Search Results for bolting

Based on the research and development of Ni-based alloy of 700°C steam turbine bolts and blades worldwide, the process, microstructure, properties characteristics and strengthening mechanism of typical 700°C steam turbine bolts and blades materials Waspaloy are discussed in this study. The result shows that Waspaloy has higher elevated temperature yield strength, creep rupture strength, anti-stress relaxation property and good microstructure stability. The Waspaloy alloy could meet the design requirements of 700°C steam turbine bolts and blades.

Research and development of 700°C A-USC steam turbine unit needs to be supported by materials with excellent overall performance. Waspaloy is a kind of γ′ phase precipitation hardening superalloy developed by the United States in the 1950s. In the 700°C R&D Plan of Shanghai Turbine Plant, it was selected as a candidate material for high temperature blades and bolts. The composition, microstructure, properties, blade die forging process and bolt rolling process of Waspaloy alloy were researched in this paper. Simultaneously, Shanghai Turbine Plant successfully manufactured Waspaloy alloy trial production for high temperature bolts and blades. The results show that Waspaloy not only has excellent processing performance, but also has good high temperature strength, long-term performance, stress relaxation resistance and long term aging performance stability at 700°C. It can fully meet the requirements of high-temperature blades and bolts of 700°C A-USC unit. It shows that the 700°C A-USC unit high temperature blades and bolts were successfully developed by Shanghai Turbine Plant.

A study is being conducted on turbine materials for use in ultra-supercritical (USC) steam power plants, with the objective of ensuring no material-related impediments regarding maximum temperature capabilities and the ability to manufacture turbine components. A review of the state-of-the-art and material needs for bolting and casing applications in USC steam turbines was performed to define and prioritize requirements for the next-generation USC turbines. For bolting, several potentially viable nickel-base superalloys were identified for service at 760°C, with the major issues being final material selection and characterization. Factors limiting inner casing material capabilities include casting size/shape, ability to inspect for discontinuities, stress rupture strength, and weldability for fabrication and repairs. Given the need for precipitation-strengthened nickel-base alloys for the inner casing at 760°C, the material needs are two-fold: selection/fabrication-related and characterization. The paper provides background on turbine components and reviews the findings for bolting and casing materials.

Advanced 700C class steam turbines require austenitic alloys instead of conventional ferritic heat-resistant steels which have poor creep strength and oxidation resistance above 650C. Austenitic alloys, however, possess a higher thermal expansion coefficient than ferritic 12Cr steels. Therefore, Ni-based superalloys were tailored to reduce their coefficients to the level of 12Cr steels. Regression analysis of commercial superalloys proves that Ti, Mo and Al decrease the coefficient quantitatively in this order, while Cr, used to secure oxidation resistance, increases it so significantly that Cr should be limited to 12wt%. The newly designed Ni-18Mo-12Cr-l.lTi-0.9Al alloy is strengthened by gamma-prime [Ni 3 (Al,Ti)] and also Laves [Ni 2 (Mo,Cr)] phase precipitates. It bears an RT/700C mean thermal expansion coefficient equivalent to that of 12Cr steels and far lower than that of low-alloyed heat resistant steels. Its creep rupture life at 700C and steam oxidation resistance are equivalent to those of a current turbine alloy, Refractaloy 26, and its tensile strength at RT to 700C surpasses that of Refractaloy 26. The new alloy was trial produced using the VIM-ESR melting process and one ton ingots were successfully forged into round bars for bolts without any defects. The bolts were tested in an actual steam turbine for one year. Dye penetrant tests detected no damage. The developed alloy will be suitable for 700C class USC power plants.

In previous investigations on life with flexible driving were highly stressed components predominantly in hot continuous pressurized part of power plants in the foreground. However cases of damage and subsequent studies on peripheral components such as the boiler circulation system (boiler circulating pump) showed that a potential failure as well as a high hazard potential respectively great consequential damage can occur when such components are operated under different conditions. To avoid damages and losses resulting from damage to peripheral components, these components have to be subjected to further analysis. Here especially the pump housing is in the focus.

Austenitic heat resistant steels are one of the most promising materials to be applied around 650°C, due to its superior creep strength than conventional ferritic steels and lower material cost than Ni based superalloys. The problem of austenitic steels is its high thermal expansion coefficient (CTE), which leads to high deformation and stress when applied in rotors, casings, blades and bolts. To develop low CTE austenitic steels together with high temperature strength, we chose the gamma-prime strengthened austenitic steel, A-286, as the base composition, and decreased the CTE by introducing the invar effect. The developed alloy, Fe-40Ni-6Cr-Mo-V-Ti-Al-C-B, showed low CTE comparable to conventional ferritic steels. This is mainly due to its high Ni and low Cr composition, which the invar effect is prone even at high temperature region. This alloy showed higher yield strength, higher creep rupture strength and better oxidation resistance than conventional high Cr ferritic steels and austenitic steels. The 2 ton ESR ingot was forged or hot rolled without defects, and the blade trial manufacturing was successfully done. This alloy is one of the best candidates for USC and A-USC turbine components.

Low thermal expansion precipitation strengthening Ni-base superalloy, Ni-20Cr-10Mo-1.2Al-1.6Ti alloy (USC141TM), was developed for 700°C class A-USC steam turbine material by Hitachi, Ltd and Hitachi Metals, Ltd. USC141 is usually solution treated and then aged to increase high temperature strength for turbine blades and bolts. As the estimated 105h creep rupture strength at 700°C is about 180MPa, USC141 could also be expected to apply for boiler tubes. On the other hand, this alloy seems to be only solution treated to apply for boiler tubes because tubes are usually jointed by welding and bended by cold working and thus tube alloys should have low hardness before welding and bending and should be used as solution treated. In this study, the creep properties of USC141 as solution treated was evaluated, and the results and microstructures after creep tests were compared with those as aged. As a result, USC141 as solution treated exhibited almost as same creep rupture properties as that as aged because precipitation at grain boundaries and in grains gradually increased at testing temperatures around 700°C. Furthermore seamless tubes of USC141 were produced and various properties including creep properties are now being evaluated.

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.

Hitachi and Hitachi Metals have developed low thermal expansion Ni-base superalloy, Ni-20Cr-10Mo-1.2Al-1.6Ti alloy (USC141) for use as A-USC steam turbine material. The approximate 10 5 h creep rupture strength at 740° C is 100MPa, so USC141 can be expected to apply for blades and bolts. Now we have been studying to get better creep properties by microstructure controlling such as grain size or grain boundary morphology. In addition, the segregation test of USC141 shows good Freckle tendencies, it means that it would be easy to make a large ingot which could be used as rotors or pipes. From these calculation results, we have been tried to make an 850mmϕ ESR ingot of USC141.

Advanced 700°C-class steam turbines require the use of austenitic alloys instead of conventional ferritic 12Cr steels, which are inadequate in creep strength and oxidation resistance above 650°C. While austenitic alloys offer improved performance, they traditionally possess a significantly higher coefficient of thermal expansion (CTE) compared to 12% Cr steels. Through extensive research, the authors systematically investigated the effects of various alloying elements on thermal expansion and high-temperature strength. As a result of these investigations, they developed "LTES700," an innovative nickel-based superalloy specifically designed for steam turbine bolts and blades. This novel alloy uniquely combines a coefficient of thermal expansion comparable to 12Cr steels with high-temperature strength equivalent to conventional superalloys like Refractaloy 26, effectively addressing the critical limitations of previous materials.

A constitutive equation, with parameters derived from the interpolation of primary and steady state stages of constant load creep curves, has been utilized to estimate the stress relaxation behavior of the martensitic steel X20Cr13, alloy used in many high temperature applications, including heavy duty gas turbines. Creep and stress relaxation tests have been performed at 350°C, close to the negligible creep temperature of the studied alloy for stresses of interest for engineering applications. The creep tests were carried out at stresses below and above the yield stress, whereas, for the relaxation stress tests, the imposed strain was in the range 0.2% to 1.2% with the purpose to have, at the beginning of the tests, the same initial stresses of the performed creep tests. After a stress relaxation period, lasting between 10 to 1000 hours, each specimen was generally reloaded at the initial stress and a new relaxation test, on the same specimen, was carried out. This “reloading procedure”, simulating the re-tightening of bolts, has been repeated several times. The proposed equation has shown to well predict the experimental creep and stress relaxation behavior of the steel under investigation.

Along with rapid development of thermal power industry in mainland China, problems in metal materials of fossil power units also change quickly. Through efforts, problems such as bursting due to steam side oxide scale exfoliation and blocking of boiler tubes, and finned tube weld cracking of low alloy steel water wall have been solved basically or greatly alleviated. However, with rapid promotion of capacity and parameters of fossil power units, some problems still occur occasionally or have not been properly solved, such as weld cracks of larger-dimension thick-wall components, and water wall high temperature corrosion after low-nitrogen combustion retrofitting.

The piping stress and thermal displacement corresponding to different types of riser rigid support and hanger devices in different installation directions have been calculated by means of finite element analysis, to further analyze the impact on cracking of adjacent steam tee welds exerted by the constraint effect of riser rigid hangers on angular displacement. It can be seen from the analysis that a riser rigid hanger has a constraint effect on angular displacement, and such a constraint effect, however, is weak and limited on the piping stress and thermal displacement, so the piping stress and supports and hangers are not the main reasons for the cracking of tee welds. In addition, the calculation results alert that for an axial limiting hanger of riser with a dynamic axial pipe clamp and rigid struts, its constraint effect on angular displacement has a significant impact on the piping stress and thermal displacement.

A failure of the upper casing of the circulation pump led to a big damage in the PP Staudinger unit 5 on 12th of May 2014. According to the §18(2) BetrSichV an extensive root cause analysis (RCA) was started. From the beginning on different lines of activities were initiated to handle the situation with the required diligence. Decisions were made, taking into account safety regulations, possibility of repair and best practice engineering. Following the board decision to repair the unit 5, a lot of detailed work was done. All of the performed work packages were linked in different timelines and needed to meet in the key points. Consequently it was a challenge to achieve the agreed date of unit 5 restart on 15th of January 2015. The unit restart on the targeted date was a proof of the excellent collaboration between all involved parties. The presentation gives a summarizing overview about the damage, the main results of the RCA and the repair activities.

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

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.

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.

Recently, a γ’ precipitation strengthened Ni-base superalloy, USC141, was developed for 700°C class A-USC boiler tubes as well as turbine blades. In boiler tube application, the creep rupture strength of USC141 was much higher than that of Alloy617, and the 105 hours’ creep rupture strength of USC141 was estimated to be about 180MPa at 700°C. This is because fine γ’ particles precipitate in austenite grains and some kinds of intermetallic compounds and carbides precipitate along austenite grain boundaries during creep tests. Good coal ash corrosion resistance is also required for tubes at around 700°C. It is known that coal ash corrosion resistance depends on the contents of Cr and Mo in Ni-base superalloys. Therefore the effect of Cr and Mo contents in USC141 on coal ash corrosion resistance, tensile properties, and creep rupture strengths were investigated. As a result, the modified USC141 containing not less than 23% Cr and not more than 7% Mo showed better hot corrosion resistance than the original USC141. This modified alloy also showed almost the same mechanical properties as the original one. Furthermore the trial production of the modified USC141 tubes is now in progress.

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.

As part of a Department of Energy (DOE) funded program assessing advanced manufacturing techniques for Small Modular Reactor (SMR) applications, the Nuclear Advanced Manufacturing Research Centre (AMRC) and the Electric Power Research Institute (EPRI) have been developing Electron Beam Welding (EBW) parameters and procedures based upon SA508 Grade 3 Class 1 base material. The transition shell, a complex component connecting the lower assembly to the upper assembly is a shell that flares up with varying thicknesses across its section. The component due to its geometry could be built by near net shape powder metallurgy hot isostatic pressing instead of conventional forging techniques. The demonstrator transition shell here is built from several sub-forging as a training exercise. The complex geometry and joint configuration were selected to assess the EBW as a suitable technique. This paper presents results from the steady state welding in the 60-110 mm material thickness range, showing that weld properties meet specification requirements. Weld quality was assured by Time-of-Flight Diffraction (ToFD). The transition shell was completed by welding a flange to the assembly. The presented transition shell assembly represents 6 welded sections all fabricated in below 100 min total welding time.