2IntroductionOxyfuel welding is a welding process where the heat for fusion is supplied by an torch using oxygen and a fuel gas.Several different fuel gasses can be used:MAPP= (A mixture of stabilized methylacetylene and propadine.)
3Fuel Gasses Propane (LPG) Natural Gas Acetylene MAPP Hydrogen Propane Different regulators recommencedLower temperature flameOxidizing flame at maximum flame temperatureNatural GasDifferent regulators and torchesDelivered as a gas by domestic pipe system or in cylinders as LNGLower temperatureGood for brazing and soldering thin metalAcetyleneProduces hottest flameWide range of flammable limitHeavier than airLeast stable of the fuel gassesMAPPSame equipment as acetyleneSlightly larger tip sizeIs not sensitive to shockLighter weigh cylindersNeutral flame has long inner coneHydrogenRecommended for welding aluminum and lead.High cost of gas limits use.GMAW and GTAW process more popular.
4Uses Traditionally oxyfuel equipment was used for: BrazingFusion weldingFlame hardeningMetalizingSolderingStress relievingCuttingBendingNew technologies in the GMAW process has almost eliminated the need for oxyfuel welding.Primary uses today are heating, brazing and cutting.
5OxyFuel SafetyThe hazards of oxyfuel welding are primarily compressed gas cylinders, flammable gases and open flame.Common concerns are (pg 294)PPE (shade 4 face shield/goggles, gloves).Store and handle cylinders correctly.Keep caps on cylinders whenever regulators are not attached.Never use oil, grease, or any hydrocarbons on fittings.Store cylinders in a locked enclosure.Check system for leaksFollow correct procedures for turning on and off.Remove combustible materials from area.Cutting slag can travel 35 feet on concreteInsure adequate ventilation
6OxyFuel systemBefore discussing how the system works, it is important to know the name of the parts.Oxygen safety discOxygen cylinder valveOxygen cylinder pressure gaugeOxygen working pressure gaugeOxygen regulatorOxygen regulator adjusting screwG. Acetylene cylinder safety discH. Acetylene cylinder valveI. Acetylene cylinder pressure gauge
8Oxygen Cylinder One piece, seamless construction. Each cylinder has unique serial number and number is recorded in national registry.Scheduled inspection required.2,200+ psi when filledSafety disc, nut, releases at 3,000 psi.Must not be dropped.Should not be used as a roller.Never use any lubricates on threads or any part of the cylinder.Three common sizes are 244, 150 & 80 cubic feet.The valve should never be left exposed. It must always have the regulator attached or the cap on.
9Oxygen Cylinder Valve Special double seat valve. Must be opened all of the way when in use.Right hand threads
10Acetylene CylinderAcetylene cylinders are filled entirely with a porous materials which must be able to stop the propagation of an acetylene decomposition within the cylinder initiated by a backfire or an external heating of the acetylene cylinder.250 psi when filled.Protected by fuse plugs that melt at 212 oF.The cylinder should be opened only 1/2 to 3/4 of a turn when in use.The withdrawal rate in cubic feet per hour should never exceed 1/7 times the cylinder capacity.Common sizes are 300, 120 and 75 cubic feet.The cylinders must always be used, transported and stored upright.Special cylinder because acetylene is unstable above 15 psi.Acetylene is shock sensitive.
11Acetylene ValveAcetylene cylinders are low pressure cylinders, therefore the valve packing can contain the cylinder pressure and only a single seat is used.Fuel cylinders are left hand threads.
12LPG Gas Cylinders Simpler hollow steel containers. New regulations require float shut-off.Because gas is under pressure, cylinder contains both liquid and vapor.Equipped with spring loaded pressure relief valve.Newer style fitting being adopted.Common sizes are 30, 70, and 100 pound.
13Pressure RegulatorsGas systems must have a pressure regulator to reduce the pressure from the high pressure in the cylinder down to the working pressure.Many different designs are used.They range from simple fixed output, commonly used for gas grills and camping stoves,to double stage regulators used for oxyfuel welding.
14Regulators Oxyfuel welding and cutting uses two types Correct use Single stageTwo stageCorrect useInsure adjusting screw is back off when shut down. Check before starting.Set correct working pressure.Two potential problemsRegulator creepGauge not returning to zero
15Regulator Problems Regulator Creep Regulator creep is a potentially dangerous condition that occurs when the regular does not maintain working pressure.When the system is on, and no gas is flowing, the working pressure slowly increases.Potential outcomes:Rupture of regulator safety relief valve.Explosion of low pressure gauge.Rupture of gas hose.CausesForeign material inside the regulator.Failure to release the regulator adjusting screw before opening the cylinder.Normal wear
16Regulator Problems Not Returning To Zero The bourdon tube inside the regulator can be damaged, distorted.When this occurs, the gauge needle does not return to zero.CausesOpening cylinder with the regulator adjusting screw turned in.Hard impact.
17Working PressureOxygen and fuel gas working pressure should be set according to manufactures recommendations for the job being performed.Potential problems with excessive pressure.Harsh flameDamaged equipmentIncreased potential of flashback.Potential problems of insufficient pressure.Insufficient heatUnstable flameIncreased plugging of welding or cutting tip.
18Welding Tip SizeExample welding tip selection and working pressure chart.
19Backfire & FlashbackBackfire: indicated when the torch goes out with a loud pop.Caused by hot metal in the tip.The gasses rapidly combust inside the tip and cause a burst of high pressure.When it occurs, stop and inspect the tip and clean if necessary.Flashback: occurs when the flame burns inside of the torch.Usually accompanied by a shrill hissing or squealing sound.May have puffs of black smoke coming out of the tip.A potentially serious condition. If not stopped the flame can travel up the hoses and into the regulator.Primary cause is a blocked tip and unequal working pressures.The potential harm of both backfires and flashbacks is controlled through the use of check valves and flashback arrestors.
20Oxyfuel TorchThe oxyfuel torch is the handle for holding and controlling the system.It the controls the flow rate of the gasses and delivers them to the welding tip, or cutting attachment.The torch valves should only be hand secured, not tightened.The valve stem packing should be tightened if gasses leak past or when the torch valve becomes too easy to turn.
21Oxyfuel TorchesSafety codes require torches to have check valves and flashback arresters.Note: this is a relative new code. Older torches will not have check valves or flashback arrestersIf not included, they should be added in line between the regulator and the torch.Flashback arrestorCheck valves
22Oxyfuel Welding TipsWhat is normally called a welding tip is actually a welding tip and a mixing chamber.Some manufacturers put the mixing chamber in the torch, Victor are in the welding tip.Tips have different sizes of orifices.Size usually indicated by number.Manufacturers use different number systems.When fuel gas other that acetylene is used a larger size tip is required.Tips for heating may have multiple orifices.Tips require periodic cleaning.A dirty tip will have a forked outer envelope.Tip orifice should be cleaned with a tip cleaner.
23Using Tip CleanerStart with the smallest size that will enter the orifice without excessive force and work up to orifice size.Be careful, a broken tip cleaner usually means a destroyed tip.Clean the face of the tip with the included file.
24Airacetylene Torch Burns a mixture of acetylene or MAPP and air. As fuel gas flows through torch it draws in the correct amount of air.Lower temperature than oxyacetylene.Primary use is in soldering and brazing copper piping.
25Hoses and Connections Requires special nonporous hoses. Hoses are color coded.Green: oxygenRed or Black: fuel gasConnectionsOxygen: right handAcetylene: left handHoses should be protected from hot metal and physical damage.
26PPE Use protection for: Eyes Body Correctly shaded lens--not sun glasses.Shade 4 or 5Fire resistant glovesLong sleevesButton shirt
27Setting Up Oxyfuel System Extinguish all open flames and stop processes that produce sparks.Steps (assuming new system)Secure cylindersRemove capsCrack cylinder valvesConnect regulatorsOpen cylinder valvesConnect hoses to cylindersConnect hoses to torch bodyConnect welding tip to torch bodySet working pressuresCheck system for leaks.
28Shutting Down System Close cylinder valves Open torch valves Leave open until regulator gauges read zero.Some sources recommend doing fuel first and oxygen last.Close torch valvesRelease tension on regulator adjusting screw.Roll up hoses and place torch in a safe position.