The application of cold weld repair techniques in the power industry has been well documented. This type of repair is only considered when a conventional repair (involving post-weld heat treatment) is impracticable or the penalties of time and cost for conventional repair are sufficiently high. A typical cold weld repair in the UK has involved low alloy ferritic steel (½Cr½Mo¼V, 2¼Cr1Mo) components welded with nickel based SMAW consumables or ferritic FCAW consumables. Modified 9Cr steel components have been used in UK power plant since the late 1980’s for a number of applications, such as superheater outlet headers, reheat drums and main steam pipework. The problems associated with this material have also been well documented, particularly premature type IV cracking of welds on creep weakened modified 9Cr steel. RWE Generation UK have developed modified 9Cr cold weld repairs on headers, pipework and tubes. These repairs have been underwritten with extensive testing. This paper will describe the work performed on developing T91 cold weld repairs and where they have been applied on power plant.

In today’s market place power generation plants throughout the world have been trying to reduce their operating costs by extending the service life of their critical machines such as steam turbines and gas turbines beyond the design life criteria. The key ingredient in plant life extension is remaining life assessment technology. This paper will outline remaining life procedures which will incorporate the defect tolerant design concepts applied to the various damage mechanisms such as creep, fatigue, creep-fatigue and stress corrosion cracking. Also other embrittlement mechanisms will also be discussed and how they will influence the life or operation of the component. Application of weld repairs to critical components such as rotors and steam chest casings will be highlighted and how defect tolerant design concept is applied for the repair procedure and the acceptance standard of the nondestructive testing applied. Also highlighted will be various destructive tests such as stress relaxation tests (SRT) which measures creep strength and constant displacement rate test (CDRT) which evaluates fracture resistance or notch ductility. Also shown will be actual life extension examples applied to steam turbine components and weld repairs. Utilization of computer software to calculate fatigue and creep fatigue crack growth will also be presented

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.

Coke drums experience failures in through-wall cracking throughout their operating life, resulting from low cycle fatigue. Coke drums are typically fabricated from Chrome Moly (CrMo) steels. This study was performed on P4 (1.25Cr-0.5Mo) base material using ER70S-B2L and Alloy 625 (ERNiCrMo-3) filler materials. Specimens were welded with the temper-bead/controlled deposition welding technique. The weld processes used were HP-GTAW, GMAW and SMAW. The fatigue performance, HAZ hardness and toughness of the weld samples was evaluated. The HP-GTAW welds exhibited an order of magnitude improvement in fatigue performance when compared to the other weld processes using ER70S-B2L filler material. The HP-GTAW welds also exhibited improved HAZ hardness and toughness when compared to the other weld processes. This presentation will introduce the HP-GTAW process, its features, and benefits and where it is applied in Coke drum repair welding. Comparative test results of the different weld processes for fatigue performance, HAZ tempering, and toughness will also be presented.

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).

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.

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.

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.

Nuclear reactor inspections occasionally identify degraded materials in irradiated reactor components. Although mechanical repair options are possible, these repair solutions may be cost prohibitive or impractical to implement due to access restraints and/or the severity of the degradation. Welding repair of reactor components may input excessive heat into these irradiated materials resulting in diffusion of trace amounts of helium within the grain boundaries of the weld heat-affected zone (HAZ). Intergranular HAZ cracking can then result from the combination of this helium diffusion and high localized tensile stresses generated during weld cooling. It is therefore critical to characterize these zones and understand limitations for welding highly irradiated components to prevent helium-induced cracking. To accomplish this, typical reactor structural materials including Types 304L and 316L stainless steels and nickel-based Alloy 600/182 materials irradiated within the High Flux Isotope Reactor facility at Oak Ridge National Laboratory were used in this study for welding and evaluation. A phased array ultrasonic inspection system has been developed to characterize cracking in the weld samples. It provides remote controlled scanning and minimizes handling the samples, minimizing operator dose. The samples are inspected from the side opposite of the welds. The material and weld grain noise were evaluated at 10 MHz and found to be conducive to detecting cracking in the material and welds. Inspection of the samples comprises a 10 MHz phased array probe sweeping a focused longitudinal wave from -60° to 60° while the probe is raster scanned over the sample in small increments. The collected data is analyzed using UltraVision 3. Several of the irradiated samples were inspected prior to welding. Some of the samples had what appear to be small lamination defects in them. One irradiated welded sample has been tested to date with no cracking detected, which has been confirmed by destructive examination.

Thick-walled valves, steam chests, and casings suffer service damage from thermal stresses due to the significant through-thickness temperature gradients that occur during operating transients. Fatigue is the primary damage mechanism, but recent examination of turbine casings has revealed extensive sub-surface creep cavitation. The low primary stress levels for these components are unlikely to cause creep damage, so detailed inelastic analysis was performed to understand the complex stress state that evolves in these components. This illustrates that fatigue cycles can cause elevated stresses during steady operation that cause creep damage. This paper will explore a case study for a 1CrMoV turbine casing where the stress-strain history during operating transients will be related to damage in samples from the turbine casing. This will also highlight how service affects the mechanical properties of 1CrMoV, highlighting the need for service- exposed property data to perform mechanical integrity assessments. Finally, the consequences for repair of damage will be discussed, illustrating how analysis can guide volume of material for excavation and selection of weld filler metal to maximize the life of the repair. This, in turn, will identify opportunities for future weld repair research and material property data development.

As long term laboratory creep data became available the original estimates of the allowable stresses for creep strength enhanced ferritic steels (CSEF) had to be reduced. Thus, even in properly processed steel, the long term performance and creep rupture strength is below that originally predicted from a simple extrapolation of short term data. One of the microstructural degradation mechanisms responsible for the reduction in strength is the development of creep voids. Nucleation, growth and inter linkage of voids also result in a significant loss of creep ductility. Indeed, elongations to rupture of around 5% in 100,000 hours are now considered normal for long term creep tests on many CSEF steels. This relatively brittle behaviour, and the associated creep void development, promotes burst rather than leak type fracture in components. Moreover, the existence of significant densities of voids further complicates in-service assessment of condition and weld repair of these steels. The present paper examines background on the nucleation and development of creep voids in 9 to 12%Cr martensitic steels and discusses factors affecting brittle behavior.

The use of the bainitic class of creep strength enhanced ferritic steels T/P23 and T24 has increased over the last decade in a wide range of applications including replacement headers, superheater and reheater tubing and in waterwall tubing. Many issues have been reported in one or both of these materials including hydrogen induced cracking, reheat cracking and stress corrosion cracking. To appropriately address these issues, work has been initiated that includes a literature review, development of a database of phase transformation temperatures, investigation of tempering behavior, and an analysis of the effect of phase transformation on residual stresses. Such information will be provided in the context of understanding why these two materials appear highly susceptible to these cracking mechanisms.

Listings of the organizing committee, international advisory board, and technical review team for the 2024 Advances in Materials, Manufacturing, and Repair for Power Plants conference.

Solidification cracking (SC) is a defect that occurs in the weld metal at the end of the solidification. It is associated with the presence of mechanical and thermal stresses, besides a susceptible chemical composition. Materials with a high solidification temperature range (STR) are more prone to the occurrence of these defects due to the formation of eutectic liquids wetting along the grain boundaries. The liquid film collapses once the structure shrinks and stresses act during the solidification. Thus, predicting the occurrence of SC before the welding process is important to address the problem and avoid the failure of welded components. The nuclear power industry has several applications with dissimilar welding and SC-susceptible materials, such as austenitic stainless steels, and Ni-based alloys. Compositional optimization stands out as a viable approach to effectively mitigate SC in austenitic alloys. The integration of computational modeling into welding has significantly revolutionized the field of materials science, enabling the rapid and cost-effective development of innovative alloys. In this work, a SC resistance evaluation is used to sort welding materials based on a computational fluid dynamic (CFC) model and the alloy's chemical composition. An index named Flow Resistance Index (FRI) is used to compare different base materials and filler metals as a function of dilution. This calculation provides insights into the susceptibility to SC in dissimilar welding, particularly within a defined dilution range for various alloys. To assess the effectiveness of this approach, the relative susceptibility of the materials was compared to well-established experimental data carried out using weldability tests (Transvarestraint and cast pin tear test). The FRI calculation was programmed in Python language and was able to rank different materials and indicate the most susceptible alloy combination based on the dilution and chemical composition.

According to ASME Case N-888-3, Similar and Dissimilar Metal Welding Using Ambient Temperature SMAW or Machine GTAW Temper Bead Technique, a 48 hr waiting period before conducting the final nondestructive examination (NDE) is required when ferritic filler weld metal is used. The purpose of the 48 hr hold is to confirm the absence of hydrogen-induced cracking in the temper bead heat-affected zone. In previous research, the effect of post-weld heat treatment (PWHT) and temper bead welding (TBW) on the hydrogen-induced cracking (HIC) susceptibility in the coarse-grained heat-affected zone (CGHAZ) in welds of SA-508, P-No. 3 Group 3, pressure vessel steel was investigated using the Delayed Hydrogen Cracking Test (DHCT). In that previous study, the Gleeble thermomechanical simulator was used to generate six CGHAZ microstructural conditions: as-welded (AW), PWHT, and AW with single a TBW reheat at 675, 700, 725, and 735°C. Hydrogen was introduced to the specimen through cathodic charging under in situ constant tensile stress. The HIC susceptibility for these microstructures was ranked by the DHCT at a diffusible hydrogen level significantly exceeding typical GTAW and SMAW processes. The work described in this paper investigates the susceptibility to HIC of these same CGHAZ microstructures with DHCT at variable current densities, further ranking each condition. Test results were analyzed by fracture surface examination of failed tests, and cross-section microstructural analysis under a scanning electron microscope (SEM). Future steps include evaluating critical hydrogen content levels using gas chromatography for each condition. The results from this study will be used to consider potential elimination of the NDE hold time requirement in Case N-888-3 when ferritic weld metal is used.

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.

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 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.

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.

ENCIO (European Network for Component Integration and Optimization) is a European project aiming at qualifying materials, components, manufacturing processes, as well as erection and repair concepts, as follow-up of COMTES700 activities and by means of erecting and operating a new Test Facility. The 700°C technology is a key factor for the increasing efficiency of coal fired power plants, improving environmental and economic sustainability of coal fired power plants and achieving successful deployment of carbon capture and storage technologies. The ENCIO-project is financed by industrial and public funds. The project receives funding from the European Community's Research Fund for Coal and Steel (RFCS) under grant agreement n° RFCPCT-2011-00003. The ENCIO started on 1 July 2011. The overall project duration is six years (72 months), to allow enough operating hours, as well as related data collection, investigations and evaluation of results. The ENCIO Test Facility will be installed in the “Andrea Palladio” Power Station which is owned and operated by ENEL, located in Fusina, very close to Venice (Italy). The Unit 4 was selected for the installation of the Test Facility and the loops are planned for 20.000 hours of operation at 700°C. The present paper summarizes the current status of the overall process design of the thick-walled components, the test loops and the scheduled operating conditions, the characterizations program for the base materials and the welded joints, like creep and microstructural analysis also after service exposure.