Welding_ Cutting_ and Brazing Su

Document Sample
Welding_ Cutting_ and Brazing Su Powered By Docstoc
					Welding, Cutting & Brazing
Common Arc Welding
and Cutting Processes
•   Shielded Metal-Arc Welding (SMAW)
•   Gas Metal Arc Welding (GMAW)
•   Gas Tungsten Arc Welding (GTAW)
•   Flux Core Arc Welding (FCAW)
•   Submerged Arc Welding (SAW)
•   Arc Cutting
•   Plasma Arc Cutting (PAC)
•   Air Carbon Arc Cutting (AAC)
•   Arc Gouging
Welding, Cutting & Brazing

• Hazards due to potential energy
• Compressed gas
   – Handling, storage, and use
• Hazards of compressed gas
   – Acetylene - flammability
   – Nitrogen - asphyxiation
   – Oxygen - augment or compound fire hazard
 Welding, Cutting & Brazing

• Those poor welders get
  blamed for a lot!
  Welding, Cutting & Brazing

• Improper fire safety
  during welding
   – Damaged 211 foot
   – Closed the ship
2004 Subpart J 1926.350-354
Welding and Cutting
                 Cylinders secured upright
 350(a)(9)                                                           91
                 Oxygen cylinder storage
350(a)(10)                                                     75
                 Valve protection caps
 350(a)(1)                               30
                 Regulators and gauges in working order

   350(h)                         24
                 Fire extinguishing equipment in area
   352(d)                         23

             0               20               40          60    80        100
Welding, Cutting & Brazing Arc
Welding and Cutting
•   Arc of electric current produces heat
•   Arc welding extensively used
•   Arc cutting for rough cuts
•   Shielding
   – Welds have better properties if air and
     contaminants are kept out
   – Shielding provided by flux
• Voltage - AC Vs DC
  Welding, Cutting & Brazing Arc
  Welding and Cutting
• Installation
   – Frame or case of welder grounded
   – Electrical conduits are not work lead circuits
• Operation and maintenance
   – Check all machine connections before work
   – No cable splices within 10 feet of holder
   – Damaged cables will be replaced
  Arc Welding
• Manual electrode holders must be designed for that purpose
  and capable of carrying the maximum rated electrode
• Only fully insulated holders to contact hands
  Arc Welding
• Arc welding cables completely insulated and flexible
• Free of splice minimum ten feet from electrode cable
• Cables in need of repair not allowed
   Arc Welding
• Ground return cables must have sufficient current carrying
  capacity for maximum voltage
• No grounding on pipelines containing gasses or flammable
• When using pipelines for ground return, continuity of
  ground must be verified for all joints
  Arc Welding
• Employers instruct employees:
   – Electrodes removed from holders when unattended
   – No hot electrodes dipped in water
   – Machine power opened when leaving machine or
     stopping work
   – Faulty equipment reported to supervisor
    Welding, Cutting & Brazing MIG
• Uses an electric arc to melt material. Uses a shielding
  gas (usually argon and CO2) to protect it from the
  atmosphere and eliminate the need for flux
• Fast, good looking welds, inexpensive
• Not suitable for thin aluminum
• Weld bead appearance not as nice as TIG welds
 Welding, Cutting & Brazing TIG
• Hand held torch with a tungsten
  electrode, melts material
• Best method for thin materials and
  aluminum, best looking weld, works on
  any weldable metal
• Expensive, requires hand, eye and foot
   Welding, Cutting & Brazing
   Resistance Welding
• Welding equipment must be installed by a qualified
• Spot and seam welding machines
   – Doors & access panels locked
   – Guarding of press welding operations
   – Foot switches will be guarded
   – Two or more safety stop buttons required
   – Safety walls or plastic used to shield sparks
   Welding, Cutting & Brazing Gas

• Uses a torch to burn oxygen and fuel gas
• Inexpensive, truly portable
• Slow, not good on thicker materials

NFPA – 51B
Discusses fire prevention in the cutting
and welding processes
ANSI – Z49.1
Safety in Welding and Cutting
 Welding, Cutting & Brazing
 Compressed Gases
• Specific gases
– OSHA regulations contain sections on-
  –   Acetylene
  –   Hydrogen
  –   Oxygen
  –   Nitrous oxide
  –   Anhydrous ammonia
  –   Liquefied petroleum gas
  Welding, Cutting & Brazing Gas
• Hazards
   – Fire and explosion
   – Asphyxiation
   – Suffocation
   – Falling cylinders
   – Flying cylinders
• Treat cylinders with care, do not bang,
  pound or use them as rollers.
• Do not thaw frozen valves with a blow-torch!
     Welding, Cutting & Brazing
•   Pressurized vessel
•   Higher than 40 pounds per square inch
•   Circular cross section
•   Does not include portable tank, tank car, cargo tanks
    Welding, Cutting & Brazing
    Cylinder Markings
•   DOT Markings
•   Serial number
•   Symbol of manufacturer, user or purchaser
•   Month and year of manufacture (6 56)
•   Disinterested inspectors official mark
•   A plus mark indicates the cylinder may be 10%
Cylinder Markings
              • Serial number
              • Symbol of manufacturer, user
                or purchaser
              • Month and year of manufacture
                (6 56)
              • A plus mark indicates the
                cylinder may be 10%
              • Retest dates
              • 5 pointed star indicates ten
                year retest interval
Operating Cylinders
•   Valve caps are not used for lifting
•   Always attach regulator before use
•   Keep free of oil and grease compounds
•   Purge valves before attaching regulators
•   Open acetylene valve 1.5 turns at the most
•   Release pressure in regulator before removing
   Welding, Cutting & Brazing Fire
   Prevention and Protection
• Destroyed a major
  supermarket in Denver
• Did they use a fire watch?
  Welding, Cutting, & Brazing
• Fire prevention and protection
– Basic precautions
   – Immobile objects require fire hazard removal
   – Immobile objects and fire hazards require use of guards
   – Cannot comply - no welding
  Welding, Cutting & Brazing Fire
  Prevention and Protection
• Suitable fire extinguishing equipment
• Fire watchers - when fire potential is great
• Welding or cutting containers - clean barrels,
  tanks, or other containers
• Confined spaces
   – Electrodes removed
   – Welding machine disconnected
   – Gas shutoff outside confined area
         General Requirements
• Fire Watch
   – Required where a minor fire may develop AND
      • when combustibles are within 35 feet
      • when combustibles are further than 35 feet but are
        easily ignited
   – Shall be maintained for at least 30 minutes after
     completion of welding
   – Fire extinguishing material must be present
      • pails of water, buckets of sand
      • hose
      • portable extinguisher
1926.352 Fire Prevention
               • When welding over walls,
                 floors, ceilings where sparks
                 may travel precautions must be
                 taken in the adjacent areas
Fire Prevention
• Before welding on drums or hollow structures which
  have contained toxic or flammable materials
   – Completely fill with water before proceeding, or
   – Thoroughly clean, ventilate, and TEST!

    Before applying heat to any container
    drum, or hollow structure a vent or
    opening must be provided
        Handling, Storing and Use
• Shall be in accordance with the Compressed Gas
  Association (CGA) Pamphlet P-1
• Pressure relief devices shall be installed and maintained in
  accordance with CGA Pamphlet S-1.1 and S-1.2
 Welding, Cutting & Brazing Storage

• Keep away from heat sources
• 20 feet from highly any combustible material
• No more than 2,000 cubic feet (300 pounds) in a building
  Welding, Cutting & Brazing Storage
• Secured from movement
   – Away from areas where it could be knocked over
   – Valve end up
• Close valves on empty cylinders
• Replace valve caps when not in use
  Transporting, Moving &
  Storing Gas Cylinders
• Valve protection caps in place & secure
• Cylinders hoisted on cradle, slingboard, or pallet
• No magnets or choker slings!
• Move by tilting & rolling on edge
• Transport by powered vehicle: secured upright
  Transporting, Moving &
  Storing Gas Cylinders
• When cylinders are in use,
  they shall be secured by
  chain, cart, or other
  steadying device
           Oxygen Storage
• Separate from fuel-gas cylinders
• Separate from combustible
  materials (oil/grease)
• Minimum separation distance is
  20 feet
• May use a non-combustible
  barrier 5 feet tall with a fire
  resistance rating of 1/2 hour

                     Acetylene + Oxygen = Willful Citation!!
Fire Prevention and Protection
  Protective Equipment,
  Hose, and Regulators
• Hose and hose connections
   – Proper hose
   – Hoses secured to withstand twice the normal
     pressure but not less than 300 psi
   – Inspect hoses to ensure serviceability
• Pressure-reducing regulators
   – Proper type for gas and pressure
   – Marked “USE NO OIL”
     Welding, Cutting & Brazing
     Hoses and Connections
• Clamped or fastened to withstand twice the normal
• Test with oil free gas or inert gas
• Examine for charred sections, tape that covers leaks
• Repair or replace as needed
   Welding, Cutting & Brazing
   Hoses and Connections
• Fuel gas
   – Usually red-sometimes
   – Has a left hand threaded
• Oxygen
   – Is green
   – Has a right hand threaded
          • Clogged tips cleaned with
            suitable devices
          • Torches inspected prior to
            each shift
          • Torches lit by strikers or
            other approved methods
          • Do not use matches!
          • Do not ignite off of hot
  Welding, Cutting & Brazing
  Oxygen-Fuel Gas Welding
• Acetylene
   – Pressure regulated at less than 15 psi
   – Stored in special cylinders to prevent decomposition
   – Cylinder have pores in calcium silicate filler that
     isolate decomposition
   – Usual cylinder hold 300 cubic feet @ 20 psig @ 70
     degrees F
Rules for Oxyacetylene Welding
• Blow out cylinder valve before connecting regulator
• Release adjusting screw before opening the valve
• Stand to one side of the regulator
   – Open cylinder valve slightly, then close it. (“cracking the
   – Cracking the valve cleans out dirt that may cause an explosion
• Open the cylinder valve slowly
• Do NOT use acetylene above 15 psig!
 Rules for Oxyacetylene Welding
• Purge acetylene and oxygen passages individually before
• Light acetylene, then open oxygen on torch
• NEVER use oil/grease on regulators, tips that contact
• Do not use oxygen as a substitute for air
• Keep burnable material out of your work area
 Welding, Cutting & Brazing
 Protection of Personnel
• Eye protection
   – Helmets or hand shields
   – Use booth with special finish & protection
• Helmets/shields
   – Must not be flammable
   – Arranged to protect from radiant energy
   – Must be capable of withstanding sterilization
• Protective Clothing
   – Use select clothing materials, wear loosely
   – Safety shoes, clean fire resistant clothing, gloves, & long sleeves
  Use Protective Clothing and
• Welders should consider using appropriate protective
  clothing which should include:
• Shield or helmet with a filtered lens
• Fire resistant gloves; a leather apron
• Boots
• Leather spats
• Felt skull-cap or beret and preferably overalls
                             Flameproof Skullcap
      Eye Safety Shield    Helmet with Filter Lens
  No Pockets                    Collar Buttoned

Full Sleeves
                                  Fire Protection
  Leather Apron or                Gauntlet Gloves
  Shirt Outside Trousers
                              Clean Fire Resistant
  No Cuffs                    Clothing

Safety Shoes
Welding, Cutting & Brazing
Protection of Personnel
• Working in a confined space
   – Welding tanks/equipment left outside
   – Welder extraction considered
   – Attendant with rescue plan
• Health protection & ventilation
   – Mechanical ventilation required
   – Compounds like zinc, lead, beryllium, cadmium,
     mercury are extremely hazardous
   Welding/Cutting in Confined
• Requires an attendant
• When welder is not in use
   – Remove electrodes
   – Turn off gas/oxygen supply
     outside the confined space
Ventilation & Protection
 • General ventilation to maintain welding smoke and
   fumes within safe limits
 • When welding in confined spaces mechanical ventilation
   or local exhaust
 • If ventilation blocks access/egress to confined space, air
   line and attendant required
 Welding Health Hazards
 Chemical Agents
• Zinc
   – In brass, galvanized metals, and alloys
   – Metal fume fever
   – Influenza like, fever, chills, nausea, fatigue
• Cadmium
   – Rust preventive coating on steel
   – Acute - severe lung irritation
   – Chronic - emphysema & kidney damage
  Welding, Cutting & Brazing
  Chemical Agents
• Beryllium
   – Alloying element with copper & other metals
   – Acute - chemical pneumonia
   – Chronic - short breath, cough, wt loss, fatigue
• Iron Oxide
   – Alloying element in steel
   – Acute - irritation of nasal, throat, & lungs
   – Chronic - iron pigmentation of lungs
  Welding, Cutting & Brazing
  Chemical Agents
• Mercury
   – Rust prevention coatings
   – Acute - stomach , diarrhea, kidney failure
   – Chronic - tremors, emotional stability, hearing
• Lead
   – Lead bearing alloys or lead based paints
   – Poisoning - appetite, nausea, cramps
   – Affects brain, CNS, circulatory, reproductive
Welding, Cutting & Brazing
Chemical Agents

• Chlorinated Hydrocarbon Solvents
   – Heating causes phosgene gas
   – Phosgene destroys lung tissue
• Carbon Monoxide
   – Incomplete combustion of fuels
   – Symptoms - heart pounding, dull headache,
     dizziness, ringing in ears, nausea
 Welding, Cutting & Brazing
 Chemical Agents
• Ozone
   – Produced by ultraviolet light when welding
   – Acute - headache, chest pain, dryness
   – Chronic - pulmonary edema (fluid in lungs)
• Nitrogen Oxides
   – Produced by ultraviolet light when welding
   – Irritates eyes, nose, and throat
   – Chronic - short breath, chest pain, pulmonary edema
  Welding, Cutting & Brazing
  Physical Agents

• Ultraviolet Radiation
   – Skin burns
   – Feeling of sand in eyes, “arc eye”
• Infrared Radiation
   – Defeated by protective clothing and helmet
• Intense visible light
   – Retinal damage results from direct viewing
  Preservative Coatings
• Before welding or cutting on a coated surface whose
  flammability is not known scrapings must be taken and
• If scrapings burn, coatings must be removed before