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

[Cadence]

If you pump the tank as dry as you can and used an absorbent you should be reasonably dry. Add some isopropanol to the tank it will mix with both water and fuel allowing you to burn off any small amount of moisture. That sounded wrong. Burn off as in running the engine.

[twoblocktom]

Vapor can be explosive depending on the mixture of fuel and air right? So water will displace that mixture from the tank. What I have done when welding or cutting on a tank is to run a hose from the exhaust of an idling engine into the tank for 15 to 30 minutes to displace the oxygen and fuel vapor. Leave this purge on durning welding! Much better than water. I am still uncomfortable welding on fuel tanks and try to avoid it if I can!

[Alastair A]

Hi. Please be most careful! Please use inert gas (co2) and not water. I have seen a barrel explode while others were cutting it in half. Serious debris flew 150m over buildings! Don't go there without the right gas to avoid an explosion.
Seriously use a welder familiar with this situation. cheers A.

[Cadence]

Originally Posted by Alastair A

Hi. Please be most careful! Please use inert gas (co2) and not water. I have seen a barrel explode while others were cutting it in half. Serious debris flew 150m over buildings! Don't go there without the right gas to avoid an explosion.
Seriously use a welder familiar with this situation. cheers A.

I think it is C0. The problem with it is not the inert gas but the unburnt fuel. Does anyone remember putting a spark plug at the end of the exhaust pipe and causing a big bang by sparking it off.

[socaldmax]

Originally Posted by Kita

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

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.

[socaldmax]

Originally Posted by Cadence

I think it is C0. The problem with it is not the inert gas but the unburnt fuel. Does anyone remember putting a spark plug at the end of the exhaust pipe and causing a big bang by sparking it off.

That had to be at least 30 yrs ago.

Today's fuel injected cars produce nearly ZERO emissions and when running produce CO2 and H2O, with just a few PPM of CO and NOX.

[Pauls]

Lets get back to basic physics:
1. Fuel cannot burn (or explode) without oxygen. Removing oxygen from the tank is vital. Water, Co2, nitrogen, all can displace the oxygen and create an environment where explosion is not possible.
2. Welding basic metallurgy requires the steel to cool slowly enough for the steel to form a strong, tough metallic structure. Cooling too fast creates a brittle steel which is much more prone to cracking. This is basic welding tech and is why thick steel sections are preheated, minimum weld bead lengths are specified, etc. Water against the steel guarantees very rapid cooling and this is definitely not optimum.
3. Co2 is heavier than air. When you fill a space with it it sinks to the bottom of the space. Small volumes of trapped gasses have a tendency to float up to the top of the pooled Co2. The Co2 will not drift up out of the tank openings.

The best practice, also the easiest to use, is Co2. You can buy dry ice (frozen C02) and use this as your source. It is cheap and commonly available. Use enough dry ice to create a gas volume several times the volume of your tank. This will give a flushing action to flush the air out of the tank. Put the dry ice in the tank (buy it in pellet form), and wait an hour or two. Then weld.

I am an engineer, and am also an experienced welder. I have used this technique on two large diesel tanks with perfect results. A water filled tank will result in substandard welds. They may very will fix the leak - any good welder can accomplish that - but they will be substandard in strength.

[Cadence]

Originally Posted by socaldmax

That had to be at least 30 yrs ago.

Today's fuel injected cars produce nearly ZERO emissions and when running produce CO2 and H2O, with just a few PPM of CO and NOX.

Closer to 55+ yrs ago.

[hamburking]

I had a similar experience when I was captain of a maple leaf 48. The owner had hit a rock and it split the keel just slightly. But being a keel tank, water flowed in and diesel fuel backed up through the fill fittings, now under pressure and filled the bilge with diesel. We quickly got to a travel lift and drained the water and remaining fuel from the tank. But the welder we hired refused to weld the tank shut. Stated that he could not weld a fuel tank unless it was either fully flushed clean and vented, or filled with water. The possibility of igniting fumes was just too great a risk. I had to agree. So I degreased the area as good as I could, filled with epoxy, then layered with glued on plastic sheets. That was good enough to keep the water out, although we could not use the tank. It was a patch job just to finish the season, and a proper repair was done during the off season. I was told my patch was still in position and watertight when the boat was hauled for the season. I had no experience in this sort of thing, and this was before the internet. I got the idea from reading about ernest shackleton's adventures in the antarctic. But where he used canvas and tar, I used sikaflex and plastic bags.

[brianlara 3]

Originally Posted by Cadence

I think it is C0. The problem with it is not the inert gas but the unburnt fuel. Does anyone remember putting a spark plug at the end of the exhaust pipe and causing a big bang by sparking it off.

Yes! Doing demos to tech college students. Probably 200 times.
Probably wouldn't happen these days, given the efficiency of catalytic converters.
When I was doing it automobile wheels were still square, round was later. Goin' back a while. T'anks for the memories.

[tonyandwendy2]

Steam cleaning diesel tanks is a known method of gas freeing. Steam clean for a considerable time i.e. 1/2 hours. If you are doing this inside the boat, to introduce an inert gas is inviting other hazards. Unless the tank has been for something else i.e. gasoline, you will be hard pressed to find any L.E.L in diesel. Take care.

[Alastair A]

Hi All. Above I suggest carbon-di-oxide. for safe tank filling. Carbon-mon-oxide is much to biologically dangerous and should never be used by anyone who wants to think straight and keep living. Cheers. A

[Johnno]

Well back in my Air Force days, we scoured fuel tanks with live steam before welding. The tanks were steamed for asround 24 hours, the heat from the steam tended to them once the steam was turned off. Once weleded they were they were purged before refitting.

[rmiker]

As a welder: Argon would be my preference for a safe quality job then either Nirtogen or CO2: Both of these cause problems in the longterm weld deposit but will make the tank safe. Try to avoid water if you possibly can: water is a very stop gap measure by anyone's ruler!

[nic26]

Nothing wrong with that, we did it all the time in the garage even with gasoline tanks. Only the fumes are explosive
.
There is actually a Mythbuster sequel where they throw a glowing cigarette into a gasoline tank more than once and nothing happens.