Top-surface modification as mitigation strategy against hydrogen embrittlement

Hydrogen, serving as a versatile energy carrier, fulfills a crucial role within the energy transition towards a carbon-neutral society. Its safe transportation through pipelines is essential, however, hydrogen embrittlement affects the pipeline's structural integrity. Top-surface modification can serve as a potential mitigation strategy against this, in particular by using ceramic-based surface coatings such as carbides, nitrides, and oxides. This research investigates the influence of chromium nitride coatings, deposited by reactive magnetron sputtering, as hydrogen permeation barriers by evaluating their influence on the hydrogen permeation behaviour of X70 pipeline steel. Hydrogen permeation tests, through the Devanathan-Stachurski cell, are used for this purpose. To gain more insight into the role of the coatings, their integrity, and defect structure in the permeation process, in-situ electrochemical impedance spectroscopy and Mott-Schottky analysis are used. External mechanical loading is applied during hydrogen permeation, to evaluate the permeation process under both elastic and plastic stress and their influence on coating performance. Furthermore, the coatings are characterised before and after hydrogen exposure by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy to get more insight into the coating’s microstructure, crystal phases, and chemical composition.