Inhibition of Atmospheric Corrosion of Mild Steel by Sodium Benzoate Treatment Ramazan Kahraman (Submitted 11 June 2001; in revised form 1 September 2001) The objective of this study was to evaluate the effectiveness of sodium benzoate as an inhibitor to slow down or prevent atmospheric corrosion/discoloration of the local mild steel during storage in the Arabian Gulf region. Test specimens were prepared from locally produced reinforcing steel products. The inhibitor solution was applied on steel specimens at a concentration of 100 mM for 1 day at room temperature. Wooden exposure racks were used to hold as-received and inhibitor-treated specimens during atmospheric exposure for different periods. Corrosion was evaluated through weight loss determination and electro- chemical technique. As expected, the Arabian Gulf atmosphere was corrosive on the as-received local mild steel. On the other hand, treatment of steel with sodium benzoate lowered its corrosion rate during initial days of its exposure to atmosphere. However, atmospheric corrosion inhibition performance of sodium benzoate deteriorated with exposure time after 30 or more days of atmospheric exposure, and the corrosion rates of sodium benzoate-treated specimens reached that of the unprotected specimens at the end of 90 days of atmospheric exposure. Keywords Arabian Gulf, atmospheric corrosion, inhibitors, so- dium benzoate, steel 1. Introduction The weather in the Arabian Gulf region is hot and humid, providing a corrosive environment for metallic structures. In Dhahran and Jubail, the relative humidity is above 50% during most of the year. In summer, air temperature may go up to 50 °C. The daily temperature fluctuations can be as high as 20 °C during hot seasons, whereas the fluctuations of relative humidity may range between 40 and 100% over a 24 h period. Petroleum and petrochemical industrial areas and the prox- imity of the inhabited areas to the shores of the Gulf have caused a dramatic increase in atmospheric corrosion of the metallic structures. The atmospheric corrosion in the Gulf re- gion is aggravated further by high salinity of Gulf water, re- sulting in the high rate of sea-salt deposition. The chloride and sulfate contents in the atmospheric air of the Gulf coast in Dhahran are 63.2 × 10 -3 and 33.8 × 10 -3 mg/m 3 , respec- tively. [1] Various inhibitors that can help in protection against metal corrosion in aqueous environments were reported in the litera- ture. Among them are 3-(toluyl)-N-(1,1-dimethyl-2-hydro- xyethyl)-alanine known as toluylalanine, [2] 3-(trimethoxysilyl) propanethiol-1, [3] cyclohexyl amine, [4] dicyclohexylamine ni- trite, [5] benzoic acid, [6] sebacic acid, [2] ethanolamine, [7] thio- phenol, [8,9] imidazole derivatives, [10] chromates, [11-13] fatty acid esters, [14] carboxylic acid, [15] benzoates, [2] sulfonates, [16] silicates, [12] phosphates, [12,17] nitrites, [2] nitrates, [18] and some commercial coolants. [19] The role of inhibitors can be due to adsorption of phase layers on the metal surface or by the interaction with one of several corrosion products to form a new protective phase, rather than by adsorption on the metal surface. Inhibitors such as sodium benzoate adsorb on the metal surface and provide a barrier for the entry of aggressive ions such as chloride. The inhibitors may also passivate the metal by stabilization of the passivating oxide film and by decreasing its dissolution rate. Inhibitors can also interact with the oxide-covered metal sur- face to form insoluble compounds that plug pores in the oxide film and prevent oxygen reduction reaction at the cathodic sites in neutral solutions. [20] The objective of this study was to investigate experimen- tally the effectiveness of sodium benzoate treatment in prevent- ing or decreasing the corrosion/discoloration of local mild steel products during storage under atmospheric conditions in the Arabian Gulf region (industrial marine environment). It should be noted that the inhibitor is not applied in the corrosive en- vironment; instead, the inhibitor solution is first applied on steel, which is then taken out of the inhibitor solution and exposed to the atmosphere. 2. Experimental 2.1 Test Specimens The test specimens were prepared from locally produced reinforcing steel products. Two groups of specimens were pre- pared. The first included 5 in. long specimens for weight loss determinations. The second included 1 in. long specimens for electrochemical measurements that were threaded at one cross- sectional side to fit them in the working electrode rod of the electrochemical cell. All specimens were washed prior to the study by using soap and water, followed by ultrasonic cleaning in acetone and methanol before drying. Ramazan Kahraman, Chemical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia. Contact e-mail: kahraman@kfupm.edu.sa. JMEPEG (2002) 11:46–50 ©ASM International 46—Volume 11(1) February 2002 Journal of Materials Engineering and Performance