The article presents the results of the experimental investigations on studying the effect of heat input on the metal-physical properties of the welded joints of pipes with the diameters of 114–406 mm and the wall thicknesses of 9–21 mm from steels X42–X46 according to API 5L standard with various welding technologies. The analysis is given concerning the thermal welding cycles using technologies of manual arc welding with electrodes with a basic and cellulose type of coating, as well as automatic welding technology under a flux layer. The parameters of thermal welding cycles were measured using 12-channel recorder, which received a signal from chromel-alumel thermocouples stamped near the weld. The data obtained was processed in accordance with the program, which included an assessment of the maximum temperatures and temperature gradients, a study of the kinetics of the accumulation of thermal effects in the near-seam zone, and the zone of thermal influence, as well as an assessment of the residence time of the welded joint metal at a temperature above 600 °C. The analysis of thermal cycles using various welding techniques and methods showed that the parameters of thermal welding cycles largely determine the metal-physical properties of the weld metal and the zones of thermal influence, the possibility of trouble-free and long-lasting operation of the structure at various ambient temperatures.
It is shown that the choice of the optimal thermal welding cycle allows to obtain high mechanical properties of metal in all the areas of the welded joint, and, also, ensures the production of weld metal with high metallurgical quality, which increases the working condition of the pipeline and the safety of maintenance personnel during its operation. The presented results of the study can serve as a basis for the development of additional requirements for welding technology of steels of various strengths considering the maintenance of the working condition of the structure as a whole.
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