Brass corrosion in tap water distribution systems inhibited by phosphate ions

The effect of sodium orthophosphate on the protective characteristics of the surface layers are studied on brass in contact with moderately hard, highly carbonated and chloride rich simulated drinkable water. The optimal inhibitor concentration is evaluated from the composition, thickness and pitting resistance of the surface film. This layer is mainly composed by zinc(II) oxide–hydroxide and cuprous oxide. By adding PO43−, the film quality improves, attributed to the incorporation of CuO or Zn(II) compounds. The changes are evident with 5 mg l−1 P, and between 10 and 20 mg l−1 P no significant differences are observed.

Research highlights
► Brass in contact with tap water is covered by Zn(II) oxide–hydroxide and Cu2O.
► With PO43− as corrosion inhibitor, the film becomes less porous, thinner and denser.
► The optimal dose of inhibitor required is 10 mg l−1 P.