Search Results for USC power plants

Current demands of the power generation market require components with improved materials properties. The focus is not only on the higher operation temperatures and pressures but also more frequent cycling to accommodate the energy produced from renewable sources. Following the successful developments of steels within the COST 501, 522 and 536 programmes, further advances are being researched. As nickel superalloys remain an expensive option for coal power plants, there is a significant drive for improvements of 9-12% Cr steels to meet new demands. The most promising of the potential candidates identified for 650°C application is MarBN steel (9Cr-3Co-3W-V-Nb). This paper reviews the current state of European developments on MarBN steel. Work on this alloy has been carried out for the last 5 years. Initial projects focused on development of the cast components. UK IMPACT and following INMAP projects successfully demonstrated manufacturing capabilities of large casting components. More recent collaborations aim to develop full-size boiler components and large rotor forgings as well as further examine the properties in the operating conditions (i.e. corrosion and oxidation resistance, creep-fatigue behaviour). Additionally significant focus is placed on modelling the behaviour of MarBN components, in terms of both microstructural changes and the resulting properties.

Nickel-based Alloy 617B (DIN 2.4673) and Alloy C-263 (DIN 2.4650) with high creep strength and good fabricability are promising material candidates for the design of next generation coal-fired “Advanced Ultra-Super-Critical A-USC” power plants with advanced steam properties and thus higher requirements on the material properties. Microstructural studies of the precipitation hardened alloy C-263 were performed with Electron Microscopy (TEM) with respect to their strengthening precipitates like carbides and intermetallic gamma prime. Specimens were subjected to different ageing treatments at elevated temperatures for different times. The microstructural results of the investigated nickel alloy C-263 are presented and discussed with respect to their correlation with required properties for A-USC, e.g. the mechanical properties, the creep resistance and the high temperature stability and compared to Alloy 617B. The manufacturing procedure for the prematernal and forgings as well as for thin walled tube components for A-USC power plants is presented.

G115 is a novel ferritic heat resistant steel developed by CISRI in the past decade. It is an impressive candidate material to make tubes, pipes, and forgings for advanced ultra super critical (A-USC) fossil fired power plants used for the temperature scope from 600°C to 650°C. The successful development of G115 extends the upper application temperature limitation of martensitic steel from 600°C to about 650°C. This breakthrough is imperative for the design and construction of 610°C to 650°C A-USC fossil fired power plants, from the viewpoint of the material availability and economics of coal fired power plant designs. This paper introduces the development history and progress of G115 steel. The strengthening mechanism of the novel martensitic steel is briefly discussed, and the optimized chemical composition and mechanical properties of G115 steel are described. The details of industrial trials of G115 tube and pipe at BaoSteel in the past years are reviewed, with the emphasis on the microstructure evolution during aging and creep testing. These tests clearly show that the microstructure of G115 steel is very stable up to the temperature of 650°C. Correspondingly, the comprehensive mechanical properties of G115 steel are very good. The creep rupture time is longer than 17000 hours at the stress of 120MPa and at the temperature of 650°C and 25000+ hours at the stress of 100MPa and at the temperature of 650°C, which is about 1.5 times higher than that of P92 steel. At the same time, the oxidation resistance of G115 steel is a little bit better than that of P92 steel. If G115 steel is selected to replace P92 pipes at the temperature scope from 600°C to 650°C, the total weight of the pipe can be reduced by more than 50% and the wall thickness of the pipe can be reduced up to about 55%. In addition, the upper application temperature limitation of G115 steel is about 30°C higher than that of P92 steel. Thus, G115 steel is a strong candidate material for the manufacturing of 600+°C advanced ultra-super-critical (A-USC) fossil fuel power plants in China and elsewhere.

This paper briefly introduces the state-of-the-art of the research and development of candidate heat resistant materials used for the manufacturing of 700°C advanced ultra-super-critical (AUSC) fossil fuel power plants (PP) in China, especially, focus on the impressive progress in the past three years. The detailed advancements (technical exploration and industrial investigation) of candidate materials spectra for the boiler system of A-USC PP will be presented in the current paper, including novel ferritic heat resistant steels, advanced austenitic heat resistant steels, Fe- Ni-based alloys and Ni-based alloys, which serve and cover the steam temperature scope from 600°C to 720°C. Some newly available data associated with above materials will be released.

This paper addresses the limitations of P92 steel used in ultra-supercritical power plants, particularly ferrite formation in thick components and its impact on short- and long-term properties. A guideline for determining ferritic content in P92 steel is presented. Furthermore, a novel 12% Cr boiler steel grade, VM12-SHC, is introduced. This new material offers good creep properties and oxidation resistance, overcoming the limitations of P92 steel. Finally, the development of matching filler metals for welding P92 and VM12-SHC steels is presented, ensuring optimal weld compatibility and performance in power plant applications.

A European project (COST 522) aims to improve power plant efficiency by developing stronger steel for steam turbines. These turbines operate with extremely hot steam (up to 650°C) to maximize efficiency and minimize emissions. The project focuses on ferritic-martensitic steel, which is suitable for the thick components used in these high-temperature environments. Building on prior advancements, COST 522 explored new steel formulations and tested them thoroughly. This has resulted in steels capable of withstanding even hotter steam (610°C live steam and 630°C reheat steam), paving the way for the next generation of highly efficient power plants.

Achieving long-term stability of the tempered martensite is considered crucial for increasing the creep resistance of steels at elevated temperatures above 700°C. It is noted that at low stress levels, the creep deformation of the tempered martensite proceeds heterogeneously around prior austenite grain boundaries, as excess dislocations inside the grain are difficult to rearrange. This paper presents a new approach using carbon-free martensitic alloys strengthened by intermetallic compounds. An iron-nickel-cobalt martensite matrix with Laves phase as the precipitate is selected. The creep characteristics are discussed across a wide range of testing conditions, and the thermal cycle test behavior is examined to evaluate the potential of these alloys for future ultrasupercritical power plants operating in severe environments.

Three Ni-base wrought alloys with different hardening mechanisms (INCONEL 706, Waspaloy and INCONEL 617) were investigated as candidates for steam turbine rotor applications at temperatures up to 700 °C in respect to their microstructure and microstructural stability. The Nb containing alloy Inconel 706 had a complex microstructure with γ', γ" and η phases which are stable in long term service up to 620 °C. At higher temperatures significant particle coarsening and phase transformation were observed. Waspaloy is hardened by γ' particles and after ageing at 700 °C and higher, it tended to a stable microstructure. Inconel 617 is a solid solution hardened material additionally hardened by homogeneously distributed fine M 23 C 6 carbides. After long term ageing at temperatures of 650 °C to 750 °C the carbides tended to form carbide films along the grain boundaries and at 700 °C to 750 °C γ' precipitated as homogeneously distributed particles with low coarsening during long term service. In order to optimize the candidate alloys Inconel 706 and Waspaloy were modified to the new alloys DT 706 and DT 750. The aspects of modification and first experimental results are reported.

Creep deformation behavior of the T122 type steels with different matrix phases such as α’ (martensite) and α’+δ (martensite and delta-ferrite) at different stress levels has been studied comparing with those of the model steels with the initial microstructures consisting of the various combination of matrices such as ferrite (α), martensite (α’) and austenite (γ), and precipitates such as MX and M 23 C 6 . The heterogeneous creep deformation is found to be pronounced at lower stress level in the steel with a dual phase matrix of α’+δ, resulting in a complex sigmoidal nature in the creep rupture life. The creep deformation process of the steel with the dual phase matrix is similar to that of the model steel with the α phase matrix which exhibits a typical heterogeneous creep deformation and the early transition to the acceleration creep at a very small creep strain. Such a heterogeneous creep deformation is much pronounced along the interfaces between the soft δ ferrite and the hard martensite (α’) phases, and has a viscous nature in creep deformation which was first identified in P91 steel. It is concluded that the homogeneous microstructure is a key for achieving the long-term creep strength in the advanced ferritic steels at elevated temperatures over 600°C.

The U.S. Department of Energy (DOE) and the Ohio Coal Development Office (OCDO) have recently initiated a project aimed at identifying, evaluating, and qualifying the materials needed for the construction of the critical components of coal-fired boilers capable of operating at much higher efficiencies than current generation of supercritical plants. This increased efficiency is expected to be achieved principally through the use of ultrasupercritical steam conditions (USC). The project goal initially was to assess/develop materials technology that will enable achieving turbine throttle steam conditions of 760°C (1400°F)/35 MPa (5000 psi), although this goal for the main steam temperature had to be revised down to 732°C(1350°F), based on a preliminary assessment of material capabilities. The project is intended to build further upon the alloy development and evaluation programs that have been carried out in Europe and Japan. Those programs have identified ferritic steels capable of meeting the strength requirements of USC plants up to approximately 620°C (1150°F) and nickel-based alloys suitable up to 700°C (1300°F). In this project, the maximum temperature capabilities of these and other available high- temperature alloys are being assessed to provide a basis for materials selection and application under a range of conditions prevailing in the boiler. This paper provides a status report on the progress to date achieved in this project.

Various carbon and nitrogen free martensitic alloys were produced for the application which required long time creep properties at high temperatures. But they were easy transformed to austenite phase before the creep tests because of low Ac1 temperature. In this paper, a new attempt has been demonstrated using carbon and nitrogen free austenitic alloys strengthened by intermetallic compounds. We choose Fe-12Ni-9Co-10W-9Cr-0.005B based alloy. Furthermore, we discussed about creep characteristics among the wide range of the testing conditions more over 700°C and steam oxidation resistance to confirm the possibility of the alloys for the future USC power plants under the severe environments.

A new nickel-base superalloy, Inconel alloy 740, is being developed for ultra-supercritical (USC) boiler applications operating above 750°C, designed to meet critical requirements for long-term high-temperature stress rupture strength (100 MPa for 10 5 hours) and corrosion resistance (2 mm/2 × 10 5 hours). Experimental investigations revealed key structural changes at elevated temperatures, including γ coarsening, γ' to η transformation, and G phase formation. To enhance strengthening effects and structural stability, researchers conducted a systematic optimization process based on thermodynamic calculations, implementing small adjustments to several alloying elements and designing modified alloy compositions. Comprehensive testing examined the long-term structural stability of these modifications, with investigations conducted up to 5,000 hours at 750 and 800°C, and 1,000 hours at 850°C. Mechanical property and oxidation resistance tests compared the modified alloys with the original Inconel alloy 740, yielding preliminary results that demonstrate minimal modifications can improve stress rupture strength while maintaining corrosion resistance. Microstructural examinations further confirmed the enhanced thermal stability of the modified alloy, positioning Inconel alloy 740 as a promising candidate for USC boiler applications at 750°C or higher temperatures.

In response to the need to reduce carbon dioxide gas emissions, Japan has been actively researching 700°C-class thermal power plants with a focus on improving overall plant efficiency. This technological advancement is fundamentally grounded in advanced materials development, encompassing the creation of high-strength alloys, fireside corrosion-resistant materials, and steamside oxidation-resistant alloys. A significant challenge emerged as some of the developed materials fell outside the scope of existing domestic technical standards. Moreover, the potential failure modes for advanced ultra-supercritical (A-USC) components operating at 700°C were anticipated to differ substantially from those observed in traditional ultra-supercritical (USC) components at 600°C. Consequently, researchers systematically examined and analyzed the potential failure modes specific to 700°C A-USC components, using these insights to establish comprehensive performance requirements. The research initiative, which commenced in June 2006, was strategically planned to develop a draft technical interpretation by March 2011. This paper provides a detailed overview of the investigative process, encompassing the comprehensive analysis of failure modes, the derivation of performance requirements, and the progression toward developing a new technical interpretation framework for high-temperature power plant components.

Inconel 740H is one of the most promising candidate Ni-base superalloys for the main steam pipe of 700 °C advanced ultra-supercritical (A-USC) coal-fired power plants. After processing and welding in manufacturing plant in solution-annealed state, large components was commonly suggested to have an extra aging treatment at 800 °C for 16 h, in order to obtain homogeneous γ′ precipitates. In this present work, creep tests and microstructure analyses were conducted on Inconel 740H pipe specimens under two different heat treatments to verify the necessity of aging process. Here we show that aging treatment has limited effect on the creep rupture life of Inconel 740H pipe. Both in grain interiors and along grain boundaries, crept specimens under two different heat treatments have the same precipitates. But the shape and distribution of γ′ in solution annealed sample is not as regular as the aged ones. Our results provide the underlying insight that aging treatment is not so necessary for the straight pipes if the on-site condition was hard to control. But for both groups of specimens, a small amount of h particles and some banded like M 23 C 6 were emerged during creep, which would be harmful to mechanical properties for the long run.

Early supercritical units such as American Electric Power (AEP) Philo U6, the world’s first supercritical power plant, and Eddystone U1 successfully operated at ultrasupercritical (USC) levels. However due to the unavailability of metals that could tolerate these extreme temperatures, operation at these levels could not be sustained and units were operated for many years at reduced steam (supercritical) conditions. Today, recently developed creep strength enhanced ferritic (CSEF) steels, advanced austenitic stainless steels, and nickel based alloys are used in the components of the steam generator, turbine and piping systems that are exposed to high temperature steam. These materials can perform under these prolonged high temperature operating conditions, rendering USC no longer a goal, but a practical design basis. This paper identifies the engineering challenges associated with designing, constructing and operating the first USC unit in the United States, AEP’s John W. Turk, Jr. Power Plant (AEP Turk), including fabrication and installation requirements of CSEF alloys, fabrication and operating requirements for stainless steels, and life management of high temperature components

By utilizing computational thermodynamics in a Design of Experiments approach, it was possible to design and manufacture nickel-base superalloys that are strengthened by the eta phase (Ni3Ti), and that contain no gamma prime (Ni3Al,Ti). The compositions are similar to NIMONIC 263, and should be cost-effective, and have more stable microstructures. By varying the aging temperature, the precipitates took on either cellular or Widmanstätten morphologies. The Widmanstätten-based microstructure is thermally stable at high temperatures, and was found to have superior ductility, so development efforts were focused on that microstructure. High temperature tensile test and creep test results indicated that the performance of the new alloys was competitive with NIMONIC 263. SEM and TEM microscopy were utilized to determine the deformation mechanisms during creep.

This overview paper contains a part of structure stability study on advanced austenitic heat-resisting steels (TP347H, Super304H and HR3C) and Ni-base superalloys (Nimonic80A, Waspaloy and Inconel740/740H) for 600-700°C A-USC fossil power plant application from a long-term joint project among companies, research institutes and university in China. The long time structure stability of these advanced austenitic steel TP347H, Super304H, HR3C in the temperature range of 650-700 °C and Ni-base superalloys Nimonic80A, Waspaloy and Inconel740/740H in the temperature range of 600-800°C till 10,000h have been detailed studied in this paper.

To improve efficiency and flexibility and reduce CO 2 emissions, advanced ultra super critical (AUSC) power plants are under development, worldwide. Material development and its selection are critical to the success of these efforts. In several research and development programs / projects the selection of materials is based on stress rupture, oxidation and corrosion tests. Without doubt, these criteria are important. To improve the operational flexibility of modern power plants the fatigue properties are of increased importance. Furthermore, for a safe operation and integrity issues the knowledge about the crack behavior is essential. Crack initiation and crack growth may be caused by natural flaws or cracks induced by component operation. In order to develop new materials, properties like tensile strength and creep strength are an important part of qualification and subsequent approval by notified bodies. Consequently short term properties as well as time-temperature dependent properties are generated and taken into considerations. In the case of high strength γ'-strengthening nickel-base alloys investigating the creep crack behavior is also strongly recommended. This article shows results of currently investigated nickel-based alloys for newly developed headers, pipes and other high temperature boiler applications and their critical creep crack propagation behavior.

A new 9%Cr steel with high boron levels (boron steel) has been developed by optimization studies on steels and alloys that are applicable to advanced ultra-super critical power plants operated at steam conditions of 700°C and 30 MPa and above. The composition and heat treatment condition of boron steel was optimized by the initial hardness, tensile strength, yield strength, and Charpy impact values on the basis of the fundamental investigation with the stability of the long-term creep strength. Creep testing of boron steel was conducted at temperatures between 600 and 700°C. The creep rupture strength at 625°C and 105 h is estimated to be 122 MPa for the present 9% Cr steel with high boron by Larson-Miller parameter method. Furthermore, physical properties as a function of temperature, metallurgical properties, tensile properties, and toughness were examined to evaluate the applicability of the steel for a 625°C USC power plant boiler. It was also confirmed that the steel has good workability for such an application by the flaring and flattening tests with tube specimens having an outer diameter of approximately 55 mm.

Recent advances in materials technology for boilers materials in the advanced USC (A-USC) power plants have been reviewed based on the experiences from the strengthening and degradation of long term creep properties and the relevant microstructural evolution in the advanced high Cr ferritic steels. P122 and P92 type steels are considered to exhibit the long term creep strength degradation over 600°C, which is mainly due to the instability of the martensitic microstructure strengthened too much by MX carbonitrides. This can be modified by reducing the precipitation of VN nitride and by optimizing the Cr content of the steels. An Fe-Ni based alloy, HR6W strengthened by the Fe2W type Laves phase is found to be a marginal strength level material with good ductility at high temperatures over 700°C and to be used for a large diameter heavy wall thick piping such as main steam pipe and hot reheat pipe in A-USC plants, while Ni-Co based alloys such as Alloys 617 and 263 strengthened by a large amount of the y’ phase are found to be the high strength candidate materials for superheater and reheater tubes, although they are prone to relaxation cracking after welding and to grain boundary embrittlement during long term creep exposure. A new Ni based alloy, HR35 strengthened by a-Cr phase and other intermetallic phases has been proposed for piping application, which is specially designed for a good resistance to relaxation cracking as well as high strength and a good resistance to steam oxidation and fire-side corrosion at high temperatures over 700°C.