The United States Department of Energy (U.S. DOE) Office of Fossil Energy and the Ohio Coal Development Office (OCDO) have been the primary supporters of a U.S. effort to develop the materials technology necessary to build and operate an advanced-ultrasupercritical (A-USC) steam boiler and turbine with steam temperatures up to 760°C (1400°F). The program is made-up of two consortia representing the U.S. boiler and steam turbine manufacturers (Alstom, Babcock & Wilcox, Foster Wheeler, Riley Power, and GE Energy) and national laboratories (Oak Ridge National Laboratory and the National Energy Technology Laboratory) led by the Energy Industries of Ohio with the Electric Power Research Institute (EPRI) serving as the program technical lead. Over 10 years, the program has conducted extensive laboratory testing, shop fabrication studies, field corrosion tests, and design studies. Based on the successful development and deployment of materials as part of this program, the Coal Utilization Research Council (CURC) and EPRI roadmap has identified the need for further development of A-USC technology as the cornerstone of a host of fossil energy systems and CO 2 reduction strategies. This paper will present some of the key consortium successes and ongoing materials research in light of the next steps being developed to realize A-USC technology in the U.S. Key results include ASME Boiler and Pressure Vessel Code acceptance of Inconel 740/740H (CC2702), the operation of the world’s first 760°C (1400°F) steam corrosion test loop, and significant strides in turbine casting and forging activities. An example of how utilization of materials designed for 760°C (1400°F) can have advantages at 700°C (1300°F) will also be highlighted.

Increasing the efficiency of the Rankine regenerative-reheat steam cycle to improve the economics of electric power generation and to achieve lower cost of electricity has been a long sought after goal. Advanced ultra-supercritical (A-USC) development for materials to reach 760C (1400F) is a goal of the U.S. Program on Materials Technology for Ultrasupercritical Coal-Fired Boilers sponsored by the United States (U.S.) Department of Energy and the Ohio Coal Development Office (OCDO). As part of the development of advanced ultra-supercritical power plants in this program and internally funded programs, a succession of design studies have been undertaken to determine the scope and quantity of materials required to meet 700 to 760C (1292 to 1400F) performance levels. At the beginning of the program in 2002, the current design convention was to use a “two pass” steam generator with a pendant and horizontal tube bank arrangement as the starting point for the economic analysis of the technology. The efficiency improvement achieved with 700C (1292F) plus operation over a 600C (1112F) power plant results in about a 12% reduction in fuel consumption and carbon dioxide emissions. The reduced flue gas weight per MW generated reduces clean up costs for the lower sulfur dioxide, nitrogen oxides and particulate emissions. The operation and start up of the 700C (1292F) plant will be similar in control methods and techniques to a 600C (1112F) plant. Due to arrangement features, the steam temperature control range and the once through minimum circulation flow will be slightly different. The expense of nickel alloy components will be a strong economic incentive for changes in how the steam generator is configured and arranged in the plant relative to the steam turbine. To offer a view into the new plant concepts this paper will discuss what would stay the same and what needs to change when moving up from a 600C (1112F) current state-of-the-art design to a plant design with a 700C (1292F) steam generator and turbine layout.

To achieve the necessary creep-rupture lifetimes at the temperatures and pressures associated with advanced ultrasupercritical (A-USC) steam conditions (100,000 h at 100 MPa and 760°C), precipitation-strengthened nickel-based alloys are required for the superheater and reheater tubing in A-USC boilers. Two alloys were considered to have potential for this application: Inconel 740 and Haynes 282 alloy. In support of this application, creep-rupture testing of several heats of Inconel 740 was conducted over a range of temperatures and stresses to develop confidence in qualitatively predicting creep lifetimes under conditions relevant to A-USC steam conditions, with the longest rupture times exceeding 30,000 h. For comparison, the creep-rupture behavior of Haynes 282 alloy was mapped as a function of temperature and stress, but with a significantly smaller dataset. Only a small difference in creep-rupture results between Inconel 740 and Inconel 740H was found although the latter alloy showed significantly greater resistance to η phase formation during testing. Little effect of prior aging treatments (for setting the γ′ precipitate structure) on creep-rupture behavior was observed. Results from a modified power law analysis showed that, while both Inconel 740 and Haynes 282 are projected to meet the A-USC lifetime requirements, the latter offered the potential for better long-term creep resistance.

Inconel alloy 740/740H (ASME Code Case 2702) is an age-hardenable nickel-based alloy designed for advanced ultrasupercritical (A-USC) steam boiler components (superheaters, reheaters, piping, etc.). In this work, creep testing, beyond 40,000 hours was conducted a series of alloy 740 heats of varying product form, chemistry, and grain size. Long-term creep-rupture strength was found to be weakly dependent on grain size. Analysis of the time-to-rupture data was conducted to ensure long-term strength projections and development of ASME stress allowables. Testing was also conducted on welded joints in alloy 740 with different filler metal and heat-treatment combinations. This analysis shows the current weld strength reduction factor of 30% (Weld Strength Factor of 0.70) mandated by ASME Code Case 2702 is appropriate for 740 filler metal but other options exist to improve strength. Based on these results, it was found that alloy 740 has the highest strength and temperature capability of all the potential A-USC alloys available today.

Advances in materials for power plants include not only new materials with higher-temperature capabilities, but also the use of current materials at increasingly higher temperatures. This latter activity builds on extensive experience of the performance of the various alloys, and provides a basis for identifying changes in alloy behavior with increasing temperature as well as understanding the factors that ultimately determine the maximum use temperatures of the different alloy classes. This paper presents results from an effort to model the exfoliation processes of steam-side oxide scales in a manner that describes as accurately as possible the evolution of strains in oxides growing inside small-diameter tubes subjected to large thermal gradients and to thermal transients typical of normal steam boiler operation. One way of portraying the results of such calculations is by plotting the evolving strains in a given oxide scale on an ‘Exfoliation Diagram’ (of the type pioneered by Manning et al. of the British Central Electricity Research Laboratory) to determine the earliest time at which the trajectory of these strains intersects a criterion for scale failure. Understanding of how such ‘strain trajectories’ differ among different alloys and are affected by the major variables associated with boiler operation has the potential to suggest boiler operating strategies to manage scale exfoliation, as well as to highlight the mode of scale failure and the limitations of each alloy. Preliminary results are presented of the strain trajectories calculated for alloys T22, T91, and TP347 subjected to the conditions experienced by superheaters under assumed boiler operating scenarios. For all three alloys the earliest predicted scale failures were associated with the increased strains developed during a boiler shut-down event; indeed, in the cases considered it appeared unlikely that scale failure would occur in any practically meaningful time due to strains accumulated during operation in a load-following mode in the absence of a shut down. The accuracy of the algorithms used for the kinetics of oxide growth appeared to be a very important consideration, especially for alloy TP347 for which large effects on oxide growth rate are known to occur with changes in alloy grain size and surface cold work.

Advanced UltraSupercritical (A-USC) Steam fossil power plants will operate at steam temperatures up to 760°C, which will require the use of Ni-based superalloys for steam boiler/superheater and turbine systems. In 2008, the Oak Ridge National Laboratory (ORNL) and the National Engineering Technology Laboratory/Albany (NETL/Albany) collaborated to make and test castings of Ni-based superalloys, which were previously only commercially available in wrought form. These cast Ni-based based alloys are envisioned for the steam turbine casing, but they may also be applicable to other large components that connect the steam supply to the steam turbine. ORNL and NETL/Albany have produced small vacuum castings of HR 282, Nimonic 105, Inconel 740, and alloy 263, which are precipitation-hardened Ni-based superalloys, as well as solid-solution superalloys such as alloys 625, 617 and 230. The initial alloy screening included tensile and creep-testing at 800°C to determine which alloys are best suited for the steam turbine casing application at 760°C. HR 282 has the best combination of high-temperature strength and ductility, making it a good candidate for the cast-casing application. Cast and wrought versions of HR 282 have similar creep-rupture strength, based on the limited data available to-date. Detailed comparisons to the other alloys and microstructures are included in this paper.

The capacity of PC power plants in Japan rose to 35GW in 2004. The most current plants have a 600 deg-C class steam temperature and a net thermal efficiency of approximately 42% (HHV). Older plants, which were built in the ‘70s and early ‘80s, will reach the point where they will need to be rebuilt or refurbished in the near future. The steam temperatures of the older plants are 538 deg-C or 566 deg-C. We have done a case study on the refurbishment of one of these plants with the advanced USC technology that uses a 700 deg-C class steam temperature in order to increase the thermal efficiency and to reduce CO 2 emissions. The model plant studied for refurbishing has a 24.1MPa/538 deg-C /538 deg-C steam condition. We studied three possible systems for the refurbishing. The first was a double reheat system with 35MPa/700 deg-C /720 deg-C /720 deg-C steam conditions, the second one was a single reheat 25MPa/700 deg-C/720 deg-C system, the last one was a single reheat 24.1MPa/610 deg-C/720 deg-C system. In addition to these, the most current technology system with 600 deg-C main and reheat temperatures was studied for comparison. The study showed that the advanced USC Technology is suitable for refurbishing old plants. It is economical and environmentally-friendly because it can reuse many of the parts from the old plants and the thermal efficiency is much higher than the current 600 deg-C plants. Therefore, CO 2 reduction is achieved economically through refurbishment.

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.

The construction of highly efficient Ultra Supercritical (USC) boiler systems to operate with steam temperatures up to 760°C (1400°F) and with steam pressures up to 34.5 MPa (5000 psi) will require the use of advanced high temperature, high strength materials. As part of a 5-year project to qualify advanced boiler materials for USC power plants, a number of austenitic materials have been selected for further development and use in USC boiler systems, including alloys 230, 740, CCA 617, HR6W, and Super 304H. In one task of this project, boiler fabrication guidelines appropriate for the use of these alloys were investigated. Because it is recognized that cold formed and mechanically strained austenitic materials can degrade in material creep strength, a study to investigate the limits of strain and temperature exposure for the USC alloys was undertaken. An objective of this work was to determine for each USC alloy a relationship between the level of cold strain and the conditions of time and temperature that will cause recrystallization and significant microstructural change. The ultimate goal of this work was to determine limits of strain, due to cold forming, that can be tolerated before heat treatment is required, similar to those limits provided for the austenitic materials (e.g., 300-series stainless steels, alloy 800H) in Table PG-19 in Section I of the ASME Boiler and Pressure Vessel Code. This paper will describe the technical approach for 1) preparing specimens having discrete cold strains ranging from about 1 to 40 percent, 2) exposing these strained specimens for selected times at various elevated temperatures, 3) identifying the onset of recrystallization in the microstructures of the exposed specimens, and 4) establishing a useful engineering method to predict conditions for the onset of recrystallization in the USC alloys using the experimental results.

Development activities initiated over a decade ago within the COST 522 program and continuing through the COST 536 Action have yielded significant progress in constructing a new generation of steam power plants capable of operating under advanced steam conditions. These innovative plants promise substantially improved thermal efficiency, with steam temperatures reaching up to 620°C (1150°F). Recent successful power plant orders in Europe and the United States stem from critical advancements, including the development, testing, and qualification of 10% Cr steels with enhanced long-term creep properties for high-temperature components such as turbine rotors and valve casings. Extensive in-house development efforts have focused on fabrication, weldability, mechanical integrity, and fracture mechanics evaluations of full-sized forged and cast components. These materials will be implemented in several new coal-fired power plants, notably the Hempstead plant in the USA, which will operate with live steam temperatures of 599°C (1111°F) and reheat steam temperatures of 607°C (1125°F). The improved creep properties enable the construction of casings with reduced wall thicknesses, offering greater thermal flexibility at lower component costs and facilitating welded turbine rotors for high-temperature applications without requiring cooling in the steam inlet region. Looking forward, further efficiency improvements are anticipated through the introduction of nickel alloys in steam turbine and boiler components, with the European AD700 project targeting reheat steam temperatures of 720°C (1328°F) and the US Department of Energy project aiming even higher at 760°C (1400°F). The AD700 project has already demonstrated the technical feasibility of such advanced steam power plants, with engineering tasks progressing toward the construction of a 550 MW demonstration plant, while DOE activities continue to address boiler concerns and focus on rotor welding, mechanical integrity, and steam oxidation resistance.

The increasing steam parameters in modern high-efficiency fossil fuel power plants demand advanced materials with enhanced creep strength for operation under extreme temperature and pressure conditions. Tenaris has focused on developing ferritic-martensitic and austenitic grades for tube and pipe applications. At TenarisDalmine, efforts on ferritic-martensitic steels include ASTM Grade 23, a low-alloyed alternative to Grade 22 with 1.5% W, offering good weldability, creep resistance up to 580°C, and cost competitiveness. Additionally, ASTM Grade 92, an improved version of Grade 91, provides high creep strength and long-term stability for components like superheaters and headers operating up to 620°C. At TenarisNKKT R&D, austenitic steel development includes TEMPALOY AA-1, an improved 18Cr-8NiNbTi alloy with 3% Cu for enhanced creep and corrosion resistance, and TEMPALOY A-3, a 20Cr-15Ni-Nb-N alloy with superior creep and corrosion properties due to its higher chromium content. This paper details the Tenaris product lineup, manufacturing processes, and key material properties, including the impact of shot blasting on the steam oxidation resistance of austenitic grades. It also covers ongoing R&D efforts in alloy design, creep testing, data assessment, microstructural analysis, and damage modeling, conducted in collaboration with Centro Sviluppo Materiali.

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.

Numerous factors, including actual chemical composition, heat treatment, microstructure, dimensions, and service conditions, determine the lifetime of creep-exposed components. This creates a wide gap between the real condition of a given steel pipe and its project specification. For a 141MW unit main steam line, the remaining life calculated according to the German Boiler Code TRD 508 was found to be almost exhausted. It was recommended to remove a pipe sample with a circumference weld for laboratory examination. Stress rupture tests were performed on three types of specimens: tangential, longitudinal, and longitudinal with a heat-affected zone in the middle of the gauge length using the isostress testing method. Metallographic examination of the broken specimens was conducted. Linear extrapolation of the rupture times to the service temperature yielded a residual service life of more than 100,000 hours.