Ni-based superalloy Haynes 282 is a prime candidate for advanced power generation systems due to its superior fabricability, weldability, and high-temperature performance. Additive manufacturing offers potential cost and time savings for gas turbine components. Wire-arc direct energy deposition can create large components but often requires post-processing treatments, such as hot isostatic pressing (HIP), to address porosity. This study explores a low heat-input, high deposition rate GMAW process to achieve fully dense Haynes 282 without HIP. Twenty-one blocks were deposited, varying travel and wire feed speeds. Initial analysis (visual inspection, microstructural examination, and CT) revealed the impact of build parameters on internal porosity and defects. Scanning electron microscopy provided insights into structural heterogeneity and microstructural properties.

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Codes (BPVC) and Code for Pressure Piping have been utilized extensively for the construction and maintenance of plants in the power generation industry. These codes consist of different relevant sections that are applicable to the various pressure retaining components and their service application. This paper presents a comparison of the welding requirements between the various ASME construction codes outside of the qualification requirements within Section IX. Topics of discussion include preheat temperature, interpass temperature, postweld heat treatment, toughness testing, filler material requirements, and use of standard welding procedure specifications. Individual paragraphs and subparagraphs specific to these topics are compared and contrasted to establish their similarities and differences.

There is a growing need to automate the gas tungsten arc welding process for fabrication and repair of nuclear components due to an increasing shortage of experienced welders. Therefore, a collaborative effort has been performed in this study to develop a fully autonomous gas tungsten arc welding system with adaptive capabilities. The system employs the application of two neural networks that have been presented in. The first utilizes a vision based convolutional neural network to perform real time control of the filler wire entry position into the weld pool. The second predicts optimal weld parameters and torch positioning for each weld pass deposited within a multi-pass groove. A commercialization path for the technology is in-progress, with the artificial intelligent algorithms currently being incorporated and tested on commercially available equipment.

The mechanical behavior of a cast form of an advanced austenitic stainless steel, CF8C-Plus, is compared with that of its wrought equivalent in terms of both tensile and creep-rupture properties and estimated allowable stress values for pressurized service at temperatures up to about 850°C. A traditional Larson-Miller parametric model is used to analyze the creep-rupture data and to predict long-term lifetimes for comparison of the two alloy types. The cast CF8C-Plus exhibited lower yield and tensile strengths, but higher creep strength compared to its wrought counterpart. Two welding methods, shielded-metal-arc welding (SMAW) and gas-metal-arc welding, met the weld qualification acceptance criteria in ASME BPVC Section IX for the cast CF8C-Plus. However, for the wrought CF8C-Plus, while SMAW and gas-tungsten-arc welding passed the tensile acceptance criteria, they failed the side bend tests due to lack of fusion or weld metal discontinuities.

As many nuclear power plants are in the license renewal operating period and some are entering subsequent license renewal, there is increased probability that repairs will be needed on components that have been exposed to significant neutron fluence. The neutron-driven transmutation of nickel and tramp boron in austenitic materials commonly used in reactor internals can lead to the generation of trapped helium and the associated risk of helium-induced cracking (HeIC) during weld repairs. In the weld heat affected zone, where temperatures are insufficient to allow the helium to diffuse out of the material, the helium can remain trapped. Upon cooling, the residual stresses, combined with weakened grain boundaries due to helium coalescence, can lead to cracking. The current ASME limit for helium content for Code repairs is 0.1 appm. Prior work has demonstrated a strong inverse correlation between helium content and permissible weld heat input for avoidance of HelC. The helium concentration in the material to be repaired is thus a critical input to the development of weld repair processes to be applied to these materials. The reliable measurement of helium in irradiated materials at concentrations relevant for the evaluation of HeIC risk is a specialized process. It is important to demonstrate that the capability is available and can be practically leveraged to support emergent repairs. This paper presents on the execution and results of a multi-laboratory test program aimed at demonstrating the industry capability of acquiring accurate, repeatable, and timely measurements of relatively low concentrations of helium (< ~20 appm) within austenitic materials commonly used in reactor internals. Participating laboratories were supplied with equivalent specimens extracted from boron-doped coupons that were irradiated to drive the boron-to-helium transmutation reaction. The results and lessons learned from the program are expected to support the development of industry guidance for the acquisition of similar measurements supporting nuclear component repairs.

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.

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 voestalpine foundry group, operating at locations in Linz and Traisen, Austria, specializes in heavy steel casting components ranging from 1 to 200 tons for power generation, oil and gas, chemical processing, and offshore applications. Their manufacturing expertise encompasses high-alloyed martensitic 9-12% Cr-steels and nickel-based Alloy 625, particularly for ultra-supercritical (USC) and advanced USC power generation systems operating at temperatures from 600°C to over 700°C. The production of these complex, thick-walled components relies on advanced thermodynamic calculation and simulation for all thermal processes, from material development through final casting. The foundries’ comprehensive capabilities include specialized melting, molding, heat treatment, non-destructive testing, and fabrication welding, with particular emphasis on joining dissimilar cast, forged, and rolled materials. Looking toward future innovations, the group is exploring additive manufacturing for mold production and robotic welding systems to enhance shaping and surface finishing capabilities.

Main steam control valves are crucial components in power plants, as they are the final elements in the steam piping system before the steam enters the turbine. If any parts of these valves become damaged, they can severely harm the steam turbines. Recently, power plants have been required to operate under cyclical loading, which increases the risk of cracks in the control valve seats. This is due to the different rates of expansion between the Stellite surface and the underlying Grade 91 steel surface when exposed to high temperatures. To ensure a reliable power supply, power plants cannot afford long downtimes, making on-site service essential. This paper presents an on-site technique for post-weld heat treatment (PWHT) of Stellite seats. By using a heating pad arrangement and an induction heater, the required PWHT temperature of 740°C, as specified in the welding specification procedure (WPS), can be achieved. This method allows for on-site valve seat repair and can be applied to other power plants as well.

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.

Additive manufacturing is a groundbreaking manufacturing method that enables nearly lossless processing of high-value materials and produces complex components with a level of flexibility that traditional methods cannot achieve. Wire arc additive manufacturing (WAAM), utilizing a conventional welding process such as gas metal arc welding, is one of the most efficient additive manufacturing technologies. The WAAM process is fully automated and guided by CAD/CAM systems on robotic or CNC welding platforms. This paper explores the fundamental concepts and metallurgical characteristics of WAAM. It focuses primarily on the mechanical properties of printed sample structures made from P91, X20, and alloys 625 and 718 wire feedstock. The study particularly addresses the anisotropy of mechanical properties through both short-term and long-term testing, comparing these results to materials processed using conventional methods.

This study conducted creep tests, microstructural, and hardness analyses on SA213T23-TP347H dissimilar weld joints of long-term serviced coal-fired boiler final superheater tube. The welded joint (SA213 T23-TP347H) of the superheater tube, after approximately 105,000 hours of service, was sampled for creep life assessment and maintenance planning. Creep tests were conducted at 600°C under three stress conditions: 100, 140, and 160MPa. Most cracks were observed in the heat-affected zone of T23, and compared to unused tubes, the creep life consumption rate was approximately 90%. All dissimilar weld joints used welding rods similar in chemical composition to T23, and significant hardness reduction occurred in the flame-affected zone.

Super Duplex stainless steels (SDSS) are alloys based on the Fe-Cr-Ni-N system. The chemical composition is tailored to achieve a balanced microstructure of 50% ferrite and 50% austenite. Hyper Duplex Stainless Steels (HDSS) are also duplex materials distinguished by their remarkable yield strength (≥700 MPa) and corrosion resistance (PREN>48). They have been developed as an alternative to the well-established SDSS when superior mechanical and corrosion performance is required. This enhanced performance is attributed to alloying additions, primarily Cr, Mo, and N. In this study, a comparison is conducted between filler metals of SDSS and HDSS for the root welding of SDSS plates. The gas tungsten arc welding (GTAW) process was used to carry out root welding passes and Gas Metal Arc Welding (GMAW) for filling passes on SDSS substrates arranged in a V groove to simulate a repair scenario. The heat input was controlled in both processes, keeping it below 2.0 kJ/mm in the GTAW and 1.2 kJ/mm in the GMAW. GTAW with constant current was used and the parameters achieved producing full penetration welds with SDSS and HDSS. In this case, Nitrogen was used as backing gas to avoid oxidation of the root. Thus, a special GMAW-Pulsed version was applied to achieve good wettability and defect-free joints. ASTM G48 tests were performed to evaluate the corrosion resistance through Critical Pitting Testing (CPT) analysis on the root pass, microstructural analysis via optical microscopy, and impact toughness. Consequently, a comprehensive examination of the welded joints outlines manufacturing conditions, limitations, and the applications of SDSS and HDSS filler metals.

In this paper, the dissimilar metal welds (DMWs) between 617B nickel-based alloy and 10%Cr martensitic heat-resistant steel filled by 617 filler metal was studied, focused on the high temperature creep rupture properties. The high temperature creep rupture properties of welded joints with different welding processes were tested, and the microstructure of welded joints before and after the creep rupture test was observed by OM and SEM. The results showed that, there were three failure modes: base metal failure, type W failure and interface failure, among which interface failure caused the most serious life reduction. The welded joints using ER NiCr-3 filler metal reduced the strain concentration at the interface, so the fracture location shifted from the interface to HAZ of 10%Cr martensitic heat-resistant steel under high temperature and low stress conditions, and creep rupture life was improved. Similarly, weld cap shifted the creep crack propagation path by changing the groove form, so as to altered the stress state of joint and prolong the creep rupture life.

High gamma prime Ni-based superalloys comprising ≥3.5 % Al are difficult to weld due to high propensity of these materials to weld solidification, heat affected zone liquation, and stress-strain cracking. In this study the root cause analysis of cracking and overview on the developed weldable Ni-based superalloys for repair of turbine engine components manufactured from equiaxed (EA), directionally solidified (DS), and single crystal (SX) materials as well as for 3D AM is provided. It is shown that the problem with the solidification and HAZ liquation cracking of turbine engine components manufactured from EA and DS superalloys was successfully resolved by modification of welding materials with boron and silicon to provide a sufficient amount of eutectic at terminal solidification to promote self-healing of liquation cracks along the weld - base material interface. For crack repair of turbine engine components and 3D AM ductile LW4280, LW7901 and LCT materials were developed. It is shown that LW7901 and LCT welding materials comprising 30 - 32 wt.% Co produced sound welds by GTAW-MA on various SX and DS materials. Welds demonstrated high ductility, desirable combination of strength and oxidation properties for tip repair of turbine blades. Examples of tip repair of turbine blades are provided.

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.

Olefin furnaces contain gravity cast U-bend fittings from Fe-Ni-Cr alloys that can experience premature failures due to a combination of harsh service conditions. The fittings undergo steep temperature variations during startup and shutdown, outer diameter (OD) oxidation from furnace flue gases, and inner diameter (ID) carburization from process fluids. As a result, cracking often occurs along large solidification grain boundaries from interconnected networks of carbides and secondary phases. To address these degradation concerns, Wire Arc Additive Manufacturing (WAAM) is being used to produce a functionally graded fitting that provides increased oxidation, carburization, creep, and thermal fatigue resistance. Three welding wire compositions have been designed based on thermodynamic and kinetic modeling techniques to address the appropriate corrosion resistance and mechanical properties needed in the OD, Core, and ID regions of the U- bend fitting cross-section. A Fe-35Cr-45Ni-0.7Nb solid welding wire is being used for the Core section, and metal-cored welding wires based around this composition with additions of Si or Al are being used for the OD and ID sections, respectively. This study involved weldability evaluation focused on understanding the microstructures and potential additive manufacturing printability challenges associated with graded WAAM structures using these welding wires. To achieve this, Cast Pin Tear Testing (CPTT) was performed to evaluate solidification cracking susceptibility of the welding wires. Additionally, Scheil calculations were performed in Thermo-Calc software to predict solidification microstructures. To validate the results, SEM characterization was conducted on cast buttons of each welding wire to identify phases in the respective microstructures. These unique data will help inform WAAM design parameters needed to produce a Functionally Graded Material (FGM) that improves the lifetime of Fe-Ni-Cr U-bend fittings in olefin furnaces.?

This study investigates a novel approach to addressing the persistent Type IV cracking issue in Grade 91 steel weldments, which has remained problematic despite decades of service history and various mitigation attempts through chemical composition and procedural modifications. Rather than further attempting to prevent heat-affected zone (HAZ) softening, we propose eliminating the vulnerable base metal entirely by replacing critical sections with additively manufactured (AM) weld metal deposits using ASME SFA “B91” consumables. The approach employs weld metal designed for stress-relieved conditions rather than traditional normalizing and tempering treatments. Our findings demonstrate that the reheat cycles during AM buildup do not produce the substantial softening characteristic of Type IV zones, thereby reducing the risk of premature creep failure. The study presents comprehensive properties of the AM-built weld metal after post-weld heat treatment (PWHT), examines factors influencing deposit quality and performance, and explores the practical benefits for procurement and field construction, supported by in-service data and application cases.

In this study, the creep strength of welded joints of Grade 91 Type 1 and Type 2 steels was evaluated. It was determined that impurity elements in the Type 1 steel reduced its creep strength. This reduction was attributed to an increase in the amount of residual carbides in the fine-grain heat-affected zone during welding.

In dissimilar welds between martensitic stainless steel F6NM and nitrogen-strengthened austenitic stainless steel FXM-19, type 209 austenitic welding consumables are used to align with the mechanical properties and chemical composition of FXM-19, with F6NM welds requiring post-weld heat treatment (PWHT) to restore ductility and toughness, raising concerns about sigma embrittlement in ER209 butter welds. This study investigated the mechanical properties and microstructure of F6NM+FXM-19 dissimilar welds, finding no detrimental sigma phase formation in the butter (PWHT) and groove weld metal (as welded) across various welding processes, indicating no sigma phase transformation due to PWHT. Submerged arc welding (SAW) and gas tungsten arc welding (GTAW) demonstrated good mechanical properties, while Gas Metal Arc Welding with 100% Ar gas shield (GMAW 100% Ar) could not be properly evaluated due to weld defects. SAW and GTAW were deemed suitable for this dissimilar weld joint, with several welding processes providing acceptable results using ER209 filler material for fabricating pressure vessels requiring F6NM to XM-19 joints.