Search Results for fusion penetration

Carbon migration in narrow-gap welding joints of dissimilar steels has been studied using bead-on-plate specimens to determine the factors that influence the formation of a soft ferrite structure in the carbon-depleted zone. Carbon migration was found to occur during tempering, with a ferrite structure formed at the intersection of multiple layers due to severe carbon migration. This was attributed to a steep gradient in Cr content caused by the low fusion penetration at the intersection. Experimental results and the relationship between fusion penetration and weld bead alignment confirmed that low fusion penetration is the main cause of ferrite-structured carbon depleted zones.

This study addresses the welding challenges encountered when joining Haynes 282, a heat-resistant superalloy, to 3.5NiCrMoV high-strength low alloy steel (HSLA) for advanced power plant applications, particularly in thick-section components like rotors. The project demonstrated successful thick-section dissimilar metal welding up to 76 mm (3 in.) using two techniques: keyhole tungsten inert gas welding and conventional gas tungsten arc welding with Haynes 282 filler metal. Various groove weld geometries were evaluated, supported by computational weld modeling to predict and minimize weld distortion. The results validate these welding approaches for critical power plant components requiring both high-temperature performance and cost-effectiveness.

In a European ultra-supercritical (USC) power station repaired reheater bundle tubes made out of 25% Chromium stainless steels developed stress relief damages at the tube-to-tube butt welds, leading to leakages after only 8.500 hours of operation. Laboratory investigations of the leakages revealed common features of stress relief cracking (SRC) such as highly localized intergranular cracking in the heat affected zone (HAZ) near the fusion line, creep void formation at the crack tip and around the crack. At that time no other SRC damages were known for the employed 25% Chromium stainless steel boiler tubes. This article briefly describes the SRC damage found on the repaired reheater bundle tubes. It further provides insight on the several laboratory tests employed to assess the SRC behavior of welded joints of different creep resistant stainless steels. Among the selected test methods were Slow-Strain-Rate-Tests (SSRT), static 3-point bending tests derived from the Van Wortel approach and component tests. The results provided by the described tests methods have shown that the SRC behavior of a given material combination must be assessed by different techniques. This is especially the case for the evaluation of potential countermeasures and for the determination of the service conditions leading to the highest susceptibility.

This paper investigates creep rupture and damage behaviors of HR6W weldment using full thickness specimen cut from the circumferentially welded pipe. Creep tests were conducted at 750°C for durations up to 8,000 hours, and damage morphology of weldment during creep was characterized. The applicability of several nondestructive detection methods to the creep damage evaluation was discussed. It was found that full thickness specimen was broken at the base metal and main crack was inclined approximately at 45 degrees to the axial direction of the specimen. Times to creep rupture of full thickness specimen were comparable with those of the standard specimen. In addition, a small crack in base metal on the outer surface was first observed at life fraction of 35% by replication. PT can detect the crack in about half of the life. The crack whose length is longer than 3mm can be detected by UT in latter half of the life.

The next generation of materials and assemblies designed to address challenges in power generation, such as molten salt or supercritical carbon dioxide thermal transfer systems, corrosion, creep/fatigue, and higher temperature operation, will likely be highly optimized for their specific performance requirements. This optimization often involves strict control over microstructure, including homogeneity, grain size, texture, and grain boundary phases, as well as precise alloy chemistry and homogeneity. These stringent requirements aim to meet the new demands for bulk mechanical performance and durability. Some advanced materials, like oxide-dispersion strengthened or high-entropy alloys, necessitate specialized synthesis, fabrication, or welding/joining processes. Traditional methods that involve melting and solidifying can compromise the optimized microstructure of these materials, making non-melting synthesis and fabrication methods preferable to preserve their advanced characteristics. This paper presents examples where solid-phase, high-shear processing has produced materials and semi-finished products with superior performance compared to those made using conventional methods. While traditional processing often relies on thermodynamics-driven processes, such as creating precipitate phases through prolonged heat treatment, high-shear processing offers kinetics-driven, non-equilibrium alternatives that can yield high-performance microstructures. Additionally, examples are provided that demonstrate the potential for more cost-effective manufacturing routes due to fewer steps or lower energy requirements. This paper highlights advances in high-shear extrusion processing, including friction extrusion and shear-assisted processing and extrusion, as well as developments in solid-phase welding techniques like friction stir welding for next-generation power plant materials.

Local vacuum electron beam welding is an advanced manufacturing technology which has been investigated at Sheffield Forgemasters to develop as part of a cost-effective, reliable, agile, and robust manufacturing route for the next generation of civil nuclear reactors in the UK. A dedicated electron beam welding facility at Sheffield Forgemasters has been installed. This includes an x-ray enclosure, 100kW diode electron gun, 100T turntable, and weld parameter development vacuum chamber. A small modular reactor demonstrator vessel has successfully been manufactured with a wall thickness of 180 mm, including indication-free slope-in, steady- state and slope-out welding parameters. Electroslag strip cladding has also been investigated to demonstrate its viability in reactor pressure vessel manufacture. The electro-slag strip cladding method has been shown to produce high quality 60 mm strips on a 2600 mm inner diameter ring.

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.

A thorough understanding of interactions between graphite and fluoride fuel salts is crucial, as graphite is a promising candidate for the moderator of molten salt reactors. This study investigates the infiltration of fluoride fuel salts into graphite and the fluorination of graphite by these salts under various pressures and temperatures. A high-pressure salt infiltration test apparatus was developed to examine the infiltration of NaF-KF-UF 4 and NaF-BeF 2 -UF 4 -ZrF 4 fuel salts into two types of graphite at high temperatures. For tests using NaF-BeF 2 -UF 4 -ZrF 4 , two different temperatures were selected to assess the impact of temperature on threshold pressure. The study observed salt infiltration into graphite at pressures exceeding its threshold pressure, and the threshold pressure for infiltration was lower at the higher temperature. In addition, the formation of carbon fluorides on the surface of post-test graphite specimens was identified.

CrMoV cast steels are widely utilized for steam turbine and valve casings, and are subjected to operating and loading conditions which can promote damage mechanisms such as thermal fatigue, creep, erosion, etc. These components are subjected to variable, and sometimes severe conditions because of flexible operation. Therefore, there is a growing need for weld repair techniques including those which do not mandate post weld heat treatment (PWHT), e.g. so-called ‘temper bead’ weld repair. In this study, a simulated weld repair was performed using a temper bead technique. The maximum hardness in the heat affected zone (HAZ) CrMoV steel was ≤400HV. The integrity of the repair methodology was investigated using destructive testing, including hardness mapping, Charpy impact tests, tensile tests, low cycle fatigue and cross-weld creep, and the microstructure was assessed using light optical microscopy and scanning electron microscopy (SEM).

In recent years continuous and extensive research and development activities have been being done worldwide on 700°C A-USC (Advanced Ultra Super Critical) power plants to achieve higher efficiency and reduce the CO 2 emission. Increasing steam temperature and pressure of such A-USC boilers under consideration require the adoption of Ni based alloys. In the Japanese national project launched in 2008, Ni based alloy HR6W (45Ni-23Cr-7W-Ti, ASME Code Case 2684) is one of the candidate materials for boiler tube and pipe as well as Alloy617, Alloy263 and Alloy740H. The most important issues in A-USC boiler fabrication are the establishment of proper welding process for thick wall components of these alloys and verification of the long term reliability of their weldments. In our previous study, the weldability of HR6W was investigated and the welding process for Ni based thick wall pipe was established with the narrow gap HST (Hot wire Switching TIG) welding procedure originally developed by Babcock-Hitachi K.K. In this paper, creep rupture strengths of HR6W weldment were verified by the long term test up to 60,000 hours for tube and 40,000 hours for pipe. In Japanese national project, narrow gap HST welding process was also applied to the welding test for the other Ni based candidate pipe materials. Furthermore, as the practical A-USC boiler manufacturing trials, header mockup test was conducted and qualified for HR6W.

The necessity to reduce carbon dioxide emissions of new fossil plant, while increasing net efficiency has lead to the development of not only new steels for potential plant operation of 650°C, but also cast nickel alloys for potential plant operation of up to 700°C and maybe 750°C. This paper discusses the production of prototype MarBN steel castings for potential plant operation up to 650°C, and gamma prime strengthened nickel alloys for advanced super critical plant (A-USC) operation up to 750°C. MarBN steel is a modified 9% Cr steel with chemical concentration of Cobalt and tungsten higher than that of CB2 (GX-13CrMoCoVNbNB9) typically, 2% to 3 Co, 3%W, with controlled B and N additions. The paper will discuss the work undertaken on prototype MarBN steel castings produced in UK funded research projects, and summarise the results achieved. Additionally, within European projects a castable nickel based super alloy has successfully been developed. This innovative alloy is suitable for 700°C+ operation and offers a solution to many of the issues associated with casting precipitation hardened nickel alloys.

Continuous and active works have been going to develop 700°C A-USC (Advanced Ultra Super Critical) power plants in Europe, United States and also Japanese national project has launched in 2008. In this new Japanese project Fe-Ni based alloy HR6W (45Ni-24Fe-23Cr-7W-Ti) is one of the candidate materials for boiler tube and pipe as well as Ni based alloys such as well-known Alloy617, Alloy263 and Alloy740. The most important issue in boiler fabrication is the welding process of these alloys and long-term reliability of their weldments. Authors investigated the weldability of HR6W thick-wall pipe. The integrity of the weldment was confirmed with metallurgical investigation, mechanical testing and long term creep rupture test. It is proved that the narrow gap HST welding procedure can meet the requirements for Ni based or Fe-Ni based alloys and provides excellent strength properties.

This study examines the corrosion resistance of additively manufactured 316L stainless steel (SS) for nuclear applications across three environments: pressurized water reactor primary water (PWR PW), hot concentrated nitric acid, and seawater. Wire-feed laser additive manufacturing (WLAM) specimens showed oxidation behavior similar to wrought 316L SS in PWR PW, though stress corrosion cracking (SCC) susceptibility varied with heat treatment. In nitric acid testing, laser powder bed fusion (L-PBF) specimens demonstrated superior corrosion resistance compared to conventional SS, primarily due to improved intergranular corrosion resistance resulting from cleaner feedstock powder and rapid solidification rates that minimized grain boundary segregation. Laser metal deposition (LMD) repair studies in seawater environments successfully produced dense, crack-free repairs with good metallurgical bonding that matched the substrate’s mechanical properties while maintaining corrosion resistance. These results emphasize the importance of corrosion testing for additively manufactured components and understanding how their unique microstructures affect performance.

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.

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.

Qualifying welding procedures for repair of components in high temperature service requires careful consideration of factors including identification of the materials involved, existing mechanical properties and service operating parameters such as temperature, pressure and environment. Selection of weld metals to match, under match or overmatch base material as well as direct and indirect consequences on the heat-affected zone also require evaluation. Application of post weld heat treatment and ramifications where dissimilar base materials are involved are discussed plus the necessity of conducting tests at the operating temperatures and conditions where information is not available from the literature. Each of these factors is discussed and examples provided.

This study investigates the steam oxidation behavior of Alloy 699 XA, a material containing 30 wt.% chromium and 2 wt.% aluminum that forms protective oxide scales in low-oxygen conditions. The research compares four variants of the alloy: conventional bulk material, a laser powder bed fusion (LPBF) additively manufactured version, and two modified compositions. The modified versions include MAC-UN-699-G, optimized for gamma-prime precipitation, and MAC-ISIN-699, which underwent in-situ internal nitridation during powder atomization. All variants were subjected to steam oxidation testing at 750°C and 950°C for up to 5000 hours, with interim analyses conducted at 2000 hours. The post-exposure analysis employed X-ray diffraction (XRD) to identify phase development and scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) to examine surface morphology, cross-sectional microstructure, and chemical composition. This study addresses a significant knowledge gap regarding the steam oxidation behavior of 699 XA alloy, particularly in its additively manufactured state.

In the late 1980s, the domestic utility industry experienced failures in dissimilar metal welds (DMWs) between low-alloy ferritic tubing and austenitic tubing in superheaters and reheaters. Extensive research by EPRI identified that nickel-based filler metals significantly improved service life compared to 309 SS filler metals. Additionally, optimized joint geometries and increased weld metal reinforcement were found to further enhance durability. A new nickel-based filler metal was developed with thermal expansion properties similar to the low-alloy base metal, along with a low chromium content designed to minimize the carbon-denuded zone. However, this filler metal was never commercialized due to its tendency to microfissure, which resulted in a shorter-than-expected service life. This paper explores further investigations into the microfissuring of this filler metal and examines long-term testing to assess its suitability for high-temperature applications.

In order to improve thermal efficiency of fossil-fired power plants through increasing steam temperature and pressure high strength martensitic 9-12%Cr steels have extensively been used, and some power plants have experienced creep failure in high temperature welds after several years operations. The creep failure and degradation in welds of longitudinally seam-welded Cr- Mo steel pipes and Cr-Mo steel tubes of dissimilar metal welded joint after long-term service are also well known. The creep degradation in welds initiates as creep cavity formation under the multi-axial stress conditions. For the safety use of high temperature welds in power plant components, the complete understanding of the creep degradation and establishment of creep life assessment for the welds is essential. In this paper creep degradation and initiation mechanism in welds of Cr-Mo steels and high strength martensitic 9-12%Cr steels are reviewed and compared. And also since the non-destructive creep life assessment techniques for the Type IV creep degradation and failure in high strength martensitic 9-12%Cr steel welds are not yet practically established and applied, a candidate way based on the hardness creep life model developed by the authors would be demonstrated as well as the investigation results on the creep cavity formation behavior in the welds. Additionally from the aspect of safety issues on welds design an experimental approach to consider the weld joint influence factors (WJIF) would also be presented based on the creep rupture data of the large size cross-weld specimens and component welds.

The susceptibilities of hot cracking and reheat cracking of A-USC candidate Ni-based alloys were evaluated relatively by Trans-Varestraint testing and Slow Strain Rate Tensile (SSRT) testing. In addition, semi-quantitative evaluation of the stress relaxation cracking susceptibility of Alloy 617 was conducted, because stress relaxation cracking in the heat affected zone (HAZ) has actually been reported for repair welds in Alloy 617 steam piping in European A-USC field-testing. Solidification cracking susceptibilities of Alloy 617 were the highest; followed by HR35, Alloy 740 and Alloy 141, which were all high; and then by HR6W and Alloy 263, which were relatively low. In addition, liquation cracking was observed in the HAZ of Alloy 617. The reheat cracking susceptibilities of Alloy 617, Alloy 263, Alloy 740 and Alloy 141 were somewhat higher than those of HR6W and HR35 which have good creep ductility due to the absence of γ’ phase precipitates. A method to evaluate stress relaxation cracking susceptibility was developed by applying a three-point bending test using a specimen with a V-notch and finite element analysis (FEA), and it was shown that stress relaxation cracking of aged Alloy 617 can be experimentally replicated. It was proposed that a larger magnitude of creep strain occurs via stress relaxation during the three-point bending test due to a higher yield strength caused by γ’ phase strengthening, and that low ductility due to grain boundary carbides promoted stress relaxation cracking. The critical creep strain curve of cracking can be created by means of the relationship between the initial strain and the creep strain during the three-point bending tests, which were calculated by FEA. Therefore, the critical conditions to cause cracking could be estimated from the stress relaxation cracking boundary from of the relationship between the initial strain and the creep strain during the three-point bending test.