Gas tank repair

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The gas tank on my tractor (1955 Ford 600) sprung a leak near two spot welds. The factory welded the mounting bracket straight to the bottom of the tank. Cracking around the weld is common. I've read a lot of comments and debate about safety of welding gas tanks. I'll admit I was a little nervous, but I would do it again without hessitation. Here's my receipe for success. Drain tank and remove. Remove shutoff valve. Wash tank three times with Simple Green. Rinse throughly with cold water, let the garden hose run in it for several minutes. Drain tank and pour in a large pot of boiling water. Swish around, concentrating on the seams. Drain and repeat hot water rinse. Use shop vac to remove excess water. Set tank out in the sun and use shop vac to blow air back into tank. This will evaporate water inside tank. I tested my tank with an gas detector from work. I found no explosive fumes inside eventhough it still smelled like gas. OK finally onto the repair. I cut the mounting bracket along the dent in the bottom of the tank and then seperated that piece from the bracket. Then I drilled out the spot weld on each piece and poped the piece loose. I ground down the areas to be welded around the holes and along the length of the bracket. I added a short weld near each factory spot weld. Then I filled each hole because the were too large to just braze. I drilled out the end of each crack. Finally, I brazed over the areas that were cracked. I tested the tank with water and did not find any leaks. SUCCESS! I'm going to sand and paint the tank before reinstalling. Hope this is helpful to someone else. Attached Images
Reply:I'm glad it worked, but I have no kudos to give, mainly because I really don't know how safe it was.Not jumpin' ya, just dunnoTanks scare the daylight outta me, but I may face the same situation one day.Be honest with you, I'll probably send it out to be done.  I don't have the expertise"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Good job.  It sounds like you did a good job of cleaning out the tank.  I have read so many different ways, I wonder what the best 'official" solution is for cleaning out a tank?
Reply:Congratulations on the safe success!  It sounds like your formula and procedure for cleansing the tank of fumes is pretty thorough.  As I was reading I almost expected to hear you say you left it filled with water but you did not.  Good.  Electric welding on a tank filled with water is an invitation to disaster.  If superheated steam doesn't cause an explosion the breakdown of water into hydrogen and oxygen caused by an arc will.Two weekends ago I patched a pinhead sized hole in the gas tank from a motorcycle.  The hole was caused by a small amount of water from condensation settling in the bottom when the bike was parked outdoors all the time with a partially filled tank.  This bike is more than 10 years old and the problem is not uncommon.  How did I remove allt he gasoline and fumes?  The tank was drained and removed from the bike and both the cap and the gauge assembly on the bottom removed.  It sat in a distant corner of my cellar for two years like that just venting and drying out.  There was no detection of fumes at all, didn't even smell.  The inside was dry as a bone in the desert sun.  I blew air through it, still no odor.  Risking all I tapped the spot with a ball-peen hammer to create a small dent, zapped the spot with the MIG, ground the crown off the asprin-sized bead, and fiilled around it with silver bearing solder and a hot soldering iron.  I finished the final surface with 600 grit W/D paper and a touch of sandable primer.  The rest is up the the owner (#1 Son).Let the scolding begin!-MondoMember, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.
Reply:I like all of you guys.  BS  with y'all every nightBut how, on a public forum, where people look at this, and maybe take it as Gospel Truth, can y'all give congrats to something that might have been unsafe at best, and lucky first time luck at worst.Tanks can kill you.It's something for lengthy discussion about the ins and outs of safety with something that contained fuel.  It's really dangerous stuff.Just the smell of gasoline means that there's some residual stuff there."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Would like to know more abouy gas detector.ThanksPeter
Reply:Peter:Google "lel gas detector" = lower explosive limit, several hits there. 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Originally Posted by Craig in DenverPeter:Google "lel gas detector" = lower explosive limit, several hits there.
Reply:You're welcome. You'll be teaching me far more than I'll be helping you. 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Well, good job, but I'm with Sam on the safety issue.Ihave fixed several gas tanks by thoroughly cleaning and then pouring in epoxy resin.  Slosh it around till the whole inside is coated, let it harden and ream out the fittings.A butterfly without wings, is just an ugly bug
Reply:My solution to a leaking gas tank is to replace it with a new one!I just replaced both tanks on my Ford pickup this spring, they where around $100.00 each.before installing each one, I coated them with a rubberized under coating by Dupont.Or if nothing else,  at the very least, send it to a shop that specializes in refurbishing old tanks.Once you find a hole, its not going to be long and you will be finding others!#1. If you don't like what I wrote, or if it offends you, then don't read it!#2. I am living life the way I see fit, if you don't like the way I'M living, tough sh**!
Reply:hi ray, glad you didnt go boom.. you think 2 years is  enough time?
Reply:Originally Posted by farmersammI like all of you guys.  BS  with y'all every nightBut how, on a public forum, where people look at this, and maybe take it as Gospel Truth, can y'all give congrats to something that might have been unsafe at best, and lucky first time luck at worst.Tanks can kill you.
Reply:The only thing I can think of that might have made it safer was a nitrogen or argon purge.Does anybody do this after using the other means mentioned as to cleaning the tank ??  We use to use a nitrogen purge on an electrolysis process we had that produced hydrogen, and we were not skimpy with the nitrogen.
Reply:If you are doing backyard tank repair, then you are lucky if the repair works. I have seen several tank explosions and none were pretty. All it takes is one spark when the percentage of combustible material is within it's explosive range, and "boom" can happen. This is one of those threads that should have a big red WARNING sign attached to it or not posted at all.
Reply:"The only thing I can think of that might have made it safer was a nitrogen or argon purge.Does anybody do this after using the other means mentioned as to cleaning the tank ??"One thing I have heard of is putting a few pieces of dry ice inside the tank.  It sublimes into gaseous CO2 and fills the tank.  Don't know what effect this would have on the weldment. Personally, I'm too paranoid to be doing this sort of thing.Tim
Reply:Originally Posted by timrb"The only thing I can think of that might have made it safer was a nitrogen or argon purge.Does anybody do this after using the other means mentioned as to cleaning the tank ??"One thing I have heard of is putting a few pieces of dry ice inside the tank.  It sublimes into gaseous CO2 and fills the tank.  Don't know what effect this would have on the weldment. Personally, I'm too paranoid to be doing this sort of thing.Tim
Reply:very nice job. where would one go about getting a flamable gas meter as you mentioned??I break things for a living...
Reply:OK, I'm gonna' catch hell with this one, but I've got to tell it anyway. I was taught, early in my welding career, by an older welder, to fill the tank with the exhaust from my welding machine. Carbon Dioxide displaces the oxygen in the tank, thereby making an explosion impossible. I watched him do it a couple of times on drilling rigs with diesel leaking out of the crack he was welding. I personally have welded diesel and gasoline tanks with the fuel still in them using this method. A guy from Minnesota was passing thru the town I was living in at the time, pulling a gooseneck travel trailer and had gasoline running out of the bed of his truck when he pulled into the trailer park I lived in. He saw my welding truck in my driveway and knocked on my door, introduced himself and told me his problem. He had a homemade tank (200 gal.) in the bed of his truck behind the cab and in front of his gooseneck. The seams were cracked and leaking (6010 welds, 1/4" plate). Early the next morning he knocked on my door again and had the tank sitting on the ground behind my truck. I hooked up the hose (duct tape and two vacuum cleaner hoses to his tank and started the welder. We went into my trailer house and made a pot of coffee and had a cup each. When we went back outside I started welding his tank after turning it so the leak, wasn't. I lived in Alamogordo NM at the time and the Stealth Fighters were stationed there. As I struck the first arc a Stealth flew in for a landing about 200 ft. above me! I almost had to change my pants, but figured it out before even breaking the arc. The man whose tank it was broke into a dead run for the highway. I welded all the way around the tank with 7018, putting a cap on all the welds. The reason I'm telling this story is because my heart was in my throat EVERYTIME I struck the first arc on a fuel tank with fuel still in it. I never had an issue, it worked everytime (at least 25 times, maybe more) for me, regardless of diesel or gasoline. Later I found out that according to the MSDS on Carbon Dioxide that it is more explosive than gasoline! I guess you'd have to say I'm very lucky to be able to even tell this story.Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.                                         -Cree Indian ProverbSA 200 LincolnVictor Torches
Reply:Just be carefull if purchasing a LEL and/or oxygen displacement meter then relying on it as a simple "go/no go" meter. Especially the low end models that most are gonna buy for use once every three years.  These things can be the subject of never ending discussion all by themselves. Most are calibrated for the most common free air gases such as methane, hexane and so-on and not necessarily for heavy liquid fuels that are soon to be super heated. They need to be calibrated on a regular and consistant basis to ensure accuracy. They need to be zeroed in a good clean free air environment before each use. They take a certain level of training for proper interpretation. Bottom line, if you think you are going to be able to buy some low budget little meter that you can throw in a drawer and pull it out two years from now, stuff a probe in a tank and have it peg on green for "okey dokey, gayrawnteed safe to weld hack and cut" it ain't gonna happen.Last edited by Sandy; 06-27-2009 at 01:42 PM.
Reply:Bottom Line, What ever way you got rid of the vapors, it worked, You are here to write about it! Lincoln Ranger 8                        Lincoln 175                          Drill pressLincoln 225 mig                            Plasma                              8 ft brake        52" jump shear
Reply:My grandfather have welder a lot of big fuel tank with fuel still in, like the other said without oxygen (air) there is no possible explosion. He was filling the tank at full capacity and then weld it. But i understand there is always a place to error and it can be very dangerous.....Francis
Reply:. Later I found out that according to the MSDS on Carbon Dioxide that it is more explosive than gasoline! I guess you'd have to say I'm very lucky to be able to even tell this story.
Reply:Originally Posted by Oldiron2Carbon Dioxide is not explosive, and won't support combustion except with Magnesium. CO2 will, at high temperature, react with carbon to produce CO, which is flammable and poisonous, but this is rarely a concern of the welder. CO2 is actually more effective in retarding fire than just by its displacement of oxygen or cooling vapors; it produces a chemical effect akin to removal of free radicals which propagate the flame. I think the OP did a god job explaining the necessary precautions and reasons;  not having any information on site won't keep situations from occurring where someone wants to do this kind of work. It's better to have the proper methods outlined occasionally so people who don't otherwise understand the possible problems can learn, rather than trying to do things they don't understand  and do everything wrong.
Reply:GG, I am/was a chemist who occasionally welds...and I enjoy how the two do interplay a bit. Also, not having played with 'puters for many years, I'm still fairly careful to double check what I tpye! The CO levels in new car exhaust is measured in parts per million; for older engines, it's still very small. The reason it is very poisonous is that it builds up in the blood, preventing transfer of oxygen by the hemoglobin. You were right that the biggest components are CO2 and water vapor, plus nitrogen which was much of the air and wasn't changed. Anyway, I think the levels of CO are hard to get to a high enough level to be dangerous by explosion, even if one tries by adjusting a carburetor too rich on an older vehicle.  Maybe it can be done, but it's not likely. It is another thing to keep in mind, though; as I aid above, life is just too complicated...The weldor that taught me the process with the exhaust off my SA200 taught welding at the local college later. He was very knowledgeable and educated. He showed a slew of us this method, but I have no idea how many actually used it. Chasing drilling rigs for 35 years, I used it many times. In a later life as a Safety Trainer for offshore operations (different State) I explained the process, drawing pictures on the board for the class. A much more seasoned Safety Man was monitoring that particular class and showed me the MSDS for Carbon Monoxide the next day, instead of calling me out in front of the class, which I appreciated. It's actually nice to know I was right. Still, after using it many times, my heart was always in my throat when I struck the first arc. I don't think advocating this method is a good idea either. Anyone using it is taking their life into their own hands. The truth of the matter is, with all of the above "solutions" you're taking your life into your own hands. A gas monitoring device would be nice to have, but for the individual weldor, working for himself, it's another expensive tool. It could actually save your life too though...life is complicated, isn't it!  Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.                                         -Cree Indian ProverbSA 200 LincolnVictor Torches
Reply:and showed me the MSDS for Carbon Monoxide the next day, instead of calling me out in front of the class,
Reply:....Well......years ago, a friend had a motorcycle repair shop....mainly machine work on engines, and straightened frames...but he did MIG and TIG...welded up quite a few fuel tanks....  What seemed to work well, and is reasonable after you think about it a little....insert an air hose in the fuel valve port...remove the fuel tank cap...if you haven't already.....and set the air to flow a good amount through the tank....as long as you have a lot of airflow....not enough chance for fumes to form and to ignite..  We did this with tanks that had just been off the bike for a few minutes.....also did a few semi-truck tanks on the trucks...used the same procedure.....  So....this is pretty much the very same pocedure I used at a job later repairing the tanker trucks/trailers that deliver gas/diesel to the gas stations......keep a lot of air flowing through there....no problems....the place I worked had the State of California DOT License, and repair procedure from the tank manufacturer...we did use a combustible gas meter with a long sensing hose, but mainly to determine if there was leakage into the dead-space between the bulkheads that separate the different sections in the tank...usually 3-4 sections....12-16" dead-space between each....  If you ever saw how thin those tanks are....it's scare you driving next to one on the road....bottom is usually 8 gauge .154"...with a horizontal seam about 1/3rd way up the side...upper tank is usually 10 gauge .134"....and contrary to popular belief.....these are NOT double wall tanks.....  Aluminum....5554-5556 series...pretty tough stuff.....  The C02 sounds like it would work OK...never tried it myself....Dougspair
Reply:I hate to bring this up, for fear someone might actually try it (PLEASE DON'T!). When I was a young lad, my uncle was a top notch auto body man. I was at his shop one day when a friend of his brought in a truck gas tank (gasoline) that had a puncture in it. He wanted my uncle to braze it for him. The tank was empty and dry, with the sending unit removed, leaving a large opening. He took the tank outside the back of the shop. What he did next was something that defies belief. He took a lit torch, and stuck the tip INTO the tank. There was a big WHOOSH sound. Afterwards, he took the tank into the shop and proceeded to braze it without incident. Several years later, I asked him how many times he got away with that, and he replied "hundreds".The man is crazy, but he's now 86, and still working on cars, and hasn't killed himself yet. As for me, I'd have to forgo the excitement and buy a new tank.Miller Thunderbolt AC/DC (Sold)Miller Dialarc 250HFMiller MM251Miller MM200 (Sold)Miller MM130Miller Spot WelderVictor O/A rigMiller Spoolmatic 1 (Sold)
Reply:If you displace all the air with inert gas like argon, nitrogen,or co2 then there is no oxygen to burn the fuel.Remove one of the three- fuel, oxygen,or heat and NO FIRE also the mixture has to be right- not to rich and not to lean.I have heard(don't know if i believe it) of a weld repair inside of a live gasoline tank 200' diameter the welder wearing a supplied breathing air. He welded inside tank with 100% gasoline vapors and no oxygen ,so no explosion. This world is full of strange things and people...
Reply:i have heard of similar situations of welding on gas tanks where they welded it with pure vapors and no O2 so there was no boom.syncrowave 180 sd
Reply:I only read through this thread once and will have to go through it againhoweverDo I understand this correctly:::Pumping automobile exhaust into a typical auto or truck gas tank WILL NOT neutralize the fumes so a tank can be welded safely?????Reason I ask is my brother-in-law mentioned to me some time back he seen this technique used on a race track for a tank repair.  Appears it was a common approach.  This is info only for me, I am with the other guy....I'll buy a new one.GeezerPower Mig 255C185 TIGBlue 175 MIGRanger 8 Kohler 20HP1974 5K Lincoln/Wisconsin Powered (Cherry)Victor/Harris O/AK 487 Spool Gun
Reply:I worked in shipyards. Plenty of times I personnaly welded on desiel fuel tanks, only if there was enough fuel in the tank to weld below the air/oxygen level. Atleast a foot or so below fuel level. This is a very dangerous process by far and dont recommend for anyone in doubt. I hate to say this but in the oil/seafood marine business, time=$$$$$$. It cost alot of time and money to drain 10,000gals of fuel.Pulling man hole covers off to clean out tanks, repairing and refilling tanks. It just depends on the situation for repair.1.tripple check fuel level by dip stick,sight glass. The valves on the sight glasses needs to be opened.2.sight glass clear tubing will become stained with fuel and hard to see the actual fuel level. It can give you a false fuel reading.3.if in doubt for any reason, (shut it down)4.have someone with the right type of fire extinguisher stand behind you, "if you can find someone to do it" 5. if someone sneaks up behind you while welding the leak and makes the "BOOM" sound.6. find the nearest bathroom.7.find the person that did this to you.8.make adjustments accordingly.I had a fuel collar leaking once and could not fix the small leak. I put a bigger collar around that collar and then welded the bigger collar then put plug or valve on it. It will catch fire but control the fire with a safe means.Dont recommend this either.As for as gas, welding below the fuel. I never did and hope I never have to..Desiel is tamed compared to gas as for as I know for direct contact.. They will explode if done wrong and will #$%^ you up!Gizzardguts! I know the feeling! Someone took a 5 pound sledge to the tank I was welding. Not funny at the time!Shipyard clowns!
Reply:[QUOTE=Shipyard clowns![/QUOTE]Which one a youse guys is the funny man?!Work HARDER, not smarter! ------------------------ Miller Bobcat 250Millermatic 251Lincoln Precision TIG 185Hypertherm PM 600Hobart 135 HandlerOxweld 400 FlameMaster
Reply:Originally Posted by Craig in DenverPeter:Google "lel gas detector" = lower explosive limit, several hits there.
Reply:Hello everyone this is my first post and I took an interest in this thread. I built and repaired Semi Tankers for many years. Aluminum, carbon steel and Stainless steel tankers. Testing and repair of these tankers is very common and the testing part is mandated by DOT. The safest way to "degas" a tank is with steam. You cant use a pressure washer or hot water pressure washer you must use a steam cleaner. Best part is this process not only degasses the tank but cleans it also, this was good for us because all leaks in the barrel were fixed from the inside of the tank. You want to get the tank "HOT". We used multiple drops and steamed the tankers through the top of the tanks in the dome lids and if the tanker had "double bulkheads" we would steam them out also. The water would run out the bottom of the tank through the internal valves and out through the piping under the tank into a separator. We steamed all the hoses and vapor piping as well. Crude Oil tankers were on the steam rack for up to 4 hours, they are full of paraffin that is very explosive! Refined tankers for 2 hours. When done you let it cool and "sniff the tank" with a 4 gas analyzer to determine if the tank was safe for the inside of the shop. We repaired thousands of automotive/equipment petroleum tanks, oil, gas, diesel, propane etc. We would steam 200 gallon tanks for 30 to 60 minutes depending on how dirty they were. Propane and natural gas are the most dangerous. My recommendation to everyone is to not attempt any hot work on these tanks period!!! Leave these to the professionals. I steamed a propane tanker for 4 days on and off the rack before I could ever even get it in the shop. The next day first thing in the morning I had to steam it again because it was "HOT" again. You can safely weld on a gas tank if you have the proper tools to make the job safe and the proper knowledge to make the job safe. Also you need to be a very proficient welder to even consider this. Meat Man, the boiling water and the gas analyzer were great steps to assure that you degassed the tank. Sounds to me that you did some research on this and took the necessary steps to make the job safe. If you need to do this again find someone with a "steam" cleaner and steam the tank for at least a half an hour and of course use the gas analyzer to confirm that the tank is safe to work on.As for everyone else that is displacing the oxygen in the tank and making no attempt to remove the explosive material inside before doing hot work, I hope I am lucky enough to be thousands of miles away when this is happening! This process is just asking for disaster. How can you be assured that all the Oxygen is displaced? I am very aware of the Navy using this method in their ships. The newest technology is to use an expandable bladder to hold explosive products not just in ships but everywhere petroleum is stored. This controls the vapor, remember that the vapor is what is explosive.Here is a question for everyone... How many of you have welded around a gas tank on a vehicle? Gas tanks on vehicles are vented through the gas cap. the vapor is what is explosive. just something to think about! I moved my rig trucks fuel fill to the right side and toward the front of the bed for added distance. I usually weld either on the left side or off the back of my truck but and I never let sparks fly toward it.Just my .02Wade
Reply:For welding on fuel rich tanks, as myself and others have posted---over and over--doing inert gas purge calc's., a purge plan, monitoring the purge outflow prior to and during welding for ZERO PERCENT O2--via a calibrated O2 monitoris an approved, safe way--per API, USAF, etc.       (In practice I normally don't care what LEL is.....I care a whole lotabout what the O2 is.)It's pretty simple, no O2--no bang......and this just escapes the backyard geniuses.Filling with water, exhaust gas, pure oxygen (yes--there's a poster on this forumthat brags about this), or some rudimentary cleaning---is simply rolling the dice.                Some people brag about running thru red lights---other brag aboutwelding up tanks, without a clue as to the dynamic, changing physics andchemistry they're dealing with.[/QUOTE]Blackbird, I totally agree with you and this process. This is a process that is widely used and I myself have used it also. I do not recommend this to the average person because they may not understand how gasses work. If not purged properly and depending on the gas used and where the outflow is on the vessel it is possible to trap oxygen inside the vessel. For the above average or professional with no experience welding on explosive vessels I would only recommend degassing it. People don't know what they don't know and that could be very dangerous if an improper purge method was used.Just to be clear my stand on this matter is I believe that you should completely understand every possible threat of life or injury before doing any job. It is not something to take lightly because this could kill you and or someone else. There is no room for error!
Reply:a good washing with a water based degreaser and an inert gas fill, whether it be exhaust fumes (which can have oxygen in them) or argon or other inert purging gas is more than practical and safe.You will get the rainbow of opinions (mine included) in the end you have to decide for yourself and what you feel comfortable with.*** disclaimer *** I have only repaired and or shortened @ 150 Big Rig diesel tanks and a few dozen motorcycle/ auto/ lawnmower fuel tanks.It is not complicated, but it does require discipline and paying attention to what your doing. Dont worry about what someone might come along and read and do. The gene pool needs dredging every now and again.insert thoughtful quote from someone else2000 Thermal Arc 300GTSW 3.5 hours1946 Monarch 20 x 54 Lathe1998 Supermax 10x54 Mill2004 Haco Atlantic 1/2" Capacity Lasernot mine but i get to play with it
Reply:Most gas tanks have the fuel pump inside the gas tank these days.  If you haven't ever seen one, this is a normal electric motor, turning a pump body.  Normal electric motor, as in it has a commutator and brushes that spark, yet you never hear of cars spontaneously exploding from this. Why? because even when the tank is almost empty and that motor is sparking above the fuel level, there is no oxygen for ignition.Regarding the criticism of the OPs taking this on, the intardweb is full of DIY forums for all sorts of 'dangerous' activities.  In the end it is up to the individual to use common sense and decide if the suggested method is safe.  I think the OP did a great job of explaining his process and methodology, and he lived to write about it, so clearly it works.  I don't see this thread as being any different from the doubtless thousands of threads out there telling how to service (or even modify) the brakes on your vehicle.  A mistake there can be even more dangerous when the brakes fail and take out other people as well..02
Reply:I like this thread. I am learning a lot. As a firefighter I am fascinated to know what may have been going through someone's mind ten minutes before we get there.
Reply:Originally Posted by maartyI like this thread. I am learning a lot. As a firefighter I am fascinated to know what may have been going through someone's mind ten minutes before we get there.
Reply:Originally Posted by gizzardgutzOK, I'm gonna' catch hell with this one, but I've got to tell it anyway. I was taught, early in my welding career, by an older welder, to fill the tank with the exhaust from my welding machine. Carbon Dioxide displaces the oxygen in the tank, thereby making an explosion impossible. I watched him do it a couple of times on drilling rigs with diesel leaking out of the crack he was welding. I personally have welded diesel and gasoline tanks with the fuel still in them using this method.
Reply:Originally Posted by 76GMC1500There is both truth and error to this method.  Rojo mentioned inerting tanks using CO2 on Navy ships.  While the Navy no longer uses the practice as they no longer carry volatile fuels on board, the commercial tanker industry does still use this practice on their crude oil and product tankers.  The CO2 used to inert cargo tanks is simply flue gas from a boiler that is run through a heat exchanger to cool it down to acceptable temperatures.  However, even on motor driven ships, inert gas is generated by a boiler and not the diesel engine.Combusion engine exhaust should not be used as an inerting agent because the oxygen content varies widely based on the operating conditions, especially with a diesel engine. Diesel engine exhaust oxygen content may only be slightly lower than the oxygen content of air under lightly loaded conditions.  Gasoline engines have exhaust oxygen contents around 6-10% which is too  high to be used as an inert gas.  Just filling the space with hot exhaust can cause an explosion, too.  The exhaust needs to be cooled first before it can be used as an inerting agent.  Boiler's exhaust oxygen content also varies based on load but it is easy to create an artificial load on a boiler to bring the oxygen content of the flue gas down to the 2-3% required for an inert athmosphere.
Reply:Originally Posted by FuzzydogMost gas tanks have the fuel pump inside the gas tank these days.  If you haven't ever seen one, this is a normal electric motor, turning a pump body.  Normal electric motor, as in it has a commutator and brushes that spark, yet you never hear of cars spontaneously exploding from this. Why? because even when the tank is almost empty and that motor is sparking above the fuel level, there is no oxygen for ignition.Regarding the criticism of the OPs taking this on, the intardweb is full of DIY forums for all sorts of 'dangerous' activities.  In the end it is up to the individual to use common sense and decide if the suggested method is safe.  I think the OP did a great job of explaining his process and methodology, and he lived to write about it, so clearly it works.  I don't see this thread as being any different from the doubtless thousands of threads out there telling how to service (or even modify) the brakes on your vehicle.  A mistake there can be even more dangerous when the brakes fail and take out other people as well..02
Reply:Originally Posted by dave powelson1-the fuel systems with the exposed in tank pump senders---are part of a closed system. The tank is sealed with a pressure/vacuum cap. The vacuum/charcoal filter vapor canister part of this, only admits fuel rich air back to the tank.2-You state there is no O2 present in the air in the tank.......that is less than correct. Any air contains 21% O2, even in the fuel tank.3-The fuel air mix, via the wetted charcoal canister, is too rich to support combustion........that's 'WHY' in tank pump/senders don't blow.However---the fuel air mix in tanks, during repair, especially if open to ambient air, and heated during welding, goesall over the map---quite unlike what's occurring in modern vehicles.
Reply:Originally Posted by FuzzydogOK, Ok, You are correct. I misspoke. There is not enough o2 in the tank to support combustion.  In this context, no O2 is the same as some O2 - the sparks from the pump motor will not ignite the vapors in either situation.  I should have elaborated more, as I am not condoning welding an open gas tank.  I was just flapping my gums (rattling my fingertips?) getting my .02 in on the talk about replacing the air in the tank with inert gases etc.  I believe in living to see the next dawn, but when appropriate precautions are taken, any hazardous task can be completed safely.Just to play devil's advocate - what do you suppose would happen if you were to try to weld up a pinhole (fuel only weeps out, doesn't shoot out) that is halfway down a fuel tank, and the fuel tank is full to the very top with gasoline (and the filler hole is completely sealed)?  Explosion, or no explosion?  my recollection (and experience) tells me the empty fuel tank is much more dangerous than the full one.
Reply:I will comment here only as a chemist who has been working with explosive materials all of my career. Toalso put my comments in perspective, I am a hobby welder with no tank repairs to brag about.Any explosion requires either an oxidizer and fuel in proper proportions or pressure that exceeds the vessel strength. (The  first, can generate the latter as well. ) Anything that is done, that you are absolutely 100% certain will either eliminate the fuel (combustible substance) or the oxidizer (air or some other oxygen source), will eliminate the possibility of a combustion event. Case 1: Fill the tank with fluid. So long as the heat from the weld is not allowed to build pressure in the tank, it will not ‘explode’ in the tank be it water or gasoline. With a hydrocarbon fluid, the heat in the weld zone may decompose the fluid into methane, etc. without oxygen the decomposition products will not oxidize (burn). Any off gassing from the tank will need to be safely exhausted away from any flame source. If the venting gasses are allowed to build outside of the tank in the ambient air to combustible levels watch out. With water you might make steam which would re-condense heating the surrounding water. If not allowed to vent, once the water reached the boiling point pressure would begin to build. (same with a closed tank of hydrocarbon). Welding on a closed tank would be tough any way since the internal pressure would tend to blow the weld zone out and you would get a jet of super heated liquid in the face. Not good.Case 2: Purge with a non oxidizing gas. If purged effectively, in other words, all oxygen is removed, no combustion could occur. Argon, Helium, CO2, Nitrogen are all non combustible gasses. Vehicle exhaust is composed of CO2, Nitrogen and Water vapor with traces of CO, NO, NO2 and O2. The Latter are oxidizers, but in small enough concentrations that there is little risk of sustained combustion. If you want to test me on this, fill a large jar holding a lit candle with exhaust. The candle will go out. For the purge to be effective, it should be continued throughout the welding to be sure oxygen is not reintroduced. Any combustible vapors produced by residue in the tank must also be purged dynamically by continued purging.Case 3: Sweep combustible gasses out of the tank to below combustible levels. This can be done with washing, steaming in preparation, and/or an ongoing stream of air.  Be sure that the washing method gets everything out. Residue left on the walls of the tank will vaporize with the heat of the weld to reestablish a combustible vapor. A continuous air purge will help sweep any building vapors out of the tank. (The solution to pollution is dilution)In closing I can only say, be absolutely certain you have eliminated the fuel, or the oxygen, and possible pressure buildups, before messing with tanks of any kind. Please recognize that all of this discussion assumes no oxidizers other than air might be present. If you are not 100% sure, don’t touch.
Reply:leokno  Solderer   Join Date: Mar 2009Posts: 1   Re: Gas tank repair --------------------------------------------------------------------------------I will comment here only as a chemist who has been working with explosive materials all of my career.
Reply:Originally Posted by leoknoI will comment here only as a chemist who has been working with explosive materials all of my career. Toalso put my comments in perspective, I am a hobby welder with no tank repairs to brag aboutIf you are not 100% sure, don’t touch.