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fuel tank repair

A

astjp2

Registered User
Utah/Alaska
I have a customer that brought me a pair of 18 gallon wing tanks. They must have been in a wreck because they are pretty beat up and dented. Does anyone have an tips or tricks to get the dents out? The customer is cheap and wont buy new tanks... :( I was thinking of making a laminated plywood form and then using compressed air...what sayeth the tribe? Thanks, Tim
 
Very very low air pressure will push out dents if they are not creased. One or two pounds at the most. Three pounds is the FAA's test pressure.
Always use caution in these matters.

I was told by a friend who saw it done, that Maule used water to form their tanks. He said they had the set up in a cage to contain any disasters. It apparently was a dramatic experience.
 
I straightened out a dented top with just under 3 lbs., but used a long hose and set it out in the yard. Worked very well and has been in my craft for over 20 yrs. It went all at once with quite a snap, but well tested as it never has leaked.
 
I was thinking of making a plywood form that would be layered up vertically with a piece of all thread to hold them together and then pressurize the take from there. both tanks are deformed enough that they may not fit inside the wing. I dont want to split and reweld because they are presently not leaking...
 
Pressure them up and try to massage the damage out, if it doesn't work, he'll have to buy new/used tanks. I wouldn't spend much time trying to repair them if they're in that bad of shape.
 
The reason items such as propane cylinders are pressure tested with water, is that fluids don't compress. Which also means that when the cylinder fails, it makes a bang but no explosion. Any time you pressurize a contained item with a gas (air) there is the danger of an explosion when one breaks. The item will crack and then the gas rushes out spreading mayhem around the immediate area.

If the tanks are deformed enough that they wont fit into a wing, replace them or get Kracke to fix them right.

Web
 
mike mcs repair said:
Fluids compress, just the FAA thinks they don’t and everyone that take a test has to lie to pass.

Water compresses something like 11 -13 % at 60000. Water jet use case.
Click to expand...
True mike, but for the purposes of our airplanes the fluid is considered not to be compressible.
 
I have pressurized flimsy tanks using a plywood disk with a center hole in it for the blowgun. I add air by burping the airgun while my hand is holding the plywood and gun over the filler hole. Too many burps and the pressure will push the plywood off the filler hole. Works like a safety valve and you can sneak up on the pressure by pushing harder on the plywood and airgun while burping. I have one handed a propane torch for heat on a crease while airing up the tank with the other hand. I came up with this method after blowing the end off a 100 gallon diesel tank using threaded connections and a regulator that creeped. A case of make do with what ya got.
 
It has to do with stored kinetic energy, look at it this way , if you fill it up with pressured air , say 3-4 pounds pressure and it splits then you are dealing with 20 gal stored air with immense energy,a split could rip with explosive forse. If you fill up the tank with water to say 19.95 gal and then apply air pressure to the tank you will only be dealing with a air volume of .05 gal at a pressure of 3-6 lbs. of pressure, a split in the tank will only result in water with a quart of air coming out. The energy stored is one quart in volume not 20 gal of air volume. a spirt of water vs. a explosive blast.
One could run a mole calculation and figure out the total energy difference if you are that conserned.
If it was me , and I have to do the same thing since I will be adding some bung holes for fittings to my tanks , I will be using water with air to pressurize. You can pressurize with 3-5 lbs of air and use a slap dolly or a broad hammer on a seam and the little bit of pressure will force the crease out.

Harley uses water pressure to form their modern bike frames except they use water under a couple of thousand lbs of pressure on thick steel. Their process starts with semi folded steel parts that have been bent to allow them to be placed in the form then they are pressurized, you do not even see the original folds or bends after the pressurization.

Plus side , it just costs the price of the water and a little electricity to pump up the air compressor and a couple of fittings . Like pumping up a tire.
 
Actually it is stored potential energy.

Kahles56 said:
It has to do with stored kinetic energy, look at it this way , if you fill it up with pressured air , say 3-4 pounds pressure and it splits then you are dealing with 20 gal stored air with immense energy,a split could rip with explosive forse. If you fill up the tank with water to say 19.95 gal and then apply air pressure to the tank you will only be dealing with a air volume of .05 gal at a pressure of 3-6 lbs. of pressure, a split in the tank will only result in water with a quart of air coming out. The energy stored is one quart in volume not 20 gal of air volume. a spirt of water vs. a explosive blast.
One could run a mole calculation and figure out the total energy difference if you are that conserned.
If it was me , and I have to do the same thing since I will be adding some bung holes for fittings to my tanks , I will be using water with air to pressurize. You can pressurize with 3-5 lbs of air and use a slap dolly or a broad hammer on a seam and the little bit of pressure will force the crease out.

Harley uses water pressure to form their modern bike frames except they use water under a couple of thousand lbs of pressure on thick steel. Their process starts with semi folded steel parts that have been bent to allow them to be placed in the form then they are pressurized, you do not even see the original folds or bends after the pressurization.

Plus side , it just costs the price of the water and a little electricity to pump up the air compressor and a couple of fittings . Like pumping up a tire.
Click to expand...
 
Eddie, thanks for the correction,
Yes you are correct, stored potential then when released becomes kinetic. I get them mixed up all of the time , just do not use them enough except when driving in hilly areas. ha, ha

The only thing more scary than a pressurized air tank is , my correction two items more scary than a air pressurized vessel is or are
1. a hot water heater that has a stuck pressure relief and a stuck thermostat on high , water becomes superheated and when released becomes instant steam if above 212 degrees and under pressure and splits a seam , Steam has a volume increase of 300 times the vol. of water. You know a steam rocket ship.
2. The next one is a propane tank that goes BLEME . I think that is the right term. The propane gets so hot that it turns into a pressurized gas and explodes the vessel. YOU DO Not Want to be around that , one hell of an explosion. Fire men can tell you about tanks going "BLEME" (sp). Also goes for Oxygen and acetylene tanks.
 
stewartb said:
You must work cheap if that's cheaper than sourcing different tanks.
Click to expand...

My exact thoughts.

Send them to Atlee and spend your time doing other stuff. Lots of stories out there of cheap owners getting mechanics to do stuff 'marginal' for cheap- then want the mechanic to replace the plane when things fail totally.

Any time you bend a solid, you compromise it's strength. The thin semi-soft material that tanks are made out of does not take long to work-harden and crack. About the time you get that tank all looking pretty, (how many hours of time to set up any of the above ideas and implement them), then the plane flies in turbulence with 1/2 tanks slopping the repair and a seam breaks, the owner and you will wish you went another path. Small dents I don't think would be bad, but your stating it won't fit in the wing makes me shudder.
 

Steam has a volume increase of 300 times the vol. of water.
not to nit pick but the expansion is 1700 times[FONT=arial, sans-serif].[/FONT]
 
astjp2 said:
I was thinking of making a plywood form that would be layered up vertically with a piece of all thread to hold them together and then pressurize the take from there. both tanks are deformed enough that they may not fit inside the wing. I dont want to split and reweld because they are presently not leaking...
Click to expand...

You can just about guarantee the tanks will leak if try this stunt. Don’t do it unless you enjoy inflicting pain to yourself.
 
Post pictures. Seen way to many damaged tanks or any other damaged sheet metal. Every case is different. Sometimes you have to pick your customers, plenty out there that will cost you time and money.
 
Have the owner sit on the tank while you are making the repair



Sent from my iPhone using SuperCub.Org
 
I was thinking in terms of flash steam where at about 260 psi a weak hot water tank might rupture where 1 cuft of condensate would flash to ~ 300 cuft at point of rupture. But yes in a pure sense the ratio is between 1600 -1700 : to 1 dependent on atmosphere and abs temp.

I might have been looking at it the wrong way, thermodynamics was never my thing.

And thanks for the correction on the BLEVE not BLEME by Gordon.
 
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