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Questions are considered of the reliability of assembled welded joints of valve fittings. It is proposed to use impact strength as a criterion of welded metal durability for welded joints. The effect of welding heating cycle on the structure and phase composition, and properties of metal around the joint (MAJ) of the heataffected zone (HAZ) of welded joints made from steel of strength categories K42 and K52 is studied. The effect of strain ageing on impact strength characteristics of the MAJ of the HAZ is analyzed for steel 17GS with different structure and phase compositions. It is shown that metal of the MAJ of the HAZ with a predominantly bainitic structure is most resistant to strain ageing. Dependences are plotted for evaluating welded joint material endurance and determination of the duration of the operating period, during which there is no critical fall in impact strength, and rational welding regimes are also established that make it possible to prolong safe operation of valve equipment to 30–35 years.

Austenite phase transformation kinetics and changes connected with them in the microstructure and hardness of steel 10G2FBYu under different welding heating cycle conditions are studied. Simulation is used for physical processes that occur during welding in the heat-affected zone and in the zone near the seam.