Abstract
In the cleaning of boilers using an acid solution added with an inhibitor, sometimes occurred considerable corrosion of pinhole-like pitting type. This is largely considered to be due to Fe3+ and Cu2+, in the acid solution formed by the dissolution of scale and corrosion products during acid cleaning.
Laboratory test was carried on the corrosion rate and pitting formation of welded steel specimens immersed in 7% inhibited hydrochloric acid containing Fe3+ and Cu2+ at 70°C for 6hrs, and also on corrosion preventive effect of stannous chloride added in the same acid solution.
The results are summerized as follows:
(1) When inhibitor alone is used, corrosion rate increases in proportion to the concentration of Fe3+ and Cu2+ and pinhole-like pitting is caused at high concentration of Fe3+ and Cu2+.
(2) Addition of stannous chloride in conjunction with the inhibitor is very effective to reduce the corrosion rate and to prevent the formation of pitting.
