Pitting Corrosion of Copper Coiled Tubes in the Air Conditioning System having the Open Heat Storage Water Tank

A Study of Water Treatment Chemical Effects on Type I” Pitting Corrosion of Copper Tubes

“…After that, although it temporarily decreased, it remained at approximately 160 mV vs. SSE, which was a noble value compared to that of the other copper tubes with low residual carbon amount. It has been reported that the potential for pitting corrosion affected by residual carbon is approximately 100 mV vs. SCE (approximately 147 mV vs. SSE in SSE conversion, broken line in Figure 5) [7]. Specimen C_6.1 B reached this potential after two weeks, and pitting was considered to have occurred during this period.…”

“…To prevent these types of corrosion, it has been proposed that in the case of type I' corrosion, the concentration of free carbonic acid be reduced to less than 15 ppm or the amount of mean residual carbon on the copper tube inner surface (hereafter referred to as "residual carbon amount") be reduced to 5 mg/m 2 or less [6]. On the other hand, type I" is suppressed by reducing the residual carbon amount to 2 mg/m 2 or less, which is lower than that of type I', or by filtering out fine particles that are the corrosion products of the main galvanized steel pipe [7]. However, due to the production cost of copper tubes as industrial products, the development of a water treatment chemical capable of suppressing pitting corrosion even in the presence of residual carbon is desired, rather than removing the residual carbon [8].…”

Relationship between Corrosion Form and Elution Behavior of Copper Tubes Surfaces with Different Residual Carbon Amounts

“…The C 0.5 specimen had an outer diameter of 15.2 mm and a wall thickness of 0.4 mm, and the C 2.5, C 5.3, C 6.6, and C 13 specimens had an outer diameter of 15.88 mm and a wall thickness of 0.8 mm. The residual carbon amount of this test material was measured by the conventional method [15]. The specimens were cut to a length of 10 cm, and each test material was cut in half.…”

“…Environmental factors, such as water quality, pH [4] [5] [6], chloride ions [7] [8] [9] [10], sulfate ions [11] [12], and dissolved oxygen [13], also had effects on this process. It was reported that pitting corrosion tended to occur when the amount of residual carbon (hereafter referred to as "residual carbon amount") was 2 mg/m 2 or higher [14] [15], but no standardized test method for pitting corrosion resistance of copper tubes had been established, and electrochemical tests and water flow tests were generally used [16] [17] [18] [19] [20]. However, these tests were difficult to apply for quality analysis because it took time to obtain the results of pitting corrosion.…”

Simple Measurement of Carbon Films on Copper Tubes and Their Effects on Corrosion

“…It has also been reported that the occurrence of pitting corrosion is suppressed even in the presence of a carbon film by adding a water treatment agent to the cooling water [5] [6]. In regard to a quantitative method to analyses this carbon film, it has been reported that after degreasing the inside of the tube with an organic solvent, the inside surface of the tube is dissolved with a mixture of nitric and hydrochloric acid to collect and analyze the attached carbon [7]. However, this method is dangerous because it uses a mixed acid.…”