13th International Conference on Fracture June 16–21, 2013, Beijing, China The inclusion of from about 50 to about 200 parts per million (ppm), preferably 100 ppm of thiourea, will insure the maintenance of any dissolved copper in a soluble state. In the absence of such a copper complexing agent, copper oxides which are present in any scale, will dissolve and then plate out as metallic copper causing severe pitting of the industrial process equipment and the piping systems [13]. In addition, while it is optional, it has been found to be beneficial if the descaling composition includes about 0.1 grams/liter of a neutral emulsifying agent, such as alkyl benzene sulfonate to make it easier to penetrate in small cracks [14]. It has also been found that the benefits of the process of the present invention can best be achieved by employing a temperature of about 300 K or above for a period of about one (1) to about ten (10) hours, with eight (8) hours being preferred. 3. Procedure and Results For a fuller understanding of the nature and objects of this invention, the following specific examples are given. These examples, however, are not to be construed as limiting the invention in any manner. Example 1 A series of 5.0 cm x 2.5 cm mild steel specimens were prepared by cutting them from a single sheet of cold-rolled 1020 steel. The specimens were then polished under running tap water using a series of silicon carbide emery paper of 100, 400 and 600 grit, respectively, and then washed with distilled water and thereafter degreased with benzene and weighed on a Mettler AJ 100 electronic balance. One group of prepared steel specimens were fully immersed in 500 cc of a cleaning and descaling solution containing 8% hydrochloric acid, 1.5% hydrofluoric acid, 80 ppm of acridine orange, 2% citric acid, 2% EDTA, 0.1 g/1 of alkyl benzene sulfonate, and 100 ppm thiourea. This is referred to herein as the "inhibited solution". Another group of steel specimens were also immersed in the foregoing cleaning and descaling solution except for the fact that the composition did not contain any acridine orange. This is referred to herein as the "uninhibited solution". Potentiostatic polarization studies were carried out for both inhibited and uninhibited solutions under isothermal conditions at 303, 313, and 323 K and under controlled conditions of flow at 600, 1000, and 1400 rpm employing a potentiostat (Model 553-AMEL-Italy). The iron electrode was polarized from -900 mV to -100 mV (vs. saturated calomel electrode) at a sweep rate of 20 mV/min [15]. Another series of potentiostatic polarization studies were conducted for the heat transfer set of conditions, with a potential of -1000 mV being applied until a steady state heat flux was attained as indicated by the constant temperature reading from the thermocouples. Then the full polarization was carried out under isothermal conditions. The duration of each of the weight loss experiments was eight (8) hours. At the conclusion of the test, the specimens were withdrawn, rinsed with water, then dried and reweighed. The percentage inhibitor efficiency (I%) was calculated by the following equation [16]:
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