Common acid pickling inhibitor is alkali, belonging to non-synergistic inhibition, and hindering the efficiency of pickling, with the vector velocity at 3—4.5%.BCT-616 is an acid pickling inhibitor, belonging to synergistic inhibition, and increasing the efficiency of pickling, with the vector velocity at 0.3—0.7%. It is applicable for oxidable acid, as well as nonoxidable acid; it is applicable for multiple inorganic acid.  High percentage of inhibition: can reach above 99.6%.  High quality of product: the products after cleaning have smooth surface, no hydrogen embrittlement, and no sag.  Save on the steels: increase the product rate of steel for 2~3kg/Ton (acid pickling steel).