2IntroductionOxyfuel welding is a fusion welding process that uses oxygen and a fuel gas to provide the heat and shielding for welding.MAPP= (A mixture of stabilized methylacetylene and propadine.)
3Requirements An oxyfuel system must: store the two gasses, regulate the pressure,set the flow rate,mix the gasses,deliver the mixed gasses to the weld.
4Fuel Gasses Propane (LPG) Natural Gas Acetylene MAPP Hydrogen 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.What are the advantages and disadvantages of each gas?
5Uses How many people have used an oxyfuel system? Is there anything else that it be used for?Why has the use of oxyfuel welding declined?Traditionally oxyfuel equipment was used for:BrazingFusion weldingFlame hardeningMetalizingSolderingStress relievingCuttingBending
6OxyFuel SafetyRemember safety is based on a conscious decision and the management of hazards.What hazards are associated with an oxyfuel system?How do we manage these hazards?cylindersregulatorsflamehot metalharmful raysfumesfluxesBest management practicesJob analysis sheet
7OxyFuel systemBefore learning to use an oxyfuel system, it is important to know the name and function of each part.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 gaugeFunctionA. Oxygen cylinder pressure reliefB. Open and close cylinderC. Indicates oxygen cylinder pressureD. Indicates oxygen working (hose) pressureE. Adjusts and regulates oxygen working pressureF. Used to adjust oxygen regulatorG. Acetylene cylinder pressure reliefH. Open and close acetylene cylinderI. Indicates acetylene cylinder pressure
8OxyFuel System--cont. J. Acetylene working pressure gauge K. Acetylene regulatorL. Acetylene regulator adjusting screwM. Acetylene hoseN. Oxygen hoseO. Acetylene torch valveP. Oxygen torch valveQ. TorchR. Welding tipS. Acetylene cylinderT. Oxygen cylinderFunctionJ. Indicates acetylene working pressureK. Sets and regulates acetylene working pressureL. Adjust acetylene regulatorM. Transfers acetylene from regulator to torchN. Transfers oxygen from regulator to torchO. Sets flow rate for acetyleneP. Sets flow rate for oxygenQ. Handle for manipulation, mounting four welding tipR. Mixes gases, different orifice sizes set welding heatS. Storage for acetyleneT. Storage for oxygen
10Oxygen Cylinder What are the characteristics of an oxygen cylinder? What are the primary hazards in the use of an oxygen cylinder?Seamless construction>2000 psi when fullValve with safety disc that releases at 3,000 psiCap for cylinder when not in useCommon sizes are 244, 150 & 80 cubic feetDo not use lubricant on any fittings.Always keep secureAlways keep cap in place when regulator is not attachedDo not drop
11Oxygen Cylinder ValveWhat is different about an oxygen valve compared to a water faucet?How far should it be open when in use?Special double seat valve.Must be opened all of the way when in use.
14Acetylene CylinderWhat are the characteristics of an acetylene cylinder?What are the primary hazards in the use of an acetylene cylinder?Acetylene cylinders are 90% full of a porous materials .250 psi when filled.Protected by fuse plugs that melt at 212 oF.Common sizes are 300, 120 and 75 cubic feet.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.The cylinders must always be used, transported and stored upright.Cap must be on unless a regulator is attached.Should not be dropped.
15Acetylene ValveWhat is different about an acetylene cylinder valve compared to an oxygen cylinder valve?single seat is used packing seals the valve stem.Fuel cylinders have left hand threads.
16LPG Gas CylindersHow is an LPG cylinder different from an oxygen or acetylene cylinder?Simpler hollow steel containers.New regulations require float shut-off.Because LPG liquidizes with less 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.
17Regulators What is the function of an oxyfuel regulator? Regulator parts:Pressure adjusting screwBonnetNeedle valveHose connectionCylinder connectionNeedle valve seatDiaphragmSpringNylon thread insertReduce pressure from cylinder pressure to working pressure and maintain a constant working pressure.When the cylinder valve is turned on, pressure from the cylinder presses against the diaphragm and closes the needle valve.As the adjusting screw is turned in, the spring is compressed which applies force to the diaphragm from the opposite direction.If the spring force is greater than the force produced by the gas pressure, the needle valve opens and gas flows through the regulator into the hose.When the torch valve is opened, the pressure on the diaphragm is reduced and the spring opens the needle valve.When the torch valve is closed, the pressure equalizes and the diaphragm closes the needle valve.How does it work?
18Regulators—cont. Do all regulators have a pressure adjusting screw? No. Some are fixed pressure.
19Regulators—cont. What hazards are associated with oxyfuel regulators? LeaksLeaving adjusting screw turned in when opening the cylinder.Creeping regulatorGauge not returning to zeroLubricants on oxygen fittings
20Regulator Creep What is regulator creep? What can cause regulator creep?What hazards are associated with 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. If the cylinder is not shut off the working pressure will eventually equal the cylinder pressure.CausesForeign material inside the regulator.Failure to release the regulator adjusting screw before opening the cylinder.Normal wearPotential outcomes:Rupture of regulator safety relief valve.Explosion of low pressure gauge.Rupture of gas hose.
21Gauge Not Returning To Zero Why would a gauge not return to zero?What can cause this condition?What are the possible outcomes of using a regulator that has a gauge that does not return to zero?The bourdon tube inside the regulator can be damaged, distorted.When this occurs, the gauge needle does not return to zero._____Opening cylinder with the regulator adjusting screw turned in.Hard impact.Unknown working pressure which could cause backfires and flashbacks.
23Backfire What is a backfire when using an oxyfuel torch? How do you know when a backfire has occurred?What is the primary cause of backfires?What are the hazards associated with a backfire?What should you do when one occurs?Backfire: The gasses rapidly combust inside the tip and cause a burst of high pressureIndicated when the torch goes out with a loud pop. May be accompanied sometimes with a loud shrieking sound. Note: flame may restart because of the heat of the weld.Caused by hot metal in the tip.High pressure burst will blow molten material into the surrounding area.When it occurs, stop and inspect the tip and clean if necessary.HIgh when fusion welding steel, will occur every time the tip is too close and the metal is overheated.What What is the risk of a backfire?
24Flashback A. What is a flashback when using an oxyfuel torch? B. How do you know when one has occurred?C. What causes flashbacks?D. What should you do if you suspect one has occurred?A. Flashback: occurs when the flame burns inside of the torch.B. Usually accompanied by a shrill hissing or squealing sound.Handle of torch will get very hot.May have puffs of black smoke coming out of the tip.C. Primary cause is a blocked tip and unequal working pressures.D. Shut off the acetylene gas and then the oxygen, clean the tip.Worse case--If left unchecked the flame will travel up the hose and ultimately reach the cylinder causing it to explode. The potential damage is so high, and the probability of occurrence is so high that all new systems must have check valves and flashback arrestors.Low if modern equipment is used or if check valve have been installed in the gas hoses.E. What is the potential hazard of a flashback?F. What is the risk of a flashback?
25Check Valves and Flashback Arrestors What is the purpose of a check valve?What does a flashback arrestor do?Check valves only allow the flow of gas in one direction.Flash back arrestor stops the propagation of a flame.
27Working PressureOxygen and fuel gas working pressure should be set according to manufactures recommendations for the job being performed.What factors influence the ideal working pressure?Can excessive working pressure cause problems when welding?Yes. What are they?Welding or cuttingIf welding, what welding processJointWelding positionMetal thicknessIf cutting, metal thicknessPotential problems with excessive pressure.Harsh flameDamaged equipmentIncreased potential of flashback.Potential problems of insufficient pressure.Insufficient heatUnstable flameIncreased plugging of welding or cutting tipCan insufficient working pressure cause problems when welding?Yes. What are they?
28Oxyfuel Torch What is the purpose of the oxyfuel torch? The 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.Don’t attach a cold welding tip or cutting attachment to a hot torch.Tips and cutting attachments use o-rings for sealing, they do not need to be very tight.Important facts when using oxyfuel torch.
29Hoses and ConnectionsAre there any unique characteristics of oxyfuel hoses?Are there any unique characteristics of oxyfuel hose connections?Requires special nonporous hoses.Material must be resistant to degradation caused by oxygen and fuel gases.Hoses are color coded.Green: oxygenRed or Black: fuel gasConnectionsOxygen: right handAcetylene: left handHoses should be protected from hot metal and physical damage.How should hoses be treated?
30PPEWhat are the three primary hazards associated with oxyfuel systems and how are they managed?Hazard ManagementHarmful light Shaded gogglesor face shieldHot metal Pliers and glovesFlying molten droplets Welding apparel
31Setting 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.
32Shutting 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.