Search Results for internal quality

Monoblock low-pressure (LP) turbine rotor shaft forgings for nuclear power plants have been produced from up to 600 ton ingots. However, ingots greater than 600 tons are necessary to increase the generator capacity. Segregation, non-metallic inclusions, and micro porosities inevitably increase with the increase in ingot size. Manufacturing such massive ingots with high soundness is quite difficult. Thus, the development of 650 ton ingot production was carried out in 2010. The 650 ton ingot was dissected and investigated to verify its internal quality. The internal quality of the 650 ton ingot was found to be equal to that of 600 ton ingots. Subsequently, in 2011, we produced a 670 ton ingot, the world’s largest, to produce a trial LP rotor shaft forging with a diameter of 3,200 mm. Results show that the internal quality, mechanical properties, and heat stability are the same as LP rotor shaft forgings made from 600 ton ingots.

Creep-fatigue crack formation (endurance) and crack growth rate data are necessary inputs for assessing the structural integrity and for estimating the design life of high temperature components in power generation and aircraft engine industries. Ensuring consistency in the reported test data, as well as an understanding of the inherent scatter and its source in the data, are both necessary for assuring quality and limitations of the analyses that rely on the data. In 2008, the American Society for Testing and Materials (ASTM) under the umbrella of its subcommittees E08.05 on Cyclic Deformation and Crack Formation and E08.06 on Crack Growth, and the sponsorship of Electric Power Research Institute (EPRI) through its international experts’ working group on creep-fatigue embarked on the task of developing separate standard test methods for creep-fatigue crack formation and creep-fatigue crack growth. The first standard entitled, “E-2714-09: Standard Test Method for Creep-fatigue Testing” was developed in 2009 and was followed up with a round-robin consisting of 13 laboratories around the world for testing the newly developed standard. This paper discusses the results of this round-robin concluded in 2012 using the widely used P91 steel that led to the formulation of the Precision and Bias statement contained in the version of the ASTM standard E2714 that was successfully balloted in the year 2013.

Growing energy demand promotes the construction of high performance energy plants with large scale. A dramatic increase of plant performance has been achieved by the enlargement of their major components such as turbine rotor shafts and pressure vessels. The Japan Steel Works, Ltd., has been continuing the efforts for improvements of production technology, material technology, reliability assessments and so on in order to attain high performance, high efficiency and reliable plants. The efforts gave birth to several epoch-making large and high quality forged components for energy plants. Recently, on the viewpoint of environmental problem such as global climate change, further development of new production technology and improvement of material has been continued. This paper gives an overview of the development of large high-quality forgings for high efficiency power generation plants.

A 9% Cr steel containing cobalt and boron, X13CrMoCoVNbNB9-2-1, has been manufactured by electroslag remelting (ESR) to evaluate its performance and to compare its creep strength and microstructure to a forging made from electroslag hot-topping ingot. The evaluation results confirm that it is possible to produce rotor forgings with homogeneous composition and good properties by the ESR process. The results of creep rupture tests up to 5000 h indicate that the creep strength of the forging made from ESR ingot is similar to that of the forging produced by the electroslag hot-topping process. Martensitic lath microstructures with high density dislocations and the precipitations of M 23 C 6 , VX, NbX and M2X are observed after the quality heat treatments at the center portion of both forgings. There is no large difference in the martensitic lath widths, distributions, and sizes of those particles between both trial forgings.

Sufficient available energy in combination with lowest environmental pollution is a basic necessity for a high standard of living in every country. In order to guarantee power supply for future generations it is necessary to use fossil fuels as efficient as possible. This fact calls for the need of power plants with improved technologies to achieve higher efficiency combined with reduced environmental impact. In order to realize this goal it is not only a challenge for power station manufacturers, but also for manufacturers of special steels and forgings, who have to produce improved components with more advanced materials and more complex manufacturing processes. This paper reports about experiences in the fabrication of forged components for gas and steam turbines followed by achievable mechanical properties and ultrasonic detectability results. The materials are the creep resistant martensitic Cr steels developed in the frame of the European Cost research programme. Whereas Boron containing 10% Cr steels are suitable for steam temperatures of 625°C and slightly higher, Ni-based alloys shall be used for temperatures of 700°C and above. One pilot rotor forging, representing a HP-rotor for welded construction, has been manufactured out of alloy Inconel 625 within the frame of the European Thermie project AD700.

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.

Welding of collector pipes, flat heads, dished ends and connector pipes performed with high temperature and creep-resistant steels most often has been performed using GTAW process combined with MMA processes. Progress in GMAW process and availability of high quality filler materials (solid wires) enables welding of the above connections also using this method. In order to prove its efficiency, this article presents the results of related tests. The range of tests was similar to that applied during the qualification of welding procedure. The investigation also involved microscopic and fractographic examinations and creep tests. The results reveal that welding with GMAW is by no means inferior to a currently applied SMAW method yet the time of the process is shorter by 50%. The article presents the world’s first known positive results in welding of P92 grade steel using GMAW welding method.

Nimonic 80A, a Ni-base superalloy mainly strengthened by Al and Ti to form γ'-Ni 3 (Al, Ti) precipitation in Ni-Cr solid solution strengthened austenite matrix, has been used in different industries for more than half century (especially for aero-engine application). In consideration of high strengths and corrosion resistance both Shanghai Turbine Company (STC) has adopted Nimonic 80A as bucket material for ultra-super-critical (USC) turbines with the steam parameters of 600°C, 25MPa. First series of two 1000MW USC steam turbines made by Shanghai Turbine Co. were already put in service on the end of 2006. Large amount of Nimonic 80A with different sizes are produced in Special Steel Branch of BAOSTEEL, Shanghai. Vacuum induction melting and Ar protected atmosphere electro-slag remelting (VIM+PESR) process has been selected for premium quality high strength Nimonic 80A. For higher mechanical properties the alloying element adjustment, optimization of hot deformation and heat treatment followed by detail structure characterization have been done in this paper. The Chinese premium quality high strength Nimonic 80A can fully fulfill the USC turbine bucket requirements.

Demand of 9-12% chromium steel rotor forgings becomes higher from point of view of environmental protection in coal fired fossil power generations. Japan Casting & Forging Corporation (JCFC) has manufactured 9-12% Cr steel rotor forgings with JCFC's original techniques since 1991. Recently, type E steel developed by European COST program has been trial melted to meet the demand of such high Cr steel forgings in the world. Full size two forgings have been manufactured from approximately 70 ton ingot applying Electro Slag Hot Topping by JCFC (ESHT-J) process. One of the trial forgings has been austenitized at higher temperature in the quality heat treatment to improve long term creep strength. Their productivities and sufficient qualities have been ascertained.

The power generation industry's need to extend run times between scheduled outages and to control maintenance budgets has increased reliance on advanced wear protection technologies to lengthen equipment life while maintaining clean, quality power production. This paper summarizes field erosion experiments conducted by the Electric Power Research Institute (EPRI) and the Tennessee Valley Authority (TVA) Kingston Power Plant on one of the plant's induced draft fans, testing several wear protection materials to reduce severe wear and extend intervals between planned outage cycles. Test results showed brazed tungsten carbide cladding's superiority in this extreme environment, successfully increasing the dirty gas fan run time from 5-8 months to over 30 months by cladding fan blades. Independent reviews of severe wear protection methods on low NOx burners and superheater boiler tubes with similar results are also presented.

Advanced 700°C-class steam turbines demand austenitic alloys for superior creep strength and oxidation resistance beyond 650°C, exceeding the capabilities of conventional ferritic 12Cr steels. However, austenitic alloys come with a higher coefficient of thermal expansion (CTE) compared to 12Cr steels. To ensure reliability, operability, and performance, these advanced turbine alloys require low CTE properties. Additionally, for welded components, minimizing CTE mismatch between the new material and the welded 12Cr steel is crucial to manage residual stress. This research investigates the impact of alloying elements on CTE, high-temperature strength, phase stability, and manufacturability. As a result, a new material, “LTES700R,” was developed specifically for steam turbine rotors. LTES700R boasts a lower CTE than both 2.25Cr steel and conventional superalloys. Additionally, its room-temperature proof strength approaches that of advanced 12Cr steel rotor materials, while its creep rupture strength around 700°C significantly surpasses that of 12Cr steel due to the strengthening effect of gamma-prime phase precipitates. To assess the manufacturability and properties of LTES700R, a medium-sized forging was produced as a trial run for a turbine rotor. The vacuum arc remelting process was employed to minimize segregation risk, and a forging procedure was meticulously designed using finite element method simulations. This trial production resulted in a successfully manufactured rotor with satisfactory quality confirmed through destructive evaluation.

Materials are developed and improved by adjusting both the alloy chemistry and the processing conditions to achieve desired microstructures and properties. Traditionally, these improvements have been made by a slow and labor-intensive series of experiments. But it is now possible to replace this expensive trial and error process by carrying out only a few ‘key’ experiments in conjunction with thermodynamic calculations. These calculations are powerful tools for alloy design, enabling improvement in the selection of alloy chemistry and the parameters used for fabrication steps such as heat treatments. In order to have the utmost confidence in the results obtained from the calculations, it is essential to have high quality thermodynamic databases. Such databases can be used not only in phase equilibrium calculations but also as the critical input for further kinetic simulations. In the present paper, we present our work on the development of reliable thermodynamic databases for nickel-based superalloys and iron alloys. We first briefly describe the methodology of developing these databases and then discuss some specific examples using the databases. With the aid of these examples, the usefulness of thermodynamic databases in aiding the development of advanced materials is discussed.

Simple and effective material examination methods are desired for the diffusion bonding process, so that bonding produced components, such as compact heat exchangers, can be used in nuclear applications. Optical microscopy of diffusion bond process samples is a quick way to examine diffusion bond-line microstructure and to evaluate material quality. The stacked nature of a diffusion bonded-block results in distinct regions of grain growth both at and away from the bond interface. Strong diffusion bond materials exhibit grain growth across the original bond interface plane, weak materials have little-to-no growth across. A series of 316H diffusion bonded specimens of differing quality and strength were examined using optical microscopy. The microstructure both at and away from the bond interface was examined over 15mm long sections of the bond-line. A metric for evaluating bond growth is proposed. This is defined as the Bond Line Growth Threshold (BLGT) and is evaluated as the percentage of the bond line with grains meeting the threshold. Here a fraction of the diffusion bond is considered bonded when its grains exceed a threshold of growth past the bond interface. The BLGT is determined through automated image processing methods.

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.

10CrMoWVNbN (X 12 CrMoWVNbN 10 1 1) steel trial forgings has been manufactured to clarify the effect of austenitizing temperature on the creep rupture strength and microstructure. From the results of creep rupture tests up to 30,000 hours, higher austenitizing temperature improves the rupture strength without large degradation of the rupture ductility. The microstructural investigations demonstrate that the prior austenite grain size and the precipitation behavior of fine M2X particles are presumed to contribute to the improvement of creep rupture strength.

Microstructural change of 10 % Cr steel trial forgings subjected to different heat treatment conditions which aim to improve the creep rupture strength and microstructural stability during creep was investigated. Creep rupture strength of the forging subjected to the quality heat treatment with the austenitizing temperature of 1090° C is higher than that of the forging solution treated at 1050°C, however, the difference of creep rupture strength is reduced in the long-term region around 40,000 h. Decrease in creep rupture ductility of the forging until 43,300 h is not observed. Progress of the martensite lath recovery in the forging solution-treated at 1090°C is slower than that in the forging austenitized at 1050°C. Higher temperature solution treatment suppresses the recovery of lath structures. Formations of Z-phase are found in the specimens creep-ruptured at 37,300 h in the forging solution-treated at 1050°C and at 43,400 h in the forging austenitized at 1090°C. Z-phase precipitation behavior in this steel is delayed in comparison with the boiler materials, regardless of austenitizing temperature.

The efforts of the European Union and Germany in particular to realize the transformation towards a climate-neutral economy over the coming decades have the establishing of a hydrogen economy as a fundamental milestone. This includes production, import, storage, transportation and utilization of great amounts of gaseous hydrogen in existing and new infrastructure. Metallic materials, mainly steels, are the most widely used structural materials in the various components of this supply chain. Therefore, the accelerated use of hydrogen requires the qualification of materials (i.e., ensuring they are hydrogen-ready) to guarantee the sustainable and safe implementation of hydrogen technologies. However, there is currently no easily applicable and standardized method to efficiently determine the impact of gaseous hydrogen on metallic materials. The few existing standards describe procedures that are complex, expensive, and only available to a limited extent globally. This article outlines the key milestones towards standardizing an efficient testing method as part of the TransHyDE flagship project. This new approach enables testing of metallic materials in gaseous hydrogen using tubular specimens. It uses only a fraction of the hydrogen required by the traditional autoclave method, significantly reducing costs associated with technical safety measures. Among the topics to be discussed are the factors influencing the test procedure, including geometrical considerations, surface quality, gas purity and strain rate.

More efficient, sustainable, flexible and cost-effective energy technologies are strongly needed to fulfil the new challenges of the German “Energiewende”. For a reduction of consumed primary resources higher efficiency steam cycles with increased operating parameters, pressure and temperature, are mandatory. Hence, advanced materials are needed. The present study focuses on stainless, high strength, ferritic (non-martensitic) steel grades, regarding thermal treatment effects on particle evolution. The heat treatment includes variations, e.g. a two phase pre heat treatment. Effects of the treatment were analysed and connected to creep performance. Experiments at differently heat treated materials show promising improvement of creep performance. These results can be linked to the stability and evolution of strengthening Laves phase particles.

Xcel Energy’s Comanche Unit 3 experienced widespread cracking of T23 membrane wall tubes within the evaporator section, initially occurring during the boiler construction phase, primarily at shop and field tube butt welds. The majority of the tube cracking was attributed to stress-corrosion cracking (SCC), and a lesser number of fabrication-related hydrogen induced cracking (HIC), weld solidification cracking, and brittle cracking within tube swage sections were also experienced. Hundreds of tubes were replaced prior to Unit commissioning, due to both actual tube leaks and those replaced due to weldment cracking and other identified weld defects during radiographic testing. Elevated stress levels and material susceptibility (i.e. hardness in the as-welded condition) were considered the critical factors in the tube cracking.

Development of steels used in the power generation industry for the production of boilers characterized by supercritical parameters poses new challenges. The introduction of new combinations of alloying agents aimed at obtaining the best possible mechanical properties, including creep resistance, affects the weldability of new steels. Each of the latter has to undergo many tests, particularly as regards bending and welding, in order to enable the development of technologies ensuring failure-free production and assembly of boiler systems. Martensitic steels containing 9% Cr, used in the manufacturing of steam superheaters, are characterized by excellent creep resistance and, at the same time, low oxidation resistance at a temperature in excess of 600°C. In turn, steels with a 12% Cr content, i.e., VM12-SHC or X20CrMoV12-1 are characterized by significantly higher oxidation resistance but accompanied by lower strength at higher temperatures, which translates to their limited application in the production of boilers operating at the most top parameters.X20CrMoV12-1 was withdrawn from most of the power plants, and VM12-SHC was supposed to replace it, but unfortunately, it failed in regards to creep properties. To fulfill the gap a new creep strength-enhanced ferritic steel for service in supercritical and ultra-supercritical boiler applications was developed by Tenaris and it is designated as Thor115 (Tenaris High Oxidation Resistance). This paper covers the experience gained during the first steps of fabrication, which includes cold bending and welding of homogenous joints.