| Abstract: | Inhibitor efficiency in long‐time protection of steel tanks for the chemical surface preparation against local corrosion by process solutions containing hydrochloric acid The efficiency of prevailing acid inhibitors is examined by age hardening heavy tank‐steel plates in technically usual hot‐galvanizing solutions for 1000 hours. With acid inhibitors local corrosion emerged as shallow pit formation first and foremost in hydrochlorid acid pickles (20 g/l HCl) at ambient temperature as well as in cleaners containing hydrochloric acid (10–30 g/l HCl) at 40°C when other conditions also applied. Above all, local corrosion was produced if the inhibitor concentration became too low (0.2 g/l) in connection with a minimum hydrochloric acid concentration (10–30 g/l). However, oxidizing agents like iron(III)‐ions (5–10 g/l), atmospheric oxygen and free chlorine (100–1000 mg/l) lead to local corrosion, too. Local corrosion did not emerge in rinse baths (2–10 g/l HCl) and fluxing material solutions of zinc chloride and ammonium chloride (pH value: 2.0–5.5). Here uniform corrosion developed. Acid inhibitors turned out to be very effective against uniform corrosion in the examined long‐time period (inhibiting values up to 99%). |
