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  1. #1
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    Jul 2008
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    Default Oxy/Acc flashback

    Has anyone experienced this ? When I was at TAFE the students on learning Oxy welding sometimes had the loud popping explosions from the torches . It seemed to be more common on the vertical welds . What is the cause ?

  2. #2
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    Jan 2004
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    Mackay North Qld
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    Default

    A flashback can be caused by:
    Acetylene Gas pressure too high.
    Poorly seated cutting nozzle.
    Nozzle touching work

    If using acetylene, keep the pressure below 100 Kpa

    Purge your hoses before lighting the torch. On a near empty oxy cylinder acetylene can find its way back up the oxy line.

    Never light your torch with a mixture of fuel and oxygen. After purging the lines, light the torch with only the fuel gas valve open.

    Check valves should be installed on both torch inlets and operating properly. Check valves can stop the reverse flow of gases, but will not prevent flashbacks.

    To prevent flashbacks, flashback arrestors must be installed on the outlets of both regulators, and/or torch inlets.


    A backfire,much worse,can find its way up the lines back to the regs and cylinders, gas lines must be fitted with flash back arrestors.

    The scariest incident with a torch I have ever experienced was when melting lead seals out of a a piece of equipment with a long heating tip.

    When heating the underside,a piece of molten lead fell through the inverted heating nozzle apertures and exploded the torch. The explosion melted the torch tube into solder like spatters and threw the cutting head some 20 metres away.

    I was not harmed due to my full PPE which I was wearing at the time.

    The flask back arrestors did their job and the flame never reached the regs or cylinders.

  3. #3
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    Aug 2010
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    Near Bendigo, Victoria, AUS
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    Default

    I agree with everything written above. I only recently fitted flashback arrestors to my oxy & acetylene regulators.
    However, the popping noise common for learniers and experts alike is simply getting the torch a bit too close and a larger spark hitting the actual orifice in the nozzle and briefly extinguishing the flame. As it relights, it makes the loud 'POP' noise that scares unwitting bystanders. In principal that's nothing to worry about as such, except that the mini explosion into the molten puddle can on occasions throw molten steel droplets in any direction.
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  4. #4
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    Jun 2012
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    melbourne
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    Default

    I know its not the same thing, but I heard of an accident of a friend of a friend many years ago, before TIG was commonplace. It put me off trying ox-acetylene.
    He was making a new custom petrol tank for a motorbike. The way it was told to me was he was joining the seams using a very small flame for the sheet metal. The hottest part of the flame being just at the tip of the cone but just before that, is unburnt gas. So he was keeping the hot bit on the seam but being a small flame its hard to keep everything exactly in place and the unburnt gas got inside the tank which then exploded and removed several of his fingers amongst other things. With oxy acetylene being more easily available form bunnings and lots of gas torches cheap on eaby, some people might think to try it without proper training, but beware. I believe the story, but I may have my facts wrong about the flame. Somehow the tank filled with fuel mixture.

  5. #5
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    I'm sorry to hear of your friend's accident and your caution that resulted. I suspect you have the facts right. My guess would be he had he flame adjusted just a smidgeon 'carborising' (rich) and not all the acetylene burnt in the flame. Acetylene is very easy to explode under lots of conditions. Brazing closed spaces like tanks or other containers is also fairly risky business with oxy acetylene, because you need the flame carborising so as not to oxydise the brazing filler or the surfaces. I've been aware of that risk and avoid it. I tend to silver solder containers with butane-air. Much safer.
    TIG with its inert gas shield is of course the safest for that purpose.
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  6. #6
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    Default Lights

    Automobiles commonly used acetylene powered headlights. A device sitting on the running board , dripped water onto something ? Never a reliable system

  7. #7
    Join Date
    Oct 2009
    Location
    Upwey VIC
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    Default

    Quote Originally Posted by morrisman View Post
    Automobiles commonly used acetylene powered headlights. A device sitting on the running board , dripped water onto something ? Never a reliable system
    Calcium Carbide.

  8. #8
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    Oct 2008
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    Cairns, Q
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    From early in the 20th century compressed acetylene in small cylinders for automotive lighting was available from the Prest-O-Lite Corporation (as in POL connecting threads for gas cylinders) to avoid the nuisance of coping with acetylene generators mounted on the vehicle. Prest-O-Lite also made acetylene headlights. When working properly the acetylene lights gave an excellent light - better in my opinion than the run of the mill old electric sealed beam lights.

    When I moved to North Queensland in the early fifties acetylene in cylinders was not always readily available outside the bigger towns and acetylene generators were in common use on oxy acetylene sets in the factory. Portable acetylene lamps with built in generators were commonly used for outdoor work at night.

    Frank.

  9. #9
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    I have childhood memories of the acetylene gernrators in local blacksmith shops. They even had one mounted on a bile trailer and would cycle to jobs to weld things on site. I believe they are still available (I considered looking for one when the cylinder rentals got ridiculous). They were quite safe, more or less automatic and very cheap to run.
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  10. #10
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    Apr 2013
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    Bunbury WA
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    When I did my appreticeship in 1964 they had an acetylene generator that aparently was fully functional but just wasn't used anymore, bet it has been thrown out years ago.

  11. #11
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    Default

    Yep can make it an undie changing time

  12. #12
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    My Dad told the story of being pulled over by a copper for no headlight on his motorbike.
    He said it had just gone out whereupon said walloper put his paw on it.
    Forget now whether he booked the old man or not but he burnt his hand.
    H.
    Jimcracks for the rich and/or wealthy. (aka GKB '88)

  13. #13
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    Apr 2013
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    Bunbury WA
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    Default

    Quote Originally Posted by clear out View Post
    My Dad told the story of being pulled over by a copper for no headlight on his motorbike.
    He said it had just gone out whereupon said walloper put his paw on it.
    Forget now whether he booked the old man or not but he burnt his hand.
    H.
    How many times have you written "hot" on something you gas cut and someone has to test it?

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