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iron-rich oxide scale
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Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 888-899, October 11–14, 2016,
... the alloys. Air aging experiments enabled a distinction between carburisation reactions and carbide precipitation as a result of alloy equilibration. The stainless steel was much less resistant to CO 2 attack, rapidly entering breakaway corrosion, developing an external iron-rich oxide scale and internal...
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Nickel-base alloys were exposed to flowing supercritical CO 2 (P = 20MPa) at temperatures of 700 to 1000°C for up to 1000 h. For comparison, 316L stainless steel was similarly exposed at 650°C. To simulate likely service conditions, tubular samples of each alloy were internally pressurised by flowing CO 2 , inducing hoop stresses up to 35 MPa in the tube walls. Materials tested were Haynes alloys 188, 230 and 282, plus HR120 and HR160. These alloys developed chromia scales and, to different extents, an internal oxidation zone. In addition, chromium-rich carbides precipitated within the alloys. Air aging experiments enabled a distinction between carburisation reactions and carbide precipitation as a result of alloy equilibration. The stainless steel was much less resistant to CO 2 attack, rapidly entering breakaway corrosion, developing an external iron-rich oxide scale and internal carburisation. Results are discussed with reference to alloy chromium diffusion and carbon permeation of oxide scales.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 1113-1125, October 11–14, 2016,
... not observe any modification of the diffusion front and only a thin oxide layer was observed on the top of VALIORTM P92 sample (Figure 3b). In contrast, a very thick iron-rich oxide scale was observed on the standard non-coated P92 sample. Typical oxide morphology is observed [11]: beneath the original metal...
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The steam oxidation behaviour of boiler tubes and steam piping components is a limiting factor for improving the efficiency of the current power plants. Spallation of the oxide scales formed during service can cause serious damage to the turbine blades. Vallourec has implemented an innovative solution based on an aluminum diffusion coating applied on the inner surface of the T/P92 steel. The functionality of this coating is to protect the tubular components against spallation and increase the actual operating temperature of the metallic components. In the present study, the newly developed VALIORTM T/P92 product was tested at the EDF La Maxe power plant (France) under 167b and 545°C (steam temperature). After 3500h operation, the tubes were removed and characterized by Light Optical Metallography (LOM), Scanning Electron Microscopy (SEM), with Energy Dispersive X-ray spectrometry (EDX) and X-Ray Diffraction (XRD). The results highlight the excellent oxidation resistance of VALIORTM T/P92 product by the formation of a protective aluminum oxide scale. In addition, no enhanced oxidation was observed on the areas close to the welds. These results are compared with the results obtained from laboratory steam oxidation testing performed on a 9%Cr T/P92 steel with and without VALIORTM coating exposed in Ar-50%H 2 O at 650°C.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 205-216, October 21–24, 2019,
... distributions in scales formed on a) MARBN and b) Super VM12 after 5,000h exposure at 625°C in Ar-50%H2O. An increase of the oxidation temperature from 625°C to 650°C resulted in the formation of a thicker iron rich oxide scale covering the surface of the MARBN specimen. EDX analyses in Fig. 7 show...
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The newly developed 12%Cr steel Super VM12 is characterized by excellent creep rupture strength properties (better than Grade 92) and enhanced steam oxidation resistance of 12%Cr steels such as VM12-SHC. Balanced properties profile of the new steel development in comparison to the existing well-established steels such as Grade 91 and Grade 92, opens opportunities for its application as construction material for components in existing or future high-efficiency power plants. In this study the oxidation behavior of typical 9%Cr steels was compared with the new steel development. The oxide scale morphologies and compositions of different oxide layers as function of temperature and exposure time in steam-containing atmospheres were characterized using light optical metallography, Scanning Electron Microscopy (SEM). Creep testing has been carried out in the temperature range between 525°C and 700°C. Selected creep specimens were investigated using the Transmission Electron Microscopy and the Atom Probe Tomography techniques.
Proceedings Papers
AM-EPRI2013, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Seventh International Conference, 1093-1103, October 22–25, 2013,
...)) that are formed on VM12-SHC steel, tend to be formed on the 9%Cr steels [15, 16]. The scales differed mainly in respect to the morphology and relative amount of the formed oxide phases. They consisted of a thick multiphase iron-rich oxide scales, an inner layer formed beneath the 1099 original metal surface...
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The recently developed 12%Cr steel VM12-SHC is characterized by very good creep properties at temperatures up to 620°C. This new material development exhibits an excellent oxidation resistance in steam atmospheres at the typical application temperature but also at temperatures up to 650°C. In comparison to the existing 9% Cr grades T/P91 and T/P92, VM12-SHC steel opens due to its excellent oxidation behavior, new possibilities for its application as a heat exchanger boiler component. It was found that outside its application temperature range VM12-SHC also shows, as all 9-12%Cr steels, the appearance of the so called Z-phase. This effect was investigated to understand its influence on creep properties of this class of ferritic/martensitic steels aiming at controlling the microstructure stabilities for future grade developments. Creep testing has been carried out in the temperature range between 525°C and 700°C. Selected crept specimens have been investigated using light optical microscopy, SEM with EDX and TEM. In this study, the oxidation behavior of a number of typical martensitic 9-12%Cr steels was compared with the newly developed 12% Cr steel VM12-SHC. The compositions and morphologies of oxide scales formed after 5000 h exposure steels in simulated steam environments as function of temperature were characterized by light optical metallography and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX).
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 832-843, October 11–14, 2016,
...]. Magnetite is reported to form via the outward diffusion of Fe cations resulting in new oxide formation primarily at the oxide/gas interface. The outward diffusion of iron is deemed to be the rate determining step and is heavily impeded by the chromium concentration within the scale making the spinel layer...
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Oxide scale formation in the inner bore of steam tubing has been identified as a key metric for determining operational parameters and life expectancy of modern boiler systems. Grade 91 tubing is commonly used for the construction of key components within boiler systems designed for power generation operating in the temperature range of 500 to 650 °C. Standard laboratory test procedures involve grinding the surface of test coupons to homogenise their surface structure and improve experimental consistency, however, data presented here shows a discrepancy between laboratory and industrial practices that has long term implications on scale growth kinetics and morphological development. Microstructural analysis of both virgin and ex-service tubing reveals the presence of a pre-existing oxide structure that is incorporated into the inwardly growing scale and is implicated in the formation of multiple laminar void networks. These void networks influence thermal diffusivity across the scale and may function as regions of spallation initiation and propagation.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 855-866, October 11–14, 2016,
.... The iron oxide can be present as both hematite and magnetite. The figure clearly shows the location of iron rich scale in the upper right-hand image. Below the iron oxide are the spinel layer and sometimes a layer of chromia. The spinel layer is enriched with nickel and chromium. The chromia layer...
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Steam-side oxidation and the resultant exfoliation of iron-based scales cause unplanned shutdowns at coal-fired power generation plants. Exfoliate removal is currently limited to frequent unit cycling to minimize the volume of exfoliated scale, upgrading a plant with a “blow down” system, or installing a higher alloy. This paper discusses the rate of steam-side oxidation on Type 304H stainless steel (304H) tube after shot peening the internal surface with commercially available techniques. Shot peening the ID of Type 304H austenitic stainless steel superheater tubes has been shown to improve the overall oxidation resistance in steam. Decreasing the oxidation rate directly impacts the volume of exfoliated scale. The adherent spinel scales are thinner and more robust than non-shot peened tubes of the same alloy. Most of the improved oxidation resistance can be attributed to the presence of a spinel oxide layer combined with a continuous chromia layer formed near the steam-touched surfaces. The presence of a continuous chromia layer vastly reduces the outward diffusion of iron and minimizes the formation of iron-based scales that exfoliate. This work showed that a uniform cold-worker layer along the tube ID has a profound effect on oxidation resistance. Incomplete coverage allows oxidation to proceed in the non-hardened regions at a rate comparable to the oxidation rate on unpeened Type 304H.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 647-654, October 21–24, 2019,
... 600 to 700 0C. A different reaction morphology was seen after exposure at 750 0C, where a thicker, duplex scale grew on the whole specimen surface. The scale consisted of an inner oxide, rich in chromium, and an outer Fe3O4 layer with a thin Fe2O3 layer on the top of the scale. It indicates...
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Sanicro 25 material is approved for use in pressure vessels and boilers according ASME code case 2752, 2753 and VdTUV blatt 555. It shows higher creep rupture strength than any other austenitic stainless steels available today. It is a material for superheater and reheaters, enabling higher steam parameters of up to about 650 °C steam (ie about max 700 °C metal) without the need for expensive nickel based alloys. The aim of the present study is the investigation of the steam oxidation resistance of the Sanicro 25. The long term test was conducted in the temperature range 600 -750 °C up to 20 000 hours. The morphology of the oxide scale and the microstructure of the bulk material were investigated. In addition, the effect of surface finish and pressure on the steam oxidation were also studied.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 327-335, October 21–24, 2019,
... alloy oxidized for 86.4 ks. The elemental mapping distinguished multilayer of oxide on the Fe-9Cr-2Nb alloy. The outer scale mostly consists of iron and oxygen, which indicated the 332 formation of iron oxide. On the other hand, the inner scale was rich in chromium together with the presence of iron...
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High Cr ferritic steels have been developed for the large components of fossil power plants due to their excellent creep resistance, low thermal expansion, and good oxidation resistance. Development works to improve the operating temperature of these steels mainly focused on the high mechanical properties such as solid solution strengthening and precipitation hardening. However, the knowledge of the correlation between Laves phase precipitation and oxidation behavior has not clarified yet on 9Cr ferritic steels. This research will be focused on the effect of precipitation of Laves phase on steam oxidation behavior of Fe-9Cr alloy at 923 K. Niobium was chosen as the third element to the Fe- 9Cr binary system. Steam oxidation test of Fe-9Cr (mass%) alloy and Fe-9Cr-2Nb (mass%) alloy were carried out at 923 K in Ar-15%H 2 O mixture for up to 172.8 ks. X-ray diffraction confirms the oxide mainly consist of wüstite on the Fe-9Cr in the initial stage while on Nb added samples magnetite was dominated. The results show that the Fe-9Cr- 2Nb alloy has a slower oxidation rate than the Fe-9Cr alloy after oxidized for 172.8 ks
Proceedings Papers
AM-EPRI2010, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Sixth International Conference, 198-212, August 31–September 3, 2010,
... establishment of a more protective, Cr-rich oxide scale (17). In an attempt to mitigate the oxide exfoliation that occurs on austenitic stainless steels containing <19% Cr, two different ID surface treatments were applied: shot peening (shot blasting - SB) and deep rolling (DR). Both SB and DR cold work...
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In the “Boiler Materials for Ultrasupercritical Coal Power Plants” program, sponsored by the U.S. Department of Energy and the Ohio Coal Development Office, various materials are being assessed for their suitability in the high-temperature, high-pressure environment of advanced ultrasupercritical (A-USC) boilers. Beyond mechanical properties and fireside corrosion resistance, these materials must also exhibit adequate steamside oxidation and exfoliation resistance. A comprehensive database of steamside oxidation test results at temperatures relevant to A-USC conditions has been compiled over recent years. These tests have been conducted on ferritic and austenitic materials with chromium content ranging from 2 to 26%. The specimens were evaluated for oxidation kinetics and oxide morphology. The findings indicate that steamside oxidation behavior is significantly affected by temperature, the chromium content of the material, and the ability of chromium to diffuse through the material's crystallographic lattice structure. Additionally, surface treatments have been applied to enhance the steamside oxidation resistance of certain materials. While these treatments have shown potential, their effectiveness can be limited by the operational temperatures.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 1004-1013, October 21–24, 2019,
... and carburization in dry CO2. However, this protection is not long lived in wet CO2 because long time exposure leads to the formation of a thick iron-rich oxide layer (Fig. 7d). As a result, breakaway oxidation and carburisation occur in Fe-20Cr-2Mn alloy in wet CO2. Gas 2 )gas 2 )gas )eq MOy M aC = K2 pC2O pCO2 2...
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Model alloys of Fe-20Cr and Ni-20Cr (all compositions in weight %) and variants containing small amounts of Si or Mn were exposed to Ar-20CO 2 and Ar-20CO 2 -H 2 O (volume %) at 650 or 700°C. Protective Cr 2 O 3 scale was more readily formed on Fe-20Cr than Ni-20Cr, as a result of the different alloy diffusion coefficients. Silicon additions slowed chromia scale growth, promoting passivation of both alloy types. Water vapour accelerated chromia scaling, but slowed NiO growth.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 924-930, October 11–14, 2016,
... condition. Test was conducted in a supercritical water autoclave environment at 700°C/250 bar with 150 ppb dissolved oxygen for up to 1000 h. All specimens were covered with chromium rich oxide, although iron rich oxide nodules had started to grow on the surface of alloy 800H. Some thickening of oxide layer...
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High efficiency in power generation is not only desirable because of economical reasons but also for enhanced environmental performance meaning reduced quantity of forming ash and emissions. In modern medium to large size plants, improvements require supercritical steam values. Furthermore, in future there will be an increasing share of renewables, such as wind and solar power, which will enhance the fluctuation of supply with the consequence that other power sources will have to compensate by operating in a more demanding cyclic or ramping mode. The next generation plant will need to operate at higher temperatures and pressure cycles coupled with demanding hot corrosion and oxidation environments. Such an operation will significantly influence the performance of materials used for boilers and heat exchanger components by accelerating oxidation rates and lowering mechanical properties like creep resistance. The paper discusses the oxidation behaviour of San25, 800H and alloy 263 in supercritical water at temperatures 650 and 700 °C at 250 bar, and compares the changes of mechanical properties of materials at these temperatures.
Proceedings Papers
AM-EPRI2013, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Seventh International Conference, 791-802, October 22–25, 2013,
... 1000 h at 675°C. The results show that the thin oxide formed on the milled surface (Fig. 9a) is chromium-rich, while the oxide formed on the spark eroded and ground surface is iron-rich up to the top. Figure 10 shows the GDOES results for S31035 after 1000 h at 625°C. The oxide on the milled surface...
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To improve the efficiency of fossil fuel power plants the operating temperatures and pressures need to be increased. However, at high temperatures the steam side oxidation resistance becomes a critical issue for the steels used especially at the final stages of superheaters and reheaters. Apart from the chemical composition of the material, surface condition is a major factor affecting the oxidation resistance in steam and supercritical water. In this paper, stainless boiler steels (UNS S34710, S31035, S31042, and S30942) are investigated for oxidation resistance in flowing supercritical water. Tests were conducted in an autoclave environment (250 bar, with 125 ppb dissolved oxygen and a pH of 7) at 625°C, 650°C and 675°C for up to 1000 h. Materials were tested with as-delivered, shot peened, milled or spark eroded and ground surface finish. The results show a strong influence of surface finish at the early stages of oxidation. Oxides formed on cold worked surfaces were more adherent and much thinner than on a spark eroded and ground surface. This effect was stronger than the influence of temperature or alloy composition within the tested ranges.
Proceedings Papers
AM-EPRI2013, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Seventh International Conference, 863-880, October 22–25, 2013,
... not have the ability to form a more protective oxide scale on the surface upon exposure to the highly oxidizing/sulfidizing combustion gases in the upper furnace of advanced coal-fired boilers. As a result, a scale morphology consisting of both iron oxide and iron sulfide was produced on the metal surface...
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A combined pilot-scale combustion test and long-term laboratory study investigated the impact of oxy-firing on corrosion in coal-fired boilers. Four coals were burned under both air and oxy-firing conditions with identical heat input, with oxy-firing using flue gas recirculation unlike air-firing. Despite higher SO 2 and HCl concentrations in oxy-firing, laboratory tests showed no increase in corrosion rates compared to air-firing. This is attributed to several factors: (1) Reduced diffusion: High CO 2 in oxy-firing densified the gas phase, leading to slower diffusion of corrosive species within the deposit. (2) Lower initial sulfate: Oxy-fired deposits initially contained less sulfate, a key hot corrosion culprit, due to the presence of carbonate. (3) Reduced basicity: CO 2 and HCl reduced the basicity of sulfate melts, leading to decreased dissolution of metal oxides and mitigating hot corrosion. (4) Limited carbonate/chloride formation: The formation of less corrosive carbonate and chloride solutes was restricted by low O 2 and SO 3 near the metal surface. These findings suggest that oxy-firing may not pose a greater corrosion risk than air-firing for boiler materials.
Proceedings Papers
AM-EPRI2010, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Sixth International Conference, 839-849, August 31–September 3, 2010,
...-coated T122 specimen that failed after 5kh at 700°C, Figure 5a. In the area shown, the coating was not breached by the formation of Fe-rich oxide, but the surface Al content had dropped to ~2.3at.% after this exposure. The maps of this region in Figures 5b-5f show a thin external alumina scale...
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Diffusion aluminide coatings have been evaluated as a strategy for improving the oxidation resistance of austenitic and ferritic-martensitic (FM) steels, particularly in the presence of steam or water vapor. The objective was to evaluate the strengths and weaknesses of these coatings and quantify their performance and lifetime. Long-term diffusion and oxidation experiments were conducted to study the behavior of various model diffusion coatings and produce a better data set for lifetime predictions. The key findings are that (1) thin coatings (<50μm) with relatively low Al contents appear to be more effective because they avoid high thermal expansion intermetallic phases and have less strain energy to nucleate a crack; and (2) the low Al reservoir in a thin coating and the loss of Al due to interdiffusion are not problematic because the low service temperatures of FM steels (<600°C) and, for austenitic steels at higher temperatures, the phase boundary between the ferritic coating-austenitic substrate inhibits Al interdiffusion. Unresolved issues center on the effect of the coating on the mechanical properties of the substrate including the reaction of N in the alloy with Al.
Proceedings Papers
AM-EPRI2010, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Sixth International Conference, 213-242, August 31–September 3, 2010,
... to total thicknesses in excess of 400 µm. CALCULATIONS FOR FERRITIC-MARTENSITIC STEEL T91 Oxide Growth The oxide scales grown on alloy T91 in steam an initially very similar to those formed on alloy T22, as summarized in Fig. 1, with the main difference being the formation of obvious Cr-rich oxide...
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Advances in materials for power plants include not only new materials with higher-temperature capabilities, but also the use of current materials at increasingly higher temperatures. This latter activity builds on extensive experience of the performance of the various alloys, and provides a basis for identifying changes in alloy behavior with increasing temperature as well as understanding the factors that ultimately determine the maximum use temperatures of the different alloy classes. This paper presents results from an effort to model the exfoliation processes of steam-side oxide scales in a manner that describes as accurately as possible the evolution of strains in oxides growing inside small-diameter tubes subjected to large thermal gradients and to thermal transients typical of normal steam boiler operation. One way of portraying the results of such calculations is by plotting the evolving strains in a given oxide scale on an ‘Exfoliation Diagram’ (of the type pioneered by Manning et al. of the British Central Electricity Research Laboratory) to determine the earliest time at which the trajectory of these strains intersects a criterion for scale failure. Understanding of how such ‘strain trajectories’ differ among different alloys and are affected by the major variables associated with boiler operation has the potential to suggest boiler operating strategies to manage scale exfoliation, as well as to highlight the mode of scale failure and the limitations of each alloy. Preliminary results are presented of the strain trajectories calculated for alloys T22, T91, and TP347 subjected to the conditions experienced by superheaters under assumed boiler operating scenarios. For all three alloys the earliest predicted scale failures were associated with the increased strains developed during a boiler shut-down event; indeed, in the cases considered it appeared unlikely that scale failure would occur in any practically meaningful time due to strains accumulated during operation in a load-following mode in the absence of a shut down. The accuracy of the algorithms used for the kinetics of oxide growth appeared to be a very important consideration, especially for alloy TP347 for which large effects on oxide growth rate are known to occur with changes in alloy grain size and surface cold work.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 197-204, October 21–24, 2019,
... and microstructural stability were enhanced. The chromium content was increased to improve steam oxidation resistance by promoting the formation of a Cr-rich, compact and passivating scale when exposed to high temperature steam. In addition, Mo and Nb contents were adjusted to prevent the formation of unwanted...
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A new ferritic steel branded as Thor 115 has been developed to enhance high-temperature resistance. The steel design combines an improved oxidation resistance with long-term microstructural stability. The new alloy was extensively tested to assess the high-temperature time- dependent mechanical behavior (creep). The main strengthening mechanism is precipitation hardening by finely dispersed carbide (M 23 C 6 ) and nitride phases (MX). Information on the evolution of secondary phases and time-temperature-precipitation behavior of the alloy, essential to ensure long-term stability, was obtained by scanning transmission electron microscopy with energy dispersive spectroscopy, and by X-ray powder diffraction on specimens aged up to 50,000 hours. The material behavior was also tested in service conditions, to validate the laboratory results: Thor 115 tubing was installed in a HRSG power plant, directly exposed to turbine flue gasses. Tubing samples were progressively extracted, analyzed and compared with laboratory specimens in similar condition. This research shows the performance of Thor 115 regarding steam oxidation and microstructure evolution up to 25,000 exposure hours in the field. So far, no oxide microstructure difference is found between the laboratory and on field tubing: in both cases, the oxide structure is magnetite/hematite and Cr-spinel layers and the oxide thickness values lay within the same scatter band. The evolution of precipitates in the new alloy confirms the retention of the strengthening by secondary phases, even after long-term exposure at high temperature. The deleterious conversion of nitrides into Z phase is shown to be in line with, or even slower than that of the comparable ASME grade 91 steel.
Proceedings Papers
AM-EPRI2019, 2019 Joint EPRI – 123HiMAT International Conference on Advances in High-Temperature Materials, 348-359, October 21–24, 2019,
... of the oxide on the inner surface of IBN1 reveals that there are two distinct parts to the oxide islands: an outer nodule-type oxide and an inner crater region. Chemical analysis of the oxide scale islands reveal that they consist of Fe-rich outer oxide with an internal crater rich in Cr. This crater region...
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Extensive research and development has been undertaken in the UK on MarBN steels. These were first proposed by Professor Fujio Abe from NIMS in Japan. Within the UK, progress has been made towards commercialisation of MarBN-type steel through a series of Government funded industrial collaborative projects (IMPACT, IMPEL, INMAP and IMPULSE). As part of the IMPACT project, which was led by Uniper Technologies, boiler tubes were manufactured from the MarBN steel developed within the project, IBN1, and installed on the reheater drums of Units 2 and 3 of Ratcliffe-on-Soar Power Station. The trial tubes were constructed with small sections of Grade 91 tubing on either side of the IBN1 to allow direct comparison after the service exposure. This is the world’s first use of a MarBN steel on a full-scale operational power plant. In September 2018 the first tube was removed having accumulated 11,727 hours operation and 397 starts. This paper reports microstructural and oxidation analysis, that has been undertaken by Loughborough University as part of IMPULSE project, and outlines future work to be carried out.
Proceedings Papers
AM-EPRI2024, Advances in Materials, Manufacturing, and Repair for Power Plants: Proceedings from the Tenth International Conference, 1066-1074, October 15–18, 2024,
... an important factor in resisting high-temperature oxidation and nitridation attack. INTRODUCTION Nitrogen or nitrogen-containing gases are widely used or present in industry. Nitrogen gas, nitrogen-rich atmospheres, and ammonia can react with alloys to form internal nitrides at high temperatures...
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Nitridation is a high-temperature material degradation issue that can occur in air and in environments containing nitrogen, ammonia, etc., and in a variety of industrial processes. The nitridation behavior of several commercial nickel- and cobalt-based alloys is reviewed in this paper. The alloys include Haynes 230, Haynes 188, Haynes 625, Haynes 617, Haynes 214, Hastelloy X, and Haynes 233. The environments discussed are high-purity nitrogen gas between 871°C and 1250°C, 100% ammonia gas at 982°C and 1092°C, and a simulated combustion atmosphere at 982°C. The results showed that nitridation occurred in all the environments containing nitrogen. The nitridation attack was strongly influenced by the alloy compositions and the type of oxide formed (i.e., chromia or alumina), as some degree of oxidation was expected in the environments in which residual oxygen was present. Thermal cycling is briefly discussed because the integrity of protective oxides is also an important factor in resisting high-temperature oxidation and nitridation attack.
Proceedings Papers
AM-EPRI2016, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Eighth International Conference, 1138-1148, October 11–14, 2016,
... that all three alloys developed extremely thin and adherent oxide scales. It has been observed in this study, that HAYNES® 282® WROUGHT alloy showed no internal oxidation process. However, in two other alloys isolated oxides rich in Al and Ti have been observed in the grain boundaries, suggesting internal...
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Prior to utilizing new advanced materials in coal power plants, a large number of experimental testing is required. Test procedures are needed in specialized high temperature laboratories with state of the art facilities and precise, accurate analytical equipment capable of performing tests at a variety of temperatures and environments. In this study, the results of a unique technique involving salt spray testing at high temperatures are presented. The Haynes 282 gamma – prime (γ’) strengthened alloy fabricated by means of three different manufacturing processes: HAYNES 282 WROUGHT alloy, Haynes 282-SINT alloy, and finally Haynes 282-CAST alloy have been tested. The materials have been exposed to a salt spray corrosion atmosphere using 1% NaCl - 1% Na 2 SO 4 . Post exposure investigations have included SEM, EDS and XRD examinations. The test using salt spray of 1% NaCl - 1% Na 2 SO 4 water solution at 550 °C for 500 hours indicted no influence on the corrosion products formation, where Cr 2 O 3 has been developed in all three alloys, whereas NiO has been found only in Haynes 282-CAST material. On the other hand, it has been found that the fabrication process of HAYNES 282 alloy strongly influences the corrosion products formation under the high temperature exposures.
Proceedings Papers
AM-EPRI2013, Advances in Materials Technology for Fossil Power Plants: Proceedings from the Seventh International Conference, 777-790, October 22–25, 2013,
... oxidation [5]. However, as the Figure 18 Fe-H-O phase diagram at 625 787 outward flux of iron ions slows due to the formation of Cr-rich oxides in the inner layer, a gradual increase in void formation at the interface between the inner and outer layer together with scale lifting enable oxidation...
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CWT (combined water treatment) was introduced in Japan in 1990 and over 50 power generation boilers are now in operation. However, the effect of oxygenated treatment on the steam oxidation of the ferritic-martensitic steels and austenitic stainless steels that are used for superheaters and reheaters is currently far from clear. In this study, laboratory tests were used to examine the effect of the oxygen level of the feed water on the scale growth and the scale exfoliation propensity of T91 ferritic-martensitic steel and 300-series austenitic stainless steels, as represented by TP316H and TP347H (coarse- and fine-grained, respectively). The oxygen level of the feed water had little effect on the steam oxidation rates of all the steels tested. Hematite (Fe 2 O 3 ) formed in the outer layer of the oxide scales on both the ferritic and austenitic steels and is considered to have been encouraged in the simulated CWT atmosphere. The adhesion strength of the oxide scale formed on T91 in the simulated CWT atmosphere, that is, scale in which hematite was present, was lower than that of the oxide scale formed in the simulated AVT (all volatile treatment) atmosphere. The oxidation rate of fine-grained TP347H was confirmed to be slower than that of coarse-grained TP316H. Hematite significantly influenced the scale exfoliation of the austenitic steels and the critical oxide thickness for exfoliation decreased with increasing proportion of hematite in the outer scale.
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