Surface coating with a high resistance to hydrogen entry under high-pressure hydrogen-gas environment

•Two-layer and three-layer aluminum-based coatings were prepared.•A hot dipping method was used for the coatings.•Coated specimens were exposed to high-pressure hydrogen gas (up to 100 MPa).•Resistance to hydrogen entry of the coating was dependent on hydrogen pressure.•Three-layer coating showed a high resistance to hydrogen entry.

Development of a surface coating with high resistance to hydrogen entry under a high-pressure hydrogen-gas environment is presented. Two aluminum-based coatings were developed on the basis of preliminary tests: two-layer (alumina/Fe–Al) and three-layer (alumina/aluminum/Fe–Al) coatings, deposited onto cylindrical and pipe (Type 304 austenitic stainless steel) surfaces by immersion into a specially blended molten aluminum alloy. The coated specimens were exposed to hydrogen gas at 10–100 MPa at 270 °C for 200 h. Specimen hydrogen content was measured by thermal desorption analysis; hydrogen distributions were analyzed by secondary ion mass spectroscopy. Both coatings showed high hydrogen-entry resistance at 10 MPa. However, resistance of the two-layer coating clearly decreased with an increase in pressure. In contrast, the three-layer coating showed excellent hydrogen-entry resistance at a wide pressure range (10–100 MPa), achieved by the combined effect of alumina, aluminum, and Fe–Al layers.