Influence of Hydrogen and Low Temperature on Pipeline Steels Mechanical Behaviour

AbstractIn the presence of H2S, metallic materials, such as carbon and low alloy steels, may suffer hydrogen damage and hydrogen embrittlement. Gas transporting pipes in low temperature environment, during the shutdown and the subsequent re-starting operations, are exposed to very low temperatures (T=-40°C). In the presence of high H2S content in the gas, the risk of brittle failure can be increased due to the effect of hydrogen on steel toughness. In this paper the influence of hydrogen and low temperature on mechanical properties of two pipeline materials, F22 low alloy and X65 micro-alloyed steels, is studied. Steels have been hydrogen charged by means of an electrochemical method: diffusible hydrogen content of steels is in the range 0.6 to 2ppm. Charpy and J-R curves tests were carried out in the range from room temperature to T=-120°C. Hydrogen affects mechanical properties of the tested materials, mainly reducing fracture toughness in J integral tests, while little influence has been observed in CV tests. Fracture surface examination confirms the results of mechanical testing