The study evaluated the condition of steel gas pipeline at the site of weld after more than 45 years ofservice. The deformation cycle of welding and particularly superposition of the thermal anddeformation cycle, results in phase transformation and precipitation processes in the thermally affectedregion. The deformation cycle has a pronounced effect on ageing of the welded joint and the associatedincrease in its hardness and reduction in notch toughness. The hardness of the weld was measuredaccording to Vickers HV0.05. The highest values of hardness were measured for the weld metal,namely 293 HV0.05. The values of mechanical properties of steel after more than 45 years of serviceof the pipeline corresponded to values defined by the respective standard. Transition temperature TTaccording to Charpy test was equal to -8.5 C. From the point of view of technical practice, with regardto pipe service properties, it is important that the construction material is loaded at temperatures abovethe transition temperature TT. Transcrystalline brittle failure was observed on the specimens that havebeen broken at TT temperature.
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