Development of in situ techniques for torsion and tension testing in hydrogen environment

Reliability of hydrogen pipelines and storage tanks is significantly influenced by the mechanical performance of the structural materials exposed to the hydrogen environment. Fracture behavior and fracture toughness are of specific interest since they are relevant to structural integrity. However, many conventional fracture testing techniques are difficult to be realized under the presence of hydrogen. Thus it is desired to develop novel in situ techniques to study the fracture behavior of structural materials in hydrogen environments. In this study, two special testing apparatus were designed to facilitate in situ fracture testing in H₂. In addition to a multi-notch tensile fixture, a torsional fixture was developed to utilize an emerging fracture testing technique, Spiral Notch Torsion Test (SNTT). The design concepts will be discussed. Preliminary in situ testing results indicated that the exposure to H₂ significantly reduces the fracture toughness of 4340 high strength steels by up to 50 percent. Furthermore, SNTT tests conducted in air demonstrated a significant fracture toughness reduction in samples subject to simulated welding heat treatment using a Gleeble machine, which illustrated the effect of welding on the fracture toughness of this material.