Use of Tungsten Welding Rods Containing Thorium

Tungsten inert gas (TIG) welding, also known as gas tungsten arc welding (GTAW), is an arc welding process that uses a tungsten electrode to transmit the electric arc to the work piece. Unlike other arc welding methods, the tungsten electrode does not provide material to the weld, so a separate filler rod is needed for that purpose. Some tungsten electrodes are made with a small amount of thorium, which is a radioactive material and improves the welding qualities of the electrode.

Welding With Tungsten
Tungsten has the highest melting point of all metals, so the electrode material does not melt when exposed to the high temperatures of the arc. Tungsten can be used to weld metals and specific alloys designed to have a high melting point. Even though the tungsten electrode doesn’t melt during the welding process, the electrode can wear or chip over time. The electrode can be reshaped to a conical or rounded shape using a grinder.

Electrodes That Contain Thorium
Thoriated tungsten electrodes are made from tungsten combined with 1 to 2 percent thorium in the form of thorium dioxide. Thoriated tungsten electrodes result in improved welding properties over pure tungsten electrodes. By using thoriated tungsten electrodes, welders find it easier to start the arc and maintain the arc, reduce weld contamination, carry a higher level of current, and achieve a longer electrode life through reduction in wear.

Concerns
Thorium is a radioactive element, so thoriated tungsten electrodes do emit some radioactivity, but the amount is relatively low. Thorium mainly emits alpha particles, which can’t pass through a sheet of paper, but could potentially damage skin tissue with prolonged exposure. Thoriated tungsten electrodes should be stored in a steel container marked with the radiation trefoil as an identifier.

The Natural Council on Radiation Protection and Measurements (NCRP) estimates that the average annual effective dose welders are exposed to when working with thoriated tungsten electrodes regularly, is a maximum of 16 millirem. The amount of background and medical doses incurred by members of the U.S. population each year is about 250 to 1,000+ millirem, so the exposure due to the thoriated tungsten electrodes is small. However, common sense safety precautions should be taken to avoid excessive exposure, including not carrying electrodes close to the body, and wearing standard welding equipment while performing TIG welding. Welders should wear a mask while grinding thoriated tungsten electrodes to avoid breathing in particulates from the grinding process.

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