^ Carefully Welded Joints are as Strong as the Base Metal(s) – Image Courtesy of LightCooker at ShutterStock.com
The Good & Bad of Welding
In many ways, welding is a unique operation. For one, it connects the base material(s) at the molecular level. This makes the weld joint as strong as the base material, and sometimes stronger. Nothing even remotely superficial about it!
A truly versatile process, it finds application in multiple industries viz. automotive, aerospace, wind power, building-construction, transportation, marine structures, and the like. Quite an impressive list, wouldn’t you say?
Welders operate underwater, in confined spaces, over ground, indoors, and outdoors to join materials in multiple positions viz. horizontal, flat, vertical, and overhead. And there are numerous sub-positions under each of these four major positions.
Despite all these qualities, welding remains cost effective. Not for nothing does the manufacturing world hold welding in such high regard. And not for nothing do forecasts expect the global welding equipment market to expand at 4%p.a. for the 2014-18 period and hit $23.78 billion by 2020.
Similar to Newton’s Third Law of Motion of there being a reaction for every action, the bad usually comes with the good. The many virtues of welding are not without inherent hazards. And there are many to speak of.
What ads to the level of danger is the singular combination of the umpteen hazards. Perhaps, no other single manufacturing process involves a blend of so many perils – fumes, gases, radiation, electric shock, particulates, noise, fire, explosion, stress, heat – you name it.
Welding Hazards & their Intensity
According to the Occupational Health & Safety Administration (OSHA) of the U.S. Department of Labor, hot jobs such as welding, brazing, and cutting create health and safety hazards for as many as 500,000 workers and cause 4 deaths per 1,000 workers over a lifetime of work.
Hazards related to hot jobs include:
- Particulate Matter
- Gases: Ozone, Carbon dioxide (CO2), and Carbon Monoxide (CO)
- Radiation: Ultraviolet (UV), Infrared (IR), and Visible
- Electric Shock
- Fire & Explosion
- Exertional Stresses
The effects of these hazards depend on the welding process, the materials being welded, and the coatings on the electrodes and the materials. This is because these factors determine the:
- amount and composition of fumes
- spectrum and intensity of radiation
- duration of exposure to these hazards
- effectiveness of control measures such as personal protective equipment and ventilation
Regulations for preventing mishaps during hot jobs cover the following areas:
- Workspace Ventilation
- Respiratory Protection in Confined Areas
- Protective Operator Clothing
- Safety Procedures for Arc Welding, Cutting, and Resistance Welding
- Professional Inspection and Maintenance of Equipment and Systems
- Storage, Conveyance, and Handling of Acetylene and Oxygen
As mentioned, welding is a multidimensional operation that incorporates numerous processes, diverse equipment, and umpteen positions and work conditions.
For example, shipyard welders are more exposed to asbestos than non-shipyard welders. They are therefore at a greater risk of developing lung cancer as well as other forms of cancer. What are common are the hazards they encounter.
- Fumes: Heat generated by welding vaporizes filler material, base metals, coverings, coatings, fluxes, and cleaning compounds. This produces fumes, many of which are toxic. Fumes created from filler material are the most septic.
Filler material, base metal, coatings, fluxes etc. vaporize and incompletely react with atmospheric oxygen. They then condense to form fumes. The base metal pool is cooler than the electrode tip. It releases fumes only if the base metals are coated.
Coatings, fillers, coverings and alloys that contain manganese, fluorides, copper, copper oxides, nickel, silica, silicates, and chromium produce the most virulent fumes.
Welding of nickel-chrome steel is similarly laced with harmful fumes. Of all the welding processes, gas metal arc welding (GMAW) and arc welding with coated consumables create the most noxious of fumes.
Some compounds of hexa-valent chromium are known to cause cancer and mutations. Welding stainless steel using GMAW creates fumes with 9.8-13.8% chromium.
Factors that influence the rate of fume generation are:
- welding current
- arc voltage
- diameter and polarity of electrode
- welding speed
- welding practices
|Lethal Element in Fumes||Source|
|Chromium||Welding of Stainless & High Alloy Steels|
|Silica / Silicates / Both||Electrode Cores in FCAW
Electrode Coatings in SMAW
Aluminum Alloys & Low Alloy Steels
|Nickel||Welding of Nickel Alloys and Stainless Steels (with 8-15% Ni)|
(mainly of Sodium, Calcium, & Potassium)
|Electrode Cores in FCAW
Electrode Coatings in SMAW
Fluxes in SAW
|Manganese||Electrode Cores in FCAW
Electrode Coatings in SMAW
High Manganese Content Sheets
|Copper||Welding of Copper & its Alloys
Electrodes in GMAW
Source of Lethal Elements in Welding Fumes
Courtesy of the American Welding Society (AWS) at http://www.aws.org/library/doclib/EWH-I.pdf
Engineers recommend shielded metal arc welding (SMAW) for welding low-alloy and carbon steels for structural applications. SMAW uses consumables coated with acidic, basic, neutral, or rutile materials such as:
- fluorspar (CaF2) and rutile (TiO2)
- magnesium and calcium carbonates
- silicon and silicate minerals viz. mica, feldspar, and asbestos
- sodium and potassium silicates
- manganese, clay, and iron
Coatings and high currents hike the fume generation rate in SMAW. The same is true for flux cored arc welding (FCAW). GMAW uses uncoated electrodes and fume generation rises when you use carbon dioxide as the shielding gas instead of argon or argon-oxygen.
Gas tungsten arc welding (GTAW) releases very low amount of fumes when you use external filler. This rate falls further if you do not use filler at all. Fume generation rates of GTAW are fairly similar to that of plasma arc welding.
Technicians routinely use GTAW to weld a whole range of materials such as steels – carbon, low-alloy, and high-alloy; silver, aluminum and its alloys, brasses, magnesium and its alloys, and copper and copper-nickel alloys.
Used to weld thick plates at high metal deposition rates, submerged arc welding (SAW) discharges insignificant amounts of fumes because the arc and the weld pool are submerged i.e. covered under the flux. Fluorides in the flux create most of the fumes.
Because the temperature of the oxy-gas / oxy-fuel flame is much lower than that of the arc, oxy-gas welding emits lesser fumes. But it does discharge more fumes when welding galvanized steel and materials that contain volatile alloying elements.
- Particulate Matter: Fumes contain particles smaller than 0.1micrometer (µm). Although particles of size 1-7µm are the most lethal and most welding fumes contain particles smaller than this size range, the small particles can gang up and expand to a destructively large size.
III. Gases: Arc and oxy-gas welding mainly emit:
- nitrogen oxides
- carbon monoxide (CO)
- carbon dioxide (CO2)
Additionally, welding radiation vaporizes hydrocarbon coatings to produce gases such as hydrogen chloride, phosgene, and diacetyl chloride.
Ozone & Nitrogen Oxides: Gas shielded arc welding emits ultraviolet (UV) radiation of under 210nm wavelength, particularly when welding aluminum. This UV radiation oxidizes atmospheric oxygen to ozone. Radiation similarly converts atmospheric nitrogen to nitrogen oxides.
GMAW that uses argon while welding aluminum and its alloys produces the maximum amount of ozone. And because UV radiation produces ozone away from the arc, you cannot easily remove it.
Intensity and wavelength of the UV radiation affect the formation rate of ozone. This intensity and wavelength depend on:
- welding variables viz. current, voltage, and arc length
- base material
- shielding gas
- electrode type
Gas shielded arc welding processes emit more ozone than SMAW and FCAW. This may be because SMAW and FCAW discharge more fumes that clog the emission of UV radiation.
Oxy-gas welding flames are not hot enough to emit UV radiation. Addition of manganese to aluminum lowers ozone generation but the addition of silicon raises it.
CO2 and CO: Decomposition of carbon dioxide used in gas shielded arc welding produces carbon monoxide. The following generate CO2:
- inorganic carbonates in coatings
- decomposition of organic compounds
- carbon in the oxyacetylene flame and in the weld metal
- Radiation: UV radiation of wavelength under 175nm generates ozone near the welder. You cannot easily flush out such ozone, something that makes this wavelength devastating.
Fumes too are no less destructive, but they cover the UV radiation. If you use blowers for flushing out fumes, you will experience more UV radiation. Radiation also increases with an increase in welding current and reflection from finely polished surfaces.
- Electric Shocks: According to the Guide for Safety at Work – Electric Shock Hazard of Manual Electric Arc Welding, welding-related electric shocks result from:
- overlooking the involved risks
- unsafe weld equipment
Annually, about 1,000 personnel die from electric shocks in the United States alone. Generally, alternating current (AC) is 2-3 times more dangerous than direct current (DC). A 100mA current is enough to kill a human as is a voltage of 50V.
Arc welding is the most lethal because of the involved currents and voltages. It creates currents of above 150amps and arc voltages of 23-33V. Open circuit voltage (no load voltage when the equipment is not operational) can however be as high as 100V.
Safer variants of welding include tungsten inert gas (TIG) welding, metal inert gas (MIG) welding, and metal active gas (MAG) welding. This is because operators can switch the welding current on and off with a foot switch in these processes.
- Noise: Operation of the welding and other machines emits excessive noise.
VII. Fire & Explosion: Sparks, torch flames, and molten metal can ignite fires and explosions. The American Welding Society (AWS) estimates that welding sparks can travel as far as 10m (35feet) horizontally. You can add another few meters that they will cover when falling.
Clothing, cracks, and other crevices hold such flying sparks. Most importantly, sparks maintain their temperature of over 2,5000F for long. In the presence of combustible material or inflammable vapors, these nearly-invisible sparks can trigger a fire or even an explosion.
VIII. Exertional Stresses: Continuous and repeated lifting of heavy loads and kneeling in uncomfortable positions induces such stresses.
- IX. Heat: Being a fusion process that involves the controlled melting and re-solidification of the base metals and filler materials, welding inherently generates heat.
Disorders & Consequences
Zinc fumes can cause metal fume fever. Symptoms include metallic taste, chills, fatigue, nausea, vomiting, thirst, and fatigue. This fever also triggers a more serious condition called leukocytosis. Herein, the number of white blood cells (WBCs) increases abnormally.
When fume particles penetrate into lungs, they can cause a wide variety of disorders such as cancer, occupational asthma, throat lung irritation, temporary reduction of lung function, and pneumonia.
Fumes can also provoke other ailments such as manganese poisoning that, in turn, stimulates Parkinson’s disease, bronchitis, stomach upsets, kidney damage, neurological disorders, and heart disease.
Manganese and lead fumes can damage the nervous system while cadmium fumes can poison kidneys. Fluorine dust and vapor can bring about bone disorders. Some fumes and gases lower the oxygen supply to auditory nerve cells and stimulate hearing loss.
Health effects of ozone and nitrogen oxides are similar. These range from petty effects such as headache and eye irritation to lung hemorrhage and even death in extreme cases. Ozone also causes severe eye irritation.
CO causes suffocation. Welders with pre-existing heart conditions will witness the worsening of their symptoms when exposed to CO for prolonged durations.
Apart from creating ozone, UV radiation can cause eye ailments such as lenticular cataracts and chorio-retinal burns. It can also lead to skin afflictions such as erythema, dermatitis, skin irritation.
Effects of electric shocks can range from minor superficial burns and pain in the chest and abdomen to the more serious internal injuries, muscle paralysis, nervous impairment, and even death.
Consistent loud noises can lead to stress and hearing loss. Loud noises damage auditory nerve cells that do not repair or regenerate. Minor damage over the years accumulates into major ailments.
Exertional stresses take their toll on the welder in the form of chronic aches in the back, shoulder, and knees. They also inflate the welder’s vulnerability to the other hazards of welding. The heat generated in welding escalates fatigue levels and exertional stresses of welders.
Sometimes the disorders from welding get so bad, welders have to find a fresh profession. This bodes ill for an economy that faces shortage of skilled welders at a time when the manufacturing sector is rebounding after a very long time.
To know more intricate details on all aspects of welding, visit our blog. And to get the best in marine fabrication services, marine pipe fitting, and large scale custom metal fabrication, contact Kemplon Engineering.