Strength assessment using destructive testing on MIAB welded alloy steel tubes and subsequent techno-economical evaluation

In this study, an attempt is being made to determine the feasibility of Magnetically Impelled Arc Butt (MIAB) welding process for joining alloy steel tubes in pressure parts. In view of this, a specially made state of art MIAB welding unit (MD1) available at WRI, BHEL, Tiruchirappalli has been employed and adequate number of welding trials is conducted to weld alloy steel tubes of 6–7 mm thickness for boiler applications. The combination of a set of values provided as input is varied for each trial. The welding current and the welding time are divided into three and four stages respectively. For each trial, either the current in stage II is varied or the time for stage III is varied while maintaining the other input parameters constant. These trials are carried out mainly to develop an optimum window (working range) for the process parameters. Further, the strength of MIAB welded specimens are examined by subjecting the welded specimens to various destructive tests. It is observed that the weld region is stronger than the base metal in most of the cases.In the next part of the study, the characteristics of MIAB welded joints for T11 steel tubes are compared with those using flash butt welding and induction pressure welding that is presently employed for alloy steel tube joining in pressure parts. It is found that the manufacturing time and incurred cost per weld drastically reduces while simultaneously increasing the productivity. Hence, the feasibility of MIAB welding process for pressure part is established.