2 Objectives Describe the history of oxyacetylene welding (OAW). List and describe the properties and distribution systems for the gases used for OAW.Explain the safety issues of OAW.List the equipment used for the OAW process.
3 Oxyacetylene Welding Definition: Join metal by heating surfaces to be joined to melting point with gas flameFusing metal into homogeneous massLetting it solidify into a single unitFlame in cone reaches temperatures as high as 5800º to 6300ºFFiller rod may or may not be used to intermix with molten pool
4 Oxyacetylene ProcessDuring first part of the 20th century it was used as a major welding process both for fabrication and construction, maintenance and repairToday its use is limited for industrial production purposesStill used for brazing, soldering, metalizing; welding metals with low melting points; general maintenance and repair work
5 History of Oxyacetylene Welding Early Egyptians, Greeks, and Romans used alcohol or oil flame to fuse metalsIn nineteenth century various gases testedUsed in laboratory in working with precious metalsIn 1847, Robert Hare fused platinum with oxyhydrogen flameIn 1880, production of oxygen and hydrogen through electrolysis of water made distribution of gases in cylinders under pressureLate 1800s experiments done with oxygen-coal gas and air-hydrogen flames
6 Discoveries Leading to the Oxyacetylene Process In 1836, Edmund Davey discovered acetylene gasIn 1862, acetylene gas produced from calcium carbideIn 1895, Thomas L. Willson produced calcium carbide commerciallyUsed for residential lightingIn 1895, LeChatelier discovered that combustion of acetylene with oxygen produced flame hotter than any other gas flame
7 Discoveries Leading to the Oxyacetylene Process In 1900, Edmond Fouche invented high pressure acetylene torchLater designed low pressure torch (worked on injector principle)In 1906, Eugene Bourbonville brought first welding torch to this countryProcess first used for maintenance and repairDuring World War I oxyacetylene welding became production tool
8 Gases Oxyacetylene welding process uses two principal gases Oxygen and acetyleneOther gases can be used for cutting and heatingPropaneNatural gasMapp® gasStored in different size cylinders
9 Various Fuel Gas Efficiencies NormalBtus Usable heat Flame Oxygen velocityFuel Gas (ft3) (s/ft2) temp. per ft3 of fuel (ft/s)Acetylene , ,420ºFMapp® , ,301ºFPropane , ,190ºFNatural gas , ,000ºF(Mpls./St.Paul)Hydrogen , ,600ºF
11 Oxygen Gaseous chemical element in air Necessary for lifeMost abundant chemical element in crust of EarthNo color, odor, or tasteDoes not burn, but supports combustionSubstances that do not burn in air will in oxygen
12 Oxygen ProductionTwo commercial processes used in production of oxygenSeparation of water into oxygen and hydrogen by electrolysis of waterSeparation of air into oxygen and nitrogen by liquefying airCommercial oxygen production
15 Gas CylindersCharged with oxygen at pressure of about 2,200 p.s.i. at 70ºFGas temperatureIncrease: gas expands and increases pressureDecrease: gas contracts and reduces pressureSafety device on cylinder valve to blow off oxygen when excess pressureOccurs, oxygen lostDO NOT store where cylinder can be overheated
16 Capacity of Cylinder Three cylinder sizes used for welding and cutting Gas suppliers fill tanks with varying amountsLarge size: 220–244 cubic feet of oxygenFull: 148 to 152 pounds; Empty: 130–133 poundsMiddle size: 110–122 cubic feet of oxygenFull: 89 to 101 pounds; Empty: 79–93 poundsSmall size: 55–80 cubic feet of gasFull: 67 pounds; Empty: 60 pounds
17 Safety PrecautionsTake special care to keep oil and grease away from oxygenWhen using, do not place cylinders where oil might drop on them from overhead bearingsNever use oxygen in pneumatic tools or to start internal combustion enginesNever use oxygen to blow out pipe or hose lines, dust clothes or create head pressure in tank of any kind
18 Safety PrecautionsDo not store oxygen cylinders near acetylene generator, carbide, acetylene, or other fuel-gas cylindersDo not use cylinder as roller or lift it by capKeep cylinders away from welding operation and close cylinder valve when work completedKeep cylinders away from any electrical contact
19 Acetylene Most widely used of all fuel gases Both welding and cuttingGenerated as result of chemical reaction that takes place when calcium carbide comes in contact with waterTests show oxyacetylene flame temperatures up to approximately 6,300ºFVery rapid rate of preheatingBurns with smoky flame, gives off carbon, has peculiar odor
20 Characteristics of an Effective Welding Fuel Gas High flame temperatureHigh rate of flame propagationAdequate heat contentMinimum chemical reaction of flame with base and filler metalAcetylene most closely matches all these requirements and is used for welding purposes.
21 Acetylene Production and Distribution Commercial acetylene made from calcium carbide – referred to as carbideGray, stonelike substanceProduct of smelting coke and lime in electric furnaceSeveral sizes availableDistributed in standard steel drums100 pounds for use in acetylene generators
22 Acetylene Cylinders Constructed differently from oxygen cylinders Free acetylene should not be stored at pressure above 15 p.s.i.Safety solved by packing cylinders with porous material saturated with acetoneAcetone: liquid chemical having property of dissolving or absorbing many times the volume of acetyleneStrong steel container (packed completely full)Handle with care
24 Valve Mechanisms Acetylene drawn off through valve Some cylinders valve located in recessed topOthers valve located on convex topSimpler in construction than oxygen valveDoes not have to stand high pressureOpened only about 1-1/2 turnsCan be turned off quickly in case of fireSafety fuse plugs also provided
25 Capacity of CylinderFull cylinder of acetylene has pressure of about 225 p.s.i.Two sizes used for welding and cuttingLarge size contains 300 cubic feet of acetylene and weighs about 232 pounds when fullSmall size contains 100 cubic feet and weighs 91 pounds when fullTwo special sizes (10 cubic ft. and 40 cubic ft.)Not all acetylene in cylinder can be used
26 Safety Precautions Remember acetylene will burn. Do not leave acetylene cylinders on their sidesStore valve end upStore cylinders in well-protected, ventilated, dry locationAway from highly combustible material or sources of heatKeep valve cap on when not in useRemember acetylene will burn.It will form explosive mixture with air.
27 Safety Precautions Handle acetylene cylinders carefully Use warm (not boiling) water on the valve if it becomes clogged with ice (Never a flame!)Fusible safety plugs melt at boiling point of waterHandle acetylene cylinders carefullyDamages could cause leakageAdvise supplier immediately if acetylene leaks around valve spindle when valve openedClose spindle and move cylinder to outside areaNever tamper with fuse plugs
28 Propane Gas Hydrocarbon present in petroleum and natural gas Used primarily for oxyfuel heating, cutting, soldering and brazingSold and transported in steel cylinders containing from 20 to 100 pounds of liquefied gasAlso supplied by tank car and bulk deliveryOxypropane flame temp less than oxyacetyleneTakes longer to bring steel to melting pointUsed for soldering and alloy brazing
29 Mapp® Gas Liquefied acetylene compound Fuel gas for oxyfuel heating and cuttingStrong smell (aid in discovering leaks)Mixed with oxygen, flame is 5,301ºFHeating and cutting somewhat slowerLower temperatureOverall expenses lower due to reduced handling costs and lower gas costs
30 Mapp® Gas Use as fuel gas for heating and cutting is growing Distributed in bulk or steel cylindersShutoff valve similar to ones on acetylene cylinderLiquefied and stabilized so can be used at pressures as high as 375 p.s.i. at 170ºFExplosive limits lower than acetyleneCan be stored in free state and at high pressures
31 Safety in Handling Mapp® Gas Forms an explosive mixture with airSame general precautions used with handling acetylene cylinders should be observedSafest of industrial fuelsExplosive limits of Mapp® gas vapor in air and oxygen much narrower than acetylene, same as propane and natural gasCan smell it at concentrations as low as 0.01%
32 General Cylinder Handling, Storage, and Operation Safety Regulations1. All portable cylinders used for the storage and shipment of compressed gases shall be constructed and maintained in accordance with the regulations of the U.S. Department of Transportation, 49 CFR Parts 171– Compressed gas cylinders shall be equipped with connections complying with the American National Standard Compressed Gas Cylinder Valve Outlet and Inlet Connections, ANSI B
33 Regulations General Cylinder Handling, Storage, and Operation Safety 3. Compressed gas cylinders shall be legibly marked, for the purpose of identifying the gas content, with either the chemical or the trade name of the gas. Such marking shall be by means of stenciling, stamping, or labeling and shall not be readily removable. Whenever practical, the marking shall be located on the shoulder of the cylinder. This method conforms to the American National Standard Method for Marking Portable Compressed Gas Containers to Identify the Material Contained, ANSI Z
34 Regulations General Cylinder Handling, Storage, and Operation Safety 4. All cylinders with a water weight capacity of over 30 pounds (13.6 kilograms) shall be equipped with means of connecting a valve protection cap or with a collar or recess to protect the valve. 5. Cylinders shall be kept away from radiators and other sources of heat.
35 Regulations General Cylinder Handling, Storage, and Operation Safety 6. Inside of buildings, cylinders shall be stored in a well-protected, well-ventilated, dry location, at least 20 feet from highly combustible materials such as oil or excelsior. Cylinders should be stored in clearly identified assigned places away from elevators, stairs, or gangways. Assigned storage spaces shall be located where cylinders will not be knocked over or damaged by passing or falling objects, or subject to tampering by unauthorized persons. Cylinders shall not be kept in unventilated enclosures such as lockers and cupboards. 7. The valves on empty cylinders shall be closed.
36 Regulations General Cylinder Handling, Storage, and Operation Safety 8. For cylinders designed to accept a valve protection cap, the cap shall always be in place, hand-tight, except when cylinders are in use or connected for use. 9. For fuel-gas cylinder storage inside a building, cylinders, except those in actual use or attached ready for use, shall be limited to a total gas capacity of 2,000 cubic feet or 300 pounds of liquefied petroleum gas. 10. Oxygen cylinders shall not be stored near highly combustible material, especially oil and grease, or near acetylene or other fuel-gas cylinders, or near any other substance likely to cause or accelerate fire.
37 Regulations General Cylinder Handling, Storage, and Operation Safety 11. Oxygen cylinders in storage shall be separated from fuel-gas cylinders or combustible materials (especially oil or grease), a minimum distance of 20 feet or by a noncombustible barrier at least 5 feet high having a fire-resistance rating of at least one-half hour. 12. Cylinders, cylinder valves, couplings, regulators, hoses, and apparatus shall be kept free from oily or greasy substances. Oxygen cylinders or apparatus shall not be handled with oily hands or gloves. A jet of oxygen must never be permitted to strike an oily surface, greasy clothes, or enter a fuel oil or other storage tank.
38 Regulations General Cylinder Handling, Storage, and Operation Safety 13. A cradle, boat, or suitable platform shall be used when transporting cylinders by a crane or derrick. Slings or electric magnets shall not be used for this purpose. Valve-protection caps shall always be in place on cylinders designed to accept a cap. 14. Cylinders shall not be dropped, roughly handled, or struck or permitted to strike each other violently. Rough handling, knocks, or falls are liable to damage the cylinder, the valve, or the safety devices and cause leakage.
39 General Cylinder Handling, Storage, and Operation Safety Regulations15. Cylinder valves shall be closed before cylinders are moved. 16. Cylinder valves shall be closed when work is finished. 17. Valve-protection caps shall not be used for lifting cylinders from one vertical position to another. Bars shall not be used under valves or valve-protection caps to pry cylinders loose when frozen to the ground or otherwise fixed; the use of warm (not boiling) water is recommended. Valve-protection caps are designed to protect cylinder valves from damage.
40 Regulations General Cylinder Handling, Storage, and Operation Safety 18. Unless cylinders are secured on a special truck, regulators shall be removed and valve-protection caps, when provided for, shall be put in place before cylinders are moved. 19. Cylinders shall never be used as rollers or supports, whether full or empty. 20. Cylinders not having fixed hand wheels shall have keys, handles, or nonadjustable wrenches on valve stems while these cylinders are in service. In multiple-cylinder installations only one key or handle is required for each manifold.
41 Regulations General Cylinder Handling, Storage, and Operation Safety 21. Cylinders shall be kept far enough away from the actual welding or cutting operation so that sparks, hot dross, or flame will not reach them, or fire-resistant shields shall be provided. 22. The numbers and markings stamped into cylinders shall not be tampered with. 23. No one shall tamper with safety devices on cylinders or valves.
42 Regulations General Cylinder Handling, Storage, and Operation Safety 24. Cylinders shall not be placed where they might become part of an electric circuit. Contacts with third rails, trolley wires, or the like shall be avoided. Cylinders shall be kept away from radiators, piping systems, and layout tables that may be used for grounding electric circuits, such as for arc welding machines. Any practice such as the tapping of an electrode against a cylinder to strike an arc shall be prohibited. 25. No person, other than the gas supplier, shall attempt to mix gases in a cylinder. No one, except the owner of the cylinder or person authorized by the owner, shall refill a cylinder.
43 Regulations General Cylinder Handling, Storage, and Operation Safety 26. A hammer or wrench shall not be used to open cylinder valves. If valves cannot be opened by hand, the supplier shall be notified. 27. Cylinder valves shall not be tampered with nor should any attempt be made to repair them. If trouble is experienced, the supplier should be sent a report promptly, indicating the character of the trouble and the cylinder’s serial number. Supplier’s instructions as to its disposition shall be followed.
44 Regulations General Cylinder Handling, Storage, and Operation Safety 28. Fuel-gas cylinders shall be placed with valve end up whenever they are in use. Liquefied gases shall be stored and shipped with the valve end up. 29. Safety devices shall not be tampered with.
45 General Cylinder Handling, Storage, and Operation Safety Regulations30. Before connecting a regulator to a cylinder valve, the valve shall be opened slightly and closed immediately. The valve shall be opened while standing to one side of the outlet; never in front of it. Never crack a fuel-gas cylinder valve near other welding work or near sparks, flame, or other possible sources of ignition. 31. Before a regulator is removed from a cylinder valve, the cylinder valve shall be closed and the gas released from the regulator.
46 General Cylinder Handling, Storage, and Operation Safety Regulations32. Nothing that may damage the safety device or interfere with the quick closing of the valve shall be placed on top of an acetylene cylinder when it is in use. 33. If cylinder valves or fittings are found to have leaks that cannot be stopped by closing the valve or fitting, the cylinders shall be plainly tagged and taken outdoors away from sources of ignition. A sign should be placed near the leaky cylinders warning unauthorized personnel not to approach them. The supplier should be promptly notified, and the supplier’s instructions for the return of the cylinders followed.
47 Manifold Distribution Supplies both oxygen and fuel gas to number of work stationsAcetylene manifolds must be equipped with flash arrester to prevent flashback through manifold into cylindersEach cylinder connected to manifold by means of an individual pigtail flash arrester and backcheck valves
53 Acetylene Generators Two general types Calcium carbide dropped into waterWater allowed to drip on carbideCarbide-to-water generators used to produce acetylene gas for welding and cuttingWater absorbs heat given off by chemical reactionGas purified by bubbling through water
55 Acetylene Generators Two classes of generators Low pressure (less than 1 p.s.i.)Medium pressure (1 to 15 p.s.i.)Generating capacities range from30 cubic feet of acetylene per hour for small portable6,000 cubic feet acetylene per hour for medium-pressure generator
56 Required Oxyacetylene Welding Equipment Oxygen regulatorAcetylene regulatorOxygen welding hoseAcetylene welding hoseHose couplingsSingle-purpose cutting torch or welding torchCylinders and cart for portabilityFlash arrestor and check valves (protective equipment)Flint lighter to ignite torch
57 Approved Protective Equipment Installed in OAW system to prevent:Backflow of oxygen into fuel-gas supply systemPassage of flashback into fuel-gas supply systemExcessive back pressure of oxygen in fuel-gas supply system
58 Protective EquipmentFunctions may be combined in one device or provided by separate devicesLocated in main supply line, head of each branch line in manifold system, or at each location where fuel gas withdrawnBackflow protection should be provided to prevent fuel gases from flowing into oxygen systemFlashback protection should be provided to prevent flame from passing into fuel-gas system
60 Pressure RegulatorsReduce high cylinder pressure to relatively low pressure of 0 to 45 p.s.i. used for weldingMaintain pressure without variation during weldingFlame remains steady and uniformTwo pressure gauges mounted on body of regulatorOne shows pressure in cylinder, other pressure of gas being supplied to torch
63 Safety Precautions Inspect all nuts and connections for leaks Before opening valve of cylinder to which regulator has been attached, check pressure adjusting screw is completely releasedNever attempt to connect acetylene regulator to cylinder containing oxygen or vice versaDo not force connections, and check if tightUse regulators only for gas and pressures they are intendedHave regulators repaired only by skilled trained mechanics
65 Regulator Construction Force that opens valve provided by tension of springForce that closes valve provided by high gas pressure from tankWhen two forces balanced, constant flow of oxygen to torch resultsDesignated as single-stage and two-stageSingle-stage regulators used with manifold systems
67 Line Regulator Regulator springs made of good grade of spring steel Diaphragm of brass, sheet spring steel, stainless steel or rubberIndividual oxygen and acetylene regulators required at each station when serviced by line gas systemSmaller than cylinder regulatorsNot subject to high cylinder pressure
69 Welding TorchesApparatus for mixing oxygen and acetylene in proportions to carry on welding operationProvides handle so welder can hold and direct the flameTwo inlet gas connections: oxygen and acetyleneValve controls volume of gas passing throughWide range of welding tip sizes
70 Two Types of Oxyacetylene Welding Torches InjectorAcetylene carried through torch and tip at low pressure by suction forceHigher oxygen pressure passing through small orifice of injector nozzleMixing head and injector integral part of tipEqual (balanced-pressure)Both gases delivered at equal pressuresMixing head separate replaceable unit in body of torch
80 Hose Construction Three layers of construction Inner lining of high grade gum rubberMiddle layer of rubber-impregnated fabricOutside layer made of colored vulcanized rubberPlain or ribbedColor used for identificationGreen for oxygenRed for acetyleneBlack for inert gas and air
81 Hose SizeDifferent sizes for different types of welding and cutting operationsDepends on amount of gas required, length of hose used, and pressures neededSizes available: 3/16, 1/4, 3/8, and 1/2 inch3/16 I.D. (inside diameter) hose very flexible, and light; used for light welding1/2 I.D. used for heavy cuttingCan be single or doubleDouble actually two pieces joined by web
83 Care of Hose Always use hose to carry only one kind of gas Test hose for leaks frequently by immersing hose at normal working pressure under waterClamp all hose connections or fasten them securely to withstand pressure of 300 p.s.i. without leakageRepair or replace all hose showing leaks, burns, worn places, or other defects
84 Care of Hose Do not attempt to repair hose with tape Handle hose carefully when weldingAvoid dragging on greasy floorAvoid contact with flame or hot metalProtect from falling articles or being stepped onShould not be kinked sharplyRoll up hose and hang it out of the way at the end of day or job
86 Filler Rod Most gas welding done with filler rod Provides additional metal to form larger weld beadMany diameters, available in bundles of 50 or 100 pounds and boxes up to 300 pounds net weight36 inches longSteel rods copper coated to prevent rustingSome aluminum rods flux coatedBoth steel and aluminum 28 inches long
87 American Welding Society Set up AWS classification numbers for steel gas-welding rodsRG-65, RG-60 and RG-45R indicates welding rod and G indicates gas weldingNumbers designate approximate tensile strength of weld metal (thousand pound per square inch)Example: RG-60 is welding rod with tensile strength of approximately 60,000 p.s.i.
88 Gas Rod Characteristics Produce welds of varying tensile strengths depending upon nature of base metalWelds made on alloy steels produce weld composition between base metal and filler metalCan be used in all positionsLimited only by skill of welder
89 Class RG-65 Gas Welding Rod Low alloy steel compositionUsed to weld sheet, plate, tubes and pipes of carbon and low alloy steelsProduce welds in range of 65,000 to 75,000 p.s.i.
90 Class RG-60 Gas Welding Rod Low alloy compositionUsed to weld carbon steel pipes for power plants, process piping, and other severe service conditionProduce welds in range of 50,000 to 65,000 p.s.i.Used extensively as general-purpose rodHighly satisfactory welds in carbon steels, low alloy steels and wrought iron
91 Class RG-45 Gas Welding Rod General-purpose welding rodsLow carbon steel compositionUsed to weld mild steels and wrought ironProduce welds in range of 40,000 to 50,000 p.s.i.
92 FluxesCleaning agent used to dissolve oxides, release gases, and slag and cleanse metal surfaces for welding, soldering, and brazingFunction of fluxCombine with oxides to form fusible slag having melting point lower than metalFlows away from weld areaNo one flux satisfactory for all metals
93 FluxesMelting point of flux must be lower than either metal or oxides formedAvailable as dry powders, pastes, thick solutions, and coatings on filler rodDiffer in composition and way they work according to metals with which they are used
94 Oxyhydrogen Welding (OHW) Form of gas welding once used extensivelyToday have limited useFlame produced by burning two volumes of hydrogen with one volume of oxygenTemperature of ~ 4,100ºFAlmost invisibleSimilar equipment to that used for oxyacetylene weldingNeed regulator specifically designed for hydrogen
95 Oxyhydrogen Welding (OHW) Relatively low flame temperatureUsed principally in welding metals with low melting pointsUsed extensively in welding of leadThicknesses of lead up to 1/4 or 3/8 inchNo deposit of carbon
96 Fuel Gases Propane, butane, city gas, and natural gas Can use standard oxyacetylene welding equipmentNeed special fuel gas regulatorVariety of suitable heating and cutting tips availableNot suitable for welding ferrous materialsOxidizing nature of flame and relatively low flame temperatureUsed extensively for manual and mechanized brazing and soldering operations
97 Air-Acetylene Welding (AAW) Air 4/5 nitrogen by volumeNeither fuel gas nor supporter of combustionWith acetylene gives lower flame temperaturesTotal heat content also loweredTorches designed to draw in proper quantity or air from atmosphereAcetylene flows through torch 2 to 15 p.s.i.Supplied from small cylinderApplications: plumbing and electrical industry
103 Safety Equipment Protective Clothing and Gloves HazardsSparks, molten bits of metal and hot scaleProtect body by apron, shop coat, or coveralls that resist fireHigh-top shoes and hard hatsGlovesMade from nonflammable materialLight welding – ordinary canvas glove with cuffKeep free from grease and oil
104 Safety Equipment Check Valves Permit forward flow of gas and closes when gas begins to flow in reverse directionOne required for acetylene hose and one for oxygen hoseMay be attached to torch or to regulatorsReverse flow can be caused by blocked torch tip, excess gas or oxygen pressure, lack of pressure or unsafe start-up or shut-down
105 Flashback Arrestors Generally made of sintered metal alloy Prevents flame from moving upstream of arrestorDoes not protect torch or tipNeither does check valveBest way to assure that accidents don’t happen is to follow all safety operating procedures.
108 General Safety Operating Procedures Protective equipment, hose, and regulators:Equipment installed and used only in service for which approved and recommended by manufacturer.Approved protective equipment installed in fuel-gas piping.Hose for oxy-fuel gas service shall comply with Specification for Rubber Welding Hose, 1958, Compressed Gas Association and Rubber Manufacturers Association.
109 General Safety Operating Procedures When parallel lengths of oxygen and acetylene hose taped together, not more than 4 out of 12 inches shall be covered by tape.Hose connections shall comply with Standard Hose Connection Specifications, 1957, Compressed Gas Association.Hose connections shall be clamped so they can withstand twice the pressure without leakage (oil-free air or inert gas used for test).
110 General Safety Operating Procedures Hose showing leaks, burns, worn places, or other defects rendering it unfit for service shall be repaired or replaced.Pressure-reducing regulators shall be used only for gas and pressures for which they are intended.Use skilled mechanics who have been properly instructed to repair regulators or parts of regulators that need repair.
111 General Safety Operating Procedures Gauges on oxygen regulators shall be marked Use No Oil.Union nuts and connections on regulators shall be inspected before use to detect faulty seats that may leak gas when regulators attached to cylinder valves.