welding on diesel tanks

admin

I have a question about welding on diesel tanks in a boat.  The boat is a 130' fishing vessel that has the tanks in the bottom.  There are 4 tanks and one of them has developed leaks in the top where it has rusted through due to moisture getting to the steel through 3 inches of concrete that was poured on top of the tanks.  We removed the concrete and there are several holes so the plan is to weld a plate over the entire top of the tank.  This is an area about 6' X 16'.  The tank is full of diesel and some has been pumped out so that it no longer comes out of the holes in the top.  I suggested purging the air space in the top of the tank with an inert gas and then doing the welding.  The tank material is 1/4" thick and the plate to be welded on top will be 1/8 inch thick and will be in 3'X4' sections to be able to handle it and get the pieces down into the boat.  We will be using a MIG welder.  Any suggestions on whether we are doing this right or not.
Reply:why would you not even empty the tank out ? ?  ! ! !
Reply:Diesel is pretty safe except when you get it hot and it vapourizes....It is just like having gasoline vapour.  I like the idea of purging however how will you know if you have purged enough and if the inert gas starts coming out of the holes in the top of the tank it could collect in the bilge and suffocate everyone.   I think you need a instrument to continually do a vapour check while you are in there welding.  Think about a fire watch and you in a harness like in confined space so that someone can pull you out by a rope if they have to.   I think if you ask for opinions people are going to tell you that you are taking a large risk.  People weld on live natural gas lines but they know what they are doing.    I am inclined to suggest that you purchase an epoxy compound that is suitable like a Devco product.  It would be much safer and you could put down half an inch or more of epoxy based filler before you replace the cement ballast on top.Google Devcon ... they have people that really know their business.Last edited by lotechman; 02-01-2012 at 03:26 PM.
Reply:When I was commercial fishing on steel boats in the range of 75-85 foot the diesel was on the sides, three tanks per side if I recall and there were sight gauges so you could see how much was in each one.  Using pumps it was possible to use from or transfer fuel in such a manner as to level the boat.  Might I guess you aren't commercial fishing as there are generally numerous welders around a shipyard or associated with places you can tie up and that was generally how we had welding done.  It is not at all uncommon to have to cut into the boat to get something in.  Periodically the boat gets hauled out of the water, dry dock and maintenance like you discuss probably would be done by the entity with the dry dock.In order to send underground oil tanks, essentially diesel, to be scrap they are cut lengthwise with a cutting torch.  There are two inch ports open to start, first cut a hole in it so you could spray water with a little pump up sprayer or garden hose if fire starts.  It will start on the edge not in the middle of the oil they didn't pump out before pulling it.  It isn't really that flammable but if one gets away and gets hot it takes a real fire extinguisher.  Of course that is out in the open near basically nothing.  If you are warned there could have been some gasoline in it the procedure was to get dry ice crush it up and put it in and/or hook up the tailpipe to the pickup.  None of them ever smelled of gasoline and why would they as they ran a furnace.  There is some education and testing to get licensed to do that.It is a tough one to give advice on the internet and I sure have no training in that.  You got th suffocation warning. They have some devices to tell how thick metal is. Maybe the insurance was the entity that sent them over but parts that were supposed to be 3/8 actually must have been 5/16.  Is there any testing, certification, or insurance or other that might come along?Fran
Reply:I did a couple 100 gallon aluminum truck tanks.  I had them steamed out and cleaned with soap by the radiator shop that also welds aluminum diesel tanks. They are cleaned until no diesel can be smelled.I won't even think about a gas tank.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:This is an ex-fishing vessel that is being converted to a yacht.  The lower portion of the boat has been emptied out so there is a lot of space there and there is ventilation so I have no worries about suffocating.  The reason not to empty the tank is because the less air space there is the less chance of an explosion.  Since we will not be welding on an open tank so that there are direct sparks into the tank I am not really worried about setting the diesel in the tank on fire and if the air is purged out so that there is no oxygen then there is even less chance of a fire.  I was just wondering if there was anyone here who had done something similar to this and what safety measures they had taken.
Reply:I would suggest using helium for your inert gas since you will be welding the top of the tank.  Helium will stay at the top of the tank, you dont need a big flow of inert gas. Other then that you're on the right track. Just make sure the tank is purge at all time. And good ventilation at all time a hole watch and evacuation procedure is a must. To many time accident happens in rusted steel hull.Good luck.
Reply:Originally Posted by DanthemanI would suggest using helium for your inert gas since you will be welding the top of the tank.  Helium will stay at the top of the tank, you dont need a big flow of inert gas.
Reply:top it off and clean the out side really good and weld a piece of plate. the diesel will act like a cooling agent just be careful not to over heat it to the point that it will boil and flash the diesel vaporsLincoln Power Arc 4000 Thermal Arc Fabricator 252 iThermal arc 186Thermal Arc 26 tigTweeko 200 amp spool gunHobart AirForce 400WP-17V-12R
Reply:I worked at a place doing the exact thing that is being done to this boat. We would never go near it until it was gas free and sniffed by a outside gas free engineer. The reason for this is insurance. If there was a flare up and the entire boat went up, the insurance company would laugh when you asked for a check to replace it. I know you CAN do it with a full tank of diesel but it is far from being legal in any shipyard anywhere. Just a thought.CERTIFICATIONS:7018M- H.V.O10718M- H.V.O11018M- H.V.O9N10- H.V.O71T-1-HYM- H.O.V100S1 PULSE ARC 0,035- H.O.V100S1 PULSE ARC 0.045- H.O.VER70S-3 PULSE ARC 0.035 H.O.VER70S-3 PULSE ARC 0.045 H.O.VER5554- H.O.V
Reply:I am not going to say "how" I repair fuel tanks because of obvious human safety factors involved, but I repair them all the time and like them to be plumb full------liquid nitrogen helps alot too and you can see when you have enough.6 Miller Big Blue 600 Air Paks2 Miller 400D6 Lincoln LN-25's4 Miller Xtreme 12VS2 Miller Dimension 812 4 Climax BW-3000Z bore welders Hypertherm 65 and 85Bug-O Track BugPair of Welpers
Reply:The holes in the top of the tank are small, 1/8 inch and less so there won't be that much leakage there especially after we lay the plate on top.  The fuel level will be an inch or more below the top so there should be little chance of boiling the diesel and creating excess vapors.   I am thinking to use argon, CO2, or nitrogen, which ever one is cheaper.   Thanks to everyone for there comments.
Reply:Originally Posted by DSWHave you by any chance PRICED helium?! It's also so light weight it's very difficult to contain. You'll end up with a LOT of leakage, especially if your fit up on the new top isn't good at all and you have a bunch of gaps. My guess would be you'd need a decent flow to maintain coverage as it "leaked" out of every seam/hole at the top of the tank.CO2 on the other hand is cheap, settles down so it will stay in the tank and you can keep a minimal flow to maintain volume to displace any air or replace leakage. Argon would be another good choice if you were concerned about the CO2 reacting with weld metal for some reason.
Reply:doesnt dry ice release CO2 if im correct it does go get a pound or two of pellets and drop them in the diesel and let the co2 fill the tank dont know if it would work but it is an idea that came in mindLincoln Power Arc 4000 Thermal Arc Fabricator 252 iThermal arc 186Thermal Arc 26 tigTweeko 200 amp spool gunHobart AirForce 400WP-17V-12R
Reply:or a coke bottle with water and dry ice and get a hose so all the gas goes into the tank to fill the cavityLincoln Power Arc 4000 Thermal Arc Fabricator 252 iThermal arc 186Thermal Arc 26 tigTweeko 200 amp spool gunHobart AirForce 400WP-17V-12R
Reply:Originally Posted by ExpatWelderI am not going to say "how" I repair fuel tanks because of obvious human safety factors involved, but I repair them all the time and like them to be plumb full------liquid nitrogen helps alot too and you can see when you have enough.
Reply:Gas or deisel we always wanted them full. I used to stretch trucks and we wouldnt allow an empty gas rig in the shop. If the vent catches on fire you just have to wipe it out. Sounds like you are ready to weld. I guess I wouldnt have any problems welding it up , but if you want to be safe then purge it with a non flamable gas or the exhaust from an engine . After you weld a few you will be more at ease. Go for it.
Reply:Aside from the technical matter of safely welding the holes in the top of the tank, I think you should be ask yourself whether the rest of the tank is in sound shape?  If the top of the tank corroded because it was damp, then the bottom seams where it rests on the vessel frames are surely going to be corroded too.If all you were contracted to do was weld the holes then you obviously don't need to worry about that, but if you happen to work for the boatyard then you might want to take that into account./boatbod(Boatyard Manager)
Reply:I weld in the oilfields, and there are times I have to weld on crude oil stock tanks that can not be properly cleaned out. We end up purging them with exhaust, when done properly it is safe. I have welded many this way, even on propane pigs that are not empty. I am just relaying how I do it, not recommending you try it because it takes extreme care and someone who is familiar with this and has done it before and needs to be done right because in a case like this we do not get a second chance. But it does work.  I have done it this way many times and got to admit, I was very nervous and scared on my very first try at this. I just hope I never become complacient. The car or truck exhaust just displaces the oxygen making it safe.
Reply:Originally Posted by boatbodAside from the technical matter of safely welding the holes in the top of the tank, I think you should be ask yourself whether the rest of the tank is in sound shape?  If the top of the tank corroded because it was damp, then the bottom seams where it rests on the vessel frames are surely going to be corroded too.If all you were contracted to do was weld the holes then you obviously don't need to worry about that, but if you happen to work for the boatyard then you might want to take that into account./boatbod(Boatyard Manager)
Reply:Originally Posted by NMWeldingI weld in the oilfields, and there are times I have to weld on crude oil stock tanks that can not be properly cleaned out. We end up purging them with exhaust, when done properly it is safe. I have welded many this way, even on propane pigs that are not empty. I am just relaying how I do it, not recommending you try it because it takes extreme care and someone who is familiar with this and has done it before and needs to be done right because in a case like this we do not get a second chance. But it does work.  I have done it this way many times and got to admit, I was very nervous and scared on my very first try at this. I just hope I never become complacient. The car or truck exhaust just displaces the oxygen making it safe.
Reply:Originally Posted by txcarbuilderThe bottom of the tank is the hull of the boat.
Reply:We got the job done.  Used nitrogen to purge the tanks by hooking a line to the vents and letting it come out of a fitting on the inspection cover.  Except for a few places where the plate was heavily pitted and it was hard to get the rust off it went well.