carbon steels in presence of nitrogen, care has to be taken to ensure the proper weld microstructure. Nitrogen increases arc stability and penetration and reduces distortion of the welded part. In duplex stainless steels assists in maintaining proper nitrogen content. 85–95% helium with 5–10% argon and 2–5% CO2 is an industry standard for short-circuit welding of carbon steel. Argon – carbon dioxide – oxygen Argon–helium–hydrogen Argon – helium – hydrogen – carbon dioxide Applications The applications of shielding gases are limited primarily by the cost of the gas, the cost of the equipment, and by the location of the welding. Some shielding gases, like argon, are expensive, limiting its use. The equipment used for the delivery of the gas is also an added cost, and as a result, processes like shielded metal arc welding, which require less expensive equipment, might be preferred in certain situations. Finally, because atmospheric movements can cause the dispersion of the shielding gas around the weld, welding processes that require shielding gases are often only done indoors, where the environment is stable and atmospheric gases can be effectively prevented from entering the weld area. The desirable rate of gas flow depends primarily on weld geometry, speed, current, the type of gas, and the metal transfer mode being utilized. Welding flat surfaces requires higher flow than welding grooved materials, since the gas is dispersed more quickly. Faster welding speeds, in general, mean that more gas needs to be supplied to provide adequate coverage. Additionally, higher current requires greater flow, and generally, more helium is required to provide adequate coverage than argon. Perhaps most importantly, the four primary variations of GMAW have differing shielding gas flow requirements—for the small weld pools of the short circuiting and pulsed spray modes, about 10 L/min (20 ft3/h) is generally suitable, while for globular transfer, around 15 L/min (30 ft3/h) is preferred. The spray transfer variation normally requires more because of its higher heat input and thus larger weld pool; along the lines of 20–25 L/min (40–50 ft3/h). See also Forming gas External links Shielding Gas Handbook References Arc welding Welding Industrial gases