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.

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.

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.

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.

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.

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.

Sanicro 25 material is approved for use in pressure vessels and boilers according ASME code case 2752, 2753 and VdTUV blatt 555. It shows higher creep rupture strength than any other austenitic stainless steels available today. It is a material for superheater and reheaters, enabling higher steam parameters of up to about 650 °C steam (ie about max 700 °C metal) without the need for expensive nickel based alloys. The aim of the present study is the investigation of the steam oxidation resistance of the Sanicro 25. The long term test was conducted in the temperature range 600 -750 °C up to 20 000 hours. The morphology of the oxide scale and the microstructure of the bulk material were investigated. In addition, the effect of surface finish and pressure on the steam oxidation were also studied.

Advanced power systems that operate at temperatures higher than about 650°C will require nickel-base alloys in critical areas for pressure containment. Age-hardened alloys offer an additional advantage of reduced volume of material compared with lower strength solid solution-strengthened alloys if thinner tube wall can be specified. To date, the only age-hardened alloy that has been approved for service in the time dependent temperature regime in the ASME Boiler and Pressure Vessel Code is INCONEL alloy 740H. Extensive evaluation of seamless tube, pipe, and forged fittings in welded construction, including implant test loops and pilot plants, has shown the alloy to be fit for service in the 650-800°C (1202-1472°F) temperature range. Since, nickel-base alloys are much more expensive than steel, manufacturing methods that reduce the cost of material for advanced power plants are of great interest. One process that has been extensively used for stainless steels and solution-strengthened nickel-base alloys is continuous seam welding. This process has rarely been applied to age-hardened alloys and never for use as tube in the creep-limited temperature regime. This paper presents the initial results of a study to develop alloy 740H welded tube, pipe and fittings and to generate data to support establishment of ASME code maximum stress allowables.

Additive manufacturing is being considered for pressure boundary applications for power plant service by ASME Boiler and Pressure Vessel Code and regulators. Both existing and new plants could benefit from the reduced lead times, design flexibility, and part consolidation possible with additive manufacturing. Various ASME code committees are working towards rules and guidance for use of additive manufacturing. To further the industry's understanding, this research program was undertaken to evaluate the properties of wire arc additive manufactured 316L stainless steel. This study included microstructural characterization, chemical composition testing, mechanical testing, and nondestructive evaluation of multiple large (1600-pound (700 kg)) 316LSi stainless steel valve bodies produced using the gas metal arc directed energy deposition process followed by solution annealing. The results showed the tensile behavior over a range of temperatures was comparable to wrought material. No variation in tensile behavior was observed with change in tensile sample orientation relative to the build direction. Room temperature Charpy V-notch absorbed energy toughness was comparable to wrought material. Large grain sizes were observed in the metallographic samples, indicating that lowering the solution anneal temperature may be worthwhile. The results of surface and volumetric examination were acceptable when compared to forged material acceptance criteria. Together these results suggest that GMA-DED can produce acceptable materials properties comparable to forged materials requirements.

Creep strength of Grade 91 steels has been reviewed and allowable stress of the steels has been revised several times. Allowable stress regulated in ASME Boiler and Pressure Vessel Code of the steels with thickness of 3 inches and above was reduced in 1993, based on the re-evaluation with long-term creep rupture data collected from around the world. After steam leakage from long seam weld of hot reheat pipe made from Grade 122 steel in 2004, creep rupture strength of the creep strength enhanced ferritic (CSEF) steels has been reviewed by means of region splitting method in consideration of 50% of 0.2% offset yield stress (half yield) at the temperature, in the committee sponsored by the Ministry of Economy, Trade and Industry (METI) of Japanese Government. Allowable stresses in the Japanese technical standard of Grade 91 steels have been reduced in 2007 according to the above review. In 2010, additional long-term creep rupture data of the CSEF steels has been collected and the re-evaluation of creep rupture strength of the steels has been conducted by the committee supported by the Federation of Electric Power Companies of Japan, and reduction of allowable stress has been repeated in 2014. Regardless of the previous revision, additional reduction of the allowable stress of Grade 91 steels has been proposed by the review conducted in 2015 by the same committee as 2010. Further reduction of creep rupture strength of Grade 91 steels has been caused mainly by the additional creep rupture data of the low strength materials. A remaining of segregation of alloying elements has been revealed as one of the causes of lowered creep rupture strength. Improvement in creep strength may be expected by reducing segregation, since diffusional phenomena at the elevated temperatures is promoted by concentration gradient due to segregation which increases driving force of diffusion. It has been expected, consequently, that the creep strength and allowable stress of Grade 91 steels can be increased by proper process of fabrication to obtain a homogenized material free from undue segregation.

Creep strength enhanced ferritic steels like T/P 91 and T/P 92 are widely used for the fabrication of pressure vessel components in the petro-chemical and thermal power industry. Today, a new generation of 9-12% Cr CSEF steels like MARBN, Save12AD, G115 and Super VM12 are entering into the market. All CSEF steels require an accurate post-weld heat treatment after welding. This paper discusses the impact of chemical composition on Ac1 as well as the transformation behavior during post-weld heat treatment in a temperature range below and above Ac1. The Ac1 temperature of weld metals with variations in chemical composition has been determined and thermodynamic calculations has been carried out. Simulations of heat treatment cycles with variations in temperature have been carried out in a quenching dilatometer. The dilatation curves have been analyzed in order to detect any phase transformation during heating or holding at post weld heat treatment. Creep rupture tests have been carried out on P91 and Super VM12 type weld metals in order to investigate the effect of sub- and intercritical post weld heat treatment on creep rupture strength.

The United States Department of Energy (U.S. DOE) Office of Fossil Energy and the Ohio Coal Development Office (OCDO) have been the primary supporters of a U.S. effort to develop the materials technology necessary to build and operate an advanced-ultrasupercritical (A-USC) steam boiler and turbine with steam temperatures up to 760°C (1400°F). The program is made-up of two consortia representing the U.S. boiler and steam turbine manufacturers (Alstom, Babcock & Wilcox, Foster Wheeler, Riley Power, and GE Energy) and national laboratories (Oak Ridge National Laboratory and the National Energy Technology Laboratory) led by the Energy Industries of Ohio with the Electric Power Research Institute (EPRI) serving as the program technical lead. Over 10 years, the program has conducted extensive laboratory testing, shop fabrication studies, field corrosion tests, and design studies. Based on the successful development and deployment of materials as part of this program, the Coal Utilization Research Council (CURC) and EPRI roadmap has identified the need for further development of A-USC technology as the cornerstone of a host of fossil energy systems and CO 2 reduction strategies. This paper will present some of the key consortium successes and ongoing materials research in light of the next steps being developed to realize A-USC technology in the U.S. Key results include ASME Boiler and Pressure Vessel Code acceptance of Inconel 740/740H (CC2702), the operation of the world’s first 760°C (1400°F) steam corrosion test loop, and significant strides in turbine casting and forging activities. An example of how utilization of materials designed for 760°C (1400°F) can have advantages at 700°C (1300°F) will also be highlighted.

Growing energy demand promotes the construction of high performance energy plants with large scale. A dramatic increase of plant performance has been achieved by the enlargement of their major components such as turbine rotor shafts and pressure vessels. The Japan Steel Works, Ltd., has been continuing the efforts for improvements of production technology, material technology, reliability assessments and so on in order to attain high performance, high efficiency and reliable plants. The efforts gave birth to several epoch-making large and high quality forged components for energy plants. Recently, on the viewpoint of environmental problem such as global climate change, further development of new production technology and improvement of material has been continued. This paper gives an overview of the development of large high-quality forgings for high efficiency power generation plants.

In flexible operation with increased number of startup, shutdown, and load fluctuations, thermal fatigue damage is exacerbated along with existing creep damage in power plant pipe and pressure vessels. Recently, cracks were found in the start-up vent pipe branching from the reheat steam pipe within a heat recovery steam generator(HRSG) of J-class gas turbine, occurring in the P92 base material and repair welds. This pipe has been used at the power plant for about 10 years. Microstructural analysis of the cross-section indicated that the cracks were primarily due to thermal fatigue, growing within the grains without changing direction along the grain boundaries. To identify the damage mechanism and evaluate the remaining life, temperature and strain monitoring were taken from the damaged piping during startup and normal operation.

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.

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.

A significant research and development effort is underway to support the qualification of Alloy 709 as a Class A construction material in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section III, Division 5, High Temperature Reactors. This initiative includes a comprehensive Alloy 709 code qualification plan aimed at generating extensive material testing data crucial for compiling the code case data package. The data package is essential in establishing material-specific design parameters for Alloy 709 to be used as Section III, Division 5 Class A construction material for fast reactors, molten salt reactors and gas-cooled reactors. An ASME Section III, Division 5 material code case requires the evaluation of mechanical properties from a minimum of three commercial heats, covering anticipated compositional ranges. A key part of the data package involves fatigue and creep-fatigue testing at elevated temperatures, needed for developing the fatigue design curves and the damage envelope of the creep-fatigue interaction diagram (D-diagram). This paper summarizes the strain-controlled fatigue testing on three commercial heats of Alloy 709 at 760 and 816°C with strain ranges between 0.25% and 3%. The fatigue failure data are used to generate a preliminary fatigue design curve. Additionally, the creep-fatigue testing results at 816°C with tensile hold times of 10, 30, and 60 minutes are presented in support of developing the D-diagram for Alloy 709.

To improve the economics of critical components, such as receivers and heat exchangers, for Generation 3 (Gen 3) concentrating solar power (CSP) plants, research was conducted to understand how manufacturing impacts the high-temperature performance of various tube production routes. Gen 3 CSP components are expected to require the use of heat-resistant nickel- based alloys due to the elevated operating temperatures in designs carrying molten salt or supercritical CO 2 . INCONEL alloy 740H (alloy 740H) was investigated as an alternative to UNS N06230 (alloy 230) as it possesses superior high-temperature creep strength which can lead to overall reductions in material cost. A key challenge is understanding how autogenous seam welding with and without re-drawing can be used to manufacture thin-wall tubing for CSP receivers and heat-exchangers to further reduce costs over traditional seamless production routes. Alloy 740H welded tube was successfully fabricated and re-drawn to several relevant tube sizes. Since traditional mechanical testing samples could not be removed from the thin-wall tubing, full-sized tubes were used for tensile, fatigue, and vessel testing (internally pressurized creep- rupture) which was critical to understanding the weld performance of the manufactured product forms. The generated vessel test data exhibited a creep strength reduction when compared to wrought product with no clear trend with temperature or test duration. It was found that redrawing the welded tubes improved the creep strength to approximately 82% of the wrought material performance and elevated temperature tensile and fatigue behavior exceeded 85% of the design minimums. Detailed, post-test characterization found that nano-sized carbides formed during the laser seam-welding process remained stable after multiple solution-annealing steps, which restricted grain growth, and impacted the time-dependent performance. This paper will focus on the time-dependent behavior of the examined welded and redrawn tubes, supporting metallographic evidence, and give perspective on future considerations for using alloy 740H in CSP components.

Laboratory-scale tests are frequently used to generate understanding of high-temperature oxidation phenomena, to characterise and rank the performance of existing, future materials and coatings. Tests within the laboratory have the advantage of being well controlled, monitored and offer the opportunity of simplification which enables the study of individual parameters through isolating them from other factors, such as temperature transients. The influence of pressure on the oxidation of power plant materials has always been considered to be less significant than the effects of temperature and Cr content, but still remains a subject of differing opinions. Experimental efforts, reported in the literature, to measure the influence of steam pressure on the rate of oxidation have not produced very consistent or conclusive results. To examine this further a series of high pressure steam oxidation exposures have been conducted in a high pressure flowing steam loop, exposing a range of materials to flowing steam at 650 and 700 °C and pressure of 25, 50 and 60 bar. Data is presented for ferritic-martensitic alloys showing the effect of increasing pressure on the mass change and oxide thickness of these alloys in the flowing steam loop. In addition the effect observed on the diffusion of aluminium from an aluminised coating in these alloys is also presented and the differences in the extent of diffusion discussed.

INCONEL 740H has been developed by Special Metals for use in Advanced Ultra Super Critical (A-USC) coal fired boilers. Its creep strength performance is currently amongst the ‘best in class’ of nickel based alloys, to meet the challenge of operating in typical A-USC steam temperatures of 700°C at 35 MPa pressure. Whilst the prime physical property of interest for INCONEL 740H has been creep strength, it exhibits other physical properties worthy of consideration in other applications. It has a thermal expansion co-efficient that lies between typical values for Creep Strength Enhanced Ferritic (CSEF) steels and austenitic stainless steels. This paper describes the validation work in support of the fabrication of a pipe transition joint that uses INCONEL 740H pipe, produced in accordance with ASME Boiler Code Case 2702, as a transition material to join P92 pipe to a 316H stainless steel header. The paper gives details of the material selection process, joint design and the verification process used for the joint.