I maybe corrected but I was told not to use oxy-acetylene fore silver soldering but oxy-prapane was ok.

H

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Why is it dodgy? Ive had mine since 1974 and followed the rules we used in the workplace and have had no problems. I believe that as acetylene is getting expensive propylene can be used instead. I would imagine that a dedicated reg would be required to match the gas.

Also think about what type of heating you want.

The Air/propane that you mention is basically a large brazing torch and will be good at heating a larger mass like a boiler though you do need a reasonable volume air blower.

OXY/Propane tends to be a more concentrated heat which is OK for chasing around the joints but you are still lilely to need some background heat and it is also more likely to overheat the filler material (or even base material) if you are not used to using it.

On 15 February 2024 at 17:47 duncan webster 1 Said:

You can get what is referred to as an ‘acetylene fire’. It’s not an actual fire, it is the acetylene spontaneously decomposing into hydrogen and carbon, no air involved, but it releases a lot of heat which raises the pressure in the bottle. All that can be done is to keep it cool by continually dousing it in water, or submerging it a a big tank of water. It is quite rare, but not unknown. As you can do silver soldering and gas cutting with oxy propane why take the risk and expense of bottle hire.

 

Hi, if an acetylene cylinder is in a fire or has an acetylene fire, on no account should you move it, douse it with water from a distance if you can, but you must call the fire brigade. Acetylene is the most explosive gas there is, and the hottest burning gas there is. The reason for not moving a hot acetylene cylinder, is there is a real risk of an impact detonation, which can be as simple as a small knock. Your insurer may well not cover you for having acetylene in a domestic environment, and it may be prudent to enquire with them.

Regards Nick.

I started with oxy acetylene in 1968 and used it until the BOC plant at Bristol blew up then had to use propane ! I use oxy propane for both brazing and cutting and there is little difference for what I do. To build a boiler 5″ I would have a Y piece in the propane line so an air propane torch can be used to warm things up whilst the silver solder is run with oxy propane. A 19kg propane and a half size oxygen. Noel.

I have oxy-acetylene at home, mostly for welding and cutting. I am afraid SoD is wrong; acetylene plays no part in cutting steel. It is simply used to bring the metal up to red heat. The reaction between hot steel and oxygen is exothermic, so once cutting has commenced the process is self-sustaining without the need for acetylene.

All my early silver soldering was done with oxy-acetylene. It is good for small items, particularly when one doesn’t want to get the whole workpiece red hot. However, it is not really suited for silver soldering a boiler on it’s own. You need bulk heating, and then use the oxy-acetylene locally, as described by AT.

I used to use Air Liquide for oxygen and acetylene but had a major run in with them a couple of years ago. Not least because they said I wasn’t allowed to transport acetylene cylinders in my car, not true. So I changed to Hobbyweld, a bit more expensive but no rental costs. Unfortunately more recently Hobbyweld never seem to have acetylene in stock, so as and when I need a refill I will change to Air Products.

I have also used oxy-acetylene for heating steel sheet to flange it around formers. But when it came to the sides for my 4″ scale traction engine tender sides I decided that using acetylene would be far to expensive, at least a small bottle per side. So I switched to oxy-propane. It uses the same torch as for oxy-acetylene but I needed a different rosebud burner, a new hose and a proper regulator for the propane.

Andrew

As Andrew J has said the oxy cutting process uses the fuel gas to start the cut, if the material has a high chrome content or is stainless it will NOT cut only melt, but once the cut is going – just because I can – I will turn the fuel gas off and continue cutting ! A clean nozzel and a steady hand is almost as good as a hacksaw, and will make almost any shape. Air plasma on the other hand will cut most metals since it is a melting process ! Noel.

On 15 February 2024 at 20:56 Andrew Johnston Said:

I have oxy-acetylene at home, mostly for welding and cutting. I am afraid SoD is wrong; acetylene plays no part in cutting steel. It is simply used to bring the metal up to red heat. The reaction between hot steel and oxygen is exothermic, so once cutting has commenced the process is self-sustaining without the need for acetylene…

 

Andrew

I plead guilty, but in mitigation what I said was ‘with an excess of Oxygen, it will ignite steel, making an effective cutter.’  Poor choice of words maybe: I should have said ‘with an excess of Oxygen, an Acetylene flame will ignite steel, making an effective cutter.’  Once the steel is hot enough to burn, the Acetylene can be turned off, so Andrew is more accurate.

Anyone used a Thermic Lance?  These consist of a bundle of steel wires packed into a long steel pipe.  Oxygen is applied under pressure at the operator end, and the far end ignited, usually with an oxyacetylene torch. Not easy to get them going, but once lit the steel wires burn ferociously at high temperature and with a high volume of heat.   The concentrated flame will cut almost anything, even under water, and is the quickest way to get into a thick steel bank-vault protected inside a hefty reinforced concrete box.    The operator has to wear a heat-proof suit, and in an enclosed space, breathing apparatus.   The amount of heat and smoke produced by a thermic lance makes them unsuitable for stealthy criminality…

Dave

Hi Brian,As a user of both Oxy acetylene and Oxy propane both for work and hobby,What no one has mentioned is the cost of  the bottles ! This is one big plus for propane which will be plenty hot enough. Unless you have all the regulators, torch, nozzles Etc this is a considerable investment.   The gases in small bottles are A expensive and B don’t last long – there is nothing worse than running out half way through a heat. I anwered your question on size from practical experience. Send me I PM I may be able to help you with the equipment Etc. Noel.

Hi Andy Your last paragraph refers to the process of flame cleaning ! Once you have this sort of gear it opens up a Whole new world. A cutting torch in skilled hands is almost like a surgeons scalpel, I’ve had 50 years of practice. Noel.

On 16 February 2024 at 20:26 Andy Stopford Said:

On 16 February 2024 at 12:16 Brian Pritchard Said:

…

The question i really want answered is if I use Oxy-Acetylene for silver soldering the boiler stays particularly in the fire box would a 10 litre bottle of each be sufficient or do you need different sizes for oxygen and acetlylene?  I have a 3 1/2” Molly boiler half completed and will also need to do the stays.

Thanks

Brian

The smallest size acetylene bottle that Hobbyweld do is 5 litres. That would be plenty for what you want. The smallest oxygen is about 10 litres which would be fine. Whatever sizes you have, they won’t do anything as convenient as running out at the same time.

…

 

I think the hazards of acetylene may be slightly exaggerated above; at one time (maybe not so much now) every garage, scrapyard, etc had oxy-acetylene equipment, and they rarely had anything terrible happen (If it was that dangerous, I’d have probably blown myself up long ago). Which isn’t to say you shouldn’t treat it with respect, of course.

…

I couldn’t answer Brian’s question, having no idea how much silver-soldering is needed to make a 3½” Molly Boiler, or how much Acetylene and Oxygen are contained in 10 litre bottles – it’s not 10 litres!

Therefore Andy’s assurance a 5 litre bottle of Acetylene is sufficient is valuable – it’s based on practical experience of similar work.

Nicholas gives a good intro to the theory, answering how much Oxygen is needed to burn Acetylene, ie the most efficient mix; minimum waste and the highest temperature.  The calculation is done by weight, not volume, and I don’t know the weight of Acetylene stored in a 10 litre cylinder:

1. The cylinder capacity is less than 10 litres because it contains a porous core.
2. The Acetylene is dissolved in Acetone.
3. The Acetylene is compressed.

Though simpler, I don’t know how much Oxygen is compressed into a 10 litre cylinder.   Although there is no core or solvent taking space inside an Oxygen cylinder, the gas is compressed, so the answer depends on pressure.

The British Oxygen site offers some clues in that they sell Acetylene and Oxygen together as a set, giving details of both bottles:

From this, we see BOC expect an average Oxyacetylene customer to burn 0.57 cubic metres of Acetylene in 0.68 cubic metres of Oxygen, which agrees with Nick’s post.  They probably expect the average customer do be doing a mix of cutting and welding:  more Oxygen is needed for cutting.

BOC’s cylinders are different shapes, maybe so they don’t get mixed up, maybe because the inert core needed inside an Acetylene bottle fits better into a squat cylinder, dunno.

BOC give approximate cylinder dimensions, from which I estimate their volumes as: Oxygen 8.8litres, Acetylene 9.4litres.   This suggests Brian only needs single bottles of each assuming the other supplier is similar to BOC.  Order one 10 litre bottle Oxygen with one 10 litre Acetylene, not 2:1 or some other ratio.

On the safety question, Andy accidentally highlights a major cause of accidents.  It is that long incident free usage creates a false sense of security.   Having ‘got away’ with sloppy bad practice for a few years, individuals tend to conclude that H&S precautions are unnecessary.  They’re wrong!  Just because an individual has successfully overtaken lorries on a blind bend 10 times does not mean it’s safe: statistics show that overtaking on a blind-bend is downright risky – luck, not judgement.

Interesting accident report here on the 2010 Bootle refilling plant explosion.   Bootle had operated without incident for 90 years, and developed some bad habits.  Despite 90 years of good news, it wasn’t safe.   As usual with accidents, a number of different errors had to align, and one day they did.

H&S is about acting to make these alignments difficult.   Not just common sense, or relying on previous experience, it’s necessary to remain alert, keep up-to-date, and apply current best-practice.   Rarely difficult, basically just requires someone to list what could go wrong, what could be done to mitigate the risk,  and what needs to be done if the worst happens.   Thinking isn’t that difficult, or is it?

One Sunday a friend of my dad’s climbed onto his roof to fit a TV aerial to the chimney, which he did successfully.  His family were out for the day.   Halfway through the job it started to drizzle.   Turning round to climb down he was faced with a steep pitched slippery roof and the need to climb backwards onto a ladder.  Going down was much more dangerous than climbing up!   He sat straddling the ridge yelling for help.  Much later, a passer-by heard him and called the fire-brigade.  By the time they turned up he was completely soaked.

Worse, the fire-brigade drew a crowd and a local journalist.   Huge humiliation: the crowd loudly said he was a fool, on the ground he was privately bollocked by the Firemen who pulled no punches, later the story, with photos, was front-page news on the local paper, and he got a permanent nickname at work – ‘ladders’.   Not difficult to think of a few simple ways he could have completed the job without the drama!  At least he knew when to stop – many experienced roofers have come to grief in similar circumstances.

Oxyacetylene is much the same – safe enough if managed thoughtfully, and not too difficult.

There are always edge cases, where I think it reasonable for individuals to decide.  Andrew J mentioned one, which is transporting acetylene laid flat in a car or van.   This has caused a few nasty accidents, first because laying flat increases the risk of polymerisation; second because a small leak turns a confined space into a bomb.  Although such accidents are extremely rare, it’s much safer to transport cylinders upright on the back of an open lorry.  That’s inconvenient and expensive when it’s not particularly risky to move a cylinder a short distance in a private car, so why not?

Although illegal in some countries, it’s allowed in the UK as far as I know. I’d do it.  Unfortunately some UK suppliers aren’t willing to risk their cylinder being involved in an accident because of the cost and hassle it will cause them.  There will be trouble if they knew a customer wasn’t following “best-practice”.    Much worse foolishness with Acetylene in a workshop doesn’t matter because suppliers don’t know about it or have any responsibility for the consequences.

Dave