DESIGN OF BACK PURGING APPARATUS FOR THE WELDING OF 304L AUSTENITIC STAINLESS STEEL USING SMAW PROCESS

Austenitic stainless steel is a family of iron-chromium-nickel (Fe-Cr-Ni) alloy systems with low level of carbon. Minimum 10.5% nickel is required to maintain austenitic structure at all the temperatures. The balance between the Cr and Ni along with Mn is normally adjusted to provide microstructure of 90-100% austenite. The type 304L, low carbon version of austenitic stainless steel type 304, is used where welding is involved due to its resistance against inter-granular corrosion and therefore this alloy can be used "as welded condition" even in severe corrosive environments. The main objective to produce a weld joint is to ensure sound weld which match the corrosion and mechanical properties of the base material and to choose a welding process that meets productivity requirements with little distortion as possible and minimum post welding treatments. It is equally important to give protective environment to the weld so that the damage could be minimized. In the present paper, a back purging fixture has been proposed to protect the rear side of the root pass weld metal against oxidation. An inert gas is used to protect the weld metal at the root until it is cooled to the point that oxidation no longer can occur. The authors are working further to study the effect of the designed fixture on the welding efficiency of austenitic stainless steel 304L.