THE EFFECT OF TENSILE STRESS ON AMMONIA VAPOR CORROSION OF UNS C71500 MATERIAL

• Main Author: Destri Pramesthi, Chevira
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/71319
• Institution: Institut Teknologi Bandung

Cupronickel 70/30 materials are frequently used in heat exchanger tubes due to their excellent corrosion resistance and high heat conductivity. Dissolved oxygen in heat exchanger systems and other industrial components is a major contributor to corrosion. Hydrazine is an oxygen scavenger added to reduce dissolved oxygen levels in water, but hydrazine also produces residual product in the form of ammonia. The accumulation of residual ammonia in the system can cause ammonia corrosion. In this final project, the ammonia vapor corrosion test was conducted using the C-Ring stress method (ASTM G-38) in ammonia solutions to determine the corrosion resistance of C71500 tubes. The test was carried out for 15 days in a container containing 3 and 5M ammonia solutions, each containing three testing specimens with tensile stress variations of 100, 120, and 140% ?yield. Corrosion evaluations were conducted by mass reduction measurements and metallographic observations to determine the type of corrosion attack. The test results indicated that pitting corrosion was the dominant type of corrosion attack. The mass reduction of testing specimens in 5M ammonia was greater than that of 3M, and increased significantly with increasing tensile stress from 100 to 120% ?yield. The mass reduction of testing specimens with tensile stress variations of 100, 120, and 140% ?yield in 3M ammonia vapor were 0.005, 0.0075, and 0.007 grams, while in 5M ammonia vapor were 0.007, 0.011, and 0.003 grams respectively. This study concludes that tensile stress affects the corrosion susceptibility of specimens in ammonia vapor because it will damage the passivation layer that increases tubes susceptibility to pitting corrosion. However, corrosion susceptibility is also affected by the initial surface conditions of the tube, the annealing effect, and the presence of Ni-Fe precipitates. The 70Cu- 30Ni tubes material has very good SCC resistance to ammonia vapor as shown by the absence of stress corrosion cracking after 15 days of exposure. The 70Cu-30Ni tubes material has better ammonia vapor corrosion resistance than the 90Cu-10Ni due to higher nickel content that reduced cathion vacancy in copper.