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Old 10 November 2005, 06:25   #1
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Crack in fuel tank

I have discovered a very small crack at the top/side on my aluminium fuel(gasoline)tank.

The tank is inside the console, and the console is attached to the deck with GRP so it will be a big job to change it.

It is possible to mount a hatch where the crack is.

Is it possible to fill the tank with a non exploding gaz ( nitrogene ? ) and weld it, or is that suecide ?

On my previus boat I had the tank out of the boat, flushed it with water in 6 ours, and had it filled with water during welding, and I still had a minor explotion !!!

The boat is still under warranty, but in that case I have to ship it to the UK, and be out of buisiness for some time.

Any advice of what to do ?

Regards
Roy
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Old 10 November 2005, 06:37   #2
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If the boat in under warrentee, would you not be able to claim losses from the UK company u bought the boat off....
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Old 10 November 2005, 06:40   #3
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Quote:
Originally Posted by RibRoy
I have discovered a very small crack at the top/side on my aluminium fuel(gasoline)tank.

The tank is inside the console, and the console is attached to the deck with GRP so it will be a big job to change it.

It is possible to mount a hatch where the crack is.

Is it possible to fill the tank with a non exploding gaz ( nitrogene ? ) and weld it, or is that suecide ?

On my previus boat I had the tank out of the boat, flushed it with water in 6 ours, and had it filled with water during welding, and I still had a minor explotion !!!

The boat is still under warranty, but in that case I have to ship it to the UK, and be out of buisiness for some time.

Any advice of what to do ?

Regards
Roy
Surely epoxy and/or glass cloth would seal such a crack? Sikaflex also perhaps?
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Old 10 November 2005, 06:44   #4
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If using the water wash in future, you need to use a detergent in the water to emulsify the remains of the fuel. I've also found powder for domestic dishwashers to be excellent. The water should be hot when flushing.

However, if you do not want to involve yourself in the hassle of a proper repair, there are products for repairing leaks in petrol tanks. The one I have used, and it worked very well, is marketed in the UK as Petropatch. You may well have something similar in Norway. I have also used the epoxy putty type but after a time it came away.

A couple of points: It is difficult to get adhesion to aluminium.
If the tank has cracked in use, that area must be flexing and a repair may only be temporary.
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Old 10 November 2005, 06:48   #5
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In simple terms, Aluminium worked hardens over time and on an area that is flexing a lot this will happen quicker Equally areas close to welds or bends where the condition of the metal has been changed by heat or movement will also be harder and more prone to cracking so if there is one crack there is probably be more
Welding tanks is very difficult and I wouldn’t want to do it still fitted in the boat

Des
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Old 10 November 2005, 07:30   #6
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Quote:
Originally Posted by Scary Des
In simple terms, Aluminium worked hardens over time and on an area that is flexing a lot this will happen quicker ..
Being a bit pedantic....pure aluminium hardly work hardens at all. Many of the alloys age harden substantially and then flexing takes it's toll.

Just a thought for you, Ribroy; you can anneal the aluminium alloy by applying heat. Unfortunately there is no colour change as there is when heating steel but, very fortunately, soap turns black at just the right temperature. Rub a bar of soap onto the surface at the crack and then heat it until the soap turns black. Do not continue heating it or it will turn into a gloop and collapse. Aluminium has a very short pasty stage. You'll need to flush the tank first though.
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Old 10 November 2005, 07:47   #7
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Quote:
Originally Posted by jwalker
Being a bit pedantic....pure aluminium hardly work hardens at all..........
No you be pedantic you are right about pure aluminium but the marine grade aluminium tends to have a bit of magnesium added to make it a bit harder and more corrosion resistant and therefore prone to cracking
I’m not sure that people working in the marine trade always apply sufficient thought to the use of the correct grade of material. For example you see carbon fibre used where it can have no benefit but hay, it looks good
Des
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Old 10 November 2005, 08:32   #8
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Quote:
Originally Posted by Tim M
If the boat in under warrentee, would you not be able to claim losses from the UK company u bought the boat off....
Go on..... You're havin' a laff aren't you? Consequential losses aren't typically covered by any warranty.
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Old 10 November 2005, 08:37   #9
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We're doing business law at the moment and some case we read came to mind. I am just lowly first year so I am probably wrong.....
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Old 10 November 2005, 08:38   #10
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You could stabilise the crack by drilling a hole at the end of it to prevent progation, the various good patching methods thus described will not be able to do this.

Aluminium can be bonded chemically in a number of circumstances aircraft are bonded. Welding aluminium is skilled and welding a tank that once contained fuel should be done after it has been steamed out for some time. More than likely the welder would also sparge the tank with the shielding gas in use so helium mix/pure or Argon mix/pure (I think?)

Bottom line is a new tank on new boat shouldnt crack it is getting stressed from somewhere. Annealing might help but could cause expansion problems. Welding does have the effect of annealing locally but either side the weld a heat affected zone is formed. This is where a failure could occurr if there is one.
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