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

[Captndave1]

If the tank is aluminum, use argon, if steel use co2.

[groundtackle]

Oxygen/gas analyzer and know how to use it... no other way than safe. Go to a pro.

[RaymondR]

I have done the fill with water thing to weld on a fuel tank a couple of times.


The first time was a disaster as the tank was in three sections and the builder had not left any limber holes between the sections claiming that they were not necessary because the baffles were not fully welded.


The problem was that although I thought I had removed all the water it was trapped in the two sections I could not access and only bled forward slowly.


In retrospect if I had raised the standpipe well off the bottom of the tank for a few months and stripped the water from the bottom of the tank at regular intervals I would have eventually have removed all the water without it causing a problem.

[brianlara 3]

Originally Posted by RaymondR

I have done the fill with water thing to weld on a fuel tank a couple of times.


The first time was a disaster as the tank was in three sections and the builder had not left any limber holes between the sections claiming that they were not necessary because the baffles were not fully welded.


The problem was that although I thought I had removed all the water it was trapped in the two sections I could not access and only bled forward slowly.


In retrospect if I had raised the standpipe well off the bottom of the tank for a few months and stripped the water from the bottom of the tank at regular intervals I would have eventually have removed all the water without it causing a problem.

They do say, don't they, that nightmares are character building. Personally, I needed a lot less character a few decades ago. Or longer than that ??

[GrowleyMonster]

Water in the fuel tank? You mean, you have NEVER had ANY water in your fuel tank? You lucky old seadog, you! A little water in your diesel tank is a common occurrence, anyway. What do you do? Well of course you check your water trap now and then. Don't have one? Add one. Any external clear bowl fuel filter setup that has a drain at the bottom will suffice. I have made a couple out of a foot long section of scrapped well casing... can't see inside, but it is a simple thing to drain a bit into a pyrex measuring cup and examine it. If you don't get water, no problem, and if you do, drain some more, and more, until you don't. Meanwhile if it is a serious problem you can raise the pickup a bit more from the bottom of the tank. It sounds like installing a drain petcock at the bottom of your fuel tank is not a doable thing. But after the weld job, sucking every last drop of intentionally introduced water from your tank should be pretty easy.

Make sure your welder has done this before. It is not something you just do.

Your tank is steel, right?

[bsurvey]

you can pump in carbon monoxide from your car exhaust, hose on to the tail pipe. it is inert gas. and will prevent explosions along as the exterior area is well ventilated you won't die.


I have done some barge and tug steel repairs in very remote locations and it is very common practice

[CaptRory]

I would consider putting a bladder in it. They come in all sizes and you could probably get a custom one done. Marine Gas/Diesel/JP-8 Fuel Bladder Tanks and FueLockers for Extended Range

[captlloyd]

Originally Posted by bsurvey

you can pump in carbon monoxide from your car exhaust, hose on to the tail pipe. it is inert gas. and will prevent explosions along as the exterior area is well ventilated you won't die.


I have done some barge and tug steel repairs in very remote locations and it is very common practice

I am a professional welder. I built a 64' steel sailboat. This man nailed it. Carbon monoxide will do the trick, Just ventilate with air hose when done, the hull first and then the tank. Use a Home Depot co detector.

[nautitrix]

Is the tank being welded on, part of the hull or is the welding being done on a tank in the keel of a fibre-glass boat?
If the tank is integral with the hull and being welded on the outside of the hull the welder will want a visible indicator (water) so s/he knows the tank is full of something other than fumes.
If the welder is not comfortable welding at the Botton of a bowl filled with heavier than air gases I can understand that as well. in any event welding a tank filled with water is a common enough practice that I would let the welder proceed. If you say no to that welder I'm sure s/he will be happier to have someone else do that particular weld.
Under-water welding is a frequent part of the diving trade. Sometimes it is gas shielded and sometimes it is your basic SMAW welding, depending on the use and metal.

[calin1967]

I've heard a neighbor welding his car tank in front of our block. Me and all the other neighbors closer than 1 km.

[Kita]

Originally Posted by captlloyd

I am a professional welder. I built a 64' steel sailboat. This man nailed it. Carbon monoxide will do the trick, Just ventilate with air hose when done, the hull first and then the tank. Use a Home Depot co detector.

PRO welder here as well,water sucks for many reasons, don't even....also makes for a poor weld,as I said many reasons not to use water! This guy nailed it for sure,exhaust from a car works great,but I can tell you that even while you are welding the co2 needs to have the tank slightly under pressure just a positive flow. I did one once on a motorcycle that I forgot to hook up the CO2 line on the second time I struck the ark and the tank jumped up in the air about 3 feet rounded out the tank and scared the hell out of me. So you need to make sure that you have a good positive CO2 air flow flowing through the tank. An even better way is to run the inert gas that you are welding with such as argon if you're using a TIG welder into the tank ,,,that works so well that the inside of the tank looks like it was welded from the inside that's how we do high performance exhaust systems so the inside of the exhaust doesn't have any hangers or ugly stuff from the contaminants such as water, but that's kind of going above and beyond the CO2 works pretty good you just gotta make sure there is enough of it in there. Definitely worth paying a professional to do that has good insurance because of mistake here could be very costly. People have died trying to do this definitely pay attention

[um saudade]

1: Many old school welders like me routinely use CO2 as a shielding gas for mild steel MIG welding. Please don’t tell me it is not inert or won’t work.


2: CO2 is heavier than air so it is easy to get the CO2 to displace the atmosphere in the tank. It won’t curl up around you like fog in a horror movie and do everyone in! Nitrogen on the other hand is slightly lighter than air and would make it more difficult to purge the O2 from the tank. Cars don’t even make carbon monoxide any longer; the catalytic takes care of most of that. Why would anyone want to cobble up some system to use vehicle exhaust when a couple of bucks of CO2 from a regulated bottle will do the job professionally and safely?


3: The tank should not be pressurized when welding, just purged. Put pressure (either liquid or gas) in the tank and it will try to escape and it will attempt to escape in the leaking area, tending to blow holes and bubbles into the weld. Does not make it impossible to weld but why make the job more difficult?


4: I have filled tanks with various liquids over the years to displace the fumes before welding. Using liquid also helps to control heat transfer which can be an issue too. This works fine when you can physically manipulate the tank but I would not try it when you could not get the leaking area slightly above the liquid level. You don’t have that option here.


5: The most important aspect of this job is to make sure it all gets repaired. Because you are talking about welding in several spots on the hull and transom, I suspect you are not talking about something that took damage but about wear and tear, meaning thin spots or old welded joints that are leaky. Thin spots on the outside are easy to detect. Thin spots that exist on the inside of the tank are very difficult to detect. Getting the rusty area clean enough to weld is very important and may be extremely difficult to do when you can clean only one side of the job. If thin or rusty areas are too big, they need to be cut out and new steel plate welded in and fared out for we can’t put a simple overlapping patch on the outside of this. Don’t think welding in terms of filling holes, it does not do that very well. The tighter the fit between two pieces of steel the easier and stronger the weld, the larger the gap, the more issues.


What I am saying is this could turn into routine maintenance over time. Depending on the head pressure of the tank a small pinhole below the waterline could leak either way. If you start noticing excess water in the fuel it could be another pinhole leaking seawater into the tank. I might even consider taking the top off the tank and getting on the inside to see what you are dealing with before trying to patch blindly.


What does the surveyor say about the hull issues? Is he confident some welding at this point of time is going to be a durable solution?

[Viking Sailor]

If the crack/hole is not to large consider patching it with fuel-proof expoxy. Did this on diesel fuel tank for a car once. Worked great! I think Autozone sells a fuel tank repair kit.

[Cadence]

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.

I have heard of it with gasoline. I would probably go with the welder since you probably vetted him prior to hiring him. He doesn't want to burn you boat to the ground.

[Rigdaddy]

Originally Posted by leftbrainstuff

Common practice in the Australian outback on gasoline tanks too.

Brazing of holed tanks was very common.

Best practice is steam cleaning which is required to meet any OSHA style requirements.

Be advised that old tanks with corrosion or lumpy welds inside will harbor hydrocarbons. You'll get a nasty surprise.

Water ballast fuel tanks were common on naval vessels to maintain stability.

The diesel will sit on the water initially. You'll want to remove as much of the water as you can before refilling. Then biocide and polish regularly.

Filling the tank with an inert gas like nitrogen or argon is not good practice if your tank has leaks. It also poses confined space asphyxiation issues.

CO2 is also a poor choice as you'll get oxidation and carburizing around the weld heat effected zone and this poses a potential corrosion issue. CO2 is not an inert gas its a weak oxidizer.

I agree with this. I've welded many fuel tanks after steaming and filling with water. If you are not able to remove virtually all the water after the weld, then the inert gas may be preferable.
Sounds like your leak is on the outside, so not an asphyxiation issue.