be worth a try. Tanks are only 2 or 3mm sheet steel.

I like the sand idea.
 
Give it a go, it'll make mincemeat of that thickness. Use the widest chisel you have and try to cut parallel to the surface you're cutting, ie cutting along, not punching through. Start at about 30 deg to the surface and as soon as you feel the tool bite, lean it in as far as you can. Just keep a little pressure on the tool, don't push it-- it will probably surprise you by how quickly it cuts anyway.

The main problem with the big SDS hammer drills is the bulk and weight, which makes them difficult to get into tight spaces and hard on the arms. This will probably mean you have to cut the tanks into smaller bits than you would with an air tool. If you're going to close off the vents be sure to use it only for very short bursts and let it cool between.

Noise? I wear ear-plugs *and* headphone-type ear defenders when I do this sort of thing.....
 
I had to do this with the under-cockpit tank on a freind's boat which had been glassed in place before the deck-mould went on. We only discovered the tank was there when the boat was under refit following a sinking.
There is no one tool which could have done the job. Once the only exposed wall of the tank was opened up with an angle grinder a section had to be removed so we could get into the baffles which were stopping the tank coming away in sections. In the end the most effective tool was a four-inch boaster and a lump hammer.
Hopefully the job will be easier on my own boat whose twin tanks either side of the cockpit need to come out. Taking the woodwork to bits to free up the tanks will be more savoury than cutting them up in situ.
 
Thanks everyone, for your input.

On closer examination, the tanks are just held suspended from short oak bars - no cutting needed.

I couldn't believe this, as they are steel tanks holding some 45 litres each, and thus quite heavy to have swinging about. All held in place by eight 2" screws. Bizarre, but thankfully not too traumatic to remove intact.
 
The only way is to hire a Reciprocating saw after advice from my maintenance engineer at work. With the correct blade it'll go through like butter. The hardest part is rotating the tank if you have to. I cut my 40 gall tank into 3 pieces but it took far longer to rotate it than to cut it! No sparks and relatively quiet.
 
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