This document discusses welding techniques for heavy engineering industries. It describes various welding processes like fusion welding and resistance welding. Fusion welding involves melting materials using heat sources like flames, electric arcs or beams. It then lists several fusion welding processes like shielded metal arc welding and gas tungsten arc welding. The document discusses applications of welding in heavy engineering like welding thick-walled reactors. It notes the challenges of welding heavy thick materials and the need for preheating, postheating and stress relieving. It also describes some mechanized welding techniques and automated systems used for applications like nozzle welding.