"Bleach at pH 11 vs pH 7 affects on Stainless Steel"

Question:

"We are looking at the use of sodium hypochlorite acidified to a pH of 7 because of its increased disinfectant properties. We are current using a 3% bleach solution (pH around 11), but wondering if the change in pH will increase corrosion of stainless steel equipment."

Answer:

Temperature, type of steel, other impurities or components make substantial difference. However, in general change of the hypochlorite pH from 11 to 7 makes definite and significant increase in corrosiveness. Many grades of stainless steels will suffer from severe pitting and crevice corrosion when continuously exposed to sodium hypochlorite. Sensitivity to attack depends significantly on the surface condition. On a clean and polished surface corrosion attack is less likely than on a surface with various defects resulting from the fabrication. Welds and flanges are attacked preferentially.

If your equipment is exposed to the hypochlorite only periodically and well rinsed after it might survive but the risk of corrosion is higher when the pH is decreased to 7.

 

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