CORROSION ENGINEERING SECTION CORROSION—Vol. 59, No. 11 1029 0010-9312/03/000191/$5.00+$0.50/0 © 2003, NACE International Submitted for publication October 2002; in revised form, March 2003. ‡ Corresponding author. * Corrosion Protection Division, National Metallurgical Laboratory, Jamshedpur-831007, India. ** Department of Chemistry, Indian Institute of Technology, Bombay, Mumbai, India. A Fresh Look at ASTM G 1-90 Solution Recommended for Cleaning of Corrosion Products Formed on Iron and Steels D.D.N. Singh ‡, * and A. Kumar** ABSTRACT ASTM G 1-90 solution, also popularly known as Clarke solu- tion, which contains concentrated hydrochloric acid (HCl, specific gravity [sp.gr.] = 1.19) + 2% antimony trioxide (Sb 2 O 3 ) and 5% stannous chloride (SnCl 2 ), shows considerable varia- tion in its corrosive effect toward steels having different chemical compositions. Plain carbon steels (PCS) and some low-alloy steels (LAS) experience faster dissolution in com- parison to LAS having copper, manganese, silicon, chromium, etc., as alloying elements. The presence of phosphorous in steels has an accelerating effect on corrosion rate. An at- tempt has been made to bring down the corrosion rate of different types of steels to an equal level by modifying the composition of the ASTM-recommended cleaning solution. Addition of 0.5% copper salt (cuprous chloride [CuCl]) to the Clarke solution has dramatically improved the performance of the solution, and an almost identical rate of corrosion is recorded for all the studied steels. This addition also acceler- ates the dissolution rate of oxide of steels with variations in their chemical compositions. Electrochemical direct current (DC) polarization and alternating current impedance spectro- scopic (EIS) studies have been performed to understand the mechanism of the action of the original and modified solu- tions in controlling the corrosion of steels. KEY WORDS: acid cleaning, acid corrosion, ASTM G1-90 solution, cleaning, descaling, electrochemical impedance spectroscopy, low-alloy steels, plain carbon steels INTRODUCTION The corrosion rate of steels exposed in different types of corrosive environments has been evaluated after removing the corrosion products formed on their sur- face. In the case of low-alloy weathering-type steels (LAS) and plain carbon steels (PCS) exposed to indus- trial, rural, and urban environments, the corrosion products are normally in the form of oxides of iron and other alloyed elements. 1-3 For the removal of cor- rosion products, ASTM G 1-90 recommends various types of cleaning solutions for metals and alloys. 4 For iron and steels, the recommended cleaning solutions are either strongly inhibited acid solutions (effective at room temperature) or alkaline solutions with different types of complexing agents (effective at elevated tem- peratures). 4 Among the various compositions recom- mended, the most commonly used and popular solution for cleaning corrosion products from iron and steel is as follows: —1,000 mL hydrochloric acid solution (HCl, spe- cific gravity [sp.gr.] = 1.19) + 20 g antimony trioxide (Sb 2 O 3 ) + 50 g stannous chloride (SnCl 2 ) This solution is effective in cleaning corrosion prod- ucts at room temperature. The solution, also known as Clarke solution, is widely used in industries and research laboratories. It is presumed that this solu- tion is highly effective in cleaning oxide rusts but has no corrosive effect on cleaned, virgin surfaces of iron and steels. In contrast, using the above-mentioned solution during the descaling process, it was noticed that it behaved differently for different types of steels with variations in their chemical compositions. The