Has anyone heard of filling the diesel tank with water before welding??

[Jim Cate]

FWIW, we had a pinhole leak welded up in our steel shell keel diesel tank with the tank 2/3 full of diesel. The welder said that as long as the weld area was below the level of the fuel that nothing bad would happen... we could hear the fuel boiling away in the weld area, and there were no bangs or flashes.

This was not a structural weld, but to stop a seepage where a button weld holding a baffle in place was porous. been 13 years now with no recurrence of the leak.

As others have pointed out, the danger, if any, is from igniting an explosive mixture of diesel and air. With the heat source below the level of fuel in the tank, this seems quite unlikely.

Jim

[MCOS]

Originally Posted by Make_My_Day

We are having some welding done on our boat as recommended by the surveyor. Along the way the bottom was sandblasted and some additional places that needed attention came to light.

One of these is the back of the keel where diesel was visible after the sandblasting. The keel is our 200 liter diesel tank.

We drained the tank completely and left it open to ventilate. This was good for the welding on the transom and on the bow, but now the welder wants to fill the tank with water prior to welding on the places that showed leaks. This is to prevent explosion.

This seems strange to me because I would never want to have water by diesel. In addition to worrying about how to get it completely dry before refilling, I am also concerned about corrosion. There is no access port from above the tank only a drain port on the bottom of the keel.

I spoke to the surveyor and he thought it was strange as well. He thinks that an inert gas like nitrogen should be used in the tank to displace the oxygen.

Has anyone heard of or used this practice of filling the tank with water for welding? What about the use of inert gas? Any insight would be appreciated.

Welded for many a year as a mill wright and as a welding shop owner, most of the replies had some merit to them, many of the methods described I have used at one time or another. For your circumstances I would steam clean, leave the steam generator running and filling the tank with steam while welding. Steam displaces the fuel vapor and will not interfere with the welding to the extent of trying to weld through a weeping rust hole or fissure. If the hull is weeping it is probably quite thin due to corrosion so expect a blow through, not too bad to handle if you don't have a deluge of water. The steam will condense and you will have some water so leave the hull drain open.

The only other idea I would consider is the co2 flooding of the tank. CO2 is used for a shielding gas when welding fuel and hydraulic tanks to minimize pin holes. I strongly disagree with the poster that indicated that Co2 was not an inert welding gas. The cheapest and easiest way to flood the tank would be to put several blocks of dry ice in the tank. Since you will be steam cleaning anyways why add to your expense ?

Consider free info for what it is, FREE. Suggestions that you should discuss with your welder - None of us have a horse in the race, it's your boat.

Best of Luck, and MERRY CHRISTMAS!!

[Reefmagnet]

Actually, in a technical sense CO2 is an "active" gas when used as a welding gas hence the more correct term "MAG" welding using shielding gases with a CO2 component . Of course this has absolutely no relevance when used as a purging gas.

For all those recommending carbon monoxide car exhaust as a purging gas, all I can say is. O. M. G, :-o

[Cadence]

Originally Posted by Reefmagnet

Actually, in a technical sense CO2 is an "active" gas when used as a welding gas hence the more correct term "MAG" welding using shielding gases with a CO2 component . Of course this has absolutely no relevance when used as a purging gas.

For all those recommending carbon monoxide car exhaust as a purging gas, all I can say is. O. M. G, :-o

Yep! carbon monoxide and lots of unburnt gas vapor. I'd take my chances with a little diesel vapor.

[MCOS]

Originally Posted by Reefmagnet

Actually, in a technical sense CO2 is an "active" gas when used as a welding gas hence the more correct term "MAG" welding using shielding gases with a CO2 component . Of course this has absolutely no relevance when used as a purging gas.

For all those recommending carbon monoxide car exhaust as a purging gas, all I can say is. O. M. G, :-o

You are 100 % correct, when used as a welding shield gas Co2 is reactive in the sense that it is broken down by the arc plasma and combines some carbon with the steel. It does allow deeper penetration of the weld but most of all, it virtually eliminates porosity. When I indicated that it was inert I was thinking along the lines of not supporting flames/fire. I still would not bother to flood the tank with Co2 and would leave the steam generator flooding the tank with steam during the welding.

[groundtackle]

I guess we all have our favorite methods, I personally just follow the rules and displace the undesirable vapor/oxygen to the correct level with a gas specific to materials. Measuring with oxygen/gas analyzer inside, in a logical manner. Release vapor/oxygen from locations until confident you have controlled levels. Only a very slight positive pressure when actually welding. Like any purge weld setup.
Steam works but sometimes makes the internal cleanup time consuming when areas are difficult to access.
The old apprentice gag... You show the kid how to set up and use all the equipment. Ensuring him it is safe to weld. Helmet goes down and as soon as he makes fire you slam a sledgehammer on the steel table beside him. Amazing how high they jump. Its fun when they are just pressure testing vessels too. They got me with it, I just continued a tradition.
ce

[Steve Bean]

Just for information, carbon monoxide is flammable! Look it up. It's lighter than air. Not much is produced by modern automobile engines. Carbon dioxide is heavier than air and can accumulate in low or enclosed areas, such as boat bilges and cabins. There it can exclude air, causing asphyxiation.

[Cap Erict3]

Water does more than prevent explosion. It also acts to dissipate heat. Getting it back out is child's play.

[skywalker]

Think logically because there are still some questions unanswered.

typically a welder is in his home town and needs a good reputation, how long has his business been welding and is he comfortable welding with gas instead?
You, on the other hand, are a boater and boats move around meaning that you get fixed, sail away and nobody hears from you again. I've seen it time and time again.
He may be the best welder in town but you still end up with water in the tank.

Bottom line: you don't want ANY water in the tank.
Cheers,

[groundtackle]

skywalker, exactly what questions are unanswered?
I usually don't get worked up until people get hurt.
ce

[Kerry1]

I once had cracking problems with a 2000 litre tank that was subjected to engine vibration. The tank had a lot of diesel in it. I took it to a local machine shop to weld the crack up and reinforce it against the vibration. To my horror, He welded it up with the diesel in situ. I asked him if he was worried about an explosion. This was his explanation: "The fuel was higher than the leak, and the tank was full enough that the volume of air present was minimal. The method of welding was using a mig welder meaning that the heat was extremely localized and dissipated through the tank wall and diesel before any explosive temperatures could be reached." He not only fixed the leak, he added strengthening members across the diameter of the cylindrical tank using the same method. All while the tank contained a large amount of diesel. NOT TO BE TRIED AT HOME! I wouldn't recommend this to anyone, but it can be done.

[GrowleyMonster]

Originally Posted by skywalker

Think logically because there are still some questions unanswered.

typically a welder is in his home town and needs a good reputation, how long has his business been welding and is he comfortable welding with gas instead?
You, on the other hand, are a boater and boats move around meaning that you get fixed, sail away and nobody hears from you again. I've seen it time and time again.
He may be the best welder in town but you still end up with water in the tank.

Bottom line: you don't want ANY water in the tank.
Cheers,

Water in a fuel tank is VERY common. I would say practically universal. Condensation, spray driven in through vents, and water in purchased fuel. If your filter system is not set up to deal with it, you will sooner or later have problems. If you are well equipped for dealing with small amounts (or big amounts) of water in a fuel tank, then a little residue is nothing to even take notice of. There are reasons to consider avoiding the practice of welding a water filled tank, but possible traces of water left after dewatering the tank is not one of them.

[chala]

Originally Posted by Sailmonkey

I've welded on diesel tanks that were pressed up (full without an air gap). I know it's not kosher, but in a pinch eliminates the possibility of an explosion or fire in the tank.

Originally Posted by Jim Cate

FWIW, we had a pinhole leak welded up in our steel shell keel diesel tank with the tank 2/3 full of diesel.

Originally Posted by Kerry1

He welded it up with the diesel in situ.

I have worked in the 60’s with a large company that was manufacturing in house large diesel tanks for central heating. Pin holes leaks on the tanks where fixed as described above. The diesel does boil at the welding but is easily cooled by the thousand of litres inside the tanks. Kosher or not that was the practice.

[Kita]

Originally Posted by Kerry1

I once had cracking problems with a 2000 litre tank that was subjected to engine vibration. The tank had a lot of diesel in it. I took it to a local machine shop to weld the crack up and reinforce it against the vibration. To my horror, He welded it up with the diesel in situ. I asked him if he was worried about an explosion. This was his explanation: "The fuel was higher than the leak, and the tank was full enough that the volume of air present was minimal. The method of welding was using a mig welder meaning that the heat was extremely localized and dissipated through the tank wall and diesel before any explosive temperatures could be reached." He not only fixed the leak, he added strengthening members across the diameter of the cylindrical tank using the same method. All while the tank contained a large amount of diesel. NOT TO BE TRIED AT HOME! I wouldn't recommend this to anyone, but it can be done.

LUCK.....he is lucky to be alive,I have seen guys killed that were smarter than that

[Kita]

Originally Posted by socaldmax

FINALLY! Someone gets to the most important point: weld quality! In order for full penetration of the weld, the parent material must melt along with the weld material. If you've got 100gal of water inside the tank cooling the steel, I can guarantee you, weld penetration will be nowhere near as deep as it should be.

Fill the tank with CO2 and then grind the area clean and weld. Find a welder who tells you that he will do it that way without you having to ask for it. The best way is the right way, everything else is just a waste of time and will usually bite you in the butt at the worst possible time. One of Murphy's Law Corollaries.

I can't believe how some people are getting this so messed up, full of desial & weld it,omg! He is brave....he is correct that the liquid is better than empty, but still....no way is that safe! The metal does absorb a certain amount of fuel no matter how many times you rinse in there will still be fuel fumes in there and the fumes are much more dangerous than the liquid fuel but still the liquid could ignite under welding temperatures. .if I seen a guy trying to weld a full tank ,full of desial, ,, not only would I fire that guy on the spot but I might even kick his ass for risking everyone's life....it's just not worth it, water will kill the penetration & cool it to much making it brittle & it may get you going but I guarantee at some point you will have to fix it again. Meantime you're getting all the water out of your system what a pain in the ass why would you do that to yourself. The exhaust gas from a car engine does have some unburnt fuel but it's already been burned once and it will not ignite no way no how not enough oxygen