In my experience simply "smelling for fumes" won't cut it. We usually empty them completely and purge with nitrogen for ample amount of time before welding. Calculate your vessel volume in cubic foot and the determine the purge time, adding more for redundancy.
He has no access to nitrogen. What about water
If you want to ignore OSHA reqirements (certified Gas Free), NFPA recommendations, ANSI / AWS Z 49.1 Recommendations and State / Jurisdictional requirements, water may work. However, it should be very soapy water. I have also used "light water" admixture (available from a Firematic Supply) with great confidence and success. I have welded many fuel (even gasoline containers ) tanks with only an active air purge that blew down the tank for several hours, then performed the welding operation with the air purge still running. Do not use "Purple K Foam" or Ox-Blood foam mixture!
I'd suggest dry ice.
Water will displace fumes where it is, but you need an air headspace where you can weld, and any remaining fuel will float on that water. So, water will reduce the volume for the fumes, but not eliminate it.
A nitrogen purge will work if you can keep a constant flow of nitrogen going in, to prevent any air from entering.
A CO2 purge can be better because being heavier than air, it is more likely to stay in the tank, IF the opening you're welding on is at the top (if the opening is at the bottom, then nitrogen would be the better choice).
If you have enough dry ice, it will continually release CO2 gas, so you would have the continuous overflow of purge gas you want that will keep any air from entering.
Oh, and when you're done, there's no cleanup.
If you can't find dry ice, ask the local ice-cream truck.
API (American Petroleum Institute) of Washington, DC, has issued a recommendeed procedure for welding tanks that have contained petroleum byproducts.
Enter www.api.org and make a search.
Giovanni S. Crisi
Sao Paulo - Brazil
I had to weld on the bung of my 1000 gallon tank. It is on a trailer so I had it filled with fuel jacked the trailer so fuel was damn near coming out the hole and welded it. The fuel dissapates the heat really fast. make sure no sparks can get to air inside the tank. I didnt have any trouble with fire but if I did all i had to do was cover the hole to cut off air to the flame. No air means no fire. I wouldnt do it with gasoline but with the crappy diesel we get there is no issues. You still need to be carefull though.
Find a diesel truck hook a dryer hose to the exhaust, run the exhaust to the tank. Weld.
You are correct Weaver, exhaust works every time. It is done this way in the oilfield and it works everytime. By displacing the oxygen with exhaust,it doesn`t matter how much unburnt fuel or product is in the exhaust stream as long as there is no oxygen. Been done by me and others I know more than I can count.
Ok, this post is starting to get on my nerves, so let me add a few words of caution.
While making weld repairs on fuel tanks is fully possible and often done, it can be extremely dangerous.
The tank is a potential bomb that has killed/injured many, many welders.
Many times I've heard people bragging about how they made repairs by simply filling the tank with fuel to avoid air pockets, or purging with exhaust fumes, or by rinsing with water.
These folks are the lucky ones who got by on a fluke.
You don't hear people talking about how when they tried these methods, it didn't work and the tank exploded, because they're dead.
Why take uneccessary risks derived from laziness.
It's like driving down the interstate at 70mph and getting something in your eyes that makes you unable to see. You can either pull over and fix the problem, or keep driving while you're fixing it. Yeah you can possibly drive on without wrecking, but why take the chance?
Fuel tanks that need to be welded on should be thouroughly cleaned with soap and water and should be fully purged with an inert gas before welding. That way you can be safe. Anything less than that is just plain haphazard.
Purging with exhaust fumes is plain stupid because exhaust fumes still contain flammable gases from un-burnt fuel.
OK, I'm done preaching now...
Tim
Thank you for saving me a lot of typing. The responses were becoming absurd.
Excuse me, Tim and Doug, but the recommended procedures of the American Petroleum Institute ARE NOT absurd.
Giovanni S. Crisi
I was referring to some of the farm procedures that were being posted.
You're right Prof. Crisi.
No offense intended to your knowledgeable post.
I was replying to those who have a death wish...
Tim
Nothing wrong with preaching if it saves someones life
TIM,
" You don't hear people talking about how when they tried these methods, it didn't work and the tank exploded, because they're dead"
Thanks.
That says it all.
You've got a one in six chance playing Russian Roulette...
In remembrance of my friend Johnny Goodner, 18 years old...
Shredded to death by a 55 gallon drum "filled" with exhaust. August, 1973
we welded on JOHN DEERE fuel tanks alot on the 4wheel drive tractors (8630,8640). they would often crack near a vertical seam or weld. we would fill the tank completely full with no or little air in the tank....and weld them up...never had a fire or explosion.
Tyler,
I have to agree with SOME of the other posters. You can't be too safe with fuel tanks, diesel or gas.
Fire and/or explosion takes three elements: Fuel, Oxygen, Heat.
Since diesel has a fairly high ignition temperature it is not difficult to keep temps relatively low, though any 'arc' will be enough with all the other factors.
Thus, the key ingredients are Fuel and Oxygen. I choose to rinse/purge a tank several times with Simple Green. It cuts fuel residue considerably. But there will still be enough fuel residue in the pores of most tanks to ignite. Even a cheap explosive atmosphere tester will give a danger reading. No matter the tester reading, I then fill the tank with either Nitrogen, Argon, or CO2. Any of these will displace the Oxygen in the tank and also displace much of the fuel fumes removing them from the equation.
So...
1) Keep the Heat factor as low as possible,
2) Remove/reduce the Fuel factor by detergent cleansing and then gas purging,
3) Finally, Remove/reduce the Oxygen factor by gas purging.
REMOVING just one of the three legs of the Fire/Explosive triangle will prevent explosion, BUT as I am not ASSURED that I have TOTALLY removed that one leg I prefer to reduce to the greatest extent all three legs.
When the Explosives Fumes meter gives a satisfactory reading it is SAFE to weld.
Personally, I just pass on most tanks anymore. Especially gas. I still do some diesel tanks. All depends on each individual case.
Have a Great Day, Brent
I'm a little puzzled that no one mentioned steaming. This tank mentioned by the op could probably cheaply be made completely safe by 24 hrs of steaming and keeping steam on while welding, after checking with a "sniffer". I worked in a tank repair shop many years ago, and this was the standard (and cheapest) way to prep all tanks for repair, from drums up to 10,000 gals. This may not be practical in some cases, but if the tank can be transported, is still in use at tank repair shops I am familiar with. Are there newer, cheaper methods?
Steam was the accepted cleaning method when My friends were in aircraft mechanics school in the early '80s.
I had suggested it on this forum a few years ago, but didn't get a favorable response.
Without knowing the configuration of the tank, it is hard to offer suggestions. If the tank only has 2 inch and smaller connections to it it will be hard to clean. Tanks like this can be cleaned with simple green and water. But then you have to deal with the contact water.
No, you cant just dump it on the ground, legally. I like Simple Green or Purple Blaster is another good cleaner.
But to make a recommendation to two guys I know nothing about with their experience except what has been posted I would recommend junking the tank and getting another one. Or taking it to somebody that has the proper tools to test test the atmosphere of the tank prior to welding and monitor it during welding and has experience in making this repair.
That said, fill the tank full with a 1/20 ratio simple green/water and weld it up. Be sure there is not a vapor space in the tank and has never held gasoline. Let your conscience be your guide with what to do with the water. Since your nose is not calibrated sniffing it will not tell you anything.
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