Thread: Petrol tank

Originally Posted by KBs PensNmore

Thanks Karl, I had forgotten about using HOT water in a tank, it's been about 20 years since I'd last done a tank, forgetting something like that may not have been healthy.
Kryn

Funny you mention that.
We had an employee at the same place where i worked at the time. His task was to weld two 1/4 BSP fittings in a fuel tank from a boat. The sort of job that was routine for our workshop.
Now this fine fellow, being, hmmm, not so smart and more than a bit lazy, discovered that the steam cleaner was out of diesel. Not to worry, cold water and detergent must be just as good he thought.
As all fishermen know, you have to let the fish take the bait before you strike. Well fickle fate let him take it hook line and sinker before dishing out her lesson. He got away with tacking in the two fittings with the MIG, but this must have put just enough heat in the tank to get a few vapours flowing. When he lined up with the TIG and struck an arc, the hammer of Thor struck him.
BOOOOM!
When we all came running, the sight which greeted us was quite surreal. Ten years worth of aluminium dust was drifting down slowly from the rafters, sparkling in the sun. The employee was laying flat on his back, totally uninjured, but with his ears ringing I'm sure.
The ex tank was the star exhibit. What was once a rectangular prism, transformed to damn near flat sheet once more.
A good lesson was learned by all that day.

I could not let this thread go without telling you all about this one.

Picture then, a Honda CB100 fuel tank, this type with the indents at the rear for your knees. The tank had a weep at a seam,where bottom meets sides.

It was brought to the attention a certain boilermaker who had just done some cert safety training training re welding and inflammables.

Full of this information the said boilermaker requested and got degreasing and then steam cleaning. He did a sniff test and prepped the tank for the silver solder process.

The tank was filled with water and strapped to the top rail of a wooden fence.

When the flame was applied and a small amount of silver solder applied the was not a boom, mind you but a muffled wump sound. The result was that the tank no longer had the indents and a boilermaker had soiled jocks.

Under intense visual examination ,it transpired that the joint was double lap joint which must have had held a tiny bit of fuel vapour- after degreasing ,after steam cleaning and after being filled with water.


I think if I had completely left the lid off and not just loosely fitted it, the indents might still be in the tank.

Just an illustration to show you the power that even a tiniest bit of fuel vapour has.

Two or so years back we lost a local ali fabricator tig welding on an ali boat.The explosion came from fuel vapour in the enclosed hull,it is thought.

Take the utmost care with this stuff

Grahame

The last tank I tried to repair, after several welds, resulted in a football shape with square corners
Kryn

While wearing my other hat as a Volunteer Fire Brigade Chief, I had the privilege to witness a somewhat amusing demonstration.
An instructor at the live fire training ground has a pot made from 12mm steel plate with a spark plug in the side and a 12mm plate for a lid. First he poured around 5-600ml of unleaded fuel in the pot, put the lid on and told everyone to retreat to what they considered a safe distance. Most went a long, long way away. The ignition switch was activated and a muffled whoomp emanated, with the lid lifting probably 2-300 mm and being thrown around a meter away. Next he poured well under 100ml of fuel in the same container and issued the same instruction. All moved much closer, so close that the instructor actually told them stop moving in. The ignitor was pressed and boy did we have lift off. The lid was hurled a good 40M away at rapid velocity.
There my friends is a real life demonstration of the effect of fuel, (vapour), mixture. The lesser amount gave the perfect explosive conditions, while the 600ml was like running your car with the choke pulled out. We make the effort to remove fuel from tanks we weld and thed little that we miss can recreate similar circumstances, that is why welding fuel tanks has created many a widow.
Kurt Johansson, the Northern Territory road train pioneer had the contract to remove all the empty fuel drums left over from World War 2 operations in the top end. His method for de gassing was simple. Place a compressed air line in the drum and drop a match in. Apparently the fuel burned quite sedately because the mixture was so weak under the influence or the compressed air.
Please don't try that one at home.