weld cut braze

8/6/2019 Weld Cut Braze

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Welding, Cutting and Brazing

NOAA Web based traininghttp://www.labtrain.noaa.gov/default.htm


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Introduction

Welding, cutting, and brazing are exceptionally dangerous.Compressed gases are often used to create an extremely hotflame. Different welding techniques can cause other hazards.

The welder can be injured or cause damage to the work area innumerous ways including fire, explosion, gas, and fume hazards.

Good work practices must be followed in all welding, cutting, andbrazing techniques to prevent injuries, fires, and explosions.

This module covers the following sections:

Compressed Gases

General RequirementsOxygen-Fuel Gas Welding and Cutting

Arc Welding and CuttingResistance Welding.


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Introduction - Objectives

At the end of this Welding, Cutting, and Brazing module, you shouldbe able to:

Understand the general requirements concerningcompressed gasesIdentify the general safety requirements for all types of weldingUnderstand the general characteristics for the various types of weldingIdentify the specific safety requirements for:

Oxygen-fuel gas welding and cutting Arc welding and cuttingResistance welding.


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Compressed Gases -Introduction

Many welding and cutting operationsrequire the use of compressed gases. Tounderstand these hazards, we mustunderstand that compressed gases arestores of potential energy. It takes energy tocompress and confine the gas. That energy

is stored until purposely released to performuseful work or until accidentally released bycontainer failure or other causes.

Some compressed gases, acetylene for example, have high flammabilitycharacteristics. Flammable compressedgases, therefore, have additional storedenergy besides simple compression-release energy. Other compressed gases,such as nitrogen, have simple asphyxiatingproperties. Some compressed gases, suchas oxygen, can augment or compound firehazards.


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Compressed Gases -Introduction

Compressed gases are regulated by many standards.Two primary standards are:

29 CFR 1910 Subpart Q Welding, Cutting, andBrazing covers the handling, storage, and use of compressed gases, such as oxygen- fuel gas, whenthey are consumed in the welding process.

29 CFR 1910 Subpart H Hazardous Materials,1910.101 - 1910.105 covers the generalrequirements for the handling, storage, and use of compressed gases other than those consumed in thewelding process. The General Requirements section of 1910.101 is concerned with:

Cylinder inspection to include required markingsHandling, storage, and utilizationInstallation and maintenance of safety relief devices


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Compressed Gases GeneralRequirements

In addition to the Occupational Safety and Health Administration (OSHA) regulations found in Subparts Qand H of 29 CFR 1910 there are other applicableregulations and information. These include theDepartment of Transportation (DOT) regulations, and theCompressed Gas Association (CGA) pamphlets. These

sources provide the requirements for the generalcategory of compressed gases and certain specificcompressed gases.

An important aspect of these regulations is the safety of compressed gas storage containers. Specificrequirements are made of employers for the inspection of the compressed gas cylinders. Visual inspections arerequired to ensure that the cylinders are safe. The nextpage will go into more detail regarding visualexaminations of compressed gas storage containers andthe safety of these containers.


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Employees shall determine that compressed gas cylinders under their control are in a safe condition to the extent that this can be determined byvisual inspection. Visual and "other" inspections are required, but "other"inspections are not defined. These inspections must be conducted asprescribed in the Hazardous Materials Regulations of the DOT contained in49 CFR Parts 171-179 and 14 CFR Part 103. Where these regulations are

not applicable, these inspections shall be conducted in accordance withCGA Pamphlets C-6 and C-8.

According to DOT regulations: "A cylinder that leaks, is bulged, hasdefective valves or safety devices, bears evidence of physical abuse, fire or heat damage, or detrimental rusting or corrosion, must not be used unless itis properly repaired and requalified as prescribed in these regulations."

The term "cylinder" is defined as a pressure vessel designed for pressureshigher than 40 psia (pounds per square inch absolute) and having a circular cross section. It does not include a portable tank, multi-unit tank car tank,cargo tank, or tank car.


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DOT Marking RequirementsEach DOT marking identified on this page must appear on all cylindersand must be maintained so that it is legible.

The circled numbers on the graphic correspond to the numbereddefinitions provided below.

1. ICC or DOT marking may appear:"ICC": Pre-existing marking " ICC 3AA2015""3AA" - specification from 49 CFR 178.37"2015" - marked service pressure."DOT": new manufacture marking must read "DOT. 49 CFR 171.14."

2. "A35798641": Serial number - no duplications permitted with anyparticular symbol- serial number combinations.

3. "PST": Symbol of manufacturer, user, or purchaser.4. "6 56": date of manufacture. Month and year. " ": disinterested

inspector's official mark.5. "+": indicates cylinder may be 10% overcharged per 49 CFR 173.302(c).6. "5-61" and "5-66": Retest dates.7. "*" (5 pointed star 0: indicates ten year retest interval.

See 49 CFR 173.34(e)(15).


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In addition to the guidance in the OSHA regulations,Compressed Gas Association (CGA) pamphletsdetermine requirements for handling, storing, andusing compressed gases in cylinders, portable tanks,rail tankcars, and motor vehicle cargo tanks. They alsoidentify how to install and maintain required pressure

relief valves on these containers.The in-plant handling, storage, and utilization of allcompressed gases in cylinders, portable tanks, railtankcars, and motor vehicle cargo tanks shall be inaccordance with CGA Pamphlet P-1.

Compressed gas cylinders, portable tanks, and cargotanks shall have pressure relief devices installed andmaintained in accordance with CGA Pamphlets S-1.1and S-1.2.


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Compressed Gases SpecificGases

The OSHA regulations contain some sectionsregulating specific compressed gases, including:

AcetyleneHydrogenOxygenNitrous oxide

Anhydrous ammoniaLiquefied petroleum gases.

Other compressed gases are in common useand fall under regulation Subpart H, 1910.101.Examples include chlorine, vinyl chloride, sulfur dioxide, methyl chloride, hydrogen sulfide,ethane, compressed air, and nitrogen.


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General Requirements - Introduction

The General Requirements section,1910.252 provides information aboutprotecting individuals during welding,cutting, or brazing operations. This sectioncontains the three topics listed on the left.

Protection of the individual includesmeasures taken to:

Prevent fires from occurringEliminate fires if they occur Protect personnel by providing appropriateclothing and equipmentProtect personnel when welding or cuttingcontainersProtect personnel working in confinedspaces.


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General Requirements FirePrevention and Protection

Fire prevention and protection include basicprecautions, special precautions, and safetyprecautions for the unique situations involvingwelding and cutting containers, and welding inconfined spaces.

The basic precautions for fire prevention in welding,cutting, and brazing focus on removal of firehazards. They include the following:

If the object to be welded or cut cannot readily bemoved, all movable fire hazards in the vicinity shallbe taken to a safe place

If the object to be welded or cut cannot be movedand if all the fire hazards cannot be removed, thenguards shall be used to confine the heat, sparks,and slag, and to protect the immovable fire hazardsIf the above requirements cannot be met, thenwelding and cutting shall not be performed.


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Complying with the basic precautions for prevention of fires in welding is notenough. Special precautions must also be taken. These include having theproper fire extinguishing equipment available and having fire watcherspresent, if needed.

Suitable fire extinguishing equipment shall be maintained in a state of readiness for instant use. Such equipment may consist of pails of water,

buckets of sand, hoses, or portable extinguishers depending upon the natureand quantity of the combustible material exposed.

Fire watchers are required whenever welding or cutting is performed inlocations where more than a minor fire might develop, or where any of thefollowing conditions exist:

Appreciable combustible materials, in building construction or contents,closer than 35 feet to the point of operation

Appreciable combustible materials more than 35 feet away, but are easilyignited by sparks.

A fire watch shall be maintained for at least a half hour after completion of welding or cutting operations to detect and extinguish possible smolderingfires.


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Even if all of the special precautions have been taken, there arestill certain situations in which welding, cutting, or brazing are notallowed.

Cutting or welding shall not be permitted in:

Areas not authorized by managementBuildings with impaired sprinkler systemsThe presence of explosive atmospheres (mixtures of flammablegases, vapors, liquids, or dusts with air)Locations where explosive atmospheres may develop, such as:

Inside unclean or improperly prepared tanks or equipment whichhave previously contained such materials (flammable gasses,vapors, liquids, or dusts)

Areas with an accumulation of combustible dusts.


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Welding and cutting certain containers mayconstitute a special situation that requiresadditional safety precautions beyond basic andspecial precautions.

No welding, cutting, or other hot work shall be

performed on used drums, barrels, tanks, or other containers until they have been thoroughlycleaned.

Cleaning must remove all flammable materialspresent or any substances such as greases, tars,acids, or other materials which might produceflammable or toxic vapors when subjected to heat.

Any pipeline or connections to the drum or vesselbeing welded shall be disconnected or blanked.


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Working in confined spaces involves additional safetyprecautions beyond the basic and specialprecautions.

A confined space is defined in 29 CFR 1910.252 as arelatively small or restricted space such as a tank,boiler, pressure vessel, or small compartment of aship.

Adequate ventilation is a prerequisite to work inconfined spaces.

When welding or cutting is being performed in anyconfined space, the gas cylinders and weldingmachines shall be left on the outside. When arcwelding is to be suspended for any substantial periodof time, such as during lunch or overnight, allelectrodes shall be removed from the holders. Theholders shall be carefully located so that accidentalcontact cannot occur and the machine shall bedisconnected from the power source.


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When suspending gas welding or cutting operations,eliminate the possibility of gas escaping through thenozzle by closing the torch valves. The gas supply tothe torch must be positively shut off at some pointoutside the confined area whenever the torch is notto be used for a substantial period of time, such as

during lunch hour or overnight. Where practicable,the torch and hose shall also be removed from theconfined space.

Where welders must enter a confined space througha manhole or other small opening, means shall beprovided for quickly removing them in case of emergency. An attendant with a pre-planned rescueprocedure shall be stationed outside to observe thewelder at all times and shall be capable of puttingrescue operations into effect.


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General Requirements Protectionof Personnel

Protection of personnel focuses on protectingthe welder from hazards other than generalfire protection. Protection of personnel inwelding or cutting operations can involve fallprotection, eye protection, and protectiveclothing.

When working at heights, a welder or helper working on platforms, scaffolds, or runwaysshall be protected against falling through theuse of:

RailingsSafety beltsLife linesSome equally effective safeguards.


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Welding, cutting, or brazing operations conducted without proper eyeprotection create a serious eye injury hazard.

Helmets and hand shields shall be arranged to protect the face, neck,and ears from direct radiant energy from the arc. They shall be usedduring all arc welding or arc cutting operations, excluding submerged arc

welding. helpers or attendants shall be provided with proper eyeprotection.

Helmets and hand shields shall be made of a material which is aninsulator for heat and electricity. Helmets, shields, and goggles shall notbe readily flammable and shall be capable of withstanding sterilization.

Where the work permits, the welder should be enclosed in an individualbooth or in a non-combustible screen painted with a finish of lowreflectivity such as zinc oxide (an important factor for absorbing ultra-violet radiation) and lamp black. Booths and screens shall permitcirculation of air at floor level. People adjacent to the welding areas shallbe protected from the rays by non-combustible or flameproof screens or shields or shall be required to wear appropriate goggles.


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Because of the danger of burns and clothing catching fire,employees exposed to the hazards created by welding,cutting, or brazing operations shall be protected bypersonal protective equipment in accordance with therequirements of 29 CFR 1910.132.

Appropriate protective clothing required for any weldingoperation will vary with the size, nature, and location of thework to be performed. Welders should always selectclothing materials which will provide maximum protectionfrom sparks and hot metal.

The shirt should have full sleeves, no pockets, and shouldbe worn outside the trousers with collar buttoned. Thetrousers should have no cuffs and should extend welldown to the safety shoes. Safety shoes and fire-resistantgauntlet gloves are also needed.


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General Requirements HealthProtections and Ventilation

Regardless of the precautionary measures taken, some materialsrequire special ventilation because they are particularlyhazardous. Mechanical ventilation and other specific controlmeasures are required when welding or cutting is done with thefollowing materials:

Fluorine compoundsZincLeadBerylliumCadmiumMercuryCleaning compoundsStainless steel


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Oxygen-Fuel Gas Welding andCutting - Introduction

In this Welding, Cutting, and Brazing module,three specific types of welding are covered.These are listed below:

Oxygen-fuel gas welding and cutting

Arc welding and cuttingResistance welding.

This section deals specifically with oxygen-fuelgas welding and cutting. The Oxygen-Fuel GasWelding and Cutting section is based on 29 CFR1910.253. This section provides information

about the five topic areas that are listed to the left.Each topic is presented with guidance informationso that you will be able to prevent accidents andpromote work safety when welding or cutting.


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General Requirements of Oxygen-Fuel Gas Welding andCutting, 29 CFR 1910.253, focuses on using acetylene safely.

Under no conditions shall acetylene be generated, piped(except in approved cylinder manifolds), or utilized at apressure in excess of 15 pounds per square inch gauge (psig)or 30 pounds per square inch absolute (psia). The 30 psia limitis intended to prevent unsafe use of acetylene in pressurizedchambers such as caissons, underground excavations, or tunnel construction.

Absolute pressure is equal to gauge pressure plusatmospheric pressure, which at sea level averages 14.7pounds per square inch (psi). Thus, at sea level, a gaugepressure reading of 15 psi is equal to an absolute pressure of 29.7 psi.

This requirement is not intended to apply to storage of acetylene dissolved in a suitable solvent in cylindersmanufactured and maintained according to DOT requirements,or to acetylene for chemical use.


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When using acetylene, experience indicates that 15psig is generally acceptable as a safe upper pressurelimit. Using acetylene at pressures in excess of 15psig pressure (or about 30 psia pressure) is ahazardous practice.

Free gaseous acetylene is potentially unstable atpressures above 15 psig and could decompose withexplosive violence.

The decomposition characteristics of acetylene gas

are avoided by keeping the gas in liquid solution andstoring it in cylinders of unique construction


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Internally, acetylene cylinders are not designedlike other kinds of compressed gas cylinders.

Acetylene cylinders are never hollow. Thesecylinders contain a porous, calcium silicate filler and a suitable solvent, usually acetone, because,under pressure, acetylene by itself is unstable.

Acetone is used because it has the ability toabsorb over 400 times its own volume of acetylene at 70 F.


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Calcium Silicate

Millions of microscopic pores make up the calciumsilicate filler. Although it appears to fill the steelshell, approximately 90 percent of the filler's volumeconsists of "pore space" for holding and evenlydistributing the acetylene/acetone solution.

When absorbed in this filler, the acetylene is dividedinto such small units that, should acetylenedecomposition take place in one pore, the heatreleased is not enough to raise the temperature of the acetylene in surrounding pores to the pointwhere it, too, will decompose.

Acetylene is usually supplied in cylinders whichhave a capacity of up to 300 cubic feet of dissolvedgas under pressure of 250 psig at 70 F.


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Oxygen-Fuel Gas Welding andCutting - Cylinders

Regardless of the interior construction of the cylinders, allportable cylinders used for the storage and shipment of compressed gases shall be constructed and maintained inaccordance with the regulations of the U.S. Department of Transportation, 49 CFR Parts 171-179.

When using or handling cylinders and containers, it isimportant to know about:Cylinder approval and markingStorage of cylindersOperating procedures.

Compressed gas cylinders shall be legibly marked, for thepurpose of identifying the gas content, with either thechemical or trade name of the gas. Such marking shall beby means of stenciling, stamping, or labeling, and shallnot be readily removable. Whenever practical, the markingshall be located on the shoulder of the cylinder.


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Appropriate marking not only enables proper use, but also assists in proper storage. The following information generally applies to all cylinders:

Cylinders shall be kept away from radiators and other sources of heatInside of buildings, cylinders shall be stored in a well-protected, well-

ventilated, dry location, at least 20 feet (6.1 m) from highly combustiblematerials. Cylinders should be stored in assigned places away fromelevators, stairs, or gangways, or other areas where they might be knockedover or damaged by passing or falling objects, or subject to tampering

Empty cylinders shall have their valves closedValve protection caps, where the cylinder is designed to accept a cap, shall

always be in place, hand-tight, except when cylinders are in use or connected for use. The valve protection cap is designed to take the blow incase the cylinder falls.

Additional requirements exist for the storage of fuel gas and oxygencylinders.


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Fuel Gas Cylinders - StorageRequirements

Inside a building, stored cylinders shall belimited to a total gas capacity of 2,000 cubicfeet (56 m3) or 300 pounds of liquefiedpetroleum gas. This limitation does not apply

to cylinders that are in actual use or areattached ready for use.

Acetylene cylinders shall be stored valve endup. If the cylinder is on its side, acetone may

leak out and create a dangerous condition.


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Ox ygen Cylinders

Oxygen cylinders in storage shall be separated from fuel-gascylinders or combustible materials (especially oil or grease), aminimum distance of 20 feet (6.1 m) or by a non-combustible barrier at least 5 feet (1.5 m) high having a fire-resistance rating of at leastone-half hour.

This requirement is intended to reduce the possibility of any firesupport when a fire occurs among the fuel gas storage.


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The potential dangers related to cylinders containingcompressed gases require that cylinders be stored andoperated properly. Operation must emphasize the absence of oily or greasy substances. Follow these rules of operation:

Cylinders, cylinder valves, couplings, regulators, hose, andapparatus shall be kept free from oily or greasy substancesOxygen cylinders or apparatus shall not be handled with oilyhands or gloves

A jet of oxygen must never be permitted to strike an oilysurface, greasy clothes, or enter a fuel oil or other storagetank.


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The valve outlet and regulator are two criticalcomponents of compressed gas cylinders thatmust be used properly.

Valve protection caps protect the valve fromdamage and oil and grease. The valve-protectioncap shall not be used for lifting cylinders from onevertical position to another. The cap mayaccidentally and suddenly come loose.

Should a cylinder without a cap fall or be knockedover, the valve may be damaged or sheared off,causing a sudden release of pressure.

If the valve outlet of a cylinder becomes cloggedwith ice, thaw with warm not boiling water.


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Like the valve outlet, the regulator must be carefullyprotected.

Unless cylinders are secured on a special truck,regulators shall be removed and valve-protectioncaps, when provided for, shall be put in place before

cylinders are moved.Cylinders not having fixed hand wheels shall havekeys, handles, or non-adjustable wrenches on valvestems while these cylinders are in service.

Unless connected to a manifold, always attach aregulator to the compressed gas cylinder before use.Make certain that the regulator is compatible for theparticular gas and service pressure.

Make sure the regulator is clean and has a clean filter installed in the inlet nipple.


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Before attaching the regulator, remove the protectivecap from the cylinder. Stand to one side of the cylinder.Open the cylinder valve slightly for an instant, and thenclose it. This "cracking" of the cylinder valve will cleanthe valve of dust or dirt which may have accumulatedduring storage. Dirt can damage critical parts of aregulator, and may cause a fire or explosion.

Before a regulator is removed from a cylinder valve,the valve shall be closed and the gas released from theregulator.

An acetylene cylinder valve shall not be opened morethan one and one-half turns of the spindle. This permitsadequate flow of acetylene and allows ready closing of the valve in an emergency situation.


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Ox ygen-Fuel Gas Welding andCutting - Manifolding of Cylinders

Sometimes when welding, a portable cylinder is not used asthe source of gas. A service pipe system can be used toprovide a manifolding effect. Manifolding is the gathering of multiple-line fluid inputs into a single intake chamber. Inother words, the combining of gases needed for welding.This can be accomplished through the use of portable outlet

headers. Each header will control the flow of a particular gas. Portable outlet headers (shown in purple) consist of thenozzle and hoses that can be connected to a portablecylinder or a service pipe.

Portable outlet headers shall not be used indoors except for temporary service where the conditions preclude a directsupply from outlets located on the service piping system.

Each outlet on the service piping from which oxygen or fuelgas is withdrawn to supply a portable outlet header shall beequipped with a readily accessible shut-off valve (shown inred in the figure).


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Ox ygen-Fuel Gas Welding andCutting - Manifolding of Cylinders

Each service outlet on portable outlet headersshall be provided with a valve assembly thatincludes a detachable outlet seal cap (shown inyellow), chained or otherwise attached to thebody of the valve.

The primary reasons for using a seal cap are toprotect the outlet pipe thread from damage andto prevent the deposit of oil or grease on thethreads.

Many times the caps are not used. Failure touse the seal cap can result in damage tothreads and ground seals. This can cause leakyconnections


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Ox ygen-Fuel Gas Welding andCutting - Service Pipe Systems

Service piping systems must meet all design andinstallation safety requirements.

Pipe shall be at least Schedule 40 and fittings shall beat least standard weight in sizes up to and including 6-inch nominal. Schedule 40 pipe is standard black iron

pipe which has a working pressure of up to 125 psi andis always tested before use. Problems might arise whenline extensions are made with other types of pipe or aluminum tubing. Therefore, a close inspection isnecessary.

There are special requirements for service pipe

systems when using oxygen or acetylene.

Oxygen

Acetylene or Acetylene Compounds


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Ox ygen When oxygen is supplied to a service piping systemfrom a low pressure oxygen manifold without an interveningpressure regulating device, the piping system shall have aminimum design pressure of 250 psig. A pressure regulatingdevice shall be used at each station outlet when the connectedequipment is for use at pressures less than 250 psig.

A cetylene or A cetylene Compounds Piping for acetylene or acetylenic compounds shall be steel or wrought iron. Unalloyedcopper shall not be used for acetylene or acetylenic compoundsexcept in listed equipment. Under certain conditions, acetyleneforms explosive compounds with copper (as well as silver and

mercury).


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Now that we understand material and designrequirements, lets consider the installation of aservice pipe system.

All piping shall be run as directly as practical. Itwill be protected against physical damage withproper allowance for expansion, contraction,

jarring, and vibration.

Pipe laid underground in earth shall be locatedbelow the frost line and protected againstcorrosion.

After assembly, piping shall be thoroughly blownout with air, nitrogen, or carbon dioxide toremove foreign materials. For oxygen piping,only oil-free air, oil-free nitrogen, or oil-freecarbon dioxide shall be used


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Low points in piping carrying moist gas shall be drained into drippots constructed so as to permit pumping or draining out thecondensate at necessary intervals. Drain valves for this purposeshall have outlets closed with screw caps or plugs.

Piping from overhead lines shall have drip pots at each station.

These drip pots either have a plug or petcock on the bottom.Underground installations have no draining system.

Open end valves or petcocks shall be used. However, drip potslocated out of doors, underground, and not readily accessible, maybe controlled by valves if they are equipped with a means tosecure them in the closed position.

Pipes leading to the surface of the ground shall be cased or jacketed where necessary to prevent loosening or breaking. Pipesleading to the surface from underground lines have to be securedto prevent breaking or to avoid other damage to them.


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Another important consideration for undergroundpiping is protection against corrosion.Underground pipe and tubing and outdoor ferrouspipe and tubing shall be covered or painted with asuitable material for protection against corrosion.

Once installation is completed, piping systemsshall be tested and proved gas tight at 1 timesthe maximum operating pressure, and shall bethoroughly purged of air before being placed inservice.

The material used for testing oxygen shall be oilfree and non-combustible. Flames shall not beused to detect leaks.


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Ox ygen-Fuel Gas Welding andCutting - Pipe System Protection

The entire service pipe systemmust be protected against build-upof excessive pressure and leaks.

This protection is accomplishedwith:

Protective equipmentRegulatorsProper hose and hose

connections.


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Protective equipment is dividedinto the two categories listedhere.

Pressure Relief DevicesPiping Protective Equipment


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Pressure Relief Devices

Service piping systems shall be protected bypressure relief devices set to function at notmore than the design pressure of thesystems. In addition, the pressure relief device should discharge upwards to a safelocation.

Pressure relief valves are required in fuel-gaspiping systems to prevent excessive pressurebuild up within the system.

Relief valves will vent automatically at presetpressures or may be manually operated torelieve pressure in the system.


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Piping Protective Equipment

Approved protective equipment shall be installed in fuel-gas pipingto prevent:

Backflow of oxygen into the fuel-gas supply systemPassage of a flash back into the fuel-gas supply system

Excessive back pressure of oxygen in the fuel-gas supply system.

The three functions of the protective equipment may be combinedin one device or may be provided by separate devices.

The protective equipment in fuel-gas piping systems shall be

located either at the main supply line, at the head of each branchline, or at each location where fuel-gas is withdrawn. Protectiveequipment placed at the main supply provides the best protection.Go to the next page to see a visual comparison of the threelocations for safety devices.


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Piping Protective Equipment

Protective equipment canbe located in the mainsupply line with one checkvalve installed before eachoutlet for the greatestprotection, as in Figure 1,or at the head of eachbranch line plus checkvalves at each outlet, as inFigure 2, or at eachlocation where fuel-gas iswithdrawn with checkvalves at each outlet, as inFigure 3.


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Another method of controlling pressure involves the use of pressure-reducing regulators. Pressure-reducing regulators shall beused only for the gas and pressures for which they are intended.

When regulators or parts of regulators, including gages, needrepair, the work shall be performed by skilled mechanics who havebeen properly instructed. Most production shops do not have theproper equipment to make repairs. For any equipment repairs or if there are questions about performance reliability, contact themanufacturer.

Gages on oxygen regulators shall be marked "USE NO O IL."


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In addition to using release devices, the system must be designed, usingproper hoses, to protect against leaks. The Oxygen hose is green and hasa right-hand threaded nut for connecting to the torch. The Acetylene fuelgas hose is usually red (sometimes black) and has a left-hand threadednut for connecting to the torch.

Hose and hose connections shall be clamped or otherwise securelyfastened in a manner that will withstand, without leakage, twice thepressure to which they are normally subjected in service, but in no caseless than a pressure of 300 psi. Oil-free air or an oil-free inert gas shall beused for the test.

Hoses showing leaks, burns, worn places, or other defects rendering itunfit for service shall be repaired or replaced. When inspecting hoses, look

for charred sections close to the torch. These may have been caused byflash-back. Also check that hoses are not taped up to cover leaks.


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A rc Welding and Cutting -Introduction

The second specific type of weldingdiscussed in this module is Arc Weldingand Cutting. This Arc Welding and Cuttingsection provides information about the

three topic areas that are listed to the left.The information presented here willprevent accidents and promote worksafety when undertaking arc welding or

cutting operations.


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In the arc welding process, an electric current passing through thewelding rod or electrode is forced to jump or arc across a gap. Theresulting arc produces the intense heat necessary for the welding or cutting operation.

Arc welding is used to fabricate nearly all types of carbon or alloy

steels, the common nonferrous metals, and is indispensable in therepair and reclamation of metallic machine parts.

Arc cutting is primarily used for rough cuts or for scrapping becauseof the uneven cut that results. It has also been used for underwater cutting in salvaging operations.

While most precautions and safe practices are common to oxy-fuelgas welding, there are some that are unique to either gas or arcwelding.


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Shielding is one of the unique requirements of arc welding.

Experience has shown that welds will havebetter chemical and physical properties if the air can be kept away from the weld puddle. Such

gases as oxygen, hydrogen, and nitrogen, alongwith water vapor (moisture) all tend to reduce thequality of the weld. Dirt, dust, and metal oxides(contaminants) also reduce the weld quality.

Shielding of the arc preserves the integrity of theweld joint. Shielding is provided either by:

Decomposition of the electrode covering,known as flux A gas (or gas mixture) which may or may not

be inert.


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Arc welding and cutting involves a variety of processes. Some of themore common processes are listed below.

Shielded Metal-Arc Welding (SMAW)Gas Metal Arc Welding (GMAW)

Gas Tungsten Arc Welding (GTAW)Flux Cored Arc Welding (FCAW)Submerged Arc Welding (SAW)

Arc CuttingPlasma Arc Cutting (PAC)

Air Carbon-Arc Cutting (AAC) Arc Gouging


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Shielded Metal- A rc Welding(SM A W)

Shielded metal-arc welding is the most widelyused type of arc welding, commonly referred toas "stick" welding. In this process, coalescence

is achieved by heating with an electric arcbetween a covered (or coated) electrode and thework surface. Shielding is provided bydecomposition of the electrode covering, known

as the flux, while filler metal is obtained from theelectrode's metal core.


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Gas Metal A rc Welding (GM A W)

Gas metal arc welding is commonly known as"MIG" welding. In the gas metal arc weldingprocess, coalescence is achieved by the heat of an electric arc maintained between the end of anelectrode and the work surface. Shielding of thearc is provided by a gas (or gas mixture) whichmay or may not be inert. The electrode is fedcontinuously to the weld where it is melted in theintense heat of the arc and deposited as weldmetal.


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Gas Tungsten A rc Welding(GT A W)

Gas tungsten arc welding is commonlyknown as "T IG" welding. In gas tungstenarc welding, coalescence is achieved bythe arc and electrode method except thatthe tungsten electrode is not consumed.Shielding is provided by an inert gas. This

process produces high precision welds.


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Flu x Cored A rc Welding (FC A W)

Flux cored arc welding is a process whichproduces coalescence by means of an arcbetween a continuous consumableelectrode and the work surface. Shieldingis provided by flux contained within thetubular electrode. Additional shielding may

be obtained from a gas or gas mixture.


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Submerged A rc Welding (S A W)

In submerged arc welding, coalescence is produced bythe heat of an arc between a bare metal electrode andthe work surface. The arc is shielded by a blanket of granular, fusible flux. The tip of the electrode and the

welding zone are surrounded and shielded by the moltenflux and a layer of unused flux in the granular state. Inthis process, there is no visible evidence of the passageof current between the electrode and the work surface.This eliminates the sparks, spatter, and smoke ordinarily

seen in other arc welding processes. Fumes are stillproduced, but not in quantities generated by other processes.


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A rc Cutting

Arc cutting is the general process in whichthe cutting or removal of metals is done bymelting with the heat of an arc between anelectrode and the base metal.


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Plasma A rc Cutting (P A C)

In plasma arc cutting, the metal is cut bymelting a localized area with a constrictedarc and removing the molten material witha high velocity jet of hot, ionized gas.


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A ir Carbon- A rc Cutting ( AA C)

Air carbon-arc cutting is a type of arccutting in which the metal is cut by meltingwith the heat of an arc, with use of an air stream to facilitate cutting.


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A rc Gouging

Arc gouging is an application of arc cuttingused to produce a groove or bevel in themetal surface.


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A rc Welding and Cutting -A pplication

When arc welding, either alternating or direct current isused. The AC and DC limits shown below shall not beexceeded.

For AC welding under wet conditions or warmsurroundings where perspiration is a factor, the use of reliable automatic controls for reducing no-load voltage isrecommended to reduce the shock hazard. Some of theolder AC machines do not have an automatic control andare on load all the time. It is easy to receive an electricshock when the equipment is not handled properly.

AlternatingCurrent (AC)

DirectCurrent (DC)

Manual 80 Volts 100 Volts Automatic 100 Volts 100 Volts


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A rc Welding and Cutting -Installation

Arc welding requires proper installation of equipment. A critical partof installation is ensuring that proper grounding is completed. Theframe or case of the welding machine (except engine-drivenmachines) shall be grounded under the conditions and according tothe methods prescribed in Subpart S, Electrical.

Conduits containing electrical conductors shall not be used for completing a work-lead circuit. Pipelines shall not be used as apermanent part of a work-lead circuit, but may be used duringconstruction, extension, or repair providing current is not carriedthrough threaded joints, flanged bolted joints, or caulked joints andthat special precautions are used to avoid sparking at connection of the work-lead cable.

A ld d


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A rc Welding and Cutting -O peration and Maintenance

Before starting operations, all connections to the machine shall bechecked to make certain that they are properly made. The work leadshall be firmly attached to the work. Magnetic work clamps shall befree from adherent metal particles of spatter on contact surfaces.Coiled welding cable shall be spread out before use to avoid seriousoverheating and damage to insulation.

During welding operations, cables with splices within 10 feet (3m) of the holder shall not be used. Welders should not coil or loop weldingelectrode cable around parts of their body.

Cables with damaged insulation or exposed bare conductors shallbe replaced. Joining lengths of work and electrode cables shall bedone by the use of connecting means specifically intended for thatpurpose. The connecting means shall have insulation adequate for the service conditions.


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Resistance Welding

The third welding process covered in this module is resistance welding.Resistance welding utilizes pressure and heat that is generated in thepieces to be welded by resistance to an electric current.

When conducting resistance welding, all equipment shall be installed by aqualified electrician in conformance with Subpart S, Electrical. If spot andseam welding machines are used, the following precautions must be taken:

All doors and access panels of all resistance welding machines and controlpanels shall be kept locked and interlocked to prevent access to liveportions of the equipment by unauthorized persons.

In all press welding operations, if there is a possibility of the operator's

fingers being under the point of operation, effective guards must be used.Examples of effective guards include an electronic eye safety circuit, twohand controls, or protection similar to that prescribed for punch pressoperations.


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Resistance Welding

The hazard of flying sparks shall be, wherever practical, eliminated byinstalling a shield guard of safety glass or suitable fire-resistant plastic at thepoint of operation. Additional shields or curtains shall be installed asnecessary to protect passing persons from flying sparks.

All foot switches shall be guarded to prevent accidental operation of themachine.

Two or more safety emergency stop buttons shall be provided on all specialmulti-spot welding machines, including 2-post and 4-post weld presses.

Additionally, all portable welding guns, transformers and related equipmentsuspended from overhead structures, eye beams, trolleys, etc., shall beequipped with safety chains or cables. Safety chains or cables shall be

capable of supporting the total shock load in the event of failure of anycomponent of the supporting system.

weld cut braze

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