CORROSION STUDIES ON TIG AND SMA WELDED STAINLESS STEEL

Abstract

Stainless steels (chromium content > 11%) are used extensively in the power generation, pulp and paper, and chemical processing industries, but are also chosen for use in many everyday household and commercial products. Joining and fabrication of austenitic stainless steels (18Cr, 8Ni) for various industrial applications is done, using different welding procedures. In this work, two processes namely, Gas Tungsten Arc Welding (GTAW) or Tungsten Inert Gas welding (TIG welding) and Submerged Metal Arc Welding (SMAW), have been used to study the corrosion behaviour of AISI 304 austenitic stainless steel weldments with welding current as a variable. The corrosion tests employed were salt spray test, static immersion test in 5% NaC1, pitting test in 6% FeCl3 and potentiodynamic polarization test. Electro etching of the welded specimens was also carried out in 10% oxalic acid solution to detect the susceptibility of the specimens to intergranular attack. When the pitting test results were compared with corrosion in conventional sodium chloride medium, it was found that heavy pitting and clear knife line attack was observed in the area slightly away from the weld metal in each specimen, whereas in NaCl medium, no signs of corrosion were observed even after a 30 days exposure in static condition. Thus in mild corrosive media, in a given range of welding current, SMA welded specimens proved to be more reliable and satisfactory as compared to TIG welded specimens. The current was varied in the range of 90 — 110 A for TIG welding and 70 — 90 A for SMAW. In this range of variation of welding current, the corrosion rates are not affected significantly.