Welding: Spot Welding, Oxyacetylene Welding, Shielded Metal-Arc Welding
Arc welding & safty
description
Transcript of Arc welding & safty
Arc Welding
Patrick V. BeboutBCN5737-8384 Advanced Construction Safety
Spring, 2009
Definition• Arc Welding – A fusion
process for joining metals. Through the application of intense heat, the metals at the joint intermix (often with a filler material) to create a metallurgical bond as strong as the original two metals.
Applications and Environment
• Arc welding is performed whenever an extremely strong metal bond is needed:– Construction– Maintenance– Manufacturing
• Arc welding is performed in all environments:– Indoors / Outdoors– Extreme Heights– Confined Spaces– Underwater
Arc Welding Components
• Arc Welding requires five main pieces of equipment:– Electrode – Electrode Holder – Electrode Cable– Welding Machine (AC or
DC)– Work Cable
Arc Welding Components
• The Welding machine– Supplies the electricity
needed to create the welding arc
– Converts 120-240 volt AC electricity to welding voltage, typically 20-30 volts AC (also DC voltages)
Lincoln Electric’s AC-225 with Wheel Kit and Gloves
The Arc Welding Process
• How it works:– The intense heat needed to
melt metals is created by the electric arc (> 6500 °F)
– The arc forms between the electrode and the work surface
– The welder guides the arc along the joint by moving the electrode
History of Arc Welding
• The electric arc was discovered by Sir Humphry Davy in 1808
• N.G. Slavianoff and C.L. Coffin developed metal electrodes in the late 1800’s
• Around 1900, A.P. Strohmenger stabilized the arc with coated metal electrodes
• In 1919, C.J. Holslag invented AC welding
Portrait by Henry Howard, 1803
Sir Humphry Davy
History of Arc Welding
• By WWI, welding began replacing rivets on ships due to time savings
• By the end of the war, Germans, Americans and British were arc welding ships and airplanes
• Other advances to strengthen the welds led to much larger usage by WWII
Source: www.wikipedia.org
Dangers of Welding
• Most fatalities that occur while welding fall into four categories*:– Falls– Crushed / Struck-By– Fire / Explosions– Electrocution
“Welding, cutting and brazing are hazardous activities ... The risk from fatal injuries alone is
more than four deaths per 1,000 workers over a working lifetime.”
- OSHA Safety and Health Topicshttp://www.osha.gov/SLTC/weldingcuttingbrazing/index.html
* Information extracted from OSHA construction worker fatality data (1990-2007)
Types of Welding Fatalities
0
10
20
30
40
50
60
Falling
Crushed /Struck-By
Fire /Explosion
Electrocution
Other
Percentageof Fatalities
Source: Information extracted from OSHA construction worker fatality data (1990-2007)
Example Fatality
• Fall:– Employee #1 was walking along
the edge of a roof to conduct some welding on an airport expansion project
– Decking along the edge became loose
– The employee fell 51 feet to the compacted soil
– He died several hours later of internal bleeding and asphyxia
Source: OSHA construction worker fatality data (1990-2007)
Example Fatality
• Crushing Injury:– Employee #1 was welding pre-cast
panels into place at a water treatment facility
– After welding the first panel, Employee #1 repositioned to complete a corner weld on the second panel
– The first panel fell over and crushed him from the rib cage down
– Employee #1 died
Source: OSHA construction worker fatality data (1990-2007)
Example Fatality
• Explosion:– 3 Workers were making repairs on a
crude oil storage tank with an arc welder
– 90 gallons of oil had been placed in the tank the previous day
– Vapors from the tank were ignited by the welding arc
– Workers #1 and #2 were killed instantly in the explosion
– Worker #3 died the next day from burns covering 90% of his body
Source: OSHA construction worker fatality data (1990-2007)
Example Fatality
• Electrocution:– Employee #1 was arc welding on his
back, drenched in his own sweat– His equipment was set at 135
ampere AC position– Equipment was in excellent
condition, with warning labels concerning amperage
– Employee was later found dead– Medical Examiner confirmed that he
died from electrocution
Source: OSHA construction worker fatality data (1990-2007)
Other Dangers
• Eye damage from flash burns or Ultraviolet (UV) Radiation (“Welder’s Eye”)
• Flash burns to the welder or surrounding workers
• Inhalation of dangerous fumes (“Metal Fume Fever”)
• Heat stress
OSHA & Arc Welding
• OSHA addresses arc welding with Regulations 1926.351
• Manual Electrode Holders:– Only use electrode holders specifically designed to
safely handle the maximum rated current required– Make sure all current carrying parts are well
insulated
OSHA & Arc Welding
• Welding Cables and Connectors:– All welding cables should be well insulated
– Repairs or splices must be at least 10ft from the electrode. Splices made closer must have the same insulating quality as the cable.
10’ Min.
Repair or splice
OSHA & Arc Welding
– Use substantial insulating material at splices or connectors
– Cables in need of repair can not be used
Splice
OSHA & Arc Welding
• Ground Returns and Machine Grounding:– Ground cables must be able to carry the specified
maximum current capacity
– Do not use pipes carrying flammable gases, flammable liquids, or electric wires as a ground
Ground Wire
Flammable Gases / Liquids
Electrical Wiring
OSHA & Arc Welding
– Must maintain electrical contact at all joints– Joints to be bonded and periodically inspected for
electrolysis or fire hazard (when continuously employed as ground return)
Joints
OSHA & Arc Welding
– Frame of welding machine must also be grounded– Ground must be able to break fuse
– Ground connections must be strong and adequate
Must Also be Grounded
OSHA & Arc Welding
• Operating Procedures:– When left unattended, remove electrodes and
place away from conductive materials – Never place hot electrode holders in water
Hot Electrode Holder
OSHA & Arc Welding
– Turn off welding machine when left unattended or when moving
– Use shielding screens if possible
Additional Safety Guidelines
• Avoid crushing injuries and falls:– Examine the workspace
prior to commencing any work to identify possible hazards
– Always properly tie-off when welding from heights
– Wear a life-jacket when working above water
FALL HAZARD
Additional Safety Guidelines
• Minimize Risk of Electrocution:– Low-level dampness increases the risk of electrocution.
Do not weld in a wet or damp environment unless an insulating mat or other non-conductive material is securely in place between all body contact points and any surrounding metal.
– Minimize electrical shock through proper equipment:• Dry gloves, rubber-soled shoes & dry clothing• Frequent changing of cotton liners to prevent welding
gloves saturated with perspiration• Standing or sitting on a dry wooden floor, a dry rubber
mat or similar insulating material
Additional Safety Guidelines
• Avoid the risk of explosion:– Where possible welding should be undertaken
outdoors in a well ventilated area– Open up structures / containers prior to welding– Ventilation during cleaning should be such that
any flammable gases are quickly and safely dispersed
– Sight or smell must not be used to determine if safe working conditions apply
– If the condition of the container is not known, it should be assumed that the container contains an explosive mixture
Personal Protective Equipment
Source: National AG Safety Databasehttp://www.cdc.gov/nasd/docs/d000801-d000900/d000873/d000873.html
• Wear the appropriate PPE for the job:– Eye Protection– Burn Protection– Inhalation Protection
Conclusions
• Welding should only be carried out by experienced welders directly supervised by a person who fully understands the hazards involved
• Always properly maintain equipment• Wear appropriate personal protective
equipment• Perform a hazard identification and
risk assessment of any workplace prior to commencement of any work