Guidelines are given on the principal health and also safety considerations because that oxyacetylene welding to ensure for sure welding practices.
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The oxyacetylene process
The oxyacetylene procedure produces a high temperature flame, end 3000 degrees C, by the burning of pure oxygen and also acetylene. That is the only gas mixture hot sufficient to melt steel; other gases (propane, LPG or hydrogen) can be used for reduced melting suggest non-ferrous metals, for brazing and silver soldering and also as a preheating/piercing gas for cutting.
Gases are usually supplied under high press in stole cylinders; in the UK, the color coding for the cylinders is in the procedure of being harmonised across Europe. For acetylene the shoulder that the cylinder is maroon and for oxygen the shoulder is white, although black color oxygen cylinders will stay in circulation for part time. The cylinder should likewise have a label marked with the type of gas. To prevent the interchange that fittings between cylinders include combustible and non-combustible gases, oxygen cylinders have a right-hand and acetylene have a left-hand thread. Every cylinders are opened by transforming the an essential or knob anticlockwise and closed by transforming them clockwise.
Oxygen will reason a fire to burn an ext fiercely and also a mixture of oxygen and a fuel gas can cause an explosion. The is, therefore, vital that the oxygen cylinders room separated indigenous the fuel gas cylinders and stored in an area complimentary from flammability material.
Safe practice and accident avoidanceStore the cylinders in a well-ventilated area, preferably in the open airThe warehouse area have to be fine away from resources of heat, sparks and also fire riskCylinders have to be save upright and well securedOxygen cylinders should be save on computer at least 3m from fuel gas cylinders or be separate by a 30 minute fire resisting barrierThe store area need to be designated "No Smoking".
Handling compressed gases
Cylinders space fitted with regulators to reduce the gas pressure in the cylinder come the working press of the torch. The regulator has actually two gauges, a high pressure gauge for the gas in the cylinder and a low press gauge for the gas gift fed to the torch. The gas circulation rate is managed by a pressure adjusting screw which set the outlet gas pressure. The BCGA password of exercise CP7 proposal the gauges are checked annually and also replaced every 5 years.
Factors come be thought about are that the gas device is perfect for the pressure rating and the hoses are associated without any leaks. Valve threads must be cleaned before screwing in the regulator. The valve of an acetylene cylinders can be opened up slightly to blow the end the threads yet the threads in oxygen cylinders are ideal cleaned making use of clean compressed waiting (the threads on hydrogen cylinders must always be swollen out utilizing compressed air).
As oxygen deserve to react violently with oils and also grease, lubricating oil or sealant because that the threads have to not be used.
Safe practice and also accident avoidanceCylinders are very heavy and must it is in securely fastened at every timesCylinder valves or valve guards have to never it is in loosenedCheck the regulator is rated for the pressure in the cylinderWhen it is registered the regulator to the cylinder the joints need to be clean and also sealant should not be usedBefore it is registered a regulator, the pressure adjustment screw should be screwed the end to stop unregulated circulation of gas right into the mechanism when the cylinder valve is opened
Using compressed gases
Gases are combined in the hand-held torch or blowpipe in the exactly proportions. Hoses in between regulator and torch need to be colour coded; in the UK, red because that acetylene and also blue because that oxygen. Hoses must be retained as short as possible and individuals should examine periodically the they room not near warm or sharp objects which can damage the water tap wall. Acetylene cylinders must constantly be supplied upright.
When connecting the system, and also at the very least at the begin of each shift, hoses and also torch should be purged to remove any kind of inflammable gas mixtures. It is essential the oxygen stream does not come into contact with oil which have the right to ignite spontaneously. Purging should additionally not be lugged out in confined spaces.
The torch have to be lit with a friction lighter or stationary pilot flame to avoid burning the hands; matches need to not it is in used and the flame have to not it is in reignited from hot metal, particularly when functioning in a confined space.
The cylinders must not come to be heated, for example by allowing the torch flame to warm locally the cylinder wall. Similarly, arc welding as well close come the cylinder could an outcome in an arc forming between the cylinder and workpiece/electrode.
Although very small UV is emitted, the welder should wear tinted goggles. The grade of filter is established by the soot of the flame which relies on the thickness of steel being welded; references for filter according to the acetylene circulation rate are given in the table (BSEN 169:1992).
Grade of filter recommended according to the acetylene circulation rate:
|up to 70||70 - 200||200 - 800||over 800|
|Welding and braze welding of hefty metals e.g. Steels, copper and also their alloys||4||5||6||7|
|Welding with emittive fluxes (notably irradiate alloys)||4a||5a||6a||7a|
Safe practice and also accident avoidanceWhen cleaning the cylinder threads, connecting the regulator and purging the hoses, safeguard face and also eyes by wearing the appropriate head shieldUse a suitable welding shield equipped v the ideal ocular defense filterWear non-combustible clothingEnsure the cylinder is not heated by the fire or through stray arcs from nearby electrical equipment
Joints and hoses must be confirm for leaks before any type of welding is attempted. Whilst acetylene may be recognize by that is distinctive smell (usually at levels of much less than 2%) oxygen is odourless.
Leak detection is best carried out using a weak (typically 0.5%) systems of a laundry detergent in water or a leak detecting equipment from one of the gas supply companies. It is applied to the joints making use of a brush and also the escaping gas will form bubbles. On curing the leak, the area need to be cleaned to eliminate the residue from the leak detecting solution. Leaks in hoses might be repaired however approved instead of hose and also couplings must be supplied in accordance with BSEN 560:1995 and also BSEN 1256:1996.
Backfire and also flashback
A backfire (a solitary cracking or "popping" sound) is when the flame has ignited the gases within the nozzle and extinguished itself. This may take place when the torch is hosted too close to the workpiece.
A flashback (a shrill hissing sound) as soon as the flame is burning inside the torch, is more severe. The flame may pass back through the torch mixing chamber come the hose. The most likely cause is not correct gas pressures offering too short a gas velocity. Alternatively, a instance may be produced by a greater pressure gas (acetylene) feeding up a lower pressure gas (oxygen) stream. This can occur if the oxygen cylinder is almost empty but other potential reasons would be hose leaks, loosened connections, or fail to adequately purge the hoses.
Non-return valves fitted to the hoses will detect and stop turning back gas flow preventing an inflammable oxygen and also acetylene mixture from forming in the hose. The flashback arrestor is an automatically flame trap device designed not just to quench the flame but also to prevent the fire from reaching the regulator.
Backfire or recall procedure
After one unsustained backfire in which the fire is extinguished:close the blowpipe regulate valves (fuel gas first)check the nozzle is tightcheck the pressures on regulatorsre-light the torch making use of the recommended procedure
If the flame continues to burn:close the oxygen valve in ~ the torch (to prevent inner burning)close the acetylene valve in ~ the torchclose cylinder valves or gas supply point isolation valves for both oxygen and also acetyleneclose outlets of flexible pressure regulators through winding out the pressure-adjusting screwsopen both torch valves come vent the press in the equipmentclose torch valvescheck nozzle tightness and also pressures on regulatorsre-light the torch using the recommended procedure
If a flashback wake up in the hose and equipment, or fire in the hose, regulator connections or gas supply outlet points:isolate oxygen and also fuel gas gives at the cylinder valves or gas supply outlet clues (only if this have the right to be done safely)if no threat of personal injury, manage fire using first aid fire-fighting equipmentif the fire cannot be put out at once, speak to emergency fire servicesafter the equipment has cooled, study the equipment and replace defective components
When a backfire has actually been investigated and also the error rectified, the torch may be re-lit. ~ a flashback, because the flame has expanded to the regulator that is vital not only to examine the torch, however the hoses and also components need to be confirm and, if necessary, replaced. The flashback arrestor should additionally be confirm according come manufacturer"s indict and, v some designs, it might be essential to change it. BCGA code of exercise CP7 recommends the non-return valves and flashback arrestors are replaced every 5 years.
The info was all set in participation with i get it Sykes, health & safety and security Executive, Newcastle ~ above Tyne.
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This job Knowledge post was originally published in Connect, might 1997. It has actually been updated for this reason the internet page no longer reflects precisely the published version.