Some classes of organic substances were tested as inhibitors for 3%HF attack on low alloyed chromium steels (ASTM A335 type steels containing 1·35−10%Cr). Only sulphur containing additives (phenylthiourea, dibenzylsulphoxide, etc.) showed inhibiting efficiency values of ∼ 99% at both 45 and 60°C regardless of steel chromium content. These additives act by inhibiting both the anodic and the cathodic processes. Alloyed chromium hinders the diffusion of atomic hydrogen into the iron lattice (hydrogen permeation), which is also influenced by sulphur containing additives. Phenylthiourea increased both the diffusivity and the permeability of hydrogen, while dibenzylsulphoxide decreased both.
