Factors influencing the pickling time required for hot-rolled steel strip

Abstract

Laboratory studies of HCl pickling of hot-rolled Type L steel under conditions spanning the range of HCl, dissolved iron, and temperature that might be encountered in actual practice show that for both iron-free solutions and solutions containing iron, the major factors that influence pickling time are temperature and acid concentration. With HCl pickling, unlike H2SO4 pickling, the influence of iron buildup in the bath causes at most a slight increase in pickling time. Although a number of sets of temperature-acid concentration conditions may be selected to achieve a given pickling time, some conditions will present more of a problem in fume control than others. To aid in choosing rapid pickling conditions that will not result in excessive fuming, reference should be made to data on the vapor pressure of HCl solutions for the conditions under consideration. The vapor pressure of HCl solutions increases with an increase in temperature and with increases in the concentrations of HCl and iron in the bath. Data are presented on acid concentrations that will achieve certain pickling times at 150, 175 and 200°F; at higher temperatures, lower HCl concentrations may be used and these conditions, particularly for short pickling times, tend to minimize fuming as compared with the alternative lower temperatures and higher HCl concentrations.