Features of Multi-Electrode Submerged-Arc Welding in the Production of High-Strength Thick-Walled Pipes

An increase in the thickness of the wall of large-diameter pipes is accompanied by an increase in heat input during the welding of the longitudinal weld. The increased heat input results in slower cooling of the heat-affected zone (HAZ) and diminishes the reliability of the welded joint. It was shown on production equipment at the Izhorsky Pipe Plant that the heat input during welding of the lengthwise joint is directly proportional to the thickness of the pipe wall. This finding contradicts the thesis adopted in existing welding technology that heat input can be reduced. Experiments involving the direct recording of thermal cycles on factory equipment established the parameters for cooling of the HAZ and showed that the rate of cooling of this zone decreases when the welding operation is performed on hot metal.