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Muriatic Acid for Fuel tank cleaning?+++++
Q. I am restoring a Porsche that has been sitting idle outside for about 7 years. I am at the point where I need to clean the fuel tank and get the rust out of it before using fresh fuel and possibly burning up a rather expensive fuel pump. I have heard that Muriatic Acid [linked by editor to product info at Amazon] was the way to go but haven't found any literature on 1: How fast acting is it? 2: Will it clean all the rust that is in the bottom of my tank? 3: Is there actually a safer product that will do the job just as well?
I have been restoring cars for some time now but this is the first time that I haven't just replaced the tank because of the expense involved. I would appreciate any advise or comments.William M [last name deleted for privacy by Editor]
Hobbyist Auto Restorer - Georgetown, Texas
A. The muriatic acid you suggest using would certainly clean the rust out but unfortunately you will experience two subsequent problems.
First, once the acid is rinsed out, the freshly cleaned steel will be very prone to oxidation (rust) unless you apply a rust inhibitor of some type. That is going to be unavailable to the home user.
Secondly, what are you going to do with extremely hazardous, corrosive substance such as Hydrochloric (muriatic) Acid? If someone like myself were to do this in an industrial setting I could go to jail and face serious fines. Since you won't have a wastewater treatment system, I urge you not to do this.
Perhaps a better solution would be to use abrasive blasting done at a shop that specializes in this type of work. Obviously the geometry of the tank will be of consequence because you may not be able to reach every remote area of the tank but it's just a suggestion.
If you're concerned about abrasive dust remaining in the tank after cleaning, you can use CO2 blasting which just evaporates as soon as it contacts the part.Daryl Spindler
- Nashville, Tennessee
A. Muriatic acid is a weaker mixture of Hydrochloric acid, don't let that fool you, it is still very potent stuff and should be handled with the utmost care. In regards to your idea for cleaning the tank with the acid I can say that yes, it will eat the rust out of your tank, and then promptly let it rust back up again, very very quickly, about 30-45 minutes you will have rust on it again. You will need to seal the tank (possibly fiberglass?), very quickly after using the acid. Overall I think this is a bad idea and you would be better off getting a new tank, but there is my prediction and suggestions for you.
Good luck with the PorscheMarc Banks
- Elizabeth City, North Carolina
A. I would caution you about using hydrochloric acid on your fuel tank. While it will do a good job dissolving the rust, you may uncover holes you didn't know you had. In addition, you will need to rinse the metal very well to remove the chlorides that can cause more corrosion. I recommend using the least aggressive method possible. I assume this rust in on the interior of the tank. If it is light rust, phosphoric acid or citric acid will do well. Try a 10% (w/w) solution and drain and rinse well after 60 minutes. Temperature is important too. Batch the solution using hot tap water and try to keep the tank at least warm throughout the process. Good luck.Joseph Lockrem
- Indianapolis, Indiana
A. As you can see, no one here thinks derusting with muriatic acid is a good idea. Muriatic is too aggressive, and you will have a subsequent rusting problem. There are two good approaches. 1). You can buy a kit which contains cleaner, deruster, and tank coating materials, and do the job yourself. I used this process on my AH tank fifteen years ago, and it is still fine. 2) You can send your tank to a company which will derust and hot dip galvanize it. Either of these methods will prevent future rust and seal small pin holes. Get a copy of "Hemmings Motor News" [link is to product info at Amazon]. You'll find both advertised there.
A. Hi William,
What Marc suggested about fibreglass seems to be a good idea.
However, this does mean REMOVING the tank first of all.
Having done that and 'cleaned' out the insides, then I'd suggest you clad the whole outside with at least one layer of mat plus a suitable fibreglass resin (Isopthallic may not be good enough chemically speaking, go for a vinylester due to its better flexibility over a Polyester). This should cover, as Joseph said, any 'holes'.
Maybe you should 'coat' the inside of the tank first of all. Ask your friendly local frp shop for some advice. They might well suggest a THIN vinylester coating by pouring it into the tank and sloshing it around ... maybe that should be first thing to do. Thinning done with Acetone [linked by editor to product info at Amazon], I believe.
Re hydrochloric, have a gander in the archives at # 12044 which might/might not be useful.
I did use fibreglass on my rear muffler ... the Volvo's rear muffler didn't last too long in winter/salt conditions. It worked out A.OK. ... but that was in Ye Olden Days of the 70's.
White Rock, British Columbia, Canada
(It is our sad duty to advise that Freeman passed away April 21, 2012. R.I.P. old friend).
A. Co-incidentally I am in the process of removing electroplating from plastic using a diluted muriatic acid.
As I have learned from other posters to your thread the environmental damage is of concern. I had not considered this before my project. I can tell you that it works very well, and be very careful about contact with anything you care about. Eyes!, Hands, clothes, even the sink can be damaged. Fumes can be very bad if not diluted so you may need breathing equipment as a dust mask won't help.
A few years back I read a motorcycle magazine DIY article covering this exact subject. The article outlined a kit with two or more parts. First a cleanser then a sealant is applied to the interior of the tank. This leaves a painted look to the tank that won't rust and can help prevent leaking.
One avenue to follow up is that Harley does this to all their tanks when manufactured, so a field trip may be in order. Check out POR-15 as a start. There is a fuel tank repair kit [linked by editor to product info at Amazon] listed.
Good luck.David M [last name deleted for privacy by Editor]
- Vancouver, Canada
Agree with David. For $55 you can't go wrong.
A. You can use 5% citric acid solution (or 50 gm citric acid/1 lit water/+ some ammonia, pH must be 3,5)! Rinse well! Much better and safer than muriatic acid! Good luck!Goran Budija
- Zagreb, Croatia
A. I can vouch for the POR-15 fuel tank repair kit [linked by editor to product info at Amazon] , and have used it in motorcycle fuel tank restoration. In addition to the kit(which includes a metal etching chemical), however, I have also used muriatic acid to remove rust from the inside of the same tank. The muriatic acid(1 qt for a 6.5 gallon tank) was put in full strength and the tank was then "rolled" for about two minutes. I immediately drained the acid into a drain pan, and rinsed the tank for about 5 minutes. Then dried the inside of the tank with hot air. As soon as it dried, the POR-15 was applied. The muriatic acid was then poured from the drain pan into the original container for proper disposal at the municipal hazardous material disposal center. The muriatic acid did a great job of removing the rust, as, overall, the inside of the tank looked like bare metal.
One word of caution regarding the POR-15; if you have any small passages(in my case the tank crossover tubes), insert a wire cable prior to applying the POR-15, as it hardens like iron, and those passageways will be impossible to clear. Let the POR-15 cure (4 days), and pull out the wire cables.
Good luck,Johann Uhrmann
A. Try Eastwood. The company has it all for restoring cars (including gas tanks)Pete Ross
- Portsmouth, Virginia
A. FYI, muriatic acid can be neutralized with baking soda [linked by editor to product info at Amazon]. It must still be properly disposed of, but neutralizing makes it much safer.Bob Nauta
- Nunn, Colorado
A. Muriatic/Hydrochloric Acid is just HCl + Water (not sure of the dilution).
Add Baking Soda (NaHCO3), and one gets NaCl + H20 + C02...
I.e., when one neutralizes HCl with Baking Soda, one gets a resulting mixture of Water, Carbon Dioxide, and SALT, none of them are considered caustic substances. If "pure", it would require no special handling.
That doesn't mean that the sludge that you are picking up isn't caustic.
You might note, your own body makes and regulates Hydrochloric acid (stomach), and regulates the sodium and carbonate levels quite effectively.
- St. Louis, Missouri
Thanks Bob, thanks Clifford. While HCl certainly can be neutralized with baking soda, we wouldn't want people to extrapolate from their experience of neutralizing vinegar, and fail to realize that this neutralization procedure will gas and foam 10X as much as they expect, even after being warned to expect extensive foaming. It can take half of forever to neutralize one cup of strong HCl with baking soda if conditions aren't right.
Also, I'd like to reconcile Daryl's warning of dire legal consequences with Bob & Cliff's more cavalier attitude. The fact is, the government "categorically" regulates some industries, such that the legal requirements can depend more upon what 'sector' you are in than what chemical you are discussing. In the plating industry, for example, every drop of hose water is regulated even if it is totally neutral and so dilute that you could safely drink a tank-car full. If you are a hobbyist rather than a professional, you are not part of any sector and can probably legally do a lot that Daryl isn't allowed to do. But if you are taking in work and being paid for it, be cautious about the fact that you may now be in a 'category' where waste disposal is strictly regulated regardless of how safe or neutral or innocuous you think it is.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
A. Suggest you look at a product POR-15 [linked by editor to product info at Amazon] I had a rust problem in the fuel tank of my Austin Healey which I treated with POR 15
I was quite impressed with the result.
- Brisbane, Australia
I have used Muriatic acid and it works great. I don't see the big deal about the stuff, dump it along the fence as I also do with used motor oil. It makes a great edging solution and I don't have to weed it. I really think everyone is going way over board about the environment stuff as if this is the worst thing that is being done to the Earth in each person's daily life.Jason Heights
That was probably a put-on, Jason, but just hope you never have to sell the property. Not sure about Florida, but in most states all that earth will have to be excavated and disposed of. The muriatic acid probably wouldn't last for too many years, but the oil will be around for many decades.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
A. THERE ARE A NUMBER OF OTHER PRODUCTS THAT WORK JUST AS WELL. Ospho [linked by editor to product info at Amazon] FOR ONE WORKS GREAT AND ANOTHER IS CALLED Rust Bullet [linked by editor to product info at Amazon]. RUST BULLET "KILLS" THE RUST AND TURNS IT INTO A PRIMER. IT SAYS IT WILL LAST FOR 10 YEARS Guaranteed BUT I DON'T KNOW about INSIDE A FUEL TANK. ANYWAY, YOU CAN CHECK THEM BOTH OUT. HOPE THIS HELPS!JEREMY MORGAN
- WESLEY CHAPEL, FLORIDA
Q. I have a gas tank that I am redoing. It was in an accident and someone was going to fix it and didn't. It has been sitting with no paint or any coverage for 2 years. There is start of rust. Should I remove the rust before I Naval Jelly [linked by editor to product info at Amazon] (Big project), or will the sanding after Bondo [linked by editor to product info at Amazon] take care of it?Joan Cooper
hobbyist - Orangevalle, California
A. I just got off the phone with Rust Bullet, and was told that their product can NOT be used for the inside of a fuel tank.Scott Flanders
- Gig Harbor, Washington
May 18, 2008
A. Have you ever tried Naval Jelly [linked by editor to product info at Amazon], it destroys rust and washes off with water.Danny Roberts
- Lawrenceville, Georgia
August 18, 2008
Q. I am planning to clean out the front and rear fuel tanks on my 1944 Ford F250 diesel truck. I will drain them, remove them, wash with Purple Power [linked by editor to product info at Amazon] cleaner and a pressure washer.
If it rusts I am planning to use muriatic acid . What effect does muriatic acid have on the internal finish (aluminum)? - Thanks
- Atlanta, Georgia
September 5, 2008
A. I have used muriatic acid for rust on motorcycle tanks. Of course, these petrol tanks can easily be removed.
I use 1:2 dilution with warm water and get good results in about an hour.
I then neutralize by rinsing with common dish soap and water. Rinse completely, and blow out with compressed air.
I then immediately coat the inside with two-stoke oil and rinse out with cheap gasoline. The tank is then ready to fill with fresh premium.
I guess they're all right for car tanks, but I have had bad results with tank liner solutions. The stuff never seems to set completely and causes paint on the outside to blister.
- Madison, Tennessee
November 2, 2008
A. You guys are missing the boat. BIG TIME. I worked in the steel treatment industry for years and Phosphoric acid is the way to go. WHY ... The FeO3 will be removed and a Phosphate coating with convert the FeO3 to a higher resistant to corrosion surface. Used to treat metal before painting for years. So go with a 5% solution, heated to 140 °F. Follow with water rinse and then alcohol rinse.
Tank will appear slightly gray in color if done correctly. Google Phosphate coatings for more info.
- Waynesboro, Virginia
August 31, 2009
A. The issue of disposal of muriatic acid should not be a problem. After use it is easy to neutralize the acid with sodium bicarbonate (baking soda) or sodium hydroxide. In the first reaction you yield CO2 Salt and Water.
HCl (muriatic acid) + NaHCO3 (sodium bicarbonate) --> H2O (water) + CO2 (carbon dioxide gas) + NaCl(Table salt)
In the second reaction you yield salt and water
NaOH(sodium hydroxide) + HCl(muriatic acid) --> NaCl(table Salt) + H2O(water)
There is no problems with disposing of this into most city sewer systems (it's just salt water). The only issue to be aware of is ensuring the material is completely neutralized. This is much easier with sodium bicarbonate because as it is buffered, so you can add too much of it and end at an acceptable pH. With Sodium Hydroxide you can create a very high pH mixture which can also be dangerous. In either instance, most water treatment plants prefer between a 7 and 10 pH. You can test this will relatively inexpensive pH strips.
Always follow proper neutralization techniques when working with acids and bases - Neutralization releases energy, so when you neutralize a solution quickly you generate a potential for explosion, and trust me... exploding acid all over you and your equipment is dangerous (and destructive).
These neutralizations are very common, and information about the techniques involved are very readily available online.
- Central Point, Oregon
March 18, 2010
A. Like Johann U. in Michigan said, I will vouch for POR-15 fuel tank repair kit. Just finished my 25th gas tank, thank you Daytona Bike Week!
Only thing I did different was first I used the Marine Clean [linked by editor to product info at Amazon] which is a very good product, it does remove any old fuel tank liner and varnish and a "small" amount of rust. I was out shaking tanks like crazy and rotating them. Usually let them sit for 24 hours then rinsed them out till they didn't feel slippery.
Then I still prefer to still use Muriatic Acid, pour a quart in raw, non diluted and added about 100 daisy bb's, and just shake the gas tank around for 4 minutes turning it constantly.
This will remove all of the rust. It's just a pain in the ass trying to get all the bb's out. Then rinse it for like ten minutes to get all the Muriatic Acid out. This stuff is very dangerous, you must wear protective gloves [linked by editor to product info at Amazon] gloves and put goggles [linked by editor to product info at Amazon] on cause it will burn through your shirt and your skin in seconds and hurt like hell.
Then I dry the tanks out with a heat gun, use a hair dryer if you don't have a heat gun for like an hour.
Then tape of the drain and air plugs and pour in the POR-15 Metal Ready and duct tape off the cap hole and roll it around for like 5 minutes. Then turn the tank on its side for 30 minutes a side for no longer than 2 hours as the instructions specify. Rinse the tank out several times then back to the drier for at least an hour.
Then pour in the tank liner and let it dry. And walla! You will have a just as good as brand new gas tank. I just did 25 this week and every one looks as good as the other.
Just remember that rust will flash in seconds, so plan on doing your tank project when you have 4 hours of free time.
- New Smyrna Beach, Florida
July 31, 2010
A. A chain or old nuts and bolts, shaken inside to remove pieces of rust, 50/50 mixture of normal swimming pool acid called hydrochloric acid and water poured inside for about 3 hours to remove all rust,rinsed with water and thereafter with acetone to remove all traces of water and your problems are solved-Andrew of South Africa.Andrew Pietersen
- Roodepoort,South Africa
December 12, 2010
Q. I had severe rust in my gas tank, could this cause damage to my fuel injectors? I just put in a used motor, ran great for first 20 miles then lost all power just like the first motor, I pulled the tank to replace fuel pump and noticed the extreme rust, replaced the tank, pump and filter but the engine running very roughLes Daniell
just me - Lubbock, Texas USA
June 4, 2011
A. I'm in process of rehabilitating a John Deere E35 edger (Kawasaki engine) with SEVERE internal fuel tank rust and some pitting on top around the breather holes. Many gardeners consider the JD E35 the Porsche of edgers.
Had no time to go to store so used ordinary household vinegar (glacial acetic acid, I think) and a bunch of nuts and bolts followed by water rinse. Got out most of the rust but got a light film of yellow corrosion, probably not enough to foul the rebuilt carb.
Found a university extension site that OK'd pouring out the vinegar on the lawn.
Also tried CLR after 66 yr. old neighbor told me he used Red Devil Lye for the job as a boy, but one has to certify they are a saponificator to get this methamphetamine ingredient today. I buy my soap at Walmart.
I maybe could try the Phosphoric acid trick above, before reassembly and use.
- Durham County, North Carolina, USA
Hi, Paul. Thanks for the info. Two small corrections:
Vinegar is rather dilute acetic acid, whereas glacial implies 100% strength;
Lye is still readily available; drain cleaner crystals are often lye. It's dangerous stuff, but has a very common household use.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
July 29, 2011
A. Look at a product called Red-Kote fuel tank liner by Damon Products =>
It can be found on the internet and eBay. It does not require that all rust be removed and bonds the rust with a flexible coating.
I have used it on several Tractor tanks in poor shape and never had a problem.
- Thomasville, North Carolina
September 3, 2011
A. The tractor restorers I talk to tumble their tanks with sharp hard pebbles, any kind of small granite or marble chips from the garden center. It's easy enough to make a tumbling jig for your tank. Or if you have a pickup truck with bad shocks and bumpy dirt roads just put the tank and pebbles in there for a few weeks, turning occasionally.Greg Reid
- Millerton, Pennsylvania, USA
February 17, 2012
I have an old Suzuki Motorcycle that once had a rusty gas tank. My buddy told me to use this stuff called Muriatic Acid (with which I was unfamiliar). The first time I messed it up and it rusted all over again (because I did nothing afterwords). The second time around I managed to get out all the rust, I washed it out with a ton of water, took a hair dryer to it, and pumped in a bunch of WD-40. Well, 2 years and 4000 miles later I see no rust in my tank. So something must have worked! And on a lighter note, don't inhale the yellow smoke. That's what you call toxic.Ryan Naro
Hot Rodding - Loveland, Ohio USA
May 30, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. Hobby is car restoration and I am wrestling with a problem of removing rust from the inside of a Porsche fuel tank. I had it professionally done but am unhappy with the outcome. Examining the internal surfaces I see some black rust patches (probably neutralised) and quite a lot more brown patches, apparently not treated. The tank has a relieved area to accommodate part of the spare wheel. As a result of this it has complex interior surfaces.
I plan to prepare about 5 litres of muriatic acid solution of 1:5 (hot water) to give enough volume to cover all surfaces with some rotation. I would leave this in for about 30 mins rotating each few minutes, then flush with water and neutralise with solutions of baking soda flushing finally with fresh water.
At this point I am considering introducing phosphoric acid to coat the entire internal surface.
I would appreciate your opinion on the ratio for the solution of phosphoric acid and the length of time to leave it in the tank. I presume final flushing with fresh water and drying would be needed to prevent further rust.
- Eltham, Victoria, Australia
June 1, 2014
A. Try 5% ammonium citrate solution (pH 3,5) ... Much safer and better for you and environment ... Hope it helps and good luck!Goran Budija
June 3, 2014
The ammoniated citric acid works great on stainless steel, but is it effective on mild steel?
- Colorado Springs, Colorado
June 4, 2014
A. Ammoniated citric acid or ammonium citrate 5% pH 3,5 must work on mild steel too. Hope it helps and good luck!Goran Budija
December 1, 2014
A. Hey guys, here is the easy answer. Use a 5-6 meter thick dog chain. Shake the chain around in the tank to get the worst rust out. Wash out the tank with clean water. Use one bottle of Deoxidene - Rust Cleaner. Tape up the filler hole and shake around vigourously till it foams. Alow to dry in the sun. Wash out using three liters of fuel. Works for me!!Kendall Williams
- Cape Town, South Africa
September 14, 2015
Hey, working on tanks is not may favorite thing; spending a load of cash for crappy products, products that work but cost too much and crappy so called PROFESSIONAL work is even more NOT MY FAV THING.
Despite my actions during my crazy younger days. I care about the environment and I try very hard to leave as small of a footprint wherever I go ( I do have size 17 feet though).
Anyway, I wanted to tell you about this thing I found about tanks when I was about 20 from a old man I was working for in Oklahoma. He told me to go to the store one day and get him 3 gallons of apple cider vinegar, cheapest they had. I thought he was making pickles, I didn't even ask him about it. I brought him his apple cider vinegar and he just went straight over to a nasty gas tank we had pulled the day before, he poured 1 and a half gallons in it, looked at me and told me to block off all those holes and shake that thing real good for a few minutes every hour until it was time to go home.
Anyway, you get the picture. I'm not even exaggerating; the next day when I was told to go empty that tank out (we left it overnight). I could see myself on the bottom through the sending unit port.
Now, that tank was shellac and some rust. The one I am working on right now is straight-up chunky nasty dry rust. So I have the vinegar in there with about 8 feet of tow chain -- cleans my chain too, LOL. I am getting too old to be swinging tanks around but I am doing it anyway. I had a thought a bit ago though where I would strap the tank to my engine stand mount so I could just turn it with a steering wheel effect. Would me much easier than picking this up and shaking it like I have been.
If I am Lying and you try this, you would have wasted a couple of bucks and made your tank smell like a fresh dyed easter egg. I'm not lying though. This works and it's cheap and won't kill you.
Flush with water, repeat if you didn't wait long enough and it's still dirty, and so on. Common sense.
- Boise Idaho, USA
Tumbling gas tanks with muriatic acidJuly 8, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. Hi, we restore steel gas tanks, in the process we use a common conversion coating. Tanks often come in with heavy rust and other unknown contaminants. Tanks are tumbled with a ceramic media and heated alkaline solution, then with tumbling media and a diluted (1:1) solution of HCl (ambient temp, inhibited or not depending on condition) to achieve the level of cleanliness required. Tanks usually require 1-2 hours of acid tumbling, occasionally heavily rusted tanks require as much as 12 hours.
My question is will 12+ hours of HCl cause long term damage to mild steel? Some tanks have stainless steel fittings installed, can they be damaged?
- North Hollywood, California, USA
A. Hi Tony. "Maybe" is not a good answer, but you have found that sometimes it doesn't, whereas it's obvious that HCl can attack steel and eventually will eat through it. So I think the answer then is to attempt more educated guesses via some documentation...
Take a tank that you plan to tumble for a long time, and measure the steel thickness at 3 or 4 different points, tumble it for a measured number of hours, and re-measure the steel thickness at those 3 or 4 points. If you are eating away a third of the thickness, that's a serious problem and the process is highly questionable. If you are eating away only 5%, it's probably not causing tanks to fail that wouldn't have failed in another day or two anyway. It may be difficult to get accurate thickness measurements and you may have to supplement them with tumbling a scrap tank until failure, cutting a scrap tank to understand the thickness profiles after years of use but before recoating, etc.
The mechanism of attack is dissolution in acid, so if the tank is sound after tumbling, and you are confident that you can fully neutralize the acid, I don't think it's a problem -- but read through the earlier postings on this thread and see if there is any additional food for thought. Good luck.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
July 8, 2016
Q. Hi Ted,
You do a wonderful job and service with this forum!
Thanks for the help, you're right, the understanding of the effects are more important to me than a detailed analysis. It was not clear to me if hydrogen embrittlement or some other type of chemical reaction would be a concern with the longer than normal exposure times required to achieve the cleanliness required. That being said, we are looking into alkaline rust removers to reduce the amount of acid use. Other than the increased handling risks do you have any thoughts on their use?
Again, thanks for your help.
- North Hollywood, California
A. Hi again. Thanks for the kind thoughts. My experience is with general metal finishing rather than restoration of fuel tanks, and alkaline rust removers are sometimes used in such cases -- but it's not nearly as common as using muriatic acid.
I have never heard of spending hours in muriatic acid even in a simple immersion application, let alone hours and hours of tumbling with media in acid. Something sounds crazy that it should take many hours of acid and tumbling to remove the rust and other contaminants. Maybe you're not getting off the old coatings in the alkaline cleaner before proceeding to the acid.
Although I have no experience in this, and you have a lot, it would have seemed to me that tumbling in hot alkaline cleaner for as long as necessary to remove grease and old organic coatings, followed by a few minutes of tumbling in phosphoric acid would get the tank ready for coating.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
July 12, 2016
HCl is very bad for stainless, so if your tanks have stainless components in them I would avoid it.
Phosphoric ought to be plenty for most rust removal and acid cleaning needs, if you really need something stronger I would look to a nitric/HF pickling formula.
Stellar Solutions, Inc.
July 13, 2016
A. Good day Tony.
Have you considered sand blasting / glass bead peening to remove the rust / contaminants?
How large are the gas tanks, and do you use "barrel" tumblers or a vibratory machine?
I'm sure AF Kenton from Nova Finishing Systems could offer some good advice.
Food for thought.
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada