Effect of Hydrogen Environment on Fatigue Behaviour of High Toughness Steels

The energy supply questions is becoming more and more urgent for all the world. As there is not one general solution, some energy sources and energy technologies have to be considered and reconsidered to ensure a continuous and safe energy source. Hydrogen as an energy carrier and hydrogen applications, as fuel cells, are considered to play an important role in clean energy utilization. Metallic materials, such as carbon and low alloy steels, may suffer embrittlement and mechanical damage in presence of hydrogen at high pressure. The study of the mechanical characteristic of steels under the influence of hydrogen embrittlement is an essential area due to the importance of these materials for utilization system like fuel cells and huge production and transportation infrastructure like pipeline and vessels. In this paper the combined influence of hydrogen and low temperature on fatigue crack growth properties of two pipeline materials, X65 micro−alloyed and F22 low alloy steels, is studied. Fatigue propagation tests were carried out on hydrogen charged and uncharged specimens, by varying the test temperature and the frequency of the load application cycle. Specimens were charged with hydrogen before fatigue testing using an electrochemical method. The experimental results show an evident effect of the hydrogen presence on the fatigue crack growth. The diffusion rate of hydrogen in the steels seems to be the most important parameter in order to explain the influence of temperature and frequency on the fatigue crack propagation rate. Fracture surface examination confirms the results of mechanical testing.