LOOP TESTING OF INCONEL, NICKEL, MONEL AND BIMETAL HEAT EXCHANGERS. ANPP CORROSION PROGRAM
A description is given of corrosion tests performed on 12 test vessels. Two sets of model heat exchangers (a set consists of a steam generator and superheater) and eight miniature heat exchangers were tested dynamically in a pressurized water loop. One set of model heat exchangers had bimetal tubes (stainless steel in the primary, carbon steel in the secondary) and the other had Inconel tubes. The set with bimetal tubes was service tested for 4890 hours and that with Inconel tubes was service tested 4747 hours. The secondary environment in the bimetal vessels sumulated the SM-1 water conditions while the secondary in the Inconel vessels simulated reactor quality water. Two of the miniature heat exchangers, MIN 10 and 11, had Inconel tubes, MIN 13 and 14 had Monel tubes, MIN 15 and 16 had bimetal tubes and nickel tubes were used in MIN 18 and 19. The test durations for the miniature heat exchangers, MIN 10, 11, 1350 hours, respectively. The Inconel, nickel, and Monel tubing performed well in both reactor grade and high chloride secondary water. Pitting occurred in all three metals but was less prevalent in the Inconel tubing. The Inconel tubing in the model vessels exposed to reactor grade water did not pit. The bimetal model vessels, which were tested using reactor grade water, performed far better than similar vessels exposed previously to a high chloride secondary environment. Nevertheless, the degree of pitting which occurred was prohibitive for long-life steam generators. Tubing in one of the bimetal miniature vessels was defected to expose stainless steel to the high chloride secondary environment. The hypothesis, that the carbon steel provides cathodic protection and prevents stress corrosion cracking of the stainless steel, was supported by the test results; no cracking of the stainless sublayer occurred. However, complete substantiation should be based on further tests. (auth) The oxidation of pure cobalt and cobalt containing small amounts of impurities was studied in air, oxygen, CO/sub 2/, and in CO-- CO/sub 2/ mixtures in the temperature range of 920 deg to ind by using an automatic recording vacuum balance. The mechanism of oxidation was ascertained through the analysis of kinetics and by marker studies, x-ray analysis, and metallographic examination of oxidized specimens. The oxidation kinetics of pure cobalt were parabolic for oxidation in air and oxygen. Oxidation in CO/sub 2/ and in CO-CO/sub 2/ mixtures resulted in linear kinetics for oxide thicknesses less than 7.3 x 10/sup -4/ cm and parabolic kinetics for greater oxide thicknesses. The mechanism of oxidation was determined to be the diffusion of cobalt ions through the oxide. For the linear regions of oxidation observed in the case of oxidation in CO-- CO/sub 2/ mixtures, the oxidation rate, for oxide thicknesses between 4 x 10/sup -6/ and 7.3 x 10/sup -5/ cm, was found to be a linear function of the mole fraction of CO/sub 2/ in the gas phase for temperatures between 1000 deg and 1200 deg C and 1 atm presstep for the process to be dissociatfon of carbon dioxide into carbon monoxfde and adsorbed oxygen atoms or ions in accordance with a mechanism proposed by C. Wagner for the oxidation of iron in CO-- CO/sub 2/ mixtures. Small amounts of impurities drastically altered the kinetics and the mechanism of oxidation of cobalt. The impurities affected the kinetics and mechanism of oxidatfon through alteration of the mechanical properties of the oxide. (auth)
- Research Organization:
- Martin Co. Nuclear Div., Baltimore
- NSA Number:
- NSA-16-009153
- OSTI ID:
- 4815612
- Report Number(s):
- MND-E-2681
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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