Search Results for surface quality

Oxide scale formation in the inner bore of steam tubing has been identified as a key metric for determining operational parameters and life expectancy of modern boiler systems. Grade 91 tubing is commonly used for the construction of key components within boiler systems designed for power generation operating in the temperature range of 500 to 650 °C. Standard laboratory test procedures involve grinding the surface of test coupons to homogenise their surface structure and improve experimental consistency, however, data presented here shows a discrepancy between laboratory and industrial practices that has long term implications on scale growth kinetics and morphological development. Microstructural analysis of both virgin and ex-service tubing reveals the presence of a pre-existing oxide structure that is incorporated into the inwardly growing scale and is implicated in the formation of multiple laminar void networks. These void networks influence thermal diffusivity across the scale and may function as regions of spallation initiation and propagation.

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.

Diode laser cladding (DLC) surfaces, valued in the nuclear industry for their wear resistance, corrosion protection, and oxidation resistance, present unique challenges in surface characterization compared to conventionally machined surfaces. While traditional machined surfaces exhibit predictable, periodic topographies that can be validated through simple linear profile measurements, DLC surfaces feature distinctive metal tracks with central peaks and inter-track troughs, creating a wave-like structure with randomly distributed spherical asperities. This complex topography cannot be adequately characterized by traditional single-trace sampling methods due to significant variations in localized features at peaks and troughs. To address this challenge, this study examines DLC surfaces produced under varying control parameters (laser power, head travel speed, powder feed rate, and track offset) using laser confocal microscopy. Both profile and areal surface measurements are compared to identify the most effective method for characterizing DLC surface structure and quality, providing a foundation for standardized quality assessment in industrial applications.

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.

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.

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.

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.

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.

To solve crack problems at the tube elbow induced by high depth-to-width ratio longitudinal defects on the inner wall of boiler tube, a number of testing experiments and testing methods have been applied to analysis on the sensitivity and correspondence of such defects, and it has been found that the flattening test has an outstanding advantage to detect such defects. However, according to relevant standards, the judgment is controversy. It can be noted from the research that if a steel tube with a ratio of wall thickness to outer diameter larger than 0.1 is turned prior to the flattening test, to reduce such ratio to be less than or equal to 0.1, the shortcomings in detection and evaluation of such defects specified in the current relevant standards of many countries can be effectively overcome. The method has been proposed and adopted preliminarily in the relevant Chinese standard.

The combustion of coal and biomass fuels in power plants generates deposits on the surfaces of superheater / reheater tubes that can lead to fireside corrosion. This type of materials degradation can limit the lives of such tubes in the long term, and better methods are needed to produce predictive models for such damage. This paper reports on four different approaches that are being investigated to tackle the challenge of modelling fireside corrosion damage on superheaters / reheaters: (a) CFD models to predict deposition onto tube surfaces; (b) generation of a database of available fireside corrosion data; (c) development of mechanistic and statistically based models of fireside corrosion from laboratory exposures and dimensional metrology; (d) statistical analysis of plant derived fireside corrosion datasets using multi-variable statistical techniques, such as Partial Least Squares Regression (PLSR). An improved understanding of the factors that influence fireside corrosion is resulting from the use of a combination of these different approaches to develop a suite of models for fireside corrosion damage.

Diffusion bonding is a key manufacturing process for nucleation applications including compact heat exchangers. Accurately predicting the alloy's behavior during the diffusion bonding process presents challenges, primarily due to the intricate interplay of microstructural evolution and physical processes such as compressive loading, temperature history, and component migration. The current study develops a phase-field model designed to simulate the diffusion bonding in 316H stainless steel, a material with exceptional high-temperature strength, corrosion resistance and suitability to high-pressure conditions. Our model incorporates a multi-phase, multi-component framework that aligns the experimental observations with the grain growth and heterogeneous nucleation, where arbitrary external compressive load and temperature history are considered. The simulations focus on grain nucleation, growth, and microstructure evolutions across diffusion bonding line under a variety of temperature profiles, mechanical loads, and surface roughness conditions, mirroring experimental setups. Our model predicts consistent simulation results with experiments in terms of the grain size and distribution near the bonding area, offering a better understanding of the diffusion bonding mechanism and the manufacturing process for building reliable compact heat exchangers.

Recent in-service experiences have revealed critical vulnerabilities in creep-strength enhanced ferritic (CSEF) steels, with cracking potentially occurring surprisingly early in a component's operational life. Fabrication irregularities have been found to introduce substantial property deficiencies compared to average material performance, raising serious concerns among industry users regarding personnel safety and equipment reliability. In response, a collaborative research program between the Electric Power Research Institute and Structural Integrity Associates, Inc. has been initiated to comprehensively address these critical material challenges. The program's extensive scope encompasses a holistic approach to material management, including rigorous investigations spanning material procurement, shop fabrication, field erection, and appropriate quality assurance procedures for each implementation phase. The research will systematically examine the behavior of both base and weld metals, with a strategic focus on developing a comprehensive life prediction methodology and optimizing maintenance protocols. Beyond its core technical objectives, the program is designed to facilitate knowledge exchange through regular participant workshops, where both program-generated findings and global utility experiences will be critically reviewed and discussed to ensure the research maintains optimal direction and relevance. This collaborative effort aims to establish a robust framework for understanding, mitigating, and managing the complex challenges associated with CSEF steel materials in high-performance industrial applications.

A paste, which contains Pt or Pt-xIr (x = 0-30 at%) alloy nano-powder was sprayed on some Ni-based single crystal superalloys. Then the annealing diffusion treatment at 1100 °C for 1 h in flowing Ar atmosphere was conducted to develop Pt and Pt-Ir diffusion coatings. Cyclic oxidation tests were carried out at 1150 °C in still air in order to investigate the thermal stability and oxidation behavior of the coatings and they were compared with electroplated diffusion coatings. It was found that Ir can retard the formation of voids in both the coatings and substrates. In addition, by replacing the electroplating method to the paste coating method, the crack problem due to the brittle feature of electroplated Pt-Ir coatings could be solved. Therefore, the Pt-Ir diffusion coating prepared by the paste- coating method is promising as the bond-coat material due to suppression of voids, cracks and stable Al 2 O 3 on the surface. The Pt-Ir paste diffusion coatings introduced above have several further advantages: they are easy to recoat, cause less damage to substrates, and offer comparable oxidation resistance. Thus, the method can be applicable to the remanufacturing of blades, which may extend the life of components. The future aspect of the paste coating will also be discussed.

In Europe and Japan, great efforts are currently being invested in the development of materials designed to increase the steam temperature in fossil power plants. In the steel segment, the COST program is concentrating on 10% Cr steels with the addition of boron with the aim of achieving a steam temperature of 650°C. With nickel-based materials, the goal is to achieve steam temperatures of 700°C and higher. Alloy 617 has proved to be a very promising candidate in this field and a modified version is currently being developed in Japan. Materials of this type are used in both the turbine and in parts of the boiler.

An approach to phase analysis called multiphase separation technology (MPST) has been developed to determine phase chemistries of precipitated particles with sizes visible under SEM/EPMA observations based on the data from the conventional EDS measurements on bulk steel/alloy material samples. Quite accurate results from its applications have successfully been demonstrated by comparisons of SEM/EPMA - EDS + MPST with some other currently available means, for instance, chemical extractions (CA), TEM-EDS, AP-FIM and Thermo-Calc. etc. Applied examples regarding the relations of change in phase parameters including type, composition, volume fraction, size and distribution of the precipitated particles with material qualities, creep rupture lives, property stabilities, property recovery and boiler tube failures for some advanced heat resistant steels (P92, Super304H, HR3C, TP347HFG (H)) are given through the use of the SEM/EPMA - EDS + MPST in this contribution. Examples on phase quantifications of some nickel base superalloys (Nimonic263, Inconel 740 and Rhenium-containing alloys) are also shown to reveal the feasibility of its use in determining phase chemistries of precipitated particles under different measurement conditions. Practical applications of this combined technology to the material quality control and assessments, processing parameter improvements, as well as fracture/failure analyses of high temperature components have shown that this technology is quite convenient and effective when used for microstructural analysis purposes during R&D, manufacturing and operating processes.

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.

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.

Approximately 75% of the worldwide energy supply is based on fossil energy but the discussions on CO 2 emission require improvements of the conventional power technologies and also an increase of renewable energy resources. Over the past 40 years, enormous efforts, especially in the development of new materials, were made to establish the technology for the ultra-supercritical power plants, which are the standard of today’s power generation. For decades voestalpine Boehler Special Steel has been a full package supplier of customized high quality special steels and forgings with close relationships to plant manufacturers to provide products ahead of their time. This paper reports on improvements and research activities of the currently best available martensitic 9% Cr steel FB2 and the latest generation, the so-called MarBN steels, raising the operating temperatures of the 9% Cr steel class from 620 °C to 650 °C. Increasing the operating temperature requires adaptations in processes and manufacturing methods to adjust optimized microstructures with improved toughness properties and increased creep rupture strength at the same time. The microstructure of two Boron containing 9% Cr steels, FB2-2 and NPM1, developed within the framework of COST / KMM-VIN, have been investigated comparatively after different heat treatments and discussed after creep rupture tests at 650°C. The results show a dependency of the creep rupture strength on the stability of precipitates and the creep rupture time of both steels was increased by more than 30 % without negatively affecting the creep rupture strain and impact values.

The inspection and evaluation of defects in the welds of P92 high temperature reheater header with a diameter of about 1000mm and a wall thickness of about 100 mm have been done by means of hardness test, nondestructive testing on the surface, ultrasonic testing, metallographic and component sampling. By analyzing the results of on-site test and samples removed from the component, it is found that cracks existing in the welds are hydrogen induced delayed cracks. During the welding process and post-heating treatment (hydrogen bake-out), dehydrogenation was insufficient. This fact, combined with welding residual stresses resulted in the observed hydrogen induced cracking.