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friend of mine had fuel leaking out of his drain hole in his offshore boat. ended up taking fuel tank out might be 80 gallons or so. siphoned the gas out before pulling the tank. there are a few corroded spots on the bottom not very large maybe an inch in diameter. i plan on fixing it rather than replacing it. its aluminum. whats the bedt way to ensure i font blow myself up.... fill it with water and drain it? hook truck exhaust to it? something else? thanks
Reply:Proper way is a steam clean then a vapour check. Tank shops have such procedures outlining how much steaming and the frequency of vapour checks. The testing units are quite expensive. In shipyards it is common to check bilges several times during the shift with these handheld units.
Reply:Be sure to open every inspection/filler port before welding. Allows the expanding gas to escape rather than blowing the unit up (assuming you got it pretty clean beforehand).Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:You could fill it with argon after washing it with soap and watergood time to build a new one if you have that much corrosion going ontrailblazer 302thunderbolt ac dc machine Hobart fluxcoreAHP tig 200x 2015
Reply:Sometimes a bolted patch is a simpler and safer option.
Reply:Don't touch it....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Originally Posted by zapsterDon't touch it....zap!
Reply:Yeah,An 80 gallon gas tank could be a little spooky. But after all of the other mentioned precautions are taken or considered, you may also provide added safety in welding it by propping the tank up in such a way so that it might be filled with water, except for a smaller air pocket where the welding is to be done.
Reply:Originally Posted by C. Livingstone...be filled with water, except for a smaller air pocket where the welding is to be done.
Reply:Exhaust is one of the worst things you can do as it has more than enough oxygen in it to allow the tank to blow. I agree with the others to do noting with it. I do diesel tanks sometimes, but won't touch a gas tank.Yeah, I know, but it'll be ok!Lincoln Square wave 255Miller Vintage mig30a spoolgunThermal Dynamics Pacmaster 100xl plasmaSmith mc torchEllis 1600 band saw
Reply:You should NEVER heat a gas tank! In the past, I have opened things up all I can, flush profusely with water. After hours of flushing, you will still have enough residue to be explosive. Air it for 24 hours. Blow it out with compressed air, a long time. Set it up with the filler neck at the bottom. Use a fuse, a long one, light the fuse, get far away. It'll burn with a weak flame for some time.An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
Reply:This is what I learned in propane classes and I have used it (at lower pressure) for gas tanks prior to welding.We did it hundreds of times for propane tanks (not for welding though - I did not weld on propane tanks).Using an inert gas it takes a minimum of 4 pressure/blowdown cycles.Clearly, do not use 15psi for any tank that it would be unsafe for - use less.Still need to check with a gauge before welding.4.1.1 Pressurization Purging (Blowdown)Pressurization purging (blowdown) is the process of introducing a purge gas to increase the system pressure to 15 psig, followed by depressurization to the atmosphere. The pressurization purging method is considered superior to other purge methods.This procedure empties the vessel and purges the vapor space in the same process (e.g., pressure vessels, manifolds, and entire plant or platform process systems).A minimum of four pressure-depressure cycles at 15 psig will be required to purge a vessel at atmospheric pressure.If a system filled with a combustible liquid needs to be emptied and then purged, a purge gas may be applied to the vapor space at a pressure consistent with equipment design limitations.
Reply:I always fill with water and leave filled for any cutting or welding.12v battery, jumper cables, and a 6013.I only have a facebook page. https://www.facebook.com/pages/VPT/244788508917829
Reply:Yup, had a rectangular auto gas tank blow and trun into a round gas tank. I was leaning over it like a dumbnut and it threw me across the shop. This after the customer swore he rinsed it out with detergent and let it dry. Still got paid but was totally pissed.Now I let it sit in the sun in the back of my pickup for a week, then purge with argon and weld. I get welding charge and $80 to purge. If the customer balks I send him around the corner.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Just had one of those gas tank repair jobs go horribly wrong at a shop not to far from me. http://www.kxlh.com/story/31096335/w...in-sun-prairie
Reply:Originally Posted by zapsterDon't touch it....zap!
Reply:Originally Posted by zapsterDon't touch it....zap!
Reply:There is no fun in repairing an aluminum gas tank! The fun is in building a new one.Dont pay any attention to meIm just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Originally Posted by CEPThere is no fun in repairing an aluminum gas tank! The fun is in building a new one.
Reply:It has been mentioned in this post already, but I second (or third) the sentiment to just build a new tank. In situations like this, I figure that the tank is likely already compromised and that a new tank (whether bought or fabricated) is cheap insurance to avoid the hassle of dealing with more leaks in the near future.
Reply:Steam clean and then fill with inert gas. Problem is that of you use a proper alkaline detergent, it will attack the aluminum. Then if you can, fill most of it with water to reduce the volume and explosive payload potential. Argon or butt-loads of dry ice. The idea is little or no residual fuel or varnish and insufficient oxygen to allow fire. By the time you have done all that properly, you have spent a lot of $$$. Try some Might Putty."USMCPOP" First-born son: KIA Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:One more time! If any of you would have seen the young fellow that used to come to my shop with car parts to be welded I don't think anyone would consider welding a gas tank. He was so horribly burned and disfigiured it was almost impossible to believe he was alive.
Reply:"danger Will Robinson ,danger, danger" If u feel u HAVE to repair, use the fill with water with VERY small air pocket right where u will weld method. Keeping in mind u will be heating close to water with the possibility of generating steam with it's pressure. I have done this many times, and there is no way you will ever eliminate combustible fumes within a tank. No matter how much flushing/etc. u do, heating the metal will release dangerous fumes that were in the pores/surface of the metal when u start to weld. On smaller tanks, like motorcycle gas tanks, u can run a shop vac in the opening while welding and the overwhelming movement of air in and out will prevent fume concentration. Won't work on anything large, and the bigger the tank the more fumes/violence the explosion.
Reply:Yes but people who don't take precautions, no matter how bad the outcome, shouldn't be taken as examples for people who will and do take the proper precautions. I'm sure there's plenty of examples of people getting horribly disfigured doing things that we do on a daily basis, but again, take the proper precautions, Not saying there isn't a risk, but risk can be mitigatedIf there's any money for a new tank, that'd be a nice little job and a safer alternative. http://www.philswelding.com
Reply:Hmmmm. Thanks for all the replies. I'm glad I asked. The tank seems like it's in good shape except where the powder coat wore off and it corroded in a small spot. It's for a friend of mine not for work, one of those good friends you feel compelled to help when you can. It just seemed crazy to pay $500 plus for a new tank when a coupe hours could fix it. I knew I needed to clean it out but it sounds a lot more complicated than that... Or is it? It's definitely not worth my health - he's a great friend but.... I like the reply that said it's more fun to build a new one. I agree. But I've challenged myself to fix it so, it's one of those deals... I think I'll leave it in my hot truck a week as one guy suggested, been there two days now any way. Then fill with dawn and water and rinse three times as suggested by another guy. Then fill with water and cut three holes in top to thoroughly inspect inside. If looks good and worth saving I'll fill again with water or argon and continue. That's my plan at this point but I'll be much more cautious than I would have without reading all the horror stories I sure don't need one of those. Thanks again for your time. Here is a pic... . It's looks dirty and crappy but it really seems to be in good shape other than the small corrosion spot.Sent from my iPhone using TapatalkThe gas must be completely removed, period. Otherwise do not weld on it.
Reply:Metalman21...... your name is remarkably similar to mine.....I'm surprise we haven't crossed paths before now http://www.philswelding.com
Reply:Well I guess I joined the welding web a the right time because being in the marine business for over 30 years has taught me a ton. I would not mess with fixing it. just getting your weld to stick would be a challenge. A person mentioned a bolt on patch which works but I would be careful as to the sealant/gasket material I chose. Aviation fuel tanks with "wet wing designs" have a special sealant that you put in that can bridge an amazing amount of daylight pinholes you my want to remember. Anyhow. here is a link to a marine surveyor who I think state some good facts about the subject. http://www.boatsurveyor.com/aluminum-fuel-tanks/ Aluminum tanks like the one your buddy has a problem with are a dime a dozen...meaning...failed ones and new ones that can be ordered, fabricated and delivered in 5 days. I would buy a new one...especially with the price of fuel being so cheap lately your buddy can take those savings have a professional tank fabricator make a new one and you and him can spend your time designing the new tank with the fabricator and also planning how best to install the new tank so it does not fail again. The fabricator will make the new tank to ABYC, NMMA, SOLAS or IMO manufacturing standards which will assure you the with the use of the proper allow, fill and vent diameters, grounding and bonding tab surface areas and wire sizes, fuel pickups, gauge sending unit, vent position and shape...alll that will prevent the tank from failing moving forward. Over the years we learned so much from failed alumimum, fiberglass, steel and plastic tanks many interesting things. The majority of Aluminum tanks to me always seem to corrode and fail from lack of bonding and thus destructive electrolysis kicks in and then the tank is doomed. Try to weld on a piece of metal that has been in a 20 year saltbath. its like trying to solder a wire that is corroded no can do unless you acid dip it then the strength of the entire structure gets degraded including the welds. Also abrasion, salt water and even ethanol is contributing to the problems of failed aluminum tanks. We had the best luck with baffled fiberglass tanks but you need to be careful of what resin is used. This is another whole science. I think I would buy a new tank made from a middle of the road fabricator who builds tanks for some of the center console boat builders on an oem basis. NJ or fla are full of these types of jobshops. then buy a few gallons of A and B closed cell pourable foam. bed the stringers where the tank is going to sit on with 5200 marine sealant and strips of rubber then place the tank on top of the stringers and mix and pour the expanding polyurathane foam in and around the tank in 2 seperate applications. depending on the amount you need to fill you can buy it in different types of expansion just be sure its for fuel duty and not from home depot out of a can. the foam is not cheap but once it sets in like an hour you can hot knife the first layer where you need to then apply the second and final mix. once the foam sets the tank is not coming out. you can bolt it in with some aluminum 2 inch flat stock again with 5200 marine sealant and rubber strips to keep the metal from touching metal. I would also make sure I ran a number 4 or 6 gauge bonding wire from the fuel tank to the any other underwater metal objects on the boat like the engine, rudder, steering gear and such. the filler neck hose and fuel vent will also have and additional grounding wire which is required to hook up to the filler neck and tank so when you fuel the boat no sparky's from static energy when the pump handle touches the boat. remember gong fast in dry air makes static. the boat collects the static energy we ground this energy when we touch the metal with a bonding system on the boat the energy is always being discharged and also it protects your running gear from getting eaten away from other folks reverse polarity electrical systems at the pirate docks or bad installs people do in the marine industry every day. good luck and hope this helps! oh you could always make the tank smaller or bigger as well. 80 gallons seems small. is the boat like 27 feet long? John
Reply:Where there is one hole, there are more hiding. If you insist on fixing it you need to have the tank boiled out, Dawn don't cut it. I have fixed a bunch of them and didn't enjoy any of them. One sheet of aluminum, have it bent up, and a few hours of welding and a new tank is ready to go.
Reply:Captain Ryan here, and I agree with Rexmarine and Zap. THE BEST way to fix an aluminum marine GASOLINE tank is to crush it and make new cans from it. #1 Safety, there are proper procedures, however they are rarely followed... 1 gallon volume of gasoline vapor has the explosive equivalent of about a stick of dynamite. (another reason inboard gasoline engines in boats are a bad idea from the start for a number of those vapor isues)#2 If it's been in a boat (fresh OR salt water) and has a leak you can see, there are lots more you can't. The tank is GUARANTEED to have other failures, either before or FROM welding it.#3 Dirty aluminum is a PITA just to get to weld properly, let alone to be water or air tight. You are trying to weld up a tank that has been sitting in the bilge exposed to oils, salts, and lots of other crap for YEARS.#4 Aluminum marine fuel tanks are almost a commodity, they are a dime a dozen. When you polish a turd, you still have a turd.RyanMiller Multimatic 200 tig/spool gun/wireless remoteMillermatic 350P, Bernard/XR Python gunsMiller Dynasty 350, Coolmate 3.5 & wireless remoteCK WF1 TIG wire feederMiller Spectrum 375 XtremeOptrel e684Miller Digital EliteMiller Weld-Mask
Reply:hog, NO PROBLEM-Oh!Don't listen to anyone trying to tell you their experiences- it's fine to weld on old gas tanks. I had one just like yours and here's how I fixed it.Washed, rinsed, heated in the sun, dried, argon purged for several hours on flow meter, and it worked out just as you see here. No problem-oh. Me laying on it and the eye damage, hearing damage and neck damage were all 'livable' but then that's just me- others may prefer to avoid those types of "trade related educational experiences"? That doggone Zap, and these other experienced welders are always trying to get people to live longer than they need too! I can't figure it out? Why would anyone listen to them; nothing worse than some old guys trying to tell you what makes sense or not!Go ahead you'll be fine proof is right here in this old photo of one of my trophies. It started life looking just like your tank- you'll be fine- right? What could go wrong? Its just a little weld?get'er done, and say hello to St Pete, I'm planning on waiting a while yet to come knocking on his gates!I'm nervous that if had to ask, online, you may be just "a bit new at the trade" to take this on? Did I mention that the older tradesmen (here) got that way from experience? Cheers,Kevin MorinKenai, AK
Reply:tell your friend that you will weld it if he sits on it while you weld. There is a hole in the 16 ft ceiling of dad's old shop from a tank he was welding on. He had steamed it out before welding on it
Reply:Kevin - that is frightening!!Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:MinnesotaDave, I wasn't frightened: I was bullet-proof back in those days. Now the picture scares the stuffing out me- who is that idiot?The top wrapped around my body from my armpits to my thighs and likely saved me a premature visit to St. Pete's gates? Since then, my hide seems to have gotten quite a bit thinner and less explosion proof, so I've toned down my experimentation with things like LEL, Stoichiometric Ratios, vapors, fumes and VOC's just to name those fundamentals that may have eluded our OP? Sure hope he's willing to learn some chemistry before he ends up learning like me- the hard way.30 years later I wear the results of that tank mod/repair but that is hard to explain to the young and bullet proof welders sometimes.Cheers,Kevin MorinKenai, AK
Reply:Originally Posted by Kevin Morinhog, NO PROBLEM-Oh!Don't listen to anyone trying to tell you their experiences- it's fine to weld on old gas tanks. I had one just like yours and here's how I fixed it.Washed, rinsed, heated in the sun, dried, argon purged for several hours on flow meter, and it worked out just as you see here. No problem-oh. Me laying on it and the eye damage, hearing damage and neck damage were all 'livable' but then that's just me- others may prefer to avoid those types of "trade related educational experiences"? That doggone Zap, and these other experienced welders are always trying to get people to live longer than they need too! I can't figure it out? Why would anyone listen to them; nothing worse than some old guys trying to tell you what makes sense or not!Go ahead you'll be fine proof is right here in this old photo of one of my trophies. It started life looking just like your tank- you'll be fine- right? What could go wrong? Its just a little weld?get'er done, and say hello to St Pete, I'm planning on waiting a while yet to come knocking on his gates!I'm nervous that if had to ask, online, you may be just "a bit new at the trade" to take this on? Did I mention that the older tradesmen (here) got that way from experience? Cheers,Kevin MorinKenai, AK
Reply:Why isn't that picture and post of Kevin Morins made a sticky about gas tank welding?
Reply:Originally Posted by Kevin MorinMinnesotaDave, I wasn't frightened: I was bullet-proof back in those days. Now the picture scares the stuffing out me- who is that idiot?The top wrapped around my body from my armpits to my thighs and likely saved me a premature visit to St. Pete's gates? Since then, my hide seems to have gotten quite a bit thinner and less explosion proof, so I've toned down my experimentation with things like LEL, Stoichiometric Ratios, vapors, fumes and VOC's just to name those fundamentals that may have eluded our OP? Sure hope he's willing to learn some chemistry before he ends up learning like me- the hard way.30 years later I wear the results of that tank mod/repair but that is hard to explain to the young and bullet proof welders sometimes.Cheers,Kevin MorinKenai, AK
Reply:Washed, rinsed, heated, dried, purged and still did that? Hmmm. I'm not sure how that happened but I also believe you. Look, I'm the guy who asked right? Maybe I should listen to older wiser people. It seems like there want a fluke or two; it seems like this has happened a lot so I am more likely to make a new one. I'm not paying for it either way so.... Rather have a first time making a fuel tank than a first time fixing one. Seems safer can I at least saw the old one up or is it better to let someone else have it... Maybe I can let it sit outside for a year then make a feeder out of it? Hogs will eat corn out of anything..... I appreciate you all taking the time to share with me all the info. It probably worked lolAnd because someone else asked... If there were beginning, intermediate, advanced and professional levels of welding I'd say transitioning from beginner to intermediate. Bought my htp 221 January of 2015 and been using it weekly for a year now. I weld 95% aluminum. Mostly all 1/8 6061 so I've gotten decent at it. I try to find things to fix and make because I enjoy it. It's not anything I get paid to do just make things for myself because I like to not rely on anyone for anything - work or personal. Id rather buy tools to do my own work rather than pay someone else to do it. It cost me more in the end but I enjoy learning. Since I have been playing with metal the last year I have bought a lot of tools. CNC router, milling machine or a gunsmith lathe is next, haven't made my mind up yet. If I make a new fuel take I'll post pics so long as it turns out good . Thanks again. I know I have a lot left to learn and my first lesson was a year ago. I'm about ready for my second one after playing a year on my own....Sent from my iPhone using TapatalkLast edited by hog guts; 02-03-2016 at 10:00 PM.
Reply:Originally Posted by CEPThere is no fun in repairing an aluminum gas tank! The fun is in building a new one.
Reply:I admit, sometimes I feel like I'm bulletproof, (I think it'd be weird if young guys didn't feel that way, it's a part of life I guess) but it's wearing off more and more every year, after a couple broken bones, fingers, a separated shoulder, and a couple other overuse injuries, man, I ain't bullet proof no more. So I appreciate the advise of the more experienced welders like Kevin and Dave cuz they been there already. Hog guts, good luck if you build a new tank, show us the pics, the good and the bad haha. http://www.philswelding.com
Reply:Just FYI here is my very first welding project and what got me started (airboat rigging mig) and my last project I'm just finishing now (tig). Lots of stuff in between....Sent from my iPhone using Tapatalk
Reply:That is some beautiful work! What does it weigh complete? I like the stingers off to one side of the square stock for strength yet the whole structure picks up the rest of the needed strength from other cross bracing and angles and flat stock. very cool design. what kind of loading is a structure like that made to deal with everyday? what type of material was it built to handle? Innovative. is it 4 inch box for the legs, 2 inch square for the stringers and cross bracing and 1 or 2 inch angle for the lengths ?? again really cool design hog guts
Reply:hog, I will give some tank and aluminum corrosion facts to encourage a new tank build. I have built plural hundreds of welded aluminum boats, more tanks than I have any idea and countless masts, booms, davits, cleats, and rigging so if there are mistakes in aluminum to make- you can count on the fact that I've made them at least once or ten times. (think my photo confirms at least one big error?)Metals corrode in general areas or in small sites called pits by the same basic chemical action. Im not going to get too techie, too far into chemical engineering here- but there are three main ways aluminum corrodes and they are: #1 by different metals contact when both are wet; #2 by acids or bases that are too strong; #3 and by electrical energy that results in the same basic chemical activity at the molecular level. All three methods result in the same basic metal chemistry, the original alloy of aluminum is reduced to non-alloy and the molecules of metal are removed from the parent material.All three are different paths to corrosion- but they result in the deterioration of aluminum alloys. #1 Metal to Metal corrosion is called Galvanic corrosion; #2 Acids and bases can corrode due to strong Chemical bonds robbing aluminum of its protective oxide (aluminum and oxygen combined) film and if aluminum is allowed to have a charge from a battery, for example, and get wet
then aluminum molecules can go into the water or whatever is wetting the metal from #3 Stray (electrical) Currents.So Galvanic, Chemical and Stray Current corrosion are all types of aluminum corrosion but when you research and explore youll find they all amount to the (molecular level) same event: aluminum molecules are removed from the parent metal into the wetting agent (salt water) or electrolyte. An electrolyte is just a conductive liquid that allows metal molecules to move from one metal structure to another, or to decompose as metal into non-metallic compounds.What does this have to do with aluminum tanks? All three variations of metal corrosion can happen to an aluminum tank and all three can be avoided or mitigated to such a degree as not to affect a tank.Lets take the chemical or acid attack first, because 99.999% of people dont seem to get this aspect of aluminum maintenance. Very strong acids or very strong bases (https://en.wikipedia.org/wiki/PH) are chemicals that have what we usually call reactivity; these chemicals will react with metals and aluminum is no exception. Strong acid or base will react with aluminum and seize the molecules of the metal and convert them to other molecules hence the description reactivity this could be called UN-refining metal since the strong chemicals actions on the aluminum do not leave the original alloy when the reaction is done.hog, this is what happened to the tank you're involved with on this thread but the owner doesn't know it.Now, this acid to aluminum reaction may be very fast due to strong (read article on Ph) or very mild and slow acting due to mild or less active acids: BUTTTTTT the acid or base beyond certain ph limits will remove aluminums healing oxide layer and then react down into the metal in a pit. This action is called pitting but the term is not limited to acid or chemical corrosion. Further; this reaction, especially the slow version can happen as a wetting cycle over and over again, once started.While were exploring acids lets look at water, yep plain ole everyday tap water. Tap water is more or less neutral ph, like sea water is in terms of acidic or basic ph. (The symbol ph stands for the amount of acid or base on the ph scale. ) However, if water loses its naturally occurring (entrained or mixed in) oxygen then it becomes deaerated- where deaerated is oxygen starved water and ends up acting as acidic. Where does this happen? When water is trapped between two pieces of metal, like two pieces of aluminum- the water initially gives up its oxygen to the aluminum to form more oxide!This is called thin film stagnation which essentially means the thickness of the layer of water is thinner than a hair, and once in that thin film, the stagnation or chemical changes happen much easier, faster and results in a stronger metal reaction than in a bucket full of the same water.Wait! Hey! aluminum oxide is good stuff, it heals aluminum so thats all good right? Well- its fine for a while- but the acidic action of that water then takes back the oxygen and the aluminum oxide is dismantled. There goes the protective film. As a result, pure aluminum is exposed to water that is slightly acidic-acting and with the oxide is stripped off the parent metal begins to corrode! This event called crevice corrosion or poultice corrosion begins a cycle that will corrode aluminum which cant get "Free Oxygen" to form aluminum oxide to heal the surface and protect the base metal from corrosion!!!Stagnate water will continue this corrosion cycle but fresh water rinses, with the free oxygen will often stop this cycle!what do you suppose happens to tank water bottoms under fuel? The condensation of the air's humidity will leave water bottoms in all marine tanks. The day is warm and humid, the tank heats up and expands- the vent allows the air on the fuel/gas to vent out as it expands. The sun goes down... the tank cools the expanded air contracts, the air on top of the fuel/gas 'pulls' or vacuums in the surround humid air and it cools on the tanks sides; inside the tank. The condensed water runs down the tank sides to the tank bottoms, it lays there and becomes robbed of oxygen, it deareates and becomes acidic: the tank bottom is attacked. The tank is junk due to lack of maintenance by the skipper. To fully grasp this series of events chemically, youll have to spend some serious reading time, a little head scratching time and some review time
but the result is this; unless aluminum can get oxygen to renew its oxide film- the metal can corrode from chemical agents.A Solution? Give aluminum oxygen and it will heal itself- starve aluminum of oxygen and it can lose its oxide film and begin to corrode.Next will be my rant portion of this post.The fact is that aluminum mill scale, if not removed from the material will promote this type of corrosion. I realize that hundreds of tanks, just as many whole boats and countless other welded aluminum products do NOT HAVE the mill scale removed(!) but that doesnt change the fact that this film will retain water, the water will become acidic and the metal will corrode if the mill scale is not removed. Mill scale, that shiny chrome looking film is porous, retains water VAPOR and is not galvanically the same as the underlying aluminum!!! Hows that for a built-in problem?But then anyone whos worked in steel knows the same is true of steel mill scale coatings. Steel mill scale will promote rust by holding water film and vapor, aluminum isn't much different except that if the mill scale is removed the metal will 'heal' but steel will continue to oxidize, but not as fast as if the scale were left on.First step to protecting a tank, clean the mill scale, inside an out with an acid wash (that is diluted and neutralized when the etch is done) or mechanical abrasion so the aluminum has the best chance to form its aluminum oxide, self-healing film to protect from at least a couple of the corrosion's sources that may deteriorate your tank. Even a dry tank with mill scale has a layer of ambient water vapor retained in the porous film- therefore what may appear as a dry tank installation can begin to corrode due to the water held in the mill scale. That is what the tiny white flowers are in the inside of boats, on tanks, and even on exposed topsides of some aluminum boats are. The beginning of mill scale supported crevice corrosion pit sites, from a vapor film of deaerated water's action working on the oxide film under the mill scale.Water on the bottom of an aluminum fuel or gas tank will become deareated and acidic, and it will begin to corrode the tank bottom unless it is removed. If the tank's plates were not cleaned using acid etch or buffers of mill scale this entire process is sped up, and the entire tank bottom will be pitted.Done ranting about aluminum mill scale, but if an aluminum tank is pitted through in some places; as has been stated above lots of times; its toast.Tool rental stores will rent color video borescopes for a few bucks- they're not all that expensive to buy: take out the fuel level sender and go in for a look; I'll wager there will be an entire 'mine field' of pits in different areas over the bottom of this tank.Hog, I've been there, done that, and as you can see, I've skipped the T-shirt but kept the trophy. Be careful of used tanks.by the way, nice air sled and great bench frame!Cheers,Kevin MorinKenai, AK
Reply:Originally Posted by zapsterDon't touch it....zap!
Reply:Originally Posted by Kevin MorinThe fact is that aluminum mill scale, if not removed from the material will promote this type of corrosion. I realize that hundreds of tanks, just as many whole boats and countless other welded aluminum products do NOT HAVE the mill scale removed(!) but that doesn’t change the fact that this film will retain water, the water will become acidic and the metal will corrode if the mill scale is not removed. Mill scale, that shiny chrome looking film is porous, retains water VAPOR and is not galvanically the same as the underlying aluminum!!! How’s that for a built-in problem?..., but if an aluminum tank is pitted through in some places; as has been stated above lots of times; its toast.
Reply:Originally Posted by Kevin Morinhog, I will give some tank and aluminum corrosion facts to encourage a new tank build. I have built plural hundreds of welded aluminum boats, more tanks than I have any idea and countless masts, booms, davits, cleats, and rigging so if there are mistakes in aluminum to make- you can count on the fact that I've made them at least once or ten times. (think my photo confirms at least one big error?)Metals corrode in general areas or in small sites called pits by the same basic chemical action. Im not going to get too techie, too far into chemical engineering here- but there are three main ways aluminum corrodes and they are: #1 by different metals contact when both are wet; #2 by acids or bases that are too strong; #3 and by electrical energy that results in the same basic chemical activity at the molecular level. All three methods result in the same basic metal chemistry, the original alloy of aluminum is reduced to non-alloy and the molecules of metal are removed from the parent material.All three are different paths to corrosion- but they result in the deterioration of aluminum alloys. #1 Metal to Metal corrosion is called Galvanic corrosion; #2 Acids and bases can corrode due to strong Chemical bonds robbing aluminum of its protective oxide (aluminum and oxygen combined) film and if aluminum is allowed to have a charge from a battery, for example, and get wet
then aluminum molecules can go into the water or whatever is wetting the metal from #3 Stray (electrical) Currents.So Galvanic, Chemical and Stray Current corrosion are all types of aluminum corrosion but when you research and explore youll find they all amount to the (molecular level) same event: aluminum molecules are removed from the parent metal into the wetting agent (salt water) or electrolyte. An electrolyte is just a conductive liquid that allows metal molecules to move from one metal structure to another, or to decompose as metal into non-metallic compounds.What does this have to do with aluminum tanks? All three variations of metal corrosion can happen to an aluminum tank and all three can be avoided or mitigated to such a degree as not to affect a tank.Lets take the chemical or acid attack first, because 99.999% of people dont seem to get this aspect of aluminum maintenance. Very strong acids or very strong bases (https://en.wikipedia.org/wiki/PH) are chemicals that have what we usually call reactivity; these chemicals will react with metals and aluminum is no exception. Strong acid or base will react with aluminum and seize the molecules of the metal and convert them to other molecules hence the description reactivity this could be called UN-refining metal since the strong chemicals actions on the aluminum do not leave the original alloy when the reaction is done.hog, this is what happened to the tank you're involved with on this thread but the owner doesn't know it.Now, this acid to aluminum reaction may be very fast due to strong (read article on Ph) or very mild and slow acting due to mild or less active acids: BUTTTTTT the acid or base beyond certain ph limits will remove aluminums healing oxide layer and then react down into the metal in a pit. This action is called pitting but the term is not limited to acid or chemical corrosion. Further; this reaction, especially the slow version can happen as a wetting cycle over and over again, once started.While were exploring acids lets look at water, yep plain ole everyday tap water. Tap water is more or less neutral ph, like sea water is in terms of acidic or basic ph. (The symbol ph stands for the amount of acid or base on the ph scale. ) However, if water loses its naturally occurring (entrained or mixed in) oxygen then it becomes deaerated- where deaerated is oxygen starved water and ends up acting as acidic. Where does this happen? When water is trapped between two pieces of metal, like two pieces of aluminum- the water initially gives up its oxygen to the aluminum to form more oxide!This is called thin film stagnation which essentially means the thickness of the layer of water is thinner than a hair, and once in that thin film, the stagnation or chemical changes happen much easier, faster and results in a stronger metal reaction than in a bucket full of the same water.Wait! Hey! aluminum oxide is good stuff, it heals aluminum so thats all good right? Well- its fine for a while- but the acidic action of that water then takes back the oxygen and the aluminum oxide is dismantled. There goes the protective film. As a result, pure aluminum is exposed to water that is slightly acidic-acting and with the oxide is stripped off the parent metal begins to corrode! This event called crevice corrosion or poultice corrosion begins a cycle that will corrode aluminum which cant get "Free Oxygen" to form aluminum oxide to heal the surface and protect the base metal from corrosion!!!Stagnate water will continue this corrosion cycle but fresh water rinses, with the free oxygen will often stop this cycle!what do you suppose happens to tank water bottoms under fuel? The condensation of the air's humidity will leave water bottoms in all marine tanks. The day is warm and humid, the tank heats up and expands- the vent allows the air on the fuel/gas to vent out as it expands. The sun goes down... the tank cools the expanded air contracts, the air on top of the fuel/gas 'pulls' or vacuums in the surround humid air and it cools on the tanks sides; inside the tank. The condensed water runs down the tank sides to the tank bottoms, it lays there and becomes robbed of oxygen, it deareates and becomes acidic: the tank bottom is attacked. The tank is junk due to lack of maintenance by the skipper. To fully grasp this series of events chemically, youll have to spend some serious reading time, a little head scratching time and some review time
but the result is this; unless aluminum can get oxygen to renew its oxide film- the metal can corrode from chemical agents.A Solution? Give aluminum oxygen and it will heal itself- starve aluminum of oxygen and it can lose its oxide film and begin to corrode.Next will be my rant portion of this post.The fact is that aluminum mill scale, if not removed from the material will promote this type of corrosion. I realize that hundreds of tanks, just as many whole boats and countless other welded aluminum products do NOT HAVE the mill scale removed(!) but that doesnt change the fact that this film will retain water, the water will become acidic and the metal will corrode if the mill scale is not removed. Mill scale, that shiny chrome looking film is porous, retains water VAPOR and is not galvanically the same as the underlying aluminum!!! Hows that for a built-in problem?But then anyone whos worked in steel knows the same is true of steel mill scale coatings. Steel mill scale will promote rust by holding water film and vapor, aluminum isn't much different except that if the mill scale is removed the metal will 'heal' but steel will continue to oxidize, but not as fast as if the scale were left on.First step to protecting a tank, clean the mill scale, inside an out with an acid wash (that is diluted and neutralized when the etch is done) or mechanical abrasion so the aluminum has the best chance to form its aluminum oxide, self-healing film to protect from at least a couple of the corrosion's sources that may deteriorate your tank. Even a dry tank with mill scale has a layer of ambient water vapor retained in the porous film- therefore what may appear as a dry tank installation can begin to corrode due to the water held in the mill scale. That is what the tiny white flowers are in the inside of boats, on tanks, and even on exposed topsides of some aluminum boats are. The beginning of mill scale supported crevice corrosion pit sites, from a vapor film of deaerated water's action working on the oxide film under the mill scale.Water on the bottom of an aluminum fuel or gas tank will become deareated and acidic, and it will begin to corrode the tank bottom unless it is removed. If the tank's plates were not cleaned using acid etch or buffers of mill scale this entire process is sped up, and the entire tank bottom will be pitted.Done ranting about aluminum mill scale, but if an aluminum tank is pitted through in some places; as has been stated above lots of times; its toast.Tool rental stores will rent color video borescopes for a few bucks- they're not all that expensive to buy: take out the fuel level sender and go in for a look; I'll wager there will be an entire 'mine field' of pits in different areas over the bottom of this tank.Hog, I've been there, done that, and as you can see, I've skipped the T-shirt but kept the trophy. Be careful of used tanks.by the way, nice air sled and great bench frame!Cheers,Kevin MorinKenai, AK
Reply:Kevin gets the longest most informative post award!! Thanks for your time it's appreciated. And I have decided to not fix this one due to other issues it probably has and the risks involved. I know when to listen to the "crowd". ThanksSent from my iPhone using Tapatalk
Reply:Great read here. Thanks Kevin, you've taught me some useful stuff today.
Reply:Leave the water in when cutting or welding. You can't leave any area for anything to build up.12v battery, jumper cables, and a 6013.I only have a facebook page. https://www.facebook.com/pages/VPT/244788508917829
Reply:So Kevin, or whoever....Condensation probably was the issue. Owner says tank with problem was port tank on the catamaran that faced the sun to the south. It's been sitting for some time and when the tank was siphoned out there was some water in the tank. My main question now is preventing that in the first place. What is the best way to keep an aluminum tank like this healthy? I'm sure using the boat and the fuel regularly is the best way but what about when they sit? Since there are aluminum experts on here I figured I could learn that too.... Thanks. Here is the tag I took a photo of today looks like it was a 100gal tank didn't look that large. What are these usually made from? 1/8 aluminum 6061 t6 or is there some material that's better? I might as well learn how to make one. ThanksSent from my iPhone using Tapatalk |
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发表于 2021-8-31 22:15:11