MATERIAL BEHAVIOR IN EXTREME CONDITIONS: DETAILS OF THE EXPERIMENTAL TESTS

In parallel to two other oral works presented in this conference [1,2], this poster contribute aims to describe in details the experimental tests carried out on two high performance pipeline steels (X65 and F22) in extreme conditions: low temperature and presence of hydrogen. An extensive experimental test was carried out, without hydrogen, and with hydrogen charge. For the J-R tests, different temperatures were taken into consideration. The procedure of hydrogen charging is innovative and described in [1]. The verified and measured percentage of hydrogen charged in all the C(T) specimens, is between 0.6 and 2 ppms. All the specimens after the hydrogen charging were put in liquid nitrogen and the experimental tests were carried out in few hours in order not to waste the hydrogen. The experimental results show a significant effect of the hydrogen on the mechanical behavior of the steels, in particular, at low temperature, the hydrogen presence prevents the plastic behavior of both the materials. In the case of X65 the behavior is more brittle with unstable crack propagation. In the case of F22, on the contrary, the hydrogen reduces the plasticization, but the material is yet ductile. The fracture surfaces of the hydrogenated specimens are examined and compared to the ones without hydrogen. In [2] all the results are described and compared with the ones obtained by an other charging procedure. In this paper the details of this testing procedure are given and commented.