STUDY ON THE IGA/SCC BEHAVIOR OF ALLOY 600 AND 690 SG TUBING MATERIALS IN HIGH TEMPERATURE SOLUTIONS.

摘要

IGA/SCC behavior of Alloy 600 and 690 in high temperature solutions was studied using constant extension rate testing (CERT) method under potentiostatic conditions. The IGA/SCC susceptible regions were investigated as a function of pH and electrode potential. The IGA/SCC resistance of SG tubing materials were ranked as, MA600 = TT600 TT690 in acidic solutions, and MA600 < TT600 < TT690 in alkaline solutions. TT690 showed higher corrosion resistance than MA600 and TT600 in both acidic and alkaline conditions. To verify the results of CERT test, long term model boiler tests were also carried out. The model boiler which consists of combinations of several SG tubing materials and tube support plate configurations, operated for more than 15000 hrs under the simulated operating plant conditions. The results of destructive examination showed good correspondence with the results of a fundamental study, CERT test. The improved performance of alternate SG tubing material was confirmed.