Steel In Supercritical Water Research Articles

Corrosion Behavior of T91 and Type AISI 403 Stainless Steel in Supercritical Water

The corrosion behaviour of a ferritic/martensitic steel T91 and a martensitic stainless steel type AISI 403 exposed to supercritical water (SCW) at 450°C and 25MPa for up 750h was investigated. After each exposure period, the amount of oxide formed on the samples was determined by gravimetry. The oxide morphology and composition were characterized using scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), and X-ray diffraction (XRD). Results show that for both materials the oxide growth follows a behaviour between parabolic and cubic growth laws. The type AISI 403 stainless steel with a higher Cr content was found to have a better corrosion-resistance performance than the T91 steel. A dual-layered oxide scale, which was mainly composed of an outer magnetite layer and an inner Fe/Cr spinel layer, formed on both T91 steel and type AISI 403 SS.

Estimation of kinetic parameters of the corrosion layer constituents on steels in supercritical water coolant conditions

A model for the distribution of individual metallic constituents (Fe, Cr, Ni, Mn) in the corrosion layers on steels in supercritical water is proposed. A detailed description of the model concept and the calculation procedure is given. To verify and validate the model, its predictions are quantitatively compared to depth profiles of the oxides on ferritic–martensitic and austenitic steels as estimated by surface analytical techniques. Estimates of kinetic and transport parameters of the oxidation process for ferritic–martensitic and austenitic stainless steels in supercritical water are obtained. Predictive calculations of the growth kinetics of the respective oxides are presented and discussed.

Development of Al added high-Cr ODS steels for fuel cladding of next generation nuclear systems

A successful example of high-Cr oxide dispersion strengthened (ODS) steels development is introduced with showing key technologies to overcome the issues to meet material requirements for next generation nuclear systems as well as fusion blanket systems. Corrosion issue requires Cr concentration more than 14wt.%, but aging embrittlement issue requires it less than 16wt.%. An addition of 4wt.%Al is effective to improve corrosion resistance of 16wt.%Cr-ODS steel in supercritical water (SCW) and lead–bismuth eutectics (LBE), while it is detrimental to high-temperature strength. An addition of small amount of Zr or Hf results in a significant increase in creep strength at 973K in Al-added ODS steels. Feasibility of high-Cr ODS steel without Al addition is assessed for fusion application in terms of corrosion resistance in SCW.

A model for the normal stress dependence of intergranular cracking of irradiated 316L stainless steel in supercritical water

The intergranular cracking behavior of irradiated 316L stainless steel in supercritical water (SCW) was found to be strongly dependent on the local grain boundary normal stress. Tensile specimens of 7 dpa proton irradiated 316L stainless steel were strained in 400 °C SCW to 2%, 5%, and 10% macroscopic plastic strain. The cracking behavior was characterized according to the distributions of cracked grain boundary plane surface trace inclinations to the tensile axis and the Schmid factors of the grains adjacent to the cracked boundaries. Cracks occurred preferentially along grain boundaries with trace inclinations perpendicular to the tensile axis and adjacent to grains with low Schmid factors. There was also a slight increase in cracking propensity for grain boundaries adjacent to grains with high Schmid factor mismatch. The normal stress dependence of intergranular cracking was confirmed by developing and applying the Schmid-Modified Grain Boundary Stress model which characterizes the normal stress acting on a grain boundary as a function of the inclination of the grain boundary plane to the tensile axis and the flow stress of the grain, as estimated from its Schmid factor. By applying this model, the Schmid factor dependence of intergranular cracking could be predicted from the distributions of cracked grain boundary trace inclinations to the tensile axis.

Stress corrosion cracking susceptibility of austenitic stainless steels in supercritical water conditions

The presented paper summarizes the results of general corrosion and stress corrosion cracking (SCC) susceptibility tests in supercritical water (SCW), studied for austenitic stainless steel 316L, with the aim to identify maximum SCW temperature usability and specific failure mechanisms prevailing during slow strain-rate tensile (SSRT) tests in ultra-pure demineralized SCW solution with controlled oxygen content. The general corrosion tests clearly revealed the applicability of austenitic stainless steel in SCW to be limited to 550 °C as maximum temperature as oxidation rates of austenitic stainless steels 316L increase dramatically above 550 °C. The SSRT tests were performed using a step-motor controlled loading device in an autoclave at 550 °C SCW. Besides the strain rate (resp. crosshead speed), the oxygen content was varied in the series of tests. The obtained results showed that even at the lowest strain rate, a serious increase of SCC susceptibility, as typically characterized by IGSCC crack growth, was not observed. The fractography confirmed that failure was due to a combination of transgranular SCC and transgranular ductile fracture. Based on fractographic findings a phenomenological map describing the SCC regime of SSRT test parameters could be proposed for AISI 316L.

Corrosion Behavior of Modified UNS N08367 Austenitic Steel in Supercritical Water

Abstract The corrosion behavior of a modified UNS N08367 austenitic steel (mod. UNS N08367) exposed to deaerated supercritical water at 650°C and 25 MPa for exposure times to 1,000 h was investigat...

General corrosion properties of modified PNC1520 austenitic stainless steel in supercritical water as a fuel cladding candidate material for supercritical water reactor

The Super-Critical Water-cooled Reactor (SCWR) has been designed and investigated because of its high thermal efficiency and plant simplification. There are some advantages including the use of a single phase coolant with high enthalpy but there are numerous potential problems, particularly with materials. As the operating temperature of supercritical water reactor will be between 280°C and 620°C with a pressure of 25MPa, the selection of materials is difficult and important. Austenitic stainless steels were selected for possible use in supercritical water systems because of their corrosion resistance and radiation resistance. The PNC1520 austenitic stainless steel developed by Japan Atomic Energy Agency (JAEA) as a nuclear fuel cladding material for a Na-cooled fast breeder reactor. The corrosion data of PNC1520 in supercritical water (SCW) is required but does not exist. The purpose of the present study is to research the corrosion properties for PNC1520 austenitic stainless steel in supercritical water. The supercritical water corrosion test was performed for the standard PNC1520 (1520S) and the Ti-additional type of PNC1520 (1520Ti) by using a supercritical water autoclave. Corrosion tests on the austenitic 1520S and 1520Ti steels in supercritical water were performed at 400, 500 and 600°C with exposures up to 1000h. The amount of weight gain, weight loss and weight of scale were evaluated after the corrosion test in supercritical water for both austenitic steels. After 1000h corrosion test performed, the weight gains of both austenitic stainless steels were less than 2 g/m2 at 400°C and 500°C . But both weight gain and weight loss of 1520Ti were larger than those of 1520S at 600°C . By increasing the temperature to 600°C, the surface of 1520Ti was covered with magnetite formed in supercritical water and dissolution of the steel alloying elements has been observed. In view of corrosion, 1520S may have larger possibility than 1520Ti to adopt a supercritical water reactor core fuel cladding.

Corrosion behavior of 9–12% Cr ferritic–martensitic steels in supercritical water

As important structural materials for advanced power plants, the corrosion of 9–12% Cr ferritic–martensitic steels exposed to both high-temperature water and supercritical water (SCW) was studied using a variety of characterization techniques. Exposure temperature and time showed significant effects on the surface morphologies, oxide scale thickness, and oxide constituents. The steels approximately followed near-parabolic oxidation kinetics in the SCW conditions. The inner spinel layer was found to be porous with a size of tens of nanometers independent upon the exposure temperature and time. High temperature accelerated the formation of a large amount of pores in the outer magnetite layer.

Tensile and stress corrosion cracking behavior of ferritic–martensitic steels in supercritical water

Tensile and stress corrosion cracking behavior of ferritic–martensitic steels in supercritical water were studied in order to evaluate the suitability of these steels for supercritical water nuclear reactor concept. The ferritic–martensitic steels tested in this study consisted of T91, HCM12A, HT-9, weld T91, and weld HCM12A. A series of constant extension rate tensile (CERT) tests at a strain rate of 3 × 10 −7 s −1 were conducted in supercritical water over a temperature range of 400–600 °C and pressure 24.8 ± 0.07 MPa. CERT tests in argon and in supercritical water with 100 and 300 appb dissolved oxygen also were performed at 500 °C to compare the effect of environment. The results show that HT-9 exhibited the highest yield and maximum stresses, followed by HCM12A, and T91. The reduction in area of T91 is the highest, followed by HCM12A, and HT-9. Temperature has a great effect on tensile behavior of these steels. An increase in test temperature from 400 to 600 °C reduces the yield stress by ∼50%. Both T91 and HCM12A weld steels exhibited a slightly lower yield and maximum stresses than the base steels. Increased dissolved oxygen in the water resulted in a significant reduction of ductility. Fractography showed that all of the specimens exhibited ductile rupture except for HT-9 that showed evidence of intergranular cracking. Intergranular cracking in HT-9 is affected by temperature and oxygen concentration in supercritical water.

Oxidation of 316 stainless steel in supercritical water

The oxide scales of 316 stainless steel (316 SS) have been examined after exposure to supercritical water (SCW) with 2.0% H 2O 2 for up to 250 h. The exposed samples were analyzed using weight measurement, scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). It was found that mass gain of all samples increased with increasing temperature and exposure time. Higher temperature SCW resulted in rougher surfaces and thicker oxide scales. Duplex layer oxide structures with Ni-enrichment at the oxide/metal interface developed on all samples exposed to SCW, which were identified as Fe 2O 3/Fe 3O 4 + spinel/Cr 2O 3/Ni-enrichment/316 SS from the outer to inner layer. The possible oxidation mechanisms are also discussed.

Transmission electron microscopy of oxide development on 9Cr ODS steel in supercritical water

Oxide layers formed on 9Cr oxide dispersion strengthened ferritic steel alloys during exposure to 600 °C supercritical water for 2- and 4-weeks were examined using cross-sectional transmission electron microscopy. A focused ion beam in situ lift-out technique was used to produce site-specific samples with electron transparent areas up to 8 μm by 10 μm. The oxide layers consist of several sub-layers: an Fe-rich outer oxide, a Cr-rich inner oxide, and a diffusion layer, extending beyond the oxide front into the metal. An evolution of the oxide layer structure is seen between 2 and 4 weeks, resulting in the development of a band of Cr 2O 3 at the diffusion layer/metal interface from the previously existing continuous mixture of FeCr 2O 4 ‘fingers’ and bcc metal. It is believed that transport in this Cr 2O 3 layer at the diffusion layer/metal interface becomes the rate-limiting step for oxide advancement, since this change in oxide structure also corresponds to a decrease in corrosion rate.

Evolution of the oxide structure of 9CrODS steel exposed to supercritical water

The corrosion behavior and oxide structure of 9CrODS steel in supercritical water has been studied. Samples were exposed to supercritical water at 500 and 600 °C for times of 2, 4 and 6 weeks. The oxide structure was studied using microbeam synchrotron X-ray diffraction and fluorescence analysis. The 600 °C samples exhibited a three-layer structure with Fe 3O 4 in the outer layer, a mixture of FeCr 2O 4 and Fe 3O 4 in the inner layer, and a mixture of metal and oxide grains (FeCr 2O 4 and Cr 2O 3) in the diffusion layer. Between the 2 and 4-week samples exposed to 600 °C supercritical water, a Cr 2O 3 film appeared at the diffusion layer–metal interface which appears to be associated with slower oxidation of the metal. The 500 °C samples also showed a three-layer structure, but both the outer and inner oxide layers contained mainly Fe 3O 4, and the diffusion layer contained much fewer oxide precipitates and was a solid solution of oxygen ahead of the oxide front.

CORROSION BEHAVIOR OF AUSTENITIC AND FERRITIC STEELS IN SUPERCRITICAL WATER

The general corrosion behavior of austenitic and ferritic steels(316L, 304, N controlled 304L, and 410) in supercritical water is investigated in this paper. After exposure to deaerated supercritical water at /25 MPa for up to 500 h, the four steels studied were characterized using gravimetry, scanning electron microscopy/energy dispersive X-ray spectroscopy(SEM/EDS), X-ray photoelectron spectroscopy(XPS), and X-ray diffraction(XRD). The results show that the 316L steel with a higher Cr and Ni content has the best corrosion-resistance performance among the steels tested. In addition to the oxide layer mixed with and that formed on all the samples, a loose outer layer was observed on the 410 steel. The corrosion mechanism of stainless steels in supercritical water is discussed based on the above results.

Stress Corrosion Crack Growth in Type 316 Stainless Steel in Supercritical Water

Abstract A crack growth rate test on a compact tension specimen of Type 316 (UNS S31600) stainless steel was conducted in pure water under both subcritical and supercritical conditions. The crack g...

Corrosion behaviour of nickel base alloys and 316 stainless steel in supercritical water under alkaline conditions

The supercritical water process is an attractive method for the decomposition of hazardous organic wastes and for the upgrading of low quality hydrocarbon resources. However, corrosion of reactors or heat exchangers is a major problem in industrial applications. It is important to select suitable structural materials, which are compatible with the supercritical water environment of each particular process, to ensure the long term integrity of the reactor components. The objectives of the present study were to evaluate the corrosion behaviour of candidate corrosion-resistant alloys in supercritical water environments under reducing atmospheres and to improve understanding of the corrosion mechanism. Four kinds of Ni-base alloys, Alloy 625, Alloy C-276, Ni–45Cr–1Mo (MC alloy) and Ni–19Cr–19Mo (MAT 21) and a Type 316 stainless steel were used in the present study. A parametric study was carried out to investigate the influences of environmental variables such as temperature, anion content, pH and the hydrogen partial pressure, on the corrosion rate and corrosion morphology of the alloys. A static autoclave was used in the present study. The exposure time was 50 h, the applied pressure was 25 MPa and the test temperature was 400°C. The susceptibility of the alloys to stress corrosion cracking was also evaluated by the slow constant strain rate technique. The corrosion rate of Type 316 stainless steel was always higher than that of any of the Ni-base alloys in supercritical water containing NaOH. While the weight change of Type 316 stainless steel was small in deionised water, the weight gain significantly increased with increasing NaOH concentrations. In a reducing atmosphere containing NaOH, the weight loss increased with increasing hydrogen partial pressure. In supercritical water under a reducing atmosphere containing NaOH, Ni-base alloys containing both Cr and Mo, such as Alloy C-276 and MAT 21, would be more resistant to corrosion than Ni–Cr binary alloys. Stress corrosion cracking did not occur in deionised water at 400°C/25 MPa. With 0·001 mol L−1 HCl or 0·01 mol L−1 NaOH, cracking occurred in Type 316 stainless steel. With 0·001 mol L−1 HCl or NaOH, cracking occurred in Alloy C-276. With 0·01 mol L−1 HCl or NaOH, cracking occurred in Alloy 625. The cracking susceptibility of Ni-base alloys in supercritical water containing either HCl or NaOH decreased as their Cr content increased.

Influence of chromizing treatment on the corrosion behavior of AISI 316 stainless steel in supercritical water oxidation

SCWO, sometimes referred to as hydrothermal waste processing, uses the solvating traits of water in its supercritical condition to effectively destroy liquid organic wastes. One major problem in the supercritical water oxidation process is corrosion, because all metallic tubes in the process are exposed to high temperature and high pressure as well as severe corrosive species such as Cl−, F−, S2−, and O2−. The presence of Cl− when the pH of a solution is very low and the solution has excess oxygen causes active corrosion and metal loss by metal-chloride and/or oxychloride formation. This study performed a chromizing treatment on 316 stainless steel and immersion tests in supercritical water. Weight change of chromized steels and untreated steels was measured, and the chemical state and composition of oxide films on 316 stainless steel were investigated. On the basis of SCWO tests using distilled water, the oxide layer was found to be very thin and homogeneous and weight gain was observed regardless of testing temperature, while the chromizing treatment slightly reduced weight gain. In the case of SCWO tests using salt water, weight loss was observed regardless of testing temperature and its corrosion mode was pitting by chloride ion, while chromizing treatment greatly decreased the corrosion rate.

1010 超臨界水中でのステンレス鋼の環境助長割れ機構に関する一考察

1010 超臨界水中でのステンレス鋼の環境助長割れ機構に関する一考察

Effect of embryo developmental stage and quality on the efficiency of in vitro produced bovine embryo splitting

The corrosion resistance of three different Cr content oxide dispersion strengthened (ODS) ferritic steels in supercritical water (SCW) and their passive films formed on the surface have been investigated. The results show that the dissolved oxygen (DO) and chemical composition have significant influence on the corrosion behavior of the ODS ferritic steels. In 2000 ppb DO SCW at 650 °C, the 14Cr-4Al ODS steel forms a tri-layer oxide film and the surface morphologies have experienced four structures. For the tri-layer oxide film, the middle layer is mainly Fe-Cr spinel and the Al is gradually enriched in the inner layer.

臨界点以上の水中における不銹鋼の腐食

臨界点以上の水中における不銹鋼の腐食

Corrosion of Stainless Steels In Supercritical Water

Abstract The behavior of stainless steels, including both hard-enable and nonhardenable grades, in degassed supercritical water at 800, 1000, and 1350 F and a pressure of 5000 psi is described. In general, the corrosion at 1350 F observed for the alloys was found to be intergranular, while at 1000 F, only Inconel X exhibited selective penetration along grain boundaries. All alloys suffered some decarburization and carbide precipitation after exposure to supercritical water at 1350 F. No significant phase changes were observed at 800 and 1000 F. The Armco 17-4PH, Armco 17-7PH, and Hastelloy F alloys were the most resistant materials at 1350 and 1000 F. All of the alloys evaluated had excellent resistance to 800 F degassed supercritical water. The AISI Type 316 material was shown to be susceptible to stress-corrosion cracking at 1350 F. 4.6.5