The need for structural materials that can resist hydrogen assisted degradation becomes critical for the continuation of the development of the hydrogen economy. Understanding reasons for the occurrence of remaining H-permeability in a duplex steel/Al/Al2O3 system by measuring the concentration of hydrogen is of crucial importance in this context. In this work, it is proposed to carry out a mass-selective NCS experiment concurrently with neutron diffraction on a series of duplex steel/Al/Al2O3 samples to calculate the concentration of hydrogen within the sample and hence the underlying reasons for the occurrence of remaining H-permeability of the barrier with changing environmental conditions such as temperature and pressure.