Abstract
Carbon steel alloys for transport and storage of hydrogen gas at high pressure are susceptible to hydrogen embrittlement (HE). Alternative material solutions are therefore investigated. Cladding with hydrogen metal barriers may be an economically viable approach to mitigate HE in the underlying base material. In this work we are investigating aluminium (EN-AW 6082) and austenitic stainless steel (EN1.4404) as prospective hydrogen barriers. Even though hydrogen permeation rates are low for both alloys, they are not impermeable. The objective of the work has been to characterize hydrogen permeation through clad materials, including surface oxides, bulk barrier materials and interphase between barrier and substrate.
To investigate the various phases separately, a PdAg alloy was applied on surfaces with and without oxides. Hydrogen charging was done electrochemically, and hydrogen diffusion was analyzed by Devanathan cell, GDOES and melt extraction.
GDOES profiles were very effective for calculating diffusion coefficients. However, no commercial GDOES standards for hydrogen are available, so quantification had to be performed by melt extraction and subsequent calculation of sub-surface concentration. The results were in good agreement with previously published values for EN1.4404. Hydrogen diffusion in aluminium is much less studied, and published diffusion coefficients vary over several decades. Aluminium is highly susceptible to corrosion in the testing, which complicated the work. The paper will focus on methodology for studying hydrogen diffusion in stainless steel and aluminum. The results show that both materials will be effective barriers to hydrogen, and that oxide cracks will have little effect on hydrogen embrittlement of the steel substrate.