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CATASTROPHIC OXIDATION OF HIGH-TEMPERATURE ALLOYS

Description: The growth of nonprotective, crust-like oxide films was encountered in high-temperature alloy systems that contain molybdenum, vanadium, or tungsten as strengthening additions. The cause of accelerated oxidation in such alloys appears to be associated with the characteristically low melting temperatures of oxides of these refractory elements. The factors that contribute to a breakdown of oxidation protection in these systems are outlined and remedial methods which may be used to avoid catastrophic oxidation are discussed. Commonly encountered service failures that have resulted from catastrophic oxidation are also described. (auth)
Date: November 10, 1961
Creator: DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Compatibility of structural materials with fusion reactor coolant and breeder fluids

Description: Fusion reactors are characterized by a lithium-containing blanket, a heat transfer medium that is integral with the blanket and first wall, and a heat engine that couples to the heat transfer medium. A variety of lithium-containing substances have been identified as potential blanket materials, including molten lithium metal, molten LiF--BeF/sub 2/, Pb--Li alloys, and solid ceramic compounds such as Li/sub 2/O. Potential heat transfer media include liquid lithium, liquid sodium, molten nitrates, water, and helium. Each of these coolants and blankets requires a particular set of chemical and mechanical properties with respect to the associated reactor and heat engine structural materials. This paper discusses the materials factors that underlie the selection of workable combinations of blankets and coolants. It also addresses the materials compatibility problems generic to those blanket-coolant combinations currently being considered in reactor design studies.
Date: January 1, 1979
Creator: DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Development of surface treatments and alloy modifications for corrosion-resistant oxide scales

Description: Alloys based on the long-range ordered system Fe{sub 3}Al are under development at Oak Ridge National Laboratory in support of coal conversion and combustion materials requirements. Of particular interest is the performance of these alloys in coal gasifiers involving product gases with relatively low oxygen activities and high sulfur activities. Using H{sub 2}S-H{sub 2}-H{sub 2}O gas mixtures, several experimental iron-aluminum alloys have been tested to assess the effects of aluminum concentration on oxidation-sulfidation response at 700 to 800{degree}C in a simulated gasifier environment. Metallographic and chemical analyses of the corrosion product scales and the underlying alloy were performed to determine the role of respective metallic elements on the sulfidation-oxidation processes. These results, together with thermogravimetric analyses, are discussed in terms of the apparent corrosion mechanisms and optimization of alloy composition for exposure to coal-derived environments. More recently, the corrosion performance of an Fe-28% Al-2% Cr alloy has been evaluated in gases produced by an operating gasifier. The reaction products and scale morphologies under actual service conditions were generally similar to the laboratory test results except for the presence of an ash deposit on the gasifier specimens. 2 refs., 7 figs., 4 tabs.
Date: January 1, 1990
Creator: DeVan, J.H.
Partner: UNT Libraries Government Documents Department

ORNL-2(A): Environmental effects on iron aluminides

Description: Alloys based on the Fe{sub 3}Al system are under development at Oak Ridge National Laboratory (ORNL) in support of coal conversion and combustion materials requirements. Using H{sub 2}S-H{sub 2}-H{sub 2}O gas mixtures, several experimental iron-aluminum alloys have been tested to assess the effects of aluminum concentration on corrosion behavior at 700 to 800{degrees}C in a simulated gasifier environment. Included in these studies are alloys that have been aluminized to convert the outer surfaces to FeAl (50 at. % Al). Thermogravimetric analyses, metallographic and chemical analyses of the corrosion product scales, are performed to determine the role of constituent metallic elements on oxidation and sulfidation processes. The corrosion resistance of Fe{sub 3}Al alloys is being evaluated by exposures at 600 to 900{degrees}C in the gas-cooler section of an operating gasifier in the United Kingdom. The nature of protective scales formed on Fe{sub 3}Al-based alloys in sulfur-containing atmospheres, as compared to air, is being evaluated using secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Marker experiments using {sup 18}O are conducted in conjunction with the SIMS studies to monitor oxide growth processes. 4 refs., 3 figs., 1 tab.
Date: January 1, 1991
Creator: DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Compatibility of stainless steel with Pb-17 AT. % Li

Description: The corrosion of type 316 stainless steel and Sandvik HT9 by static Pb-17 at. % Li between 300 and 500/sup 0/C was studied. The resulting weight losses were significantly greater than those of these steels in lithium. The corrosive attack was very uniform, and the room-temperature tensile properties of the steels were unaffected by the exposure. The application of molten Pb-17 at. % Li as a tritium-breeding fluid in conjunction with ferrous alloys in a fusion reactor may be limited to 400/sup 0/C or below.
Date: January 1, 1982
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Investigation of breached depleted UF sub 6 cylinders

Description: In June 1990, during a three-site inspection of cylinders being used for long-term storage of solid depleted UF{sub 6}, two 14-ton cylinders at Portsmouth, Ohio, were discovered with holes in the barrel section of the cylinders. An investigation team was immediately formed to determine the cause of the failures and their impact on future storage procedures and to recommend corrective actions. Subsequent investigation showed that the failures most probably resulted from mechanical damage that occurred at the time that the cylinders had been placed in the storage yard. In both cylinders evidence pointed to the impact of a lifting lug of an adjacent cylinder near the front stiffening ring, where deflection of cylinder could occur only by tearing the cylinder. The impacts appear to have punctured the cylinders and thereby set up corrosion processes that greatly extended the openings in the wall and obliterated the original crack. Fortunately, the reaction products formed by this process were relatively protective and prevented any large-scale loss of uranium. The main factors that precipitated the failures were inadequate spacing between cylinders and deviations in the orientations of lifting lugs from their intended horizontal position. After reviewing the causes and effects of the failures, the team's principal recommendation for remedial action concerned improved cylinder handling and inspection procedures. Design modifications and supplementary mechanical tests were also recommended to improve the cylinder containment integrity during the stacking operation. 4 refs., 2 figs.
Date: January 1, 1991
Creator: DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Liquid metal corrosion considerations in alloy development

Description: Liquid metal corrosion can be an important consideration in developing alloys for fusion and fast breeder reactors and other applications. Because of the many different forms of liquid metal corrosion (dissolution, alloying, carbon transfer, etc.), alloy optimization based on corrosion resistance depends on a number of factors such as the application temperatures, the particular liquid metal, and the level and nature of impurities in the liquid and solid metals. The present paper reviews the various forms of corrosion by lithium, lead, and sodium and indicates how such corrosion reactions can influence the alloy development process.
Date: January 1, 1984
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

CORROSION BEHAVIOR OF REACTOR MATERIALS IN FLUORIDE SALT MIXTURES

Description: Molten fluoride salts, because of their radiation stability and ability to contain both Th and U, offer important advantages as high-temperature fuel solutions for nuclear reactors and as media suitable for nuclear fuel processing. Both applications have stimulated experimental and theoretical studies of the corrosion processes by which molten salt mixtures attack potential reactor materials. Corrosion experiments with fluoride salts which were conducted in support of the Molten-Salt Reactor E xperiment and analytical methods employed to interpret corrosion and masstransfer behavior in this reactor system are discussed. The products of corrosion of metals by fluoride melts are soluble in the molten salt; accordingly passivation is precluded and corrosion depends directly on the thermodynamic driving force of the corrosion reactions. Compatibility of the container metal and molten salt, therefore, demands the selection of salt constituents which are not appreciably reduced by useful structural alloys and the development of container materials whose components are in near thermodynamic equilibrium with the salt medium. Utilizing information gained in corrosion testing of commercial alloys and in fundamental interpretations of the corrosion process, an alloy development program was conducted to provide a high temperature container material that combined corrosion resistance with useful mechanical properties. The program culminated in the selection of a high-strength Nibase alloy containing 17% Mo, 7% Cr, and 5% Fe. The results of several long-term corrosion loops and in-pile capsule tests completed with this alloy are reviewed to demonstrate the excellent corrosion resistance of this alloy composition to fluoride salt mixtures at high temperatures. Methods based on thermodynamic properties of the alloy container and fused salt are presented for predicting corrosion rates in these systems. The results of radiotracer studies conducted to demonstrate the proposed corrosion model also are discussed. (auth)
Date: September 19, 1962
Creator: DeVan, J.H. & Evans, R.B. III
Partner: UNT Libraries Government Documents Department

Mass transfer behavior of a modified austenitic stainless steel in lithium

Description: An austenitic stainless steel that was developed to resist neutron damage was exposed to lithium in the high-temperature part of a thermal convection loop for 6700 h. Specimens of this Prime Candidate Alloy (PCA) composed of 65.0 Fe-15.9 Ni-13.0 Cr-1.9 Mo-1.9 Mn-1.7 Si-0.5 Ti-0.05 C (wt %) were exposed at 600 and 570/sup 0/C in both solution annealed and cold worked forms. The dissolution process was found to be similar to other austenitic alloys in flowing lithium: weight losses of PCA eventually became linearly proportional to exposure time with the specimen surfaces exhibiting porous layers depleted in nickel and chromium. However, the measured weight losses and dissolution rates of these PCA specimens were higher than those of type 316 stainless steel exposed under similar conditions and can be attributed to the higher nickel concentration of the former alloy. The effect of cold work on dissolution rates was less definitive, particularly at 570/sup 0/C. At longer exposure times, the annealed PCA specimen exposed at 600/sup 0/C suffered greater dissolution than the cold worked material, while no effect of prior deformation was observed by analysis of the respective surfaces.
Date: January 1, 1983
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Mass transfer deposits in lithium-type 316 stainless steel thermal-convection loops

Description: In spatially nonisothermal flowing liquid metal systems, selected constitutents of the containment materials characteristically dissolve into the liquid metal in the hotter zones and are deposited in the colder areas. The accumulation of deposits is often a more serious problem than dissolution because of attendant flow restrictions and, in reactor applications, the aggregation of radioactive species in the coolant circuits. Accordingly, the deposition processes in lithium-type 316 stainless steel thermal convection loops is studied. The morphology and composition of deposits varied with loop operating time. Initially, chromium-rich dendritic crystals formed in the colder region of a loop, but later the deposits changed in structure and contained significant amounts of nickel and iron. Deposition rates were also measured as a function of time and temperature and were correlated with the above observations. A plug extracted from one loop consisted of an aggregate of chromium-rich crystals.
Date: January 1, 1980
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Thermal-gradient mass transfer in lithium-stainless steel systems

Description: The corrosion of type 316 stainless steel by flowing Li was studied as a function of time in thermal-convection loops. After a transient period, the corrosion rates were observed to be constant with time with values ranging from 10 to 20 mg/m/sup 2/ h. Preliminary analysis indicated that the corrosion rate is controlled by the diffusion of Fe through the liquid Li boundary layer. The deposition processes involved the formation of crystals of nearly pure Cr in the cold legs of the loops.
Date: January 1, 1979
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Corrosion of high-temperature materials in AFBC environments. Part 2: 4500-h tests

Description: Candidate heat exchanger tube materials were tested for times to 4500 h in a small atmospheric-pressure fluidized bed combustor (AFBC) operated by the FluiDyne Engineering Corporation of Minneapolis, Minnesota. The materialso included alloy 800H; types 304, 310, and 316 stainless steel; and aluminized alloy 800H and type 310 stainless steel. These air-cooled tubes were exposed to the AFBC environment with wall temperatures ranging from 820 to 875/sup 0/C, a Ca/S molar ratio of 3.3 to 5.3, 2.5 to 3.5% excess O/sub 2/, and a fluidizing velocity of 0.7 m/s (2.3 fps). A set of low-temperature tubes was also included in the test for the final 3000-h period. These tubes were composites of 2-1/4 Cr-1 Mo steel and type 304 stainless steel and were air-cooled to temperatures in the range 480 to 590/sup 0/C. Tubes were removed at intermediate times for metallographic examination. In general, the materials performed well. With one exception, metal wastage was at the lower limit of detection and intergranular corrosion was not severe. Most of the high-temperature samples, however, contained subsurface specks of metal sulfides, primarily of manganese, extending to depths of about 50 ..mu..m. The exception to the good performance noted above was a type 316 stainless steel high-temperature tube exposed for the final 3000-h portion of the 4500-h test. This tube suffered severe sulfidation-oxidation over most of its surface. The absence of such attack on eight other type 316 stainless steel tubes indicated that the position of the affected tube in the bed may have been a more significant corrosion factor than the steel composition per se.
Date: August 1, 1981
Creator: Godfrey, T.G. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Corrosion of an Fe-12 Cr-1 Mo VW steel in thermally-convective lithium

Description: A thermal-convection loop of Fe-12 Cr-1 Mo VW steel circulated pure lithium between 500 and 350/sup 0/C for 10,088 h. Periodic weighings of coupons at different temperatures around the loop revealed small weight losses and corrosion rates. Surface analysis showed a relatively thin corrosion layer with an underlying carbide-free zone and some depletion of chromium from the hottest specimen. While some mass transfer of chromium and nickel was detected, this mechanism did not strongly influence the weight loss process as it does with austenitic steels. Therefore, it appeared that reactions with carbon and nitrogen must be the dominant corrosion processes such that weight loss was maximized at the lowest temperature (350/sup 0/C). Overall, the lithium-steel reactions in the temperature range of this experiment were relatively sluggish and the corrosion was not severe.
Date: January 1, 1983
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Corrosion of Fe-Cr-Mn alloys in thermally convective lithium

Description: A series of austenitic Fe-Cr-Mn steels was exposed to circulating lithium at temperatures up to 500/sup 0/C. Two groups of the alloys, which contained 12 to 30 wt % Mn and 2 to 20 wt % Cr, were sequentially exposed for periods greater than 3000 h in a type 316 stainless steel thermal convection loop. Mass transfer of manganese caused very large weight losses from the steels containing 30 wt % Mn. However, the actual magnitude of corrosion losses for alloys containing 12 to 20 wt % Mn was difficult to establish due to competing surface reactions involving chromium.
Date: January 1, 1986
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Corrosion of ferrous alloys exposed to thermally convective Pb-17 at. % Li

Description: A type 316 stainless steel thermal convection loop with type 316 stainless steel coupons and a Fe-9 Cr-1 Mo steel loop containing Fe-12 Cr-1 MoVW steel specimens circulated molten Pb-17 at. % Li at a maximum temperature of 500/sup 0/C. Specimens were exposed for greater than 6000 h. Mass loss and surface characterization data were compared for these two alloys. At any particular exposure time, the corrosion of type 316 stainless steel by Pb-17 at. % Li was more severe, and of a different type than that of similarly exposed Fe-12 Cr-1 MoVW steel. The austenitic alloy suffered nonuniform penetration and dissolution by the lead-lithium, whereas the Fe-12 Cr-1 MoVW steel tended to be more uniformly corroded. The presence of a ferritic layer on the type 316 stainless steel, and its susceptibility to spalling during specimen cleaning, were shown to be important in evaluating the data and in comparing corrosion losses for the type types of alloys. A model for the nonuniform penetration of type 316 stainless steel by Pb-17 at. % Li was suggested.
Date: January 1, 1986
Creator: Tortorelli, P.F. & DeVan, J.H.
Partner: UNT Libraries Government Documents Department

Materials compatibility considerations for a fusion-fission hybrid reactor design

Description: The Tandem Mirror Hybrid Reactor is a fusion reactor concept that incorporates a fission-suppressed breeding blanket for the production of /sup 233/U to be used in conventional fission power reactors. The present paper reports on compatibility considerations related to the blanket design. These considerations include solid-solid interactions and liquid metal corrosion. Potential problems are discussed relative to the reference blanket operating temperature (490/sup 0/C) and the recycling time of breeding materials (<1 year).
Date: January 1, 1983
Creator: DeVan, J.H. & Tortorelli, P.F.
Partner: UNT Libraries Government Documents Department

EXAMINATION OF ORNL 1 AND 2 INTERMEDIATE HEAT EXCHANGERS, TYPE IHE-3

Description: Failure, which resulted in the stoppage of fluoride flow in ORNL No. 1, occurred as a NaK to fuel leak in the vicinity of the NaK inlet heater. The reaction of NaK with fuel at this point caused the deposition of nearly pure UF/ sub 3/ around the tubes and, finally, a sufficient increase in the melting point of the fuel to produce solidification. Fluorides throughout the heat exchangers were found to be depleted in uranium and to contain some potassium. Thus it would appear that stoppage of flow occurred after considerable NaK pick-up had taken place. Fluoride attack observed in these heat exchangers, with the exception of the area of failure, agreed substantially with what would be predicted from other dynamic systems. However, in those tubes near the point of failure, attack on the&quot;tension&quot; side of the tubes occurred to depths approximately twice those observed in &quot;unstressed&quot; tubes at comparable temperatures. Mass transferred particles were present in the NaK circuit of ORNL No. 1 to a maximum thickness of 15 mils. Deposit thicknesses varied markedly from header to header. (auth)
Date: July 20, 1956
Creator: DeVan, J H & Crouse, R S
Partner: UNT Libraries Government Documents Department

An Evaluation of Electro-Machining for the Analysis of Metal Surfaces

Description: A procedure is described for the uniform removal of very thin sections of metal surfaces by electrolysis. Equipment requirements and the various parameters affecting operation are considered, and the results of applying the technique to studies of solid-state diffusion are discussed. The technique appears to offer considerable promise for evaluating chemical changes at metal surfaces which have taken place as a result of corrosion or diffusion processes. (auth)
Date: June 25, 1959
Creator: DeVan, J. H.
Partner: UNT Libraries Government Documents Department