Abstract
The deleterious consequences of hydrogen on materials, commonly referred as hydrogen embrittlement (HE), is a well-known phenomenon that can lead to unexpected and sudden structural failures. Therefore HE is of concern for the structural integrity of subsea pipelines and their weldments, where atomic hydrogen can be made available from the cathodic protection (CP) system, welding consumables and/or moisture in the hyperbaric weld chamber atmosphere during weld repair. Moreover, the material susceptibility to HE depends on a number of factors whose impact should always be considered when assessing the materials resistance to HE: hydrogen pressure or cathodic potential, strain rate, temperature and stress conditions are some examples. The work described is part of a wider research effort with the purpose to establish a Cohesive Zone Modelling (CZM) framework for hydrogen enhanced cracking of complete pipeline's weldments in hyperbaric conditions. In order to develop cohesive elements with the most general validity, the influence of stress concentration factors on HE susceptibility on weld simulated Coarse Grained Heat Affected Zone (CGHAZ) for an X70 API 5L pipeline steels has been studied experimentally. Three types of specimens with different notch severity have been tested: smooth, v-notched and pre-fatigued cracked specimens were loaded in tension while in-situ hydrogen electrochemically charged at room temperature. The results show a clear influence of the stress concentration factor on the resistance toward HE.
