Since 2008, Japanese boiler, turbine and valve manufacturers, research institutes and utility companies have been working together to develop 700V A·USC technology, with support from the Japanese government. The key areas of discussion are technology development of high temperature materials such as nickel-based alloys and advanced 9Cr steels, and their application to actual power plants. At the EPRI conference in 2013, our report mainly focused on the development of fundamental material and manufacturing technology during the first five years of the project, and the preparation status of the boiler component test and turbine rotor test for the latter four years of the project. The boiler component test, using a commercially-operating boiler, began in May 2015 and is scheduled to be finished by the end of 2016. The turbine rotor test at 700°C with actual speed will be carried out from September 2016 to March 2017. At this year’s conference, we will: l) briefly summarize the development of fundamental material and manufacturing technology and 2) provide an update on the progress of the boiler component test and the turbine rotor test.

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.

We have reported on the effort being done to develop the A-USC technology in Japan, which features the 700 deg-C steam condition, since the 2007 EPRI conference. Our 9 year project began in 2008. There have been some major changes in the electricity power market in the world recently. At first, the earthquake changed the power system violently in Japan. Almost all nuclear power plants have been shut down and natural gas, oil and coal power plants are working fully to satisfy the market's demands. In the USA, the so called ‘Shale gas revolution’ is going on. In Europe, they are working toward the target of reducing CO 2 emissions by the significant use of renewables with the backup of the fossil fuel power systems and enhancing power grids. A very rapid increase in power generation by coal is being observed in some countries. Despite some major changes in the electric sector in the world and the CO 2 problem, the global need for coal power generation is still high. We can reconfirm that the improvement of the thermal efficiency of coal power plants should be the most fundamental and important measure for the issues we are confronting today, and that continuous effort should be put towards it. Based on the study we showed at the 2007 conference, we developed 700 deg-C class technology mainly focusing on the material and manufacturing technology development and verification tests for key components such as boilers, turbines and valves. Fundamental technology developments have been done during the first half of the project term. Long term material tests such as creep rupture of base materials and welds will be conducted for 100,000hrs continuing after the end of the project with the joint effort of each participating company. Today, we are preparing the plan for the second half of the project, which is made up of boiler components test and the turbine rotating tests. Some boiler superheater panels, large diameter pipes and valves will be tested in a commercially operating boiler from 2015 to 2017. The turbine rotor materials which have the same diameter as commercial rotors will be tested at 700 deg-C and at actual speed.

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.

Tenaris' High Oxidation Resistance (THOR) 115, or T115, is a creep strength-enhanced ferritic (CSEF) steel introduced in the past decade. It is widely used in constructing high-efficiency power plants and heat recovery steam generators (HRSGs) due to its superior steam oxidation resistance and long-term microstructural stability, making it a viable alternative to stainless steels at elevated steam temperatures. The creep damage tolerance of T115 has been recently validated under ASME BPVC CC 3048 guidelines, which address safety concerns related to creep damage in boiler components. Testing confirmed T115's consistent creep damage-tolerant behavior, with cross-weld creep behavior reassessed through extensive metallographic examination of specimens from a 1.5-inch thick pipe girth weld, providing insights into creep damage distribution and hardness, and its relative performance compared to Grade 91 CSEF steel.

Development of the advanced USC (A-USC) boiler technology has been promoted in recent years, which targets 700°C steam condition. HR6W (Ni-23Cr-7W-Ti-Nb-25Fe) and HR35 (Ni-30Cr-6W-Ti-15Fe) have been developed for A-USC boiler tubes and pipes. The former alloy is mainly strengthened by Fe 2 W type Laves phase. The latter one employs precipitation strengthening of α-Cr phase in addition to Laves phase. Characteristic alloy design of both alloys, which does not use precipitation strengthening of γ′ phase (Ni 3 Al), leads to superior ductility and resistance to stress-relaxation cracking. Stability of creep strength and microstructure has been confirmed by long-term creep rupture tests. The 100,000h average creep rupture strength of HR6W is 85MPa at 700C. That of HR35 is 126MPa at 700°C which is comparable with conventional Alloy617. Tubes of both alloys have been evaluated by the component test in Japanese national A-USC project with γ′ hardened Alloy617 and Alloy263. Detailed creep strength, deformation behavior and microstructural evolution of these alloys are described from the viewpoint of the difference in strengthening mechanisms. Capability of these alloys for A-USC boiler materials has been demonstrated by the component test in the commercial coal fired boiler as the part of the A-USC project.

23Cr-45Ni-7W alloy (HR6W) is a material being considered for use in the high temperature parts of A-USC boilers in Japan. In order to establish an assessment method of creep damage for welded components made using HR6W, two types of internal pressure creep tests were conducted. One is for straight tubes including the circumferential weld and the other is for welded branch connections. The test results for the circumferential welds ensured that the creep rupture location within the area of the base metal, as well as the time of rupture, can be assessed by mean diameter hoop stress. On the other hand, the creep rupture area was observed in the weld metal of the branch connections, although the creep strength of Inconel filler metal 617 was higher than that of HR6W. FE analyses were conducted using individual creep strain rates of the base metal, the heat affected zone and the weld metal to clarify this difference in the failures of these two specimens. Significant stress was only produced in the weld metal as opposed to the base metal, due to the difference in creep strain rates between the welded branch connections and creep crack were initiated in the weld metal. The differences between the two failure types were assessed using the ductility exhaustion method.

A recent engineering design study conducted by the Electric Power Research Institute (EPRI) has compared the cost and performance of an advanced ultra-supercritical (A-USC) pulverized coal (PC) power plant with main steam temperature of 700°C to that of conventional coal-fired power plant designs: sub-critical, supercritical, and current USC PC plants with main steam temperatures of 541°, 582°, and 605°C, respectively. The study revealed that for a US location in the absence of any cost being imposed for CO 2 emissions the A-USC design was a slightly more expensive choice for electricity production. However, when the marginal cost of the A-USC design is compared to the reduction in CO 2 emissions, it was shown that the cost of the avoided CO 2 emissions was less than $25 per metric ton of CO 2 . This is significantly lower than any technology currently being considered for CO 2 capture and storage (CCS). Additionally by lowering CO 2 /MWh, the A-USC plant also lowers the cost of CCS once integrated with the power plant. It is therefore concluded that A-USC technology should be considered as one of the primary options for minimizing the cost of reducing CO 2 emissions from future coal power plants.

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.

Following the successful completion of a 14-year effort to develop and test materials which would allow advanced ultra-supercritical (A-USC) coal-fired power plants to be operated at steam temperatures up to 760°C, a United States-based consortium has started on a project to build an A-USC component test facility, (A-USC ComTest). Among the goals of the facility are to validate that components made from the advanced alloys can perform under A-USC conditions, to accelerate the development of a U.S.-based supply chain for the full complement of A-USC components, and to decrease the uncertainty for cost estimates of future commercial-scale A-USC power plants. The A-USC ComTest facility will include a gas fired superheater, thick-walled cycling header, steam piping, steam turbine (11 MW nominal size) and valves. Current plans call for the components to be subjected to A-USC operating conditions for at least 8,000 hours by September 2020. The U.S. consortium, principally funded by the U.S. Department of Energy and the Ohio Coal Development Office with co-funding from Babcock & Wilcox, General Electric and the Electric Power Research Institute, is currently working on the Front-End Engineering Design phase of the A-USC ComTest project. This paper will outline the motivation for the project, explain the project’s structure and schedule, and provide details on the design of the facility.

Components in ultrasupercritical steam (USC) boilers will operate under significantly more severe conditions than current subcritical and supercritical steam boilers. Existing construction rules for power boilers lack design guidance or criteria to assess the adequacy of designs for USC conditions. A Department of Energy (DOE) project addresses this by evaluating advanced materials under conditions similar to potential USC service environments. The project focuses on six tubing alloys and four thick-section alloys. Testing is underway for pressurized tube bends, notched thick-section bars, fatigue, and thermal shock on thick-section tubing made of materials like CCA617, Alloy 230, and Alloy 740. Further testing is planned for pressurized tubes, dissimilar metal welds, and thick-section weldments. This paper summarizes the status of this initial testing program aimed at enabling USC boiler material qualification.

The spalling of oxide scales at the steam side of superheater and reheater of ultra-supercritical unit is increasingly serious, which threatens the safe and economic operation of the boiler. However, no effective monitoring method is proposed to provide an on-line real-time detection on the spalling of oxide scales. This paper proposes an on-line magnetic non-destructive testing method for oxide granules. The oxide scale-vapor sample from the main steam pipeline forms liquid-solid two-phase flow after the temperature and pressure reduction, and the oxide granules are separated by a separator and piled in the austenitic pipe. According to the difference of the magnetic features of the oxide scales and the austenitic pipe, the oxide granule accumulation height can be detected through the spatial gradient variations of the magnetic induction. The laboratory test results show that the oxide scale accumulation can be accurately calculated according to the spatial gradient changes around the magnetized oxide granules, with the detection error not exceeding 2%.

Addressing the growing concern of supercritical and ultra-supercritical boilers as potential safety hazards in power plants, a new Boiler Risk Management and Life Prediction System (BRMLPS) has been developed. This system leverages risk-based inspection and assessment techniques alongside life prediction and management methods. The BRMLPS focuses on evaluating and ranking the risk associated with critical boiler components, such as heating surfaces, headers, and drums. This risk assessment allows for the development of targeted and efficient inspection plans and repair strategies, ultimately aiming to minimize accident rates, reduce potential losses, and optimize safety investments. By implementing this system, power plants can achieve maintenance optimization, balancing safety and economic considerations for their specialized equipment.

This paper presents an overview of China’s electric power development and the National 700°C Ultra-Supercritical (USC) Coal-Fired Power Generation Technology Innovation Consortium. Besides, the R&D plan and latest progress of China 700°C USC coal-fired power generation technology is also introduced in this paper.

Power generation technology selection is driven by factors such as cost, fuel supply security, and environmental impact. Coal remains a popular choice due to its global availability, but efficient, reliable, and cost-effective methods are essential. In Europe, efforts focus on advancing coal-fired steam power plants to ultrasupercritical conditions, with boilers and turbines now operating at up to 600°C. This has improved efficiency and maintained reliability comparable to subcritical plants. Orders are in detailed planning for plants exceeding 600°C, thanks to improved high-temperature steels for components like turbine rotors, casings, steam pipes, and boiler tubes, which undergo rigorous development and testing. Further efficiency gains are expected by increasing steam temperatures to over 700°C using nickel-based alloys. Test facilities are being built for pilot components, leading to a full demonstration plant. This systematic approach to materials development and proven design principles ensures operational reliability.

This paper introduces the GKM (Grosskraftwerk Mannheim AG) test rig, designed to evaluate new Ni-based alloys and austenitic steels for components in advanced 700°C power plants under real operational conditions. The test rig, integrated into a conventional coal-fired power plant in Mannheim, Germany, simulates extreme conditions of up to 725°C and 350/200 bar pressure. After approximately 2000 hours of operation, the paper presents an overview of the rig's design, its integration into the existing plant, and the status of ongoing tests. It also outlines parallel material investigations, including creep rupture tests, mechanical-technological testing, and metallurgical characterization. This research is crucial for the development of materials capable of withstanding the severe conditions in next-generation power plants, potentially improving efficiency and performance in future energy production.

In order to reduce CO 2 emissions and improve power generation efficiency, a development project involving an advanced USC (A-USC) plant has been carried out in Japan since 2008. Nibased alloys are candidate materials for boiler components with high temperature steam conditions, which are much stronger than conventional heat resistant steel. However, Ni-based alloys have never been applied with respect to the high pressure parts and thick walled components of USC coal-fired power plants. In this study, therefore, fabrication and characteristic properties, such as weldability, the weld joint and bent part properties, and weld cracking susceptibilities of Ni-based alloys such as HR6W, HR35 and two types of Alloy617 (High B and Low B) pipes were evaluated. Additionally, two types of HR6W header mock-ups and a HR6W tube element mock-up were fabricated. With the exception of Alloy617 (High B), the fabrication trials of Ni-based alloy pipes were conducted successfully, and the long-term creep strength of weldments and bends of Ni-based alloy pipes were found to be nearly equivalent to those of base metal. In the case of Alloy617 (High B), hot cracking was observed.

Following the successful completion of a 15-year effort to develop and test materials that would allow advanced ultra-supercritical (A-USC) coal-fired power plants to be operated at steam temperatures up to 760°C, a United States-based consortium has been working on a project (AUSC ComTest) to help achieve technical readiness to allow the construction of a commercial scale A-USC demonstration power plant. Among the goals of the ComTest project are to validate that components made from the advanced alloys can be designed and fabricated to perform under A-USC conditions, to accelerate the development of a U.S.-based supply chain for key A-USC components, and to decrease the uncertainty for cost estimates of future commercial-scale A-USC power plants. This project is intended to bring A-USC technology to the commercial scale demonstration level of readiness by completing the manufacturing R&D of A-USC components by fabricating commercial scale nickel-based alloy components and sub-assemblies that would be needed in a coal fired power plant of approximately 800 megawatts (MWe) generation capacity operating at a steam temperature of 760°C (1400°F) and steam pressure of at least 238 bar (3500 psia).The A-USC ComTest project scope includes fabrication of full scale superheater / reheater components and subassemblies (including tubes and headers), furnace membrane walls, steam turbine forged rotor, steam turbine nozzle carrier casting, and high temperature steam transfer piping. Materials of construction include Inconel 740H and Haynes 282 alloys for the high temperature sections. The project team will also conduct testing and seek to obtain ASME Code Stamp approval for nickel-based alloy pressure relief valve designs that would be used in A-USC power plants up to approximately 800 MWe size. The U.S. consortium, principally funded by the U.S. Department of Energy and the Ohio Coal Development Office under a prime contract with the Energy Industries of Ohio, with co-funding from the power industry participants, General Electric, and the Electric Power Research Institute, has completed the detailed engineering phase of the A-USC ComTest project, and is currently engaged in the procurement and fabrication phase of the work. This paper will outline the motivation for the effort, summarize work completed to date, and detail future plans for the remainder of the A-USC ComTest project.

A new martensitic steel for power generation applications was developed: Tenaris High Oxidation Resistance (Thor) is an evolution of the popular ASME grade 91, offering improved steam oxidation resistance and better long-term microstructural stability, with equal or better creep strength. Thanks to its design philosophy, based on consolidated metallurgical knowledge of microstructural evolution mechanisms, and an extensive development performed in the last decade, Thor was engineered to overcome limitations in the use of ASME grade 91, yet allow being processed in the same fashion, permitting the re-use of consolidated best practices for boiler fabrication. In order to evaluate the possibility to produce complete pressure part systems, various tests to manufacture components have been performed on Thor pipes and tubes (i.e. finning, bending, welding) and on Thor forged material (i.e. flanges). In all cases consolidated industrial best practices used on ASME grade 91 were applied, and resulting properties met ASME requirements.

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.