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Contrary to popular wives tale - Welding Galvanised steel is NOT Poisonous, as the article below demonstrates. That is not to say that it is advisable or to be recomended, just that it is not poisonous and you will not suffer long term problems if you do.
Welding Galvanized Steel -- Safely
© Sperko Engineering Services, Inc.,1999, Page 1 of 6
Background
Galvanizing has been used to protect iron and steel from rusting for over a hundred years in places as diverse as the wire rope used for the suspension cables on the Brooklyn Bridge to gutters on houses.
Galvanizing is simply coating of zinc over steel. Like paint, galvanizing protects steel from rusting by forming a barrier between the steel and the environment, but galvanizing goes one giant step further than paint -- it also provides electrochemical protection of the steel. Since zinc is electrochemically more reactive than steel, it oxidizes to protect the steel near it; as a result, even if a galvanized steel surface is scratched down to the bare steel, the galvanizing coating will prevent the steel from rusting. Galvanized steel is, therefore, a superior product to steel with any other type of coating on it since it protects the steel even when the coating is damaged in handling or in service.
Galvanizing is simply coating of zinc over steel. Like paint, galvanizing protects steel from rusting by forming a barrier between the steel and the environment, but galvanizing goes one giant step further than paint -- it also provides electrochemical protection of the steel. Since zinc is electrochemically more reactive than steel, it oxidizes to protect the steel near it; as a result, even if a galvanized steel surface is scratched down to the bare steel, the galvanizing coating will prevent the steel from rusting. Galvanized steel is, therefore, a superior product to steel with any other type of coating on it since it protects the steel even when the coating is damaged in handling or in service.
Welding of Galvanized Products
Welding of galvanized steel is done almost exactly the same way as welding of the bare steel of the same composition; the same welding processes, volts, amps, travel speed, etc. can be used with little modification when the switch is made from uncoated steel to galvanized steel -- unless the zinc coating is unusually thick.
The difference between welding galvanized steel and welding uncoated steel is a result of the low vaporization temperature of the zinc coating. Zinc melts at about 900°F and vaporizes at about 1650°F. Since steel melts at approximately 2,750°F and the welding arc temperature is 15,000 to 20,000°F, the zinc that is near the weld does not stand a chance -- it's vaporized!
By the time the weld pool freezes, the zinc is gone. This has two immediate consequences:
The vaporized zinc increases the volume of welding smoke and fumes.
The zinc at and near any welds is actually burned off by the heat of the arc, removing the protective zinc coating.
The difference between welding galvanized steel and welding uncoated steel is a result of the low vaporization temperature of the zinc coating. Zinc melts at about 900°F and vaporizes at about 1650°F. Since steel melts at approximately 2,750°F and the welding arc temperature is 15,000 to 20,000°F, the zinc that is near the weld does not stand a chance -- it's vaporized!
By the time the weld pool freezes, the zinc is gone. This has two immediate consequences:
The vaporized zinc increases the volume of welding smoke and fumes.
The zinc at and near any welds is actually burned off by the heat of the arc, removing the protective zinc coating.
Zinc Fumes -- A Safety Hazard?
When zinc vapor mixes with the oxygen in the air, it reacts instantly to become zinc oxide. This is the same white powder that you see on some noses at the beach and the slopes. Zinc oxide is non-toxic and non carcinogenic. Extensive research
1 into the effects of zinc oxide fumes has been done, and although breathing those fumes will cause welders to think that they have the flu in a bad way, there are no long-term health effects. Zinc oxide that is inhaled is simply absorbed and eliminated by the body without complications or chronic effects. Current research2 on zinc oxide fumes is concentrated in establishing the mechanism by which zinc oxide causes "metal fume fever," how its effects are self-limiting and why zinc oxide fume effects ameliorate after the first day of exposure even though the welder may continue to be exposed to zinc during subsequent days ("Monday-morning fever"). Other research3 is being done using zinc oxide fumes together with various drugs which results in a synergetic effect for treatment of cancer and AIDS. Another area of research is use of zinc compounds as the active ingredients in throat lozengers that are recognized as significantly effective in reducing the duration and intensity of the common cold.
Typical metal fume fever begins about 4 hours after exposure, and full recovery occurs within 48 hours. The symptoms include fever, chills, thirst, headache and nausea. All of these symptoms, pain and suffering, as well as lost work (and play) time, can be avoided entirely by simply not inhaling the zinc oxide fumes. This can easily be done using any of the methods described later.
Unlike other heavy metals, such as copper, lead and mercury, zinc is an essential micro nutrient. Zinc is essential to the proper growth of plants and animals. Zinc forms part of the enzyme system that regulates biological processes throughout the body. As shown on any multi-vitamin/mineral bottle, the recommended minimum adult intake is 15 mg/day.
Typical metal fume fever begins about 4 hours after exposure, and full recovery occurs within 48 hours. The symptoms include fever, chills, thirst, headache and nausea. All of these symptoms, pain and suffering, as well as lost work (and play) time, can be avoided entirely by simply not inhaling the zinc oxide fumes. This can easily be done using any of the methods described later.
Unlike other heavy metals, such as copper, lead and mercury, zinc is an essential micro nutrient. Zinc is essential to the proper growth of plants and animals. Zinc forms part of the enzyme system that regulates biological processes throughout the body. As shown on any multi-vitamin/mineral bottle, the recommended minimum adult intake is 15 mg/day.
1
Walsh, Sandstead, Prasad, Newberne and Fraker, Environmental Health Perspectives, Volume 102, Supplement 2,
June 1994, 5-46. Provides summary plus 471 references.
June 1994, 5-46. Provides summary plus 471 references.
2
Kuschner,D'Alessandro, et. al., Pulmonary Responses to Purified Zinc Oxide Fumes, Journal of Investigative
Medicine, 1995:43:371-378.
Medicine, 1995:43:371-378.
3Robert Sabin, Zinc Activated Profile, COPE, March/April 1995: 16,17
