Search Results for surface measurements

Both non-destructive and traditional microsectioning techniques have been used to measure the oxide thickness of steam grown oxides between two close contacting surfaces. Different power plant materials, nickel based alloys and ferritic-martensitic steels, were exposed to steam oxidation at temperatures ranging from 650 °C up to 750 °C and periods from 500 h to 3000 h. Ultrasonic measurements of thickness, based on the speed of sound in the oxide, were performed and compared to optical thickness measurements based on conventional metallographic microsectioning with promising results. Improvements on the measurement resolution have been practically demonstrated with oxides down to 65 μm thickness being measured successfully.

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.

This research compares creep crack growth behavior of two heats of creep strength enhanced ferritic (CSEF) steel, grade 91. These heats represent extremes of creep damage susceptibility, one heat exhibiting low creep ductility and the other high creep ductility. Creep crack growth tests were performed with compact tension specimens and were monitored with direct current potential drop and optical surface measurements. Load line displacement was measured throughout the duration of the tests. Specimens were sectioned, mounted, and analyzed using optical and scanning electron microscopy to assess the presence of oxidation, micro-cracking, creep damage, and void density. Tests were performed over a range of initial stress intensities on the low ductility material to investigate the impact of creep ductility. Metallurgical evidence and test data for each crack growth test was assessed to evaluate crack growth behavior linked to creep crack growth parameter (C*) and stress/creep damage distribution in the vicinity of the crack.

A material test loop has been installed at GKM Mannheim, which enables thick-walled components of future highly-efficient power plants to be exposed to steam temperatures of up to 725 °C. The project goal was to demonstrate the feasibility of a 700 °C power plant.

The measurement of damage from high temperature solid particle erosion (HTSPE) can be a lengthy process within the laboratory with many lab-based systems requiring sequential heat and cooling of the test piece to enable mass and/or scar volume measurements to be made ex situ. Over the last few years a new lab-based system has been in development at the National Physical Laboratory which has the ability to measure the mass and volume change of eroded samples in situ without the need to cool the sample. Results have previously been shown demonstrating the in situ mass measurement, more recently the in situ volume measurement capability has been added and used to evaluate the erosion performance of additively manufactured materials. Selective laser melting (SLM) is an advanced manufacturing method which is growing in popularity and application. It offers the ability to manufacture low volume complex parts and has been used in rapid prototyping. As the technique has developed there is increasing interest to take advantage of the ability to manufacture complex parts in one piece, which in some case can be more cost and time effective than traditional manufacturing routes. For all the benefits of SLM there are some constraints on the process, these include porosity and defects in the materials such as ‘kissing bonds’, surface roughness, trapped powder and microstructural variation. These features of the processing route may have implications for component performance such as strength, fatigue resistance wear and erosion. To investigate this further SLM IN718 has been used to evaluate factors such as surface roughness, microstructure and morphology on the erosion performance as measured in situ and compared with conventional produced wrought IN718 material.

Extended storage of spent nuclear fuel (SNF) in intermediate dry cask storage systems (DCSS) due to lack of permanent repositories is one of the key issues for sustainability of the current domestic Light Water Reactor (LWR) fleet. The stainless steel canisters used for storage in DCSS are potentially susceptible to chloride-induced stress corrosion cracking (CISCC) due to a combination of tensile stresses, susceptible microstructure, and a corrosive chloride salt environment. This research assesses the viability of the cold-spray process as a solution to CISCC in DCSS when sprayed with miniature tooling within a characteristic confinement in two different capacities: cleaning and coating. In general, the cold-spray process uses pressurized and preheated inert gas to propel powders at supersonic velocities, while remaining solid-state. Cold-spray cleaning is an economical, non-deposition process that leverages the mechanical force of the propelled powders to remove corrosive buildup on the canister, whereas the cold spray coating process uses augmented parameters to deposit a coating for CISCC repair and mitigation purposes. Moreover, both processes have the potential to induce a surface compressive residual stress that is known to impede the initiation of CISCC. Surface morphology, deposition analysis, and microstructural developments in the near-surface region were examined. Additionally, cyclic corrosion testing (CCT) was conducted to elucidate the influence of cold-spray cleaning and coating on corrosion performance.

This paper discusses the design of a prototype for accurately inspecting the degree of wall thinning in boiler tubes, which plays a critical role in power plants. The environment in power plants is characterized by extreme conditions such as high temperatures, high pressure, and ultrafine dust (carbides), making the maintenance and inspection of boiler tubes highly complex. As boiler tubes are key components that deliver high-temperature steam, their condition critically affects the efficiency and safety of the power plant. Therefore, it is essential to accurately measure and manage the wall thinning of boiler tubes.

The incore instrumentation system of a pressurized water reactor (PWR) facilitates neutron flux mapping and temperature measurements at specific core locations. A guide conduit, extending from the seal table to the lower reactor pressure vessel head, guides and protects each incore guide thimble between the table and the lower reactor vessel head. Each flux thimble houses a detector and drive cable. Once filled with reactor coolant, the conduit becomes an extension of the reactor coolant pressure boundary. This paper reports the examination results of cracking detected in a TP304 stainless steel guide conduit adjacent to a fillet weld at the upper surface of a TP304 seal table. The cracking resulted in reactor coolant leakage that was detected by the presence of boric acid deposits on the exterior of the conduit and table. Failure analysis including dimensional measurements, chemical analysis, stereomicroscopy, metallography, and scanning electron microscopy showed that extensive cracking of the conduit and seal table material occurred due to stress corrosion cracking (SCC). Assessment showed that chlorine-containing deposits were present on the exterior of the conduit and on the surfaces of the seal table and were due to the design and operation of HVAC systems at the coastal plant. Stainless steels are susceptible to SCC in environments with elevated temperatures, chloride contents, and increased tensile stress – particularly in non-post weld heat treated (PWHT) weld regions and the heat affected zone (HAZ). This was the apparent primary cause of the failure. However, chloride-induced SCC of such materials typically results in transgranular crack propagation, whereas the observed cracks were indicative of intergranular stress corrosion cracking (IGSCC). Microstructural analysis showed that the observed cracks initiated in sensitized areas of material adjacent to the weld. Sensitization of the material caused chromium depletion from adjacent areas and increased susceptibility of the depleted areas to IGSCC. In this case, the most probable source of sensitization was related to welding and the long-term growth of grain boundary carbides nucleated during welding. This was considered a contributing cause to the failure.

This study evaluates various nondestructive testing methods for detecting creep damage and assessing residual life in Grade 91 steel welds. Three primary detection techniques were investigated: phased array ultrasonic testing (PAUT), eddy current testing with high-temperature superconductor direct current and superconducting quantum interference device (ECT•HTS-dc-SQUID), and replica observation. PAUT detected creep damage between 60-80% of creep life, while ECT•HTS-dc-SQUID showed detection capability between 80-90% of creep life. Replica observation revealed creep voids only in the final stages before rupture. Additionally, three strain measurement methods were evaluated: capacitive strain sensors (providing continuous monitoring during creep exposure), laser displacement meters (used during test interruptions), and SPICA strain measurement. Both capacitive sensors and laser meters produced results comparable to conventional extensometer measurements. The SPICA method proved particularly effective in measuring heat-affected zone (HAZ) strain after creep exposure, revealing higher strain values in the HAZ compared to base and weld metal, with a consistent increase during creep exposure.

An internal pressure creep test has been carried out on a Gr. 91 steel longitudinal welded pipe at 650°C to examine the type IV failure behavior of actual pipes, using a large-scale experiment facility “BIPress”, which can load internal pressure and bending force on large diameter pipes at high temperatures. The creep test was also interrupted three times to measure hardness and voids density in the HAZ region of the outer surface of the test pipe. Results of the measurement of the hardness and voids density at the interruption did not indicate creep damage accumulation. The welded pipe suddenly ruptured with large deformation, which caused crushing damage to the surrounding facility. Type IV cracking occurred in the longitudinal welded portion of the test pipe, and the length of the crack reached 5000mm. SEM observation was carried out at the cross section of the welded portion of the test pipe and voids density was measured along the thickness direction in the HAZ region. To clarify the stress/strain distribution in the welded portion, creep analysis was conducted on the test pipe, where the materials are assumed to consist of base metal, weld metal and HAZ. After stress redistribution due to creep deformation, stress and strain concentrations were observed inside the HAZ region. Then, the authors' creep life prediction model was applied to the creep test result to examine its validity to actual size pipes. It was demonstrated that the life prediction model can evaluate damage of the Gr. 91 steel longitudinal welded pipe with sound accuracy.

Steam-side oxidation and the resultant exfoliation of iron-based scales cause unplanned shutdowns at coal-fired power generation plants. Exfoliate removal is currently limited to frequent unit cycling to minimize the volume of exfoliated scale, upgrading a plant with a “blow down” system, or installing a higher alloy. This paper discusses the rate of steam-side oxidation on Type 304H stainless steel (304H) tube after shot peening the internal surface with commercially available techniques. Shot peening the ID of Type 304H austenitic stainless steel superheater tubes has been shown to improve the overall oxidation resistance in steam. Decreasing the oxidation rate directly impacts the volume of exfoliated scale. The adherent spinel scales are thinner and more robust than non-shot peened tubes of the same alloy. Most of the improved oxidation resistance can be attributed to the presence of a spinel oxide layer combined with a continuous chromia layer formed near the steam-touched surfaces. The presence of a continuous chromia layer vastly reduces the outward diffusion of iron and minimizes the formation of iron-based scales that exfoliate. This work showed that a uniform cold-worker layer along the tube ID has a profound effect on oxidation resistance. Incomplete coverage allows oxidation to proceed in the non-hardened regions at a rate comparable to the oxidation rate on unpeened Type 304H.

High-temperature solid particle erosion (SPE) is a major threat to efficiency in power plants and jet engines, potentially reducing turbine efficiency by 7-10% and causing significant CO 2 emissions. The sources of these particles vary widely, from volcanic ash in engines to fly ash in boilers and scale in turbines. While better surface engineering and coatings offer solutions, their development is hampered by a lack of standardized test methods and reliable models. To address this, the METROSION initiative aims to establish a comprehensive framework for characterizing the high-temperature SPE performance of new materials and coatings. This framework will require a step change in test methods and control, focusing on accurately measuring key parameters like temperature, flow rate, particle properties, and impact angles. This paper outlines the initiative’s goals, with a particular focus on the techniques used for in-situ measurements of temperature, particle velocity, and 3D shape/size.

Supercritical carbon dioxide cooling during machining has been identified as an effective measure to mitigate the risk of stress corrosion cracking in materials utilized in the primary circuit of light water reactors, particularly in pressure vessel structural steels. This study aims to compare two different cooling methods, the novel supercritical carbon dioxide and conventional high pressure soluble oil, employed during both milling and turning processes for SA508 Grade 3 Class 2 and AISI 316L steels. As the surface conditions of materials are critical to fatigue properties, such as crack initiation and endurance life, the fatigue performance of both cooling methods for each process were then evaluated and the impact on properties determined. To compare the potential benefits of supercritical carbon dioxide cooling against conventional soluble oil cooled machining, fatigue specimens were machined using industry relevant CNC machine tools. Surface finish and machining methods were standardized to produce two different specimen types, possessing dog- bone (milled) and cylindrical (turned) geometries. Force-controlled constant amplitude axial fatigue testing at various stress amplitudes was undertaken on both specimen types in an air environment and at room temperature using a stress ratio of 0.1. The fatigue performance of the supercritical carbon dioxide cooled specimens revealed substantially greater endurance lives for both SA508 and 316L materials, when compared with specimens machined using high pressure soluble oil cooling.

Through inner wall oxidation scale thickness measurement, sampling tests and installation of wall temperature measuring device in the boiler, the equivalent wall temperature and its distribution of secondary high temperature reheater tube were estimated and verified, and the temperature field distribution of tube platen which is of single peak distribution in the direction vertical to tube platen and an apparent lower temperature distribution covered by the smoke shield at the side of boiler wall were both obtained. For the middlemost 10CrMo910, the wall temperature of individual tube was getting close to 600°C. Afterwards material state and residual creep life of tube platen were estimated and calculated. The results of estimate and calculation show that the tube platen in the middle is not suitable for further service due to its degraded material states and lower antioxidant ability. Thus with consideration of distribution characteristics of temperature field, parts of tube platens in the middle are proposed to be replaced with T91 tubes. Furthermore, to avoid onsite heat treatment, 10CrMo910 tube covered by the smoke shield in the boiler was reserved, and a small piece of 10CrMo910 tube was welded at the inlet and outlet ends respectively in the manufactory.

This study aims to examine the effects of grain boundary oxidation and creep on crack initiation and fracture behaviors in cold worked surface layer, under static tensile stresses in air. To determine these effects in relation to percent cold work and hardness scale, cold-rolled plates with a reduction ratios between 10% and 50% were prepared. Uniaxial constant load (UCL) tests were conducted at elevated temperature in air using smooth round bar specimen. UCL tests with a load of 0.9σy (926MPa) at 550°C show that rupture time for all cold- rolled materials were shorter than that of as-received material. From cross-sectional observation after UCL testing, surface crack at grain boundary and voids were observed in as-received material, whereas creep cracks were also observed in cold-rolled materials. This implied that crack initiation was assisted by cold working. Comparing test results with a load reduced to 0.8σy (823MPa), difference of rupture time was expected as a factor of 5 for as-received material, and measured as 2-3 for cold-rolled materials. It was suggested that cold worked layer was more sensitive to creep than base metal.

This work describes the repair procedure conducted on the High Pressure/Intermediate Pressure (HP/IP) and generator rotors of a 180 MW steam turbine General Electric (GE) - STAG207FA type D11 installed at La Sierra Thermoelectric Power Plant in Puerto Nare, Colombia. A lubricant supply failure at base load caused severe adhesive damage to the shafts in the bearing support areas and a permanent 3.5 mm bow at the HP/IP rotor mid span section, which required a complex intervention. The repair process began with the identification of the rotors manufacturing material through in-situ metallographic replicas, handheld XRF analysis and surface hardness measurements. Volumetric manual Gas Tungsten Arc Welding (GTAW) welding reconstruction of cracked areas followed by a surface overlay using GTAW and Plasma Arc Welding (PAW) welding processes were applied with a modular mechanized system, where a stress relief treatment through vibration was implemented with the help of computational simulations carried out to determine the fundamental frequencies of the rotors. Geometric correction of the HP/IP rotor mid span section was achieved thanks to the excitation of the rotor at some fundamental frequencies defined by the dynamic modeling and the use of heat treatment blankets at specific locations as well. Finally, after machining and polishing procedures, the power unit resumed operation eleven months after the failure and remains in service to the present date.

The use of the bainitic creep strength enhanced ferritic steel T/P23 has increased over the last decade in a wide range of applications including headers, superheater and reheater tubing and in waterwall tubing. Many issues have been reported in weldments of this material, such as hydrogen induced cracking, reheat cracking and stress corrosion cracking. In order to help characterize high temperature cracking phenomena, including reheat cracking, a limited number of laboratory creep crack growth tests are being conducted as part of an ongoing project. Tests were run on as-welded sections with the test specimen crack-tip located in select zones of the weldment. Test temperatures are intended to bookend the range of applications from a waterwall condition of ~482°C (900°F) to the superheat/reheat condition of 565°C (1050°F). This paper describes the results of some early testing at 482°C (900°F). The tests provided useful insight into the cracking susceptibility of the material at this temperature with respect to not only time-dependent cracking, but also fatigue crack growth and fracture toughness. The paper includes details of the test method and results, as well as findings from post-test metallographic examinations of the tested specimens.

A prototype small punch test rig has been developed to extend the range of data output. Through the introduction of a probe, vertical displacements can be measured across a region of the specimen underside. This information provides much greater understanding of the specimen deformation. Having displacement data at a series of measurement points also facilitates the calculation of strains across the sample. The probe can also be used during a test to provide time dependent data from small punch creep tests. The measured displacement data have been used in conjunction with FE analysis to determine a set of calibration curves for inferring strain at any given vertical displacement. Some creep strain data are also presented.

Extensive research and development has been undertaken in the UK on MarBN steels. These were first proposed by Professor Fujio Abe from NIMS in Japan. Within the UK, progress has been made towards commercialisation of MarBN-type steel through a series of Government funded industrial collaborative projects (IMPACT, IMPEL, INMAP and IMPULSE). As part of the IMPACT project, which was led by Uniper Technologies, boiler tubes were manufactured from the MarBN steel developed within the project, IBN1, and installed on the reheater drums of Units 2 and 3 of Ratcliffe-on-Soar Power Station. The trial tubes were constructed with small sections of Grade 91 tubing on either side of the IBN1 to allow direct comparison after the service exposure. This is the world’s first use of a MarBN steel on a full-scale operational power plant. In September 2018 the first tube was removed having accumulated 11,727 hours operation and 397 starts. This paper reports microstructural and oxidation analysis, that has been undertaken by Loughborough University as part of IMPULSE project, and outlines future work to be carried out.

Materials are the key to develop advanced ultra-supercritical (A-USC) steam generators. Operating at temperature up to 760°C and sustained pressure up to 4500 psi. Pressure vessel and piping materials may fail due to creep, oxidation, and erosion. Valves are particularly subjected to loss of function and leakage due to impermeant of the sealing surfaces. New materials, less susceptible to the above damage modes are needed for A-USC technology. Two Ni-based superalloys have been identified as prime candidates for valves based materials. Hardfacing is applied to sealing surfaces to protect them from wear and to reduce friction. Stellite 6 (Cobalt-based alloy) is the benchmark hardfacing owing to its anti-galling properties. However, the latest results tend to indicate that it is not suitable for high pressure application above 700°C. An alternative hardfacing will be required for A-USC. New Ni- and Co- based alloys are being developed for applications where extreme wear is combined with high temperatures and corrosive media. Their chemistry accounts for the excellent dry-running properties of these alloys and makes them very suitable for use in adhesive (metal-to- metal) wear. These new alloys have better wear, erosion, and corrosion resistance than Stellite 6 in the temperature range 800°C ~ 1000°C. As such, they have the potential to operate in A-USC. Velan recently developed an instrumented high temperature tribometer in collaboration with Polytechnique Montreal to characterize new alloys including static and dynamic coefficients of friction up to 800°C. We present herein the methodology that has been devolved to explore the effects of elevated temperature on the tribological behavior of those advanced material systems, with the goal of capturing the basis for the specification, design, fabrication, operation, and maintenance of valves for A-USC steam power plants.