Effect of Inhibitors on Scale Removal in HCl Pickling Solutions

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Abstract
Inhibitors are available which effectively reduce the loss of metal because of corrosion occurring in the hydrochloric acid pickling baths. Selection of these inhibitors, however, must take into consideration the effect the inhibitor will have on scale dissolution. The optimum concentration of inhibitor must consider the functional relationship between inhibitor concentration and the rate of scale removal. This relationship is not the same as that between inhibitor concentration and metal dissolution rate. Data are shown on scale dissolution rates for two corrosion inhibitors in 10 percent by weight hydrochloric acid at temperatures of 55 through 85 C (131-185 F). Extrapolations to somewhat higher temperatures of some pickling operations can be made. However, it was observed that all corrosion inhibitor effects on scale removal became somewhat temperature-dependent at, or near, 80 C. The experimental acid corrosion inhibitors (B and C) exhibit surfactant behavior between 55-75 C, removing scale more quickly than did the uninhibited acid.
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