Effect of hydrogen charging on Charpy impact toughness of an X70 pipeline steel

Hydrogen uptake in steel structures can cause a degradation in mechanical properties such as toughness, and can induce cracks. This phenomenon is widely known as hydrogen embrittlement. For structural steels subjected to cathodic protection or pipelines transporting high-pressure hydrogen gas, hydrogen embrittlement represents an important challenge. Charpy V-notch testing provides a fast and inexpensive method for quantifying the impact toughness of a steel. However, its validity for assessing hydrogen embrittlement is uncertain. In this work, the influence of hydrogen uptake on the impact toughness of an API 5L X70 pipeline steel is investigated. Charpy V-notch impact tests are performed in air, both uncharged and after electrochemical hydrogen pre-charging. Different charging times are used, and the influence of hydrogen-induced cracking is studied. The temperature range of the Charpy impact tests is between -80 degrees C and +20 degrees C. A rising upper shelf phenomenon is observed in the uncharged specimens and the ductile-to-brittle transition temperature (DBTT) is not reached for the tested temperatures. For this material, hydrogen uptake causes a reduction in Charpy impact energy at the higher test temperatures, with the highest reduction measured at room temperature. A post-mortem analysis of the fracture surfaces suggests that the presence of hydrogen in the lattice aids the formation of separations during fracture, lowering the absorbed energy. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the 23 European Conference on Fracture - ECF23