It is suggested that during the process of the chemical cleaning of boilers with restrained acid, enhanced attack upon the steel may take place if significant quantities of copper are present. Laboratory experiments simulating this process have given similar corrosion results whether the copper is deposted from solution or derived from the steel, having been concentrated at the oxide-metal interface during heat treatment. It is suggested that the proprietary restrainer used in the present work was preferentially adsorbed on the copper leaving the steel unprotected.
