Influence of test temperature on impact toughness of long-term operated API 5L X67 steel depending on the orientation of specimens and notches

Keywords

pipe steel, microstructure, operational degradation, impact toughness, mechanical properties, temperature, fractographic analysis.

Cite as

Zvirko О. І., Demianchuk D. O., Tsyrulnyk O. T., and Nykyforchyn H. M. Influence of test temperature on impact toughness of long-term operated API 5L X67 steel depending on the orientation of specimens and notches. Physicochemical Mechanics of Materials. 2026. 62(3), 88-94.

Abstract

The impact toughness KCV of API 5L X67 steel with a ferrite-pearlite structure in the as-received state and after 34 years of operation on a natural gas transit pipeline was determined depending on the test temperature (from –196 to 20°C), the orientation of the specimens and notches relative to the rolling direction. Extremely low values of fracture energy (1–3 J/cm²) were obtained for impact tests at –196°C. For specimens with notches oriented in the longitudinal and transverse directions, typical cold-brittleness curves were obtained in the temperature range of –70–+20°C with a decrease in the KCV level for a decreasing test temperature. However, for longitudinal specimens made of operated steel and with a notch oriented in the short transversal direction, the opposite pattern was observed in the temperature range of –40–+20°С. This effect of the fracture energy intensity increase with decreasing test temperature was associated with the complex morphology of fracture surfaces.