STUDY ON THE USE OF INTERNAL PROTECTION ATMOSPHERE IN PIPE WELDING FOR THE FOOD INDUSTRY

Abstract

A problem in the manufacture of pipes for the food industry is the formation of internal defects generated during the welding process. The most common defect occurs at the weld root, due to oxidation at high temperatures, and does not allow access for subsequent finishing process. One of the control methods is the use of a controlled atmosphere (purging gas) inside the tubes during welding. This study addresses the adequacy of the use of purging gas and the addition of metal during the union of AISI 304L stainless steel tubes through the GTAW (Gas Tungsten Arc Welding) process. For this purpose, round profile tubes were welded with different  purging gas flow rates to protect the joint root. After welding, visual analysis of the internal surface of the tubes and macrography were carried out to evaluate the weld, in addition to microhardness and tensile strength tests, in order to evaluate the mechanical properties. It has been found that the use of purging gas contributes to the formation of a cleaner surface at the weld root. The increase in flow from 5 to 10 l/min generated similar root finish levels, indicating that low flow rates are already sufficient to eliminate the defect. The use of filler metal did not generate a significant increase in mechanical properties, indicating that autogenous welding, if properly performed, guarantees continuity of properties in the piping.