FCAW

Reflecting the estimated increase in natural gas demand, there has been a recent interest in the development of cost-effective materials to be used for the transportation and storage of liquefied natural gas (LNG). Mn could be used in high concentration (between 20~28 wt%) as an alloying addition to create an austenitic steel with mechanical properties similar to traditional LNG tank materials. In this study, microstructural analysis of welded joints in elbow of high-Mn steel was carried out. The samples that were studied were cut from elbows of LNG transportation pipes that were welded by Gas Tungsten Arc welding (GTAW) and Flux Cored Arc Welding (FCAW). This work is concentrated on the analysis of defects and the microstuctural changes at various region of the weldments. A comparative study was done between the GTAW and FCAW weldment of high-Mn steel. It was found that the most of the defects were found in the FCAW weldments. Defects were present at the fusion zone and the reheated fusion zone. Fusion zone of FCAW weldment had the dendritic microstructure, where as fusion zone of GTAW weldment had the equiaxed microstructure. It was also observed that the grain size of heat-affected zone (HAZ) is larger than the other regions. Internal defects, present in the FCAW welded samples, were responsible for lowering the impact energy.

Austenitic high-Mn based twinning-induced plasticity (TWIP) steels having their excellent tensile strength-ductility property combination, provide great potential in applications for structural components. In certain cases, these steels might also replace  austenitic Cr-Ni stainless steels due to lower price and higher speed welding process. Hence a significant increase in the research activity on the weldability of TWIP steels have been proposed in the past decades. In this study, continuous butt welding of Gas Tungsten Arc [1st and 2nd pass] and Flux Cored Arc [2nd pass] welding of pipe elbows were examined. The weldments were characterized by metallography and microhardness tests. Tensile specimens, cut perpendicular to the welding line, were also tested and then subjected to fractographic examinations. Fusion zones, containing dendritic microstructure had lower hardness than HAZ and base metal. Internal cracks, present in the Flux Coated Arc welded samples, were responsible for lowering the tensile properties.

Due to the increase in demand of power in our day to day activities has lead india move once through supercritical technologies but fabrication of [OTSC] has been a challenge to power sector company in India. This is because of quantum of welding in its fabrication stage. So, which increase the cycle time of the fabrication. So, to increase the cycle time of the product in power sector industries has gone to faster welding process like FCAW. In BHEL this FCAW process has been used to weld header with plates as well as pipe with plates manually which reduces cycle time considerably. So, we proposed an idea to automate the FCAW process which reduces cost and cycle time of the product. Once through supercritical (OTSC) techniques developed with FCAW for automation process. It has 4 degree of freedom by using rack and pinion mechanism moves upward, downward, forward and backward. It devices is semiautomatic. An operator is needed for ON and OFF of using limit switch. By using this device there is now need for experienced handler with FCAW semi automation process, for operation of welding easy to operate, faster process completion.