0.3847, 0.0891, 0.096 และ0.2829 mm 2 เที ยบกั บ 1.143, 0.246, 0.108 และ 0.269 mm 2 ตามลํ าดั บ เมื ่ อประเมิ นจากกระแส สู งสุ ดสํ าหรั บปลากระป องทั ้ ง 3 ยี ่ ห อและผั กผสมดองเค็ มซี เซ็ กฉ าย) คํ าสํ าคั ญ: แผ นเหล็ กเคลื อบแล็ กเกอร , เทคนิ คโพเทนชิ โอสแตติ ก, กล องจุ ลทรรศน
AbstractLacquer coated steel can is widely used for different types of food e.g. sea-food and fruit. Thus, can factories have to inspect the quality of lacquered can for corrosion resistance on surrounding food. For this purpose electrochemical technique was used to accelerate corrosion process by DC voltage. 6V potential was applied for 10 seconds to lacquered can containing different kinds of solutions i.e., 2%w/w NaCl, 2%w/w NaOH, 2%w/w citric acid and 2%w/w Na 2 S 2 O 5 , respectively. Lacquered can which could not endure the solution at high voltage would corrode. Failure of lacquered can could be analyzed quantitatively from the amount of maximum currents and total amount of charges (current time) released. Current was potentiostatically plotted against time and calibration curve was made from maximum of the dissolution currents and charges of different sites of wires in various solutions. Corrosion currents and charges of dissolved wires were plotted against corroded area on the calibration curve. Lacquered cans from factory were tested and it was found that the currents were in the range of 10-1700 µA. The results showed that these cans were in good conditions and least or no corrosion was found. Food cans were purchased from supermarket and were tested in similar ways. Maximum currents and charges were determined and calculated as corroded areas. When compared the outcome from calibration curve with the result from microscope, it was evidently revealed that corroded areas calculating from optical microscope images were under estimated which were a little bit lower than those calculated from calibration curves of maximum currents and charges [evaluated values from microscope were 0.3847, 0.0891, 0.096 and 0.2829 mm 2 compared with 1.143, 0.246, 0.108 and 0.269 mm 2 , respectively, which were evaluated from maximum current for sardines in tomato sauce (Three brands) and salted mixed vegetables].
Crevice corrosions of duplex stainless steels were investigated under the aggressive condition of sea water pumps in offshore petroleum platforms. The study aims to compare crevice corrosion behavior of three grades of duplex stainless steels, UNS S32101 (2101), UNS S31803 (2205) and UNS S32750, in seawater with 200 ppm of hypochlorite. Duplex steels were compared with a widely used austenitic steel UNS S31603 (316). Specimens were tested under synthetic sea water prepared at pH4, pH6 and pH8 by the cyclic potentiodynamics polarization technique and the potentiostatic technique. The results show that the duplex stainless steels had higher corrosion resistance compared with the 316. The released charges and the corrosion rates of the 2101 and the 2205 were similar, but much lower than those of the 2507especially after 3 months period.
Acoustic emission (AE) is a non-destructive technique which is well known for crack monitoring. Moreover, it has been widely used for corrosion and erosion damage on metallic structures. In this study, AE technique was applied for quick monitoring of corrosion resistance of lacquer coatings on tin free steel and laminated steel for food can-packaging. There were three types of coatings: (A) BPA-NI lacquer, (B) BPA-complied lacquer, and (C) PET lamination. These coatings were investigated in flat-sheet and in deformed sheet. Cathodic disbonding (CD) technique was carried out to cause separation between the coating and the metal substrate and initialize corrosion damage. AE signals was detected immediately with potential excitation, and showed good correlation with coating corrosion resistance during corrosion development. AE count signal matched with resulting current during CD, and proportional to corroded areas. In addition, coatings properties were measured before and after the CD process by electrochemical impedance spectroscopy (EIS). A combination of AE and CD techniques offers an in-situ non-destructive corrosion monitoring of coating quality before and during delamination development, and useful for can-packaging testing.
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