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.

Creep rupture strength is the principal material property prioritized in designing power generation plants against the steady-state stress due to internal pressure. Increasingly plants must cycle so there is a possibility of life reduction due to creep-fatigue interaction. Grade 92 steel is one of the creep strength enhanced ferritic (CSEF) steels which has superior creep strength compared to other CSEFs. It is expected to be widely used in coal-fired ultra-super critical plants as well as in LNG-fired combined cycle plants. However, at present there is insufficient information regarding the creep-fatigue behavior of this material. A joint study has been conducted to understand the behavior of this steel under creep-fatigue condition and see how accurate the failure life can be estimated. Three kinds of base materials as well as two kinds of welded joints have been tested under strain-controlled cyclic loading with or without hold times as well as under constant load creep condition. Continued decrease in the number of cycles to failure was observed with the extension of hold time in all the base metals and cross-weld specimens. It was found that the modified ductility exhaustion approach based on inelastic strain, as well as its extension employing the inelastic strain energy density, made reasonably accurate predictions of failure lives under a wide range of test conditions. Temperature- and rate-dependencies of fracture limits in terms of inelastic strain and energy density were able to be uniquely expressed using simple thermal activation energy parameters.

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.

For safe operation of thick-walled components for Advanced Ultra Super Critical (A-USC) power plants, detailed knowledge of the creep crack initiation and growth behavior is essential. The high loading and high temperature conditions in an A-USC power plant require, in many cases, the employment of nickel base super alloys. Unfortunately, both manufacturing and nondestructive evaluation (NDE) of thick-walled components (> 50 mm) made of nickel base super alloys are quite challenging. In this paper, one candidate material for such applications, Alloy C-263, was tested for creep and creep crack behavior at 700 °C. Objective of the study was to determine a critical flaw size. In order to establish this size, the duration to achieve the 1%-strain limit at a given load is compared with the time to grow the initial flaw for Δa = 0.5 mm when the component was loaded with the same given load. It will be shown that manufacturing parameters, e. g. heat treatment procedures, have a significant influence on the creep crack initiation and growth behavior and thus on component life. Decoration of grain boundaries with precipitates, for instance caused by the manufacturing process, can reduce the creep crack resistance and thus increase the risk for premature component failure.

In order to establish a induction bending technique for Ni-based alloy HR6W large pipe, induction bending test was conducted on HR6W, which is a piping candidate material of 700°C class Advanced Ultra-Super Critical. In this study, a tensile bending test in which tensile strain was applied and a compression bending test in which compression strain was applied to the extrados side of the pipe bending part. As the results of these two types of induction bending tests, it was confirmed that a predetermined design shape could be satisfied in both bending tests. In addition, the wall thickness of the pipe was equal to or greater than that of the straight pipe section in compression bending. Therefore, if compression bending is used, it is considered unnecessary to consider the thinning amount of the bent portion in the design. Next, penetrant test(PT) on the outer surface of the bending pipes were also confirmed to be acceptable. Subsequently, metallographic samples were taken from the outer surface of the extrados side, neutral side and intrados side of the pipe bending portion. Metallographic observation confirmed that the microstructures were normal at all the three selected positions. After induction bending, the pipe was subjected to solution treatment. Thereafter, tensile tests and creep rupture tests were carried out on samples that were cut from the extrados side, neutral side and intrados side of the pipe bending portion. Tensile strength satisfied the minimum tensile strength indicated in the regulatory study for advanced thermal power plants report of Japan. Each creep rupture strength was the almost same regardless of the solution treatment conditions. From the above, it was possible to establish a induction bending technique for HR 6W large piping.

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.

Since the 1990s, the power plant market has shifted towards more flexible and efficient Steam Power Plants (SPPs) with fewer service inspections and lifetimes of ≥200,000 hours, including combined-cycle applications. This shift has driven efforts to enhance both design and materials. One approach is the installation of super-critical SPPs with live steam temperatures of T ≥580°C and optimized steam cycles. Siemens Power Generation is leveraging its experience with Ultra Super Critical SPPs from the 1950s, which operated at up to 650°C/320bar, to develop modern turbo-set solutions using new technology from the past decade. Proven design features, such as material combinations (welded or bolted rotors and casings) and advanced cooling techniques, are being adapted for current use. Past limitations with austenitic materials have been reassessed, leading to the conclusion that improved materials are necessary for today's USC SPPs. Global material development programs, such as COST in Europe, are focusing on new 10%Cr martensitic steels, which offer cost-effectiveness and operational flexibility. Additionally, joint R&D projects are underway to evaluate the long-term creep properties and service behavior of new 10%CrMoV steels for 600/620°C applications. These projects aim to ensure the materials can withstand relevant loading conditions and multiaxial stresses.

Recently advanced ultra-super critical (A-USC) pressure power plants with 700°C class steam parameters have been under development worldwide. Japanese material R&D program for A- USC beside the plant R&D program started in 2008, launched in 2007 under the METI/NEDO foundation includes not only alloy design explores and novel ideas for developing new steels and alloys that can fill critical needs in building 700°C class advanced power plants, but also fundamental studies on creep strength and degradation assessment, which are absolutely needed to assure the long-term safe use of newly developed steels and alloys at critical temperature conditions, for instance, 650°C for ferritic steels, 700°C for austenitic steels and 750°C for Ni- based alloys. This program concept has been based on the lessons from materials issues recently experienced in the creep strength enhanced ferritic steels used for 600°C class ultra-super critical power plants. Particular outputs from the program up to now are recognized as the ferritic steel having the creep strength of 100MPa at 650°C beyond 30,000h without any Type IV degradation and as the austenitic steel developed by means of inter-metallic compounds precipitation strengthening of grain boundary which should be strongest in creep ever found. Concurrently great progresses have been seen in the research works with positron annihilation life monitoring method applicable to various kinds of defects, structural free energy values, small punch creep test data for very limited interest area, crystallographic analyses, optimum time-temperature parameter regional creep rupture curve fitting method, hardness model, etc. which would highly contribute to find out and establish the structural parameters affecting to creep strength and degradation resulting in accurately estimating the 100,000h creep strength.

India's current installed power generating capacity is about 225,000 MW, of which about 59% is coal based. It is projected that India would require an installed capacity of over 800,000 MW by 2032. Coal is likely to remain the predominant source of energy in India till the middle of the century. India is also committed to reducing the CO 2 emission intensity of its economy and has drawn up a National Action Plan for Climate Change, which, inter alia, lays emphasis on the deployment of clean coal technologies. With this backdrop, a National Mission for the Development of Advanced Ultra Supercritical Technology has been initiated. The Mission objectives include development of advanced high temperature materials, manufacturing technologies and design of equipment. A corrosion test loop in an existing plant is also proposed. Based on the technology developed, an 800 MW Demonstration A-USC plant will be established. Steam parameters of 310 kg/cm 2 , 710 °C / 720 °C have been selected. Work on selection of materials, manufacture of tubes, welding trials and design of components has been initiated. The paper gives details of India's A-USC program and the progress achieved.

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.

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.

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.

Alloy 718, widely used for its high-temperature performance in various applications, is being investigated for use in advanced power plants. Driven by the need for efficiency improvements, these plants demand higher temperatures and pressures, putting significant stress on critical components like boiler tubes and turbines. With existing steels and alloys struggling at such high temperatures, researchers are exploring alternatives. New generation plants target steam turbine inlet temperatures of 720°C and pressures of 350MPa, necessitating superalloys for high- and intermediate-pressure rotor sections. The Thermie Advanced project explored the potential of 718 for these applications. A trial rotor disk, forged using advanced processes, underwent a novel heat treatment to enhance microstructural stability and improve creep behavior. Ongoing creep tests exceeding 100,000 hours suggest a potential 50°C increase in the operational limit compared to standard 718. This 12-year research effort holds promise for utilizing 718 in forged components of advanced ultra-supercritical power plant steam turbines, potentially operating up to 700°C.

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.

18Cr-9Ni-3Cu-Nb-N steel is widely used for heat exchanger tubes such as super-heaters and reheaters of ultra-super critical power generation boilers. In this study, long-term creep rupture tests were carried out on 18Cr-9Ni-3Cu-Nb-N seamless steel tubes of 7 heat materials, and the specimens of 2 heat materials with different creep rupture strengths were observed by ultra-low voltage scanning electron microscope after creep rupture tests. The results of the investigation of the creep rupture specimens and the coverage ratios of M 23 C 6 on grain boundary were different. The cause of this was estimated to be the difference in B content between the 2 heat materials. Creep rupture tests with different final ST temperatures were also carried out using the same heat material, and it was revealed that the higher final ST temperature, the higher the creep rupture strength. As the final ST temperature is higher, the amount of Nb(C, N) solid solution in the matrix increases, and the amount of precipitation of NbCrN and M 23 C 6 increases during creep, therefore it is assumed that the creep rupture strength increases.

Super 304H is a new generation of advanced austenitic stainless steels that is increasingly being used in superheater/ reheater (SH/RH) sections of thermal ultra-supercritical steam power plants due to its high creep strength combined with good oxidation resistance and microstructure stability. However, recent studies have shown significant microstructural changes and associated degradation in creep performance during long-term service exposure in this alloy. Microstructure evolution during service and its effect on the long-term creep performance has not been comprehensively assessed. In this work, variations in the microstructure of long-term service exposed Super 304H RH tubes (~99,600 hours at 596°C steam temperature) are documented. The results for the ex-service material are compared to well-documented laboratory studies to provide perspective on improved life management practices for this mainstay advanced stainless steel.

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.

The oxide exfoliation is one of the main problems that cause the explosion of superheater or reheater, which threaten the safety of power plant units, but there is no direct test method of the particle concentration of the scales in high temperature steam. Based on the study of ferromagnetic and optical characteristics of scales, the technology and equipment were developed for on-line measurement based on magnetic sensitivity and granularity behavior. Through numerical simulation and dynamic simulation experiments of scale movement under high temperature and high pressure steam, calculating method of the particle concertation of scales in the main steam or reheated steam pipeline was retrieved by local sampling concentration.

ASTM Grade 23 is a 2.25Cr-0.3Mo-1.5W-V-Nb-B steel widely used for the fabrication of boiler components of the most recent ultra super critical power plants; it combines high creep resistance, enhanced oxidation and corrosion resistance and good weldability. Microstructural, mechanical, and creep properties of seamless tubes and pipes after normalizing and tempering heat treatment are compared with those obtained after cold bending and hot induction bending. The creep resistance is obtained through the precipitation of fine carbides after tempering. A broad program of TEM investigations on crept samples has been carried out in order to assess the evolution of the microstructure and its phases after long term high-temperature exposure, in terms of chemical composition, size and distribution of precipitates.

Dissimilar metal welds (DMWs) between ferritic and austenitic materials at elevated temperatures have long posed challenges for boiler manufacturers and operators due to their potential for premature failure. As the industry moves towards higher pressures and temperatures to enhance boiler efficiencies, there is a need for superior weld metals and joint designs that optimize the economy of modern boilers and reduce reliance on austenitic materials for steam headers and piping. EPRI has developed a new filler metal, EPRI P87, to enhance the performance of DMWs. Previous work has detailed the development of EPRI P87 for shielded metal arc welding electrodes, gas-tungsten arc welding fine-wire, and its application in an ultra-supercritical steam boiler by B&W. This study examines the weldability of EPRI P87 consumables through various test methods, including Varestraint testing (both trans and spot), long-term creep testing (approximately 10,000-hour running tests), procedure qualification records for tube-to-tube weldments between traditional/advanced austenitic steels and creep-strength enhanced ferritic steels, and elevated temperature tensile testing. Macroscopic examinations from procedure qualification records using light microscopy confirmed the weldability and absence of cracking across all material combinations. The findings demonstrate that EPRI P87 is a weldable alloy with several advantages for DMW applications and highlight that specific weld joint configurations may necessitate the use of high-temperature tensile data for procedure qualifications.