Ni-P Coatings as Hydrogen Permeation Barriers—A Review

Hydrogen became one of the most studied energy carriers after the global energy crisis and can replace gas and oil as clean fuels. The main challenge is its safe storage and long-distance transportation: steel is among the materials most used for hydrogen storage and transportation. However, steel is susceptible to hydrogen embrittlement (HE). HE can be prevented by depositing hydrogen barrier coatings on the steel surface. This review provides an overview of the hydrogen permeation mechanism and the analytical methods employed to evaluate the performance of the hydrogen permeation barriers. The focus is on Ni and electroless Ni-P coatings deposited on steel as hydrogen barriers. These coatings have been used so far for their anti-corrosion and wear properties; they are currently of interest due to their low hydrogen permeability. The simplicity of production and the possibility of achieving a homogeneous coating, regardless of the geometry of the substrate, make the electroless deposition process of the Ni-P alloy a candidate for 'in situ' applications in existing pipelines. This process can be implemented by using and adapting the established pig batch technology.