Search Results for advanced ultra super critical boilers

The use of high-nickel superalloys has greatly increased among many industries. This is especially the case for advanced coal-fired boilers, where the latest high temperature designs will require materials capable of withstanding much higher operating temperatures and pressures than current designs. Inconel alloy 740H (UNS N07740) is a new nickel- based alloy that serves as a candidate for steam header pipe and super-heater tubing in coal-fired boilers. Alloy 740H has been shown to be capable of withstanding the extreme operating conditions of an advanced ultra-super-critical (AUSC) boiler, which is the latest boiler design, currently under development. As with all high nickel alloys, welding of alloy 740H can be very challenging, even to an experienced welder. Weldability challenges are compounded when considering that the alloy may be used in steam headers, where critical, thick-section and stub-to-header weld joints are present. This paper is intended to describe the proper procedures developed over years of study that will allow for ASME code quality welds in alloy 740H with matching composition filler metals.

Seeking to reduce CO 2 emissions and improve power generation efficiency, a project to develop a 700°C A-USC (advanced ultra super critical) power plant has been under way in Japan since 2008. HR6W (44Ni-23Cr-7W) is a candidate material for application in the maximum temperature areas of A-USC boilers. In this study, the creep rupture properties of plastic deformed material were investigated in comparison with those of solution treated material, in order to clarify the capability of HR6W as a material for use in A-USC plants. The creep strength of 20% pre-strained HR6W was found to increase substantially as compared with the solution treated material. 20% pre-strained material is in a state where high dislocation density has been introduced by plastic forming strain, with M 23 C 6 and Laves phase precipitating preferentially by dislocation diffusion from the early stages of creep. In particular, since high dislocation density is accumulated in connection with creep deformation near the grain boundaries, precipitation is accelerated and the grain boundaries are covered with M 23 C 6 from the early stages of creep. Then, even though the intragranular precipitate density decreases, given that the fraction of grain boundaries affected by precipitation is maintained in a high state, it is presumed that a high density of dislocation is maintained in the long-term region. This was considered to be the reason why the creep rupture strength of the 20% pre-strained material increased so remarkably in comparison with the solution treated material.

Grade 91 steel has achieved broad acceptance within the modern boiler industry to fabricate a variety of critical pressure components including tubing, piping and headers, particularly in Ultra Super Critical (USC), Advanced Ultra Super Critical (A-USC) and Combined Cycle Power Plants (CCPP). The applications for which this material is used enforce severe requirements on strength, corrosion, creep properties and thermal stability during service. The properties of Creep Strength Enhanced Ferritic steels (CSEF) such as Grade 91 are critically dependent on manufacturing factors like steelmaking, heat treatments and welding: poor control of these parameters can severely compromise material properties. In scientific literature, several studies correlate low creep ductility to high content of trace elements such As, Sn, Sb, Pb, Cu, P and S. Since the current reference Codes, namely ASTM/ASME, don’t require particular restrictions for these elements, Electric Power Research Institute (EPRI) has issued guidelines for grade 91 which enforce a significant reduction of impurities and trace elements. This paper discusses steelmaking operating challenges to produce Grade 91 steel with very low contents of the above mentioned residual elements, starting from the furnaces charges, up to the chemical composition measuring equipment used in the steel shop laboratories.

CO 2 emission reduction from coal power plants is still a serious issue to mitigate the impact of global warming and resulting climate change, though renewables are growing today. As one of the solutions, we developed A-USC (Advanced Ultra Super Critical steam condition) technology to raise the thermal efficiency of coal power plants by using high steam temperatures of up to 700℃ between 2008 and 2017 with the support of METI (Ministry of Economy, Trade and Industry) and NEDO (New Energy and Industrial Technology Development Organization). The temperature is 100℃ higher than that of the current USC technology. Materials and manufacturing technology for boilers, turbines and valves were developed. Boiler components, such as super heaters, a thick wall pipe, valves, and a turbine casing were successfully tested in a 700℃-boiler component test facility. Turbine rotors were tested successfully, as well, in a turbine rotating test facility under 700℃ and at actual speed. The tested components were removed from the facilities and inspected. In 2017, following the component tests, we started a new project to develop the maintenance technology of the A-USC power plants with the support of NEDO. A pressurized thick wall pipe is being tested in a 700℃ furnace to check the material degradation of an actual sized component.

The “Cool Earth-Innovative Energy Technology Program,” launched by the Japanese government in March 2008, aims to significantly reduce global greenhouse gas emissions. Among the 21 selected technologies is the Advanced Ultra Super Critical (A-USC) pressure power generation, which targets the commercialization of a 700°C class pulverized coal power system with a power generation efficiency of 46% by around 2015. As of 2004, Japan's pulverized coal power plant capacity reached 35 GW, with the latest plants achieving a steam temperature of 600°C and a net thermal efficiency of approximately 42% (HHV). Older plants from the 1970s and early 1980s, with steam temperatures of 538°C or 566°C, are nearing the need for refurbishment or rebuilding. A case study on retrofitting these older plants with A-USC technology, which uses a 700°C class steam temperature, demonstrated that this technology is suitable for such upgrades and can reduce CO 2 emissions by about 15%. Following this study, a large-scale development of A-USC technology began in August 2008, focusing on developing 700°C class boiler, turbine, and valve technologies, including high-temperature material technology. Candidate materials for boilers and turbine rotor and casing materials are being developed and tested. Two years into the project, useful test results regarding these candidate materials have been obtained, contributing to the advancement of A-USC technology.

In recent years continuous and extensive research and development activities have been being done worldwide on 700°C A-USC (Advanced Ultra Super Critical) power plants to achieve higher efficiency and reduce the CO 2 emission. Increasing steam temperature and pressure of such A-USC boilers under consideration require the adoption of Ni based alloys. In the Japanese national project launched in 2008, Ni based alloy HR6W (45Ni-23Cr-7W-Ti, ASME Code Case 2684) is one of the candidate materials for boiler tube and pipe as well as Alloy617, Alloy263 and Alloy740H. The most important issues in A-USC boiler fabrication are the establishment of proper welding process for thick wall components of these alloys and verification of the long term reliability of their weldments. In our previous study, the weldability of HR6W was investigated and the welding process for Ni based thick wall pipe was established with the narrow gap HST (Hot wire Switching TIG) welding procedure originally developed by Babcock-Hitachi K.K. In this paper, creep rupture strengths of HR6W weldment were verified by the long term test up to 60,000 hours for tube and 40,000 hours for pipe. In Japanese national project, narrow gap HST welding process was also applied to the welding test for the other Ni based candidate pipe materials. Furthermore, as the practical A-USC boiler manufacturing trials, header mockup test was conducted and qualified for HR6W.

Energy requirements and environmental concerns have promoted a development in higher-efficiency coal fired power technologies. Advanced ultra-super critical power plant with an efficiency of higher than 50% is the target in the near future. The materials to be used due to the tougher environments become therefore critical issues. This paper provides a review on a newly developed advanced high strength heat resistant austenitic stainless steel, Sandvik Sanicro 25, for this purpose. The material shows good resistance to steam oxidation and flue gas corrosion, and has higher creep rupture strength than any other austenitic stainless steels available today, and has recently obtained two AMSE code cases. This makes it an interesting option in higher pressures/temperature applications. In this paper, the material development, structure stability, creep strength, steam oxidation and hot corrosion behaviors, fabricability and weldability of this alloy have been discussed. The conclusion is that the Sanicro 25 is a potential candidate for superheaters and reheaters in higher-efficiency coal fired boilers i.e. for applications seeing up to 700°C material temperature.

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.

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.

INCONEL 740H has been developed by Special Metals for use in Advanced Ultra Super Critical (A-USC) coal fired boilers. Its creep strength performance is currently amongst the ‘best in class’ of nickel based alloys, to meet the challenge of operating in typical A-USC steam temperatures of 700°C at 35 MPa pressure. Whilst the prime physical property of interest for INCONEL 740H has been creep strength, it exhibits other physical properties worthy of consideration in other applications. It has a thermal expansion co-efficient that lies between typical values for Creep Strength Enhanced Ferritic (CSEF) steels and austenitic stainless steels. This paper describes the validation work in support of the fabrication of a pipe transition joint that uses INCONEL 740H pipe, produced in accordance with ASME Boiler Code Case 2702, as a transition material to join P92 pipe to a 316H stainless steel header. The paper gives details of the material selection process, joint design and the verification process used for the joint.

Continuous and active works have been going to develop 700°C A-USC (Advanced Ultra Super Critical) power plants in Europe, United States and also Japanese national project has launched in 2008. In this new Japanese project Fe-Ni based alloy HR6W (45Ni-24Fe-23Cr-7W-Ti) is one of the candidate materials for boiler tube and pipe as well as Ni based alloys such as well-known Alloy617, Alloy263 and Alloy740. The most important issue in boiler fabrication is the welding process of these alloys and long-term reliability of their weldments. Authors investigated the weldability of HR6W thick-wall pipe. The integrity of the weldment was confirmed with metallurgical investigation, mechanical testing and long term creep rupture test. It is proved that the narrow gap HST welding procedure can meet the requirements for Ni based or Fe-Ni based alloys and provides excellent strength properties.

Enhancement of the steam conditions is one of the most effective measures to achieve the goal of higher thermal efficiency. 700°C class A-USC (Advanced Ultra Super Critical Steam Conditions) power plant is one of the remarkable technologies to achieve the goal and reduce CO 2 emissions from fossil fuel power plants. Toshiba has been working on the A-USC development project with subsidy from METI (Ministry of Economy, Trade and Industry) and NEDO (New Energy and Industrial Technology Development Organization). In this project, A-USC power plants with steam parameters of 35MPa 700/720/720°C were considered. To date, various materials have been developed and tested to verify their characteristics for use in A-USC power plants. And some of these materials are being investigated as to their suitability for use in long term. Together with members of the project, we carried out the boiler component test using a commercially-operating boiler. We manufactured a small-scale turbine casing made of nickel-based alloy, and supplied it for the test. In addition, we manufactured a turbine rotor for turbine rotation tests, and carried out the test at 700°C and rotating speed of 3,600rpm conditions. In this paper, we show the results of the A-USC steam turbine development obtained by the project.

Continuous and extensive works have been going to develop 700°C A-USC (Advanced Ultra Super Critical) power plants worldwide. Since Japanese national project launched in 2008, Ni based alloy HR6W (45Ni-24Fe-23Cr-7W-Ti, ASME Code Case 2684) was selected as one of the promising candidate materials of A-USC boiler tube and pipe for long-term creep strength evaluation and field exposure test. In the present study, to establish the creep damage and life assessment method for Ni based alloy component, long-term creep rupture properties, microstructural stability, and creep damage morphology of HR6W weldment were experimentally investigated. Creep tests of HR6W weldment were conducted at temperature range of 700 to 800°C for durations up to 70,000 hours. Failure behavior of creep void formation and creep crack growth was identified, and damage mechanism of weldment during creep were discussed and characterized. Furthermore, uniaxial interrupted creep tests were carried out, the creep damage evaluation was conducted and life assessment approach was proposed based on the metallographic quantification evaluation of creep void and microstructure evolution. It demonstrated the possibility and validity to evaluate creep damage of Ni based alloy component with creep void and microstructure parameters.

Advanced Ultra-Super-Critical (A-USC) technology is one of the remarkable technologies being developed to reduce CO 2 emissions. The 700°C class A-USC steam turbine project was launched in 2008 to contribute to substantial reductions in CO 2 emissions and major Japanese manufacturers of boilers and turbines joined forces with research institutes to bring the project to reality. The use of Ni-base alloys is necessary for high temperature component of 700°C class AUSC steam turbine, and which is required increasing in size of Ni-base casting alloys to apply inner casing, valve body, nozzle block and so on. Therefore, trial production and verification test of Step block (weight: 1.7 ton) with actual component thickness 100-300mm were firstly performed to investigate basic casting material properties in this study. As candidate alloy, alloy 617 was chosen from a commercially available Ni-base alloy, from the viewpoint of large component castability and balance of mechanical properties stability at 700°C use. Microstructure test, high temperature mechanical test and long-term heating test of each thickness part specimen were carried out and good creep rupture strength was obtained. Next, the nozzle block of alloy 617 was manufactured for the trial casting of the actual machine mock-up component with complex shape (weight: 1.2 ton). For a comparison, alloy 625 was cast at the same time. Both castings of alloy 617 and alloy 625 were able to manufacture without a remarkable defect. Detailed comparisons to microstructures and mechanical properties are included in this paper.

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.

The rapid development of Chinese economy (recently in the order of 10%/year) is requiring sustainable growth of power generation to meet its demand. In more than half century after the foundation of People's Republic of China, the Chinese power industry has reached a high level. Up to now, the total installed capacity of electricity and annual overall electricity generation have both jumped to the 2 nd position in the world, just next to United States. A historical review and forecast of China electricity demand to the year of 2010 and 2020 will be introduced. Chinese power plants as well as those worldwide are facing to increase thermal efficiency and to decrease the emission of CO 2 , SO X and NO X . According to the national resources of coal and electricity market requirements in the future 15 years power generation especially the ultra-super-critical (USC) power plants with the steam temperature up to 600°C or higher will get a rapid development. The first two series of 2×1000MW USC power units with the steam parameters 600°C, 26.25MPa have been put into service in November and December 2006 respectively. In recent years more than 30 USC power units will be installed in China. USC power plant development will adopt a variety of qualified high temperature materials for boiler and turbine manufacturing. Among those materials the modified 9- 12%Cr ferritic steels, Ni-Cr austenitic steels and a part of nickel-base superalloys have been paid special attention in Chinese materials market.

Current state-of-the-art coal-fired supercritical steam power plants operate with high-pressure turbine inlet steam temperatures close to 600°C. The best of the recently developed and commercialized advanced 9-12Cr martensitic-ferritic steels may allow prolonged use at temperatures to about 620°C, but such steels are probably close to their inherent upper temperature limit. Further increase in the temperature capability of advanced steam turbines will certainly require the use of Ni-based superalloys and system redesign, as seen in the European programs that are pioneering advanced power plants capable of operating with 700°C steam. The U.S. Department of Energy (DOE) has recently undertaken a concerted effort to qualify ultra-supercritical boiler tubing and piping alloys for 720/760°C steam for increased efficiency and reduced emissions. It is, therefore, necessary to develop the corresponding USC steam turbine, also capable of reliable operation at such conditions. This paper summarizes a preliminary assessment made by the Oak Ridge National Laboratory (ORNL) and the National Energy Technology Laboratory (NETL) of materials needed for ultra-supercritical (USC) steam turbines, balancing both technical and business considerations. These efforts have addressed an expanded portfolio of alloys, that includes austenitic stainless steels and alloys, in addition to various Ni-based superalloys for critical turbine components. Preliminary input from utilities indicates that cost-effective improvements in performance and efficiency that do not sacrifice durability and reliability are prime considerations for any advanced steam turbine technology.

The Chinese power industry has experienced rapid development in the past decade. The newly built 600+°C ultra-super-critical (UCS) fossil fire power plants and pressed water reactor nuclear power plants in China are the world’s most advanced level technically and effectively. The available capacity of 600+°C UCS fossil fire power plant in China is more than 200 GW by the end of 2015, which has greatly contributed to the energy-saving and emission-reduction for China and the whole world. In China, the 610°C and 620°C advanced USC (A-USC) fossil fire power plants had been combined into the grid, 630°C A-USC fossil fire power plant is about to start to build, the feasibility of 650°C A-USC fossil fire power plant is under evaluation, 700°C AUSC fossil fire power plant has been included in the national energy development plan and the first Chinese 700°C A-USC testing rig had been put into operation in December 2015. The advanced heat resistant materials are the bottlenecking to develop A-USC fossil fire power plant worldwide. In this paper, the research and development of candidate heat resistant steels and alloys selected and/or used for 600+°C A-UCS fossil fire power plant in China is emphasized, including newly innovated G115 martensitic steel used for 630°C steam temperature, C-HRA-2 fully solid-solution strengthening nickel alloy used for 650°C steam temperature, C-HRA-3 solid-solution strengthening nickel alloy used for 680°C steam temperature, 984G iron-nickel alloy used for 680°C steam temperature, C-HRA-1 precipitation hardening nickel alloy and C700R1 solid-solution strengthening nickel alloy used for 700+°C steam temperature.

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.

One of the pathways for achieving the goal of utilizing the available large quantities of indigenous coal, at the same time reducing emissions, is by increasing the efficiency of power plants by utilizing much higher steam conditions. The US Ultra-Supercritical Steam (USC) Project funded by US Department of Energy (DOE) and the Ohio Coal Development Office (OCDO) promises to increase the efficiency of pulverized coal-fired power plants by as much as nine percentage points, with an associated reduction of CO 2 emissions by about 22% compared to current subcritical steam power plants, by increasing the operating temperature and pressure to 760°C (1400°F) and 35 MPa (5000 psi), respectively. Preliminary analysis has shown such a plant to be economically viable. The current project primarily focuses on developing the materials technology needed to achieve these conditions in the boiler. The scope of the materials evaluation includes mechanical properties, steam-side oxidation and fireside corrosion studies, weldability and fabricability evaluations, and review of applicable design codes and standards. These evaluations are nearly completed, and have provided the confidence that currently-available materials can meet the challenge. While this paper deals with boiler materials, parallel work on turbine materials is also in progress. These results are not presented here in the interest of brevity.