Welding a fuel tank

[vpt]

The tank should either be steamed clean or have an inert gas piped in whilst working to maintain a non flammable mixture, a very easy way to achieve the second is to pipe the exhaust from an internal combustion engine into the tank, clean breathing air for the welder should be a consideration ;-)
Filling with water and just leaving the area to be welded unfilled doesn't make a tank safe, it confines the potential explosion with an incompressible liquid - very un-smart and well documented bad practice for tank welding!

- Nick

Exhaust gasses from a gas engine are not always inert.

I always have and always will use water. Yes I have had gasses ignite inside of the tanks while welding in the void where the water isn't, the most you ever get is a little "blurp"...

[GNM109]

Yes, sometimes I qualify as an idiot, to this day even.
But never did I spout off about "safe and easy". Idiot or no, you do what it takes to be safe, and that might not be "easy", meaning that time and procedures are adhered to regardless of anyone's financial bottom line.

As GNM said, "Welding or cutting on fuel tanks often causes serious injuries and fatalities. It is inherently unsafe."

An inarguable statement. If it is your employment, and you wish to live another day, you do what must be done.

"Driving a two ton vehicle at 70 MPH on a highway full of other two ton vehicles moving at different speeds often causes serious injuries and fatalities. It is inherently unsafe."

The analogy being nobody drives a car without prior knowledge and degree of control. Drivers are always at risk. Sometimes the hazard is other drivers.

Hot work in a professional setting doesn't have "other drivers".

Working in your own shop shouldn't have "other drivers" either. It is your responsibility to police the area, safe off, and verify conditions that lead to safety. Many a building burned down from cutting/welding, no fuel tanks involved.

+5!!!!!!..........

[jdunmyer]

Let's remember that the OP was wondering about working on a motorcycle tank. This is inherently less dangerous than an automobile tank, which is inherently less dangerous than a fuel storage tank, whether it's 300 gallons or 3000 gallons. Making the tank safe uses the same procedures, but consequences of an "incomplete" job is quite different. Also, doing a "complete" job is much easier on a M/C tank. Some of us are trained and experienced enough to tackle the large job, most of us aren't. However, if one follows the advice given here, you can safely weld/solder/braze a small tank.

[macona]

Yes, argon, don't know where it comes from or how they collect it but I use it to weld. They say it is inert.

It is collected from fractional distillation of air, the same way they get liquid oxygen and liquid nitrogen. About 1% of the atmosphere is argon. It IS inert, it is one of the noble gases and only in extreme conditions will it bond with anything and then for only a very short term, an excimer.

[Carm]

"ex·ci·mer


/ˈeksəmər/


noun
Chemistry

noun: excimer; plural noun: excimers


Excimer

an unstable molecule that is formed in an excited state by the combination of two smaller molecules or atoms and rapidly dissociates with emission of radiation. Such species are utilized in some kinds of lasers.

[aribert]

Several posters mentioned steam cleaning or boil out. I took my car gas tank to a radiator shop and had them "kill" it (their term). I am guessing that it was boiled out. When I got the tank back there was no gasoline smell. COst was about $25 about 15 years ago with a day or so turn around.

"There are only two methods that I know of to make the tanks safe: One is to do a complete hot boil out. The other is to completely purge the tank with an inert gas--in both cases a test should be made to verify the results."

[vpt]

Some say that boiling/steaming out tanks doesn't get all the gas out of the seams.

How do you check for leaks in a tank after welding? Then if there is a hole what do you do?

[GNM109]

Many years ago when I was a kid in Chicago, I owned a 500cc Matchless motorcycle. It developed a pinhole leak on the boss that held the petcock into the bottom of the tank.

I took it to a weld shop and the owner did what he could to make it ready. His take was to start his car, let it idle and set the tank so that the exhaust was blowing into the fuel filler cap on top. He left it that way for about 20 minutes. He then filled the tank with water and set it up on a stand so that he could weld it from underneath.

He had no sooner touched the area to be welded when there was an explosion. It didn't blow he tank out, but rather there was a terrific bang and flame shot upwards out of the filler cap hole about 30 feet in the air, scaring the Billy Bejesus out of all those in attendance.

Encouraged, (LOL) he touched it with the torch again and there was another bang, much less with a much shorter flame. After that, he quickly welded the spot, did a nice job and that was that.

I suspect that several people watching needed some cleanup after that. I was OK, but I think the welder may have had some difficulty.

I'm not saying that using a car exhaust was effective in any way, in fact, it probably did little to stop a potential explosion. The water was sort of a backup but also proved to be ineffective. The tank could only be welded after the residual petrochemicals that had seeped into the metal had been burned out.

All I'm saying is that when welding fuel tanks that have held fuel, you just never know what will happen. Yes, I'm well aware that there are many methods: from boiling the tank in a radiator shop to filling it with Argon or other inert gas. I've done a couple of Harley tanks myself in the past by filling them with water and gotten away with it.

All that said, I never felt good about it and I sure wouldn't do it for a living.

[vpt]

That sounds like quite the story about the motorcycle gas tank. But I won't buy the flames to the ceiling with a tank full of water. Either the tank wasn't full of water (just washed out and drained?) or the "bang and flame" has been exaggerated like a fish story over the years.

[GNM109]

That sounds like quite the story about the motorcycle gas tank. But I won't buy the flames to the ceiling with a tank full of water. Either the tank wasn't full of water (just washed out and drained?) or the "bang and flame" has been exaggerated like a fish story over the years.

So you doubt that it happened. So what? So now it's a fish story?

Being from Wisconsin as you are, and with the high levelof fishing activity there, I suspect that you tend to find most everything "fishy". This brings to mind many other areas of your life that you may possibly consider "fishy". Please tell us more. LOL.

As to the gas tank story, I guess that you had to be there and you weren't. Calling it a fish story is just a nice way of calling me a liar, something you would not do to my face.

[vpt]

So you doubt that it happened. So what? So now it's a fish story?

Being from Wisconsin as you are, and with the high levelof fishing activity there, I suspect that you tend to find most everything "fishy". This brings to mind many other areas of your life that you may possibly consider "fishy". Please tell us more. LOL.

As to the gas tank story, I guess that you had to be there and you weren't. Calling it a fish story is just a nice way of calling me a liar, something you would not do to my face.

Well, if you told me this story to my face I might call you a liar. The story doesn't add up, something in the story isn't as it actually happened. Like I said either the tank wasn't 'full' of water or the flames to the ceiling is exaggerated.

I have done to many for to long to believe it.

[GNM109]

Well, if you told me this story to my face I might call you a liar. The story doesn't add up, something in the story isn't as it actually happened. Like I said either the tank wasn't 'full' of water or the flames to the ceiling is exaggerated.

I have done to many for to long to believe it.

There was no ceiling. The work was done outside.

Tell us more about your vast experience in welding fuel tanks. I'm eager to hear.

[vpt]

Tell us more about your vast experience in welding fuel tanks. I'm eager to hear.

You fill them with water so when they explode the water puts the fire out.

[GNM109]

You fill them with water so when they explode the water puts the fire out.

You used the term "explode" and in the same sentence you convert an explosion to a fire. In the case that I mentioned, there was no fire, just an explosion which everyone knows is rapid combustion. Furthermore, in physics we can state that heat lost equals heat gained. So you are telling us, that all of the heat generated by the explosion when the welder touched the torch to the fuel tank thereby igniting some amount of residual fuel was immediately and instantly absorbed by the water, raising its temperature to some degree so that the explosion was not seen to exit the top of the Matchless fuel tank through the filler cap opening. I see. So you are telling me that I heard and saw nothing.

Well, I could agree with you but I'm afraid that both of us would then be wrong.

EDIT: I'm retired now and I can continue this as long as required.

[vpt]

If there is no air/oxygen there is no flame/explosion. IF the motorcycle gas tank was full of water with the place to be welded submerged where was the air/oxygen for the explosion/bang you mentioned that sent water/fire 30 feet into the air?

What about the method of welding on a gas tank full of gas? If explosions happen while submerged why are the guys that weld on full tanks still around to talk about it?

You said you were a younger kid at the time and now retired, so it must have been some many years ago. Possibly you missed when he dumped the water out of the tank before welding it?