Browsing by Author "Draycott, A"

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    High temperature compatibility of 25/20 type austenitic stainless steel with carbon dioxide
    (Australian Atomic Energy Commission, 1962-09) Lee, EJ; Draycott, A
    The 25% Cr, 20% Ni type stainless steel has been proposed for use in the Australian High Temperature Gas Cooled Reactor in core structures, and in hot gas ducting. Thus a knowledge of the compatibility of this steel with high pressure carbon dioxide was required. Rates and mechanisms of corrosion were investigated for machined, vapour blasted, and etched pretreated samples of this steel, exposed to carbon dioxide up to 5,000 hours in the temperature range 650ºC to 800ºC at gas pressures from 3 p.s.i.g. to 280 p.s.i.g. Oxide film flaking was apparent at all temperatures investigated, but was only severe for pre—ground samples at 710ºC and above, and for pre—vapour blasted samples at 760ºC and above. However, severe intergranular penetration was observed in preetched samples on exposure to carbon dioxide at 650ºC and above. Pressure of the gas appeared to have no systematic effect on the corrosion rate, at least in the temperature range investigated. The maximum useful temperature for which the steel could be used would be limited by the amount of oxide flaking permissible. In reactor gas circuits where a small amount of scale flaking could be tolerated, the steel is satisfactory up to 750ºC.
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    Initial results on the compatibility of austenitic stainless-steel with carbon-dioxide.
    (Australian Atomic Energy Commission, 1960-08) Draycott, A; Smith, R
    The possibility of selecting stainless-steel as either a canning or structural material in the projected Australian H.T.G.C. reactor has stimulated interest in the compatibility of this material with CO2. The first series of experiments has been carried out on the oxidation behaviour of an 18-8-Ti stabilized steel in CO2 in the temperature range 550-700ºC, under varying conditions of surface preparation, pressure, velocity and impurity content of the gas. The rate of oxidation was followed by measuring the weight increase of specimens as a function of time of exposure in tests of up to 2500 hours of duration. Supporting information on the nature of the oxidation process was obtained from metallographic and x-ray diffraction techniques. It was found that work-hardened surfaces oxidized at a much lower rate than etched surfaces. In the case of work-hardened surfaces a protective film of Cr2O3 formed which persisted throughout the duration of the tests. On etched surfaces, rapid oxidation occurred to give a non-protective multiplayer scale. In many specimens a thin layer of a second austenite formed below the oxide scale. In no case studied was there any evidence of carburisation. Both pressure and velocity of the gas had considerable effects on the rate of attack of the steel. This investigation has shown that in the range of pressure and velocity investigated, the 18-8-Ti austenitic stainless-steel can be used in CO2 at temperatures up to 675ºC.
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    Oxidation of 1% Cr, 0.5% Mo steel in carbon dioxide.
    (Australian Atomic Energy Commission, 1961-06) Draycott, A; Hubery, RW
    Carbon steels do not suffice as structural materials in carbon-dioxide cooled reactors at gas temperatures above 410ºC, because of insufficient creep resistance. Low alloy steels of the Croloy variety appear to be the first alternatives as the small additions of chromium and molybdenum provide increased creep resistance. The corrosion of a 1% Cr, 0.5% Mo steel in carbon dioxide has been measured over the range of 450 to 525ºC under varying conditions of surface preparation, pressure, velocity, and impurity content of the gas. Weight changes were measured as a function of time of exposure in tests of up to 4,000 hours. It has been found that surface preparation of the specimens and pressures of the gas have little effect on the rate of oxidation of this steel in CO2. Also, presence of moisture up to 20,000 p.p.m. does not materially alter the rate of attack. Weigh-gains of specimens in pure oxygen were always found to be less than weight-gains obtained in carbon dioxide under identical conditions of temperature, pressure, and moisture content. Scaling of the oxide layer was never encountered under static or semi-static conditions. However, scaling occurred on many specimens exposed in flow gas; the extent depended on the temperature and gas velocity. Metallographic examination verified that a protective Cr2O3 film was never likely to be formed on this steel under the conditions of the tests. The major products of the reaction were Fe3O4 and another unidentified spinal. This study has shown that it is not safe to recommend this steel for use in carbon dioxide cooled reactors at temperatures above 450ºC.
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    Oxidation of 2¼% Cr, 1% Mo steel in carbon dioxide.
    (Australian Atomic Energy Commission, 1962-09) Draycott, A; Fox, BJ
    Alloy steels were studied to find types suitable for nuclear use in carbon dioxide-cooled reactors at temperatures in the range 400 — 600ºC. The corrosion of 2¼% Cr, 1% Mo steel in carbon dioxide was measured in the temperature range 460º to 525ºC and the gas pressure range 0 to 225 ps.i.g. The effect of gas velocity, specimen surface treatment, and water content of the gas were also determined. Adherent oxide scales of the Fe304 — Fe203 type were formed under semi—static conditions together with an unidentified spinel. A Cr203 film was never formed under any conditions. Weight gain depended mainly on temperature and varied little with gas pressure, surface treatment, or water content of the gas. The relationship between weight gain and time varied between parabolic and cubic with weight gains ranging from 1.7 mg/cm2 to 5.7 mg/cm2 after 1000 hours exposure within the temperature range investigated. Estimated penetration depths after 10,000 hours ranged from 6.8 x 10—4 to 18.5 x 10—4 inches. In high velocity gas, that is, at 150 ft/sec, weight gains varied from 0.7 mg/cm2 at 460ºC to 2.0 mg/cm2 at 525ºC after 100 hours. No scaling occurred during any experiment not involving thermal cycling but this may have been due to the short duration of the tests. The relative thickness of the outer Fe203 layer in the scales examined was much greater under flowing gas than under semi—static conditions. It appears that the limiting temperature for 2¼% Cr, 1% Mo steel in carbon dioxide—cooled reactors is 490ºC; above this temperature excessive scale formation occurs which, on flaking, could seriously contaminate any gas circuit.
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    Purification of carbon dioxide for reactor purposes, Part III - drying
    (Australian Atomic Energy Commission, 1962-04) Draycott, A; Kerr, AC
    Comparison of the adsorption characteristics of the desiccants silica gel, alumina, and molecular sieves has shown that molecular sieves have by far the greatest capacity of the desiccants at the low partial pressures considered. Equilibrium data in the form of isotherms were established over the range of variables expected in the coolant circuit of a proposed Australian H.T.G.C. reactor. The mass transfer from the gas phase to molecular sieves is such that no correlation could be attempted for the adsorption zone height; the height proved to be too small.
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    Purification of carbon dioxide for reactor purposes. Part 1 - literature survey and recommended programme
    (Australian Atomic Energy Commission, 1960-01) Draycott, A; Kerr, AC
    The impurities likely to be present in carbon dioxide are listed; water is considered to be the most important in view of its adverse effect on the compatibility of many reactor materials with the gas. The literature on various desiccants is reviewed and a suggested experimental programme on drying of the carbon dioxide is outlined. Other major impurities are oxygen and nitrogen. Some chemical means for continually removing the oxygen appear possible. It is likely that the nitrogen content can only be lowered on charging the reactor; no continual method seems feasible at this stage. Minor impurities such as the oxides of nitrogen and sulphur are mentioned and the continual removal of dust in the coolant circuit is considered.
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    Purification of carbon dioxide for reactor purposes. Part II - pressure losses through packed beds of selected desiccants
    (Australian Atomic Energy Commission, 1961-05) Draycott, A; Kerr, AC
    Pressure losses have been measured for the flow of carbon dioxide, air, argon, helium, hydrogen and methane through beds of molecular sieves, and for carbon dioxide and air through beds of activated alumina. It is shown that at the levels of moisture impurity expected in the Australian H.T.G.C. reactor no increased pressure loss caused by adsorption should be encountered. The effect of temperature was studied but in all cases found to be slight. Generally, good correlations were obtained although the low molecular weight gases, particularly hydrogen, showed considerable deviation.
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    Study of the variables affecting the corrosion of beryllium in carbon dioxide
    (Australian Atomic Energy Commission., 1961-12) Draycott, A; Nicholson, FD; Price, GH; Stuart, WI
    Beryllium is a favoured canning and/or moderating material in the proposed Australian High Temperature Gas Cooled Reactor. With carbon dioxide as the most likely coolant a detailed knowledge of the corrosion of beryllium in this gas is required. Two separate investigations have proceeded simultaneously. First the effect of the following variables was studied; surface preparation of the specimen, temperature (100—725ºC), pressure (0—280 p.s.i.g.), velocity, and impurity content of the gas. The influence of irradiation has not yet been studied. Autoclaves, thermobalances, and dynamic loops were used. The results were statistically analysed and kinetic data obtained. In all cases specimens with etched surfaces yielded approximately 25 — 30 per cent, greater weight gains than specimens with ground or polished surfaces. On extruded material no "breakaway" oxidation was encountered below 650ºC in commercially dry gas (< 20 p.p.m. moisture). The rate of attack was to some extent affected by the pressure of the gas. Breakaway was only observed in one series of specimens at 650ºC. In this particular case the gas pressure was 280 p.s.i.g. However, it seems that surface temperatures of beryllium cans made from extruded material should be maintained below 650ºC in a reactor system using the commercially pure carbon dioxide as coolant. In the second approach a more basic study of the chemistry of the reaction was made as well as a detailed investigation into the variation caused by differences in the composition and fabrication of the metal. Spiral spring balances at atmospheric pressure were used. Extruded material made from beryllium powder oxidized in dry oxygen for a short period of time had greatly enhanced oxidation resistance when exposed to carbon dioxide. Some of the material exposed to wet carbon dioxide at 700ºC and atmospheric pressure did not exhibit "breakaway" oxidation. The weight gains after 1,000 hours exposure under these conditions were never greater than 0.5 mg/cmZ, Some comparisons were made between the reaction rates of beryllium with oxygen and carbon dioxide. In certain circumstances dry oxygen gave breakaway oxidation whereas carbon dioxide did not.