Fossil Materials and Repair - Program 87

Transcription

1 Fossil Materials and Repair - Program 87 Program Description Program Overview Today s fossil power plants increasingly are adopting market-driven operating strategies such as cycling, pushing for maximum output during peak price periods, and frequent fuel switching to take advantage of spot market opportunities. These practices can accelerate material damage in major power block components. New materials are being introduced for replacement of components in aging plants and in the building of higher efficiency power plants. Improved knowledge of materials behavior in such environments allows for accurate prediction of remaining life, proper selection of repair strategies, and optimized material selection, fabrication, and repair. To address these needs, the Electric Power Research Institute s (EPRI s) Fossil Materials and Repair program (Program 87) provides the integrated materials selection guidance, corrosion mitigation methods, and repair and welding technologies needed to improve equipment performance, reliability, and profitability. Research Value Safety and availability loss due to failures are two key issues driving R&D on major fossil power plant components, especially in older plants. Improved efficiency and reliability are two reasons for the selection of new materials for retrofit and new-build projects. EPRI s Materials and Chemistry programs provide data on critical material degradation mechanisms, conduct materials and chemistry-related R&D for advanced generation technologies, and quantify the benefits of chemistry improvements. The programs help utilities balance the risks and costs of the largest, most costly equipment, and focus on using new technologies to create solutions. Members of the Fossil Materials and Repair program can use the R&D to: Increase availability through better understanding of plant materials; Eliminate repeat failures, minimize equipment damage, and reduce outage frequency and duration by using improved knowledge of damage mechanisms and life assessment methods; Reduce failures from high- and low-temperature corrosion; Obtain in-depth knowledge of advanced ferritic and austenitic alloys and processes used to fabricate and join these alloys; Use new and advanced repair technologies; and Maximize component life through improved materials selection guidance and procurement specifications. Approach Through a continuum of materials and repair guidelines, handbooks, technical projects, and conferences/workshops, the program helps manage and reduce the operating risks associated with material degradation and failure. Projects develop resources to estimate remaining life, assess and conduct state-of-theart repairs, decide on replacement materials, and address costly corrosion and erosion problems faced in realworld business settings. Research into availability increases through improved materials performance focuses on all aspects of materials used in power production, including degradation, failure analysis, selection, component life assessment, and advancements in materials technologies. Key areas of research include materials guidelines, failure analysis guidelines, materials selection and advancements, new tools for evaluating inservice degradation of materials, and life prediction. Developments and repair solutions in fossil repair applications are provided to members via demonstrations, procedures, reports, conferences, and workshops. Deliverables are targeted to provide applications technologies to extend component life, reduce repair costs, improve materials performance, and reduce downtime for repair activities. p. 1

2 R&D of reliability of materials in corrosive, abrasive, and high-temperature operation is aimed at reducing corrosion in power plant piping, heat exchangers, boiler tubing, and other components which costs power companies millions of dollars each year through improved understanding of corrosion mechanisms, innovative coatings assessments, and the development of models to predict and control corrosion phenomena. Accomplishments EPRI s Fossil Materials and Repair program is a proactive industry leader in all aspects of plant materials performance, repair and welding technology development, and corrosion mitigation. Provided industry leadership in addressing fabrication, installation, welding, and degradation of creepstrength-enhanced ferritic steels and advanced austenitic stainless steels Developed comprehensive International Steam Boiler and Steam Turbine Metallurgical Guidelines Provided guidance on behavior and remaining life of austenitic stainless steel materials used for superheater and reheater tubing applications Developed welding guidelines for boiler applications and advanced ferritic and austenitic alloys Published a series of metallurgical handbooks (Grade 11, Grade 22, X20, carbon steels, and stainless steels) Developed new models for assessing oxide growth and exfoliation Provided innovative solutions and new welding consumables for dissimilar metal weld damage repair and advanced steels Current Year Activities The program R&D for 2012 will focus on key member issues, including the application of small specimen testing for qualitative and quantitative life assessments; application of knowledge on creep-fatigue damage; novel tools to improve the application of materials knowledge in the use of creep strength enhanced ferritic steels; improving failure analysis; and improved understanding of weldment cracking phenomenon in new boiler steels, oxidation of superheaters/reheaters, erosion issues in steam turbine components, and corrosion in environmental control equipment. Key specific efforts are expected to include: Material database for small specimen remaining life assessments Improved Grade 91 handbook Stress corrosion cracking and reheat cracking in T23/24 alloy welds Application of nanocoatings Steamside exfoliation model deployment Survey of corrosion and erosion issues in flue gas desulfurization system components Estimated 2012 Program Funding 2.75M Program Manager John Shingledecker, , jshingledecker@epri.com Fossil Materials and Repair - Program 87 p. 2

3 Summary of Projects Project Number Project Title Description P Availability Increases Through Improved Materials Performance P Fossil Repair Applications and Welding Technology P Reliability of Materials In Corrosive, Abrasive, and High-Temperature Operation This project performs research on all aspects of plant material performance, including damage mechanisms, metallurgical phenomenon, failure analysis, material selection, and component life assessment. This project provides members new repair technologies that are critical for maintaining the plant, addressing emergency failures, reducing outage times, and reducing the risk of future damage. Research addresses these needs through new innovative repair tools, new welding consumables, fabrication and installation guidance, productivity improvements in welding, and the performance of welded structures. This project performs research to understand the often complex corrosion and erosion issues related to plant materials. Solutions in the form of guidelines, technical reports, and coating technology are provided to program members. P Availability Increases Through Improved Materials Performance (058205) Key Research Question Today s fossil power plants increasingly adopt market-driven operating strategies, such as cycling, pushing for maximum output during peak price periods, and frequent fuel switching to take advantage of spot market opportunities. These new operating modes can accelerate material damage in virtually all major power plant components, including pressure parts and rotating components. Proper selection of materials and the right operating strategy can eliminate damage while increasing plant availability and reducing repair costs. To accomplish this goal, improved understanding of damage mechanisms and material degradation is needed. The construction of new plants, mainly supercritical pulverized coal power plants and heat recovery steam generators (HRSG) in combined cycle plants, is using new materials for which specification guidance and data on performance are required. Approach This project focuses on all aspects of materials used in power production, including materials degradation, failure analysis, material selection, component life assessment, and advances in materials technologies. Developments in this area will be integrated with repair applications developed in Project and corrosion and oxidation damage mechanisms evaluation in Project Key areas of research will include materials guidelines, improved understanding of failure mechanisms, failure analysis guidelines, materials selection and advancements, and material-specific lifeprediction methodologies and data. When appropriate, joint activities with Programs 63, 65, and 88 are included to improve component life. Impact Apply comprehensive metallurgical guidelines for both metallurgical property information and the tools to predict component life Help members evaluate advanced materials entering the market and the components fabricated from them and to select optimum materials for long-term operation Provide industry with tools and databases for small specimen testing to improve life assessment and understanding of in-plant material degradation Fossil Materials and Repair - Program 87 p. 3

4 Work with industry leaders in addressing creep-strength-enhanced ferritic steels (Grades 91, 92, 122, 23, and 24) and advanced austenitic alloys (347HFG, Super 304H, and HR3C.) Participate in the international development of guidelines and improved methodologies for assessing creep-fatigue damage in components, the result of unit cycling and deployment of a host of new alloys How to Apply Results Members can use the research information in this project to select optimum materials for a variety of components, ranging from piping, tubing, and headers to steam turbines and discs; gain the technical basis for improving internal material procurement specifications to ensure long-term material reliability; consistently apply improved remaining-life techniques to assess component life; address advanced ferritic and austenitic alloy issues; better understand the factors that can influence component damage and remaining life; and improve the methods used to conduct failure investigations Products New & d Grade 91 Handbook: EPRI completed a four-year effort, combined with information from more than 40 members, covering all aspects of initial material integrity and damage development in Grade 91 components. The project also produced a practical life management strategy. Based on the recently completed research and material guidance, a new "pocket-sized" handbook will be produced to distill this information into a practical tool that power plant engineers can use to optimize Grade 91 component life. In addition to a hard copy book, the handbook is intended to be interactive and available as an easy-to-use electronic document for new smart phone applications. Expansion of HRSG Materials Selection Guide: With the anticipated increased need for gas turbine combined-cycle plants, the construction of new heat recovery steam generators (HRSG) with improved performance is expected. In 2011, EPRI completed a detailed materials selection guide for HRSG high-pressure tubing components, covering a range of potential operating conditions and materials. A rigorous analytical approach was used to select optimum materials. In 2012, this work will be expanded to cover additional critical components including nonpressure parts such as duct burners. Expanded Material Database for Small-Specimen Testing: In 2010 and 2011, EPRI program 87 developed the test equipment, baseline data, and an approach to improve small punch testing (SPT) for qualitative creep life assessment of boiler piping, used for improved life assessments of high-energy piping systems in aging plants. In 2012, this database will be expanded to include Grade 91 and 22, and work will begin to provide more quantitative assessment of data. An EPRI-led International SPT Experts Group will elaborate and harmonize testing and analyses of SPT data, which will form the basis for the development for correlation of SPT data with standard tensile and creep data for materials P22 and P91. This correlation will serve for condition assessment of components in service. Failure Analysis Workshop: Power plant engineers, while technically competent, have limited background and knowledge of the collection, documentation, and preservation of both failed and unfailed parts, which may be critical to fully establishing root cause and prevent future failures. EPRI P87 has produced a three-volume failure analysis guideline to aid plant engineers. This workshop/training course will educate participants on the use of this guideline and other relevant P87 resources to improve participants abilities to conduct a proper failure investigation. Multiple examples of good and poor practices during field failures will be used for this approach. Report Resource Fossil Materials and Repair - Program 87 p. 4

5 Implementation of Creep-Fatigue Databases to Components: EPRI has led an international effort to produce a state-of-knowledge on creep-fatigue damage interaction, establish creep-fatigue testing standards, and develop material databases for life assessment. In 2012, EPRI will use these tools to identify operation modes and components that may be subjected to creep-fatigue damage. A creep-fatigue failure assessment method will be developed for materials subjected to cyclic loading at high temperature, based on a creepfatigue failure assessment diagram (C-F FAD). Advanced Stainless Steel Pocket Handbook: 347HFG, Super 304H, HR3C: EPRI has completed a state-of-knowledge report on the experience and behavior of a wide range of advanced austenitic stainless steels. A welding guideline also has been produced. The current worldwide application of this class of alloy in boiler tubes in modern supercritical and ultra-supercritical plants largely has been relegated to three main alloys: 347HFG (Fine-grained 347H), Super 304H, and HR3C (310HCbN). Using the available data, a convenient reference guide in the form of a pocket handbook (in the manner of the other EPRI P87 pocket handbooks) will be produced. The guide will be an easy-toread quick reference for plant engineers with these alloys in their power plants. The Effect of Chemistry on Strain-Induced Precipitation Hardening of Stainless Steels: Failures in cold-formed stainless steels due to strain-induced precipitation hardening (SIPH) have been observed over a number of years, and practical guidance for heat-treatment now exists. However, the role of alloy chemistry in the manifestation of the damage mechanism, especially trace alloying elements, niobium, and boron (within specifications and between alloys), remains unclear. This project aims to evaluate a series of austenitic stainless steels for the propensity for SIPH failures, with particular emphasis on the role of chemical composition of the base metal. Report Future Year Products 7th International Conference on Advances in Materials Technology for Fossil Power Plants Quantitative Life-Assessment of Grade 22 Piping Using Small Punch Testing 11/30/13 12/31/13 Workshop, Training, or Conference P Fossil Repair Applications and Welding Technology (058206) Key Research Question Reliable repair technologies are a key part of any organization s run-repair-replacement decisions and are invaluable to power plant owners in maintaining the plant and addressing emergency failures. Repair of damage mechanisms investigated in and corrosion evaluations from will be key to this project. It incorporates two key topics: fossil plant repair applications (immediate repair needs) and advanced repair and welding technologies (focused on development of longer-reaching repair technologies, including improved welding consumables and improved understanding of weld performance). Fossil Materials and Repair - Program 87 p. 5

6 Approach Developments and repair solutions will be provided to members via demonstrations, procedures, reports, conferences, new products, and workshops. Deliverables include applications technologies to extend component life, reduce repair costs, improve materials performance, and reduce downtime for repair activities. Participants in this project gain direct access to EPRI s welding, materials, and power plant repair experts, as well as the collaborative expertise of fellow program participants. Impact Improve practices, equipment, and methodologies to reduce the cost and time involved in repairing and replacing superheat and reheat tubing Provide innovative solutions for grade 91 welding and repair Ensure quality new plant and component performance by using welding, fabrication, and installation guidance when working with OEMs, vendors, and architectural engineering firms Apply guidelines for selecting weld metal and processes for the appropriate application Disseminate best practices How to Apply Results Members will have access to research results on advanced repair technology through guidelines and reports, such as the Fabrication and Installation Guidelines, which can be used to specify and follow fabrication practices used by vendors and OEMs. Members are encouraged to attend the conferences on welding and repair to ensure effective technology transfer. These conferences are supplemented by workshops and technical support services as required. Members will be able to use the adaptation of existing repair technology in new applications and development of repair technologies. Newly available consumable products, such as P87 filler metal, will be made available to improve welded component performance Products Welding and Repair Technology for Power Plants: An international conference, jointly sponsored by EPRI's Nuclear Welding and Repair Technology Center (WRTC) and EPRI P87 (Fossil Materials and Repair), to provide a forum for sharing recent advancements in manufacturing, fabrication, welding, installation, and repair of nuclear and fossil power plant components. The program is designed around technical exchange through presentations covering welding and repair research and experience, invited keynote speakers, a vendor fair, and ample opportunities for informal discussions with plant owners, power plant engineers, research scientists, welding and fabrication vendors, and original equipment manufacturers (OEMs). New Interactive Grade 91 Welding Guideline: Most of the early failures and fabrication issues with the implementation of Grade 91 steel (P91, T91, F91) have been due to improper welding and post-weld heat-treatment (PWHT) of components in the field. Field engineers, welding engineers, and power plant staffs need tools that can be used to educate welders and quality assurance staff working in the field and on the construction site who have little to no knowledge of the complex metallurgy of these alloys. A small guide is envisioned, to provide a tool for quickly educating these staff members on proper handling, welding, and PWHT of Grade 91. The use of smart phone technology to accomplish this goal will be explored. The document will reference the much larger body of research already completed within EPRI programs and projects on Grade /01/12 Resource Report Fossil Materials and Repair - Program 87 p. 6

7 Repair Without PWHT for Thin-Section CSEF Steels: With increased pressure to reduce plant maintenance time during peak loads or market opportunities, short-term repairs can have significant economic benefit. However, the increasing use of creep strength enhanced ferritic (CSEF) steels such as T91, T92, T23, and T24 in thin-section tubular applications necessitates longer repair times due to the need for post-weld heat-treatment (PWHT). In 2011, EPRI P87 conducted a scoping study on the applicability of temperbead repair techniques (welding with PWHT) on grade 91. Based on these initial tests, additional work to develop and optimized the procedures will be conducted for a range of applicable materials. Improved Understanding of SCC in CSEF steels: Stress corrosion cracking (SCC) has been reported in creep-strength-enhanced (CSEF) steels, including Grade 91 and 23, during fabrication or after welding when post-weld heattreatment (PWHT) is not performed properly and the material is exposed to a moist environment. The current guidance given for humidity, storage time, and material hardness is "rule-of-thumb,"' and needs to be revisited. Materials such as T23 and T24 are thought to be immune from this type of damage, but experience suggests otherwise. Limits for material hardness, time in environment, and residual stress have not been examined and compared for this class of alloy. The limits may be different, depending on alloy composition and other factors. This work will conduct fundamental studies on SCC in moist environments for these alloys to give scientifically based guidance on material handling as a function of material. Stress-Relief Cracking in Chromium Molybdenum Steels 23 and 24: Steels T23 and T24 are increasingly used in boiler waterwall and heat recovery steam generators (HRSGs). HRSG construction is expected to expand to meet shortterm demands for power in gas turbine combined-cycle plants due to low cost of natural gas. Welding of these alloys is significantly more challenging than traditional T22. This work will investigate the susceptibility of these alloys to stress-relief cracking and reheat cracking. Using this information, the project will develop improved weld bead placement, joint geometry, and heat-treatment recommendations for both new construction and component repair. Future Year Products Welding and Repair Technology for Power Plants 07/01/14 Weld Metal & Process Selection for Joints Operating in High-Temperature Service 12/31/14 Resource Improved Understanding of SCC in CSEF Steels 12/31/14 Report Fossil Materials and Repair - Program 87 p. 7

8 P Reliability of Materials In Corrosive, Abrasive, and High-Temperature Operation (058207) Key Research Question Corrosion in power plant piping, heat exchangers, boiler tubing, and other components costs power companies millions of dollars each year. At high temperatures, oxides growing in steam circuits control many of the failure and damage mechanisms around the plant, including remaining life, solid particle erosion, and short-term overheating. Hot corrosion attack and wastage due to erosion reduce tube life and require coatings, weld overlay, or alternate materials. Additionally, fossil power plants experience a multitude of low-temperature corrosion problems in a variety of plant systems, including raw water and pretreatment systems, cooling water, service water and fire protection systems, condensers, cooling towers, auxiliary heat exchangers, low-pressure feedwater heaters and piping, deaerators, steam turbines, electric generators, air heaters and ducts, flue gas desulfurization systems, and flue gas ducts and stack. Corrosion problems with high cost impact on the fossil power industry will receive highest priority. Approach This project addresses corrosion and abrasive damage at both low and high temperatures through the development of a fundamental understanding of these damage mechanisms affecting power plant materials and components. Various coatings, including nanostructured coatings, will be investigated for mitigation of both corrosion and erosion in various components. Modeling of the corrosion process and methodologies to control key industry issues such as exfoliation of stainless steel tubing will be undertaken. Impact Temperature effects as a result of an oxide scale buildup can have an adverse impact on remaining life, and how the oxide exfoliates can determine if tube pluggage and resulting short-term overheat or turbine solid particle erosion (SPE) damage is a concern. This project will investigate new materials as they are developed and installed in power plants to understand the oxidation rate, oxide morphology, and eventual exfoliation of the oxide. Develop improved understanding of high-temperature erosion and corrosion in hard-facing alloys Improve many aspects of power plant equipment condition, including oxidation, corrosion, and erosion resistance, with developments in nanostructured coatings Minimize damage and address all metallurgical aspects of low-temperature corrosion How to Apply Results Results delivered through guidelines, reports, and workshops can give members a fundamental understanding of damage mechanisms affecting power plant components. Knowing how oxides exfoliate can assist in determining if tube plugging is likely and in understanding solid particle erosion of turbine blade diaphragms. The guidelines can be integrated in members processes and procedures to improve operations and reduce damage caused by high-temperature operations Products Nanostructured Coatings for Improved Erosion Resistance of Steam Turbine Valve Stems: EPRI has developed tough, adherent, erosion-resistant nanocoatings and completed a research project for coating typical steam turbine valve stem materials. Field trials were initiated in Additional field trials will be conducted in 2012 when required, and will evaluate materials after removal from the field. This project will document progress made and performance of the field trials. Fossil Materials and Repair - Program 87 p. 8

9 Review of FGD Materials Performance: A new generation of flue gas desulfurization (FGD) systems has been constructed for improved sulfur removal. The materials of construction for various components vary greatly depending on utility, manufacturer, and operating needs. Additionally, older units continue to run. In addition to work being conducted on corrosion in the metallic tanks and piping of these new units constructed with metallic alloys (often duplex stainless steel), there are many other materials and components with performances not widely documented. This project will use surveys and site visits to identify the materials of construction for the major components in these systems; document the performance of the alloys, coatings, refractories, composites, and plastics; and compare the industry experiences. Participants will gain firsthand knowledge of how components are performing, helping them make informed inspections, repairs, and materials selections for a variety of FGD system components. Application of EPRI Model to Predict and Control Steam-Side Oxide Scale Growth and Exfoliation: Tube failures and erosion damage from the release of steam-grown oxides from boiler superheater and reheater tubing continues to plague new plants and retrofit components. Material behavior differs between alloys, alloy class, and surface-finishing techniques (i.e., shot-peening). EPRI's model to predict and control steamside oxidation will be improved with the latest data and refinements from 2011 research. Improved guidance on temperature limits for materials to minimize tube failures will be researched and compared to data gathered during site visits. Nanostructured Coatings for Erosion and Wear Protection of Power Plant Components: Initiation of Field Trials: EPRI has evaluated tough, adherent, dense, and hard nanocoatings, which show improvement compared to traditional coatings for wear, solid particle erosion, and liquid droplet erosion tests. EPRI has identified many possible applications for these coatings, including coal mills, tank impellers, steam turbine blades and vanes. EPRI will work with members who are experiencing wear and erosion issues to test the coating technology for the specific application by conducting field trials. The report will cover field trials initiated, in-plant performance, and post-trial observations as they become available. Steam Turbine Valve Material Selection: Steam turbine valve stems, seats, and bushings often are selected based on manufacturer experience with alloys in other steam turbine components and the mechanical properties required. However, oxidation of valve stems and the tight clearances with bushings can cause valves to jam and stick, which is a constant headache for valve owners. Even if a material has good oxidation resistance, surface engineering techniques such as nitriding can improve wear resistance but decrease oxidation resistance. The interaction between these competing phenomena has not been studied in detail, and the limited studies suggest coatings or alternate materials may provide improved performance. Based on these observations, this project will conduct a test program for selection of optimum material combinations for combined oxidation, wear, and galling resistance between valve stems and bushing. Fossil Materials and Repair - Program 87 p. 9

10 Supplemental Projects Corrosion in Wet Flue Gas Desulfurization Systems (071261) Background, Objectives, and New Learnings State-of-the-art flue gas desulfurization (FGD) technologies have been or are being installed on most large coalfired electric generating units in response to new regulatory emission requirements. Aggressive corrosion has been noted in some of these systems, presumably from the low-ph, high-chloride environments created in the FGD process. A variety of materials (metallic, organic, plastics, coating) are available to construct these systems, but due to cost, fabricability, and availability, the absorber vessels, tanks, piping, and spray towers in many new installations have been constructed using duplex stainless steel Alloy 2205, which had not been used on systems constructed before Unfortunately, many of these newer units are experiencing severe corrosion attack in operation over as little as three months. The primary mode appears to be pitting in weld heataffected zones (HAZ), weld metal, and under deposit areas. Some corrosion due to surface contamination and surface finish (crevice corrosion) also has been reported. Some reports suggest this corrosion will extend to other duplex and standard stainless steel alloys. This project will collect data on FGD units experiencing problems to determine the root cause(s) of the corrosion. Information on fabrication techniques, construction quality assurance/quality control, and operating environments (chemistry and scaling) will be gathered at as many sites as possible. These data will be used to identify gaps in knowledge, and missing data will be generated using laboratory and field corrosion tests for Alloy 2205, welds, and alternative materials/coating systems. Repair strategies and other mitigation strategies will be explored anddocumented if proven and widely applicable. Project Approach and Summary Determination of root cause(s) will utilize available information from currently known failures, identify missing data or information, and where possible, include inspection of several sites. A survey to collect information on materials and fabrication practices, including vessels and piping systems, is currently under way. It is anticipated that additional laboratory and field testing of materials will be necessary, which could include stainless steels, duplex alloys (2205), nickel-based alloys, welds/weldments, surface preparation/finishes, and coatings. Fabrication guidelines for metallic FGD systems will be prepared, covering proper construction practices, contamination and surface acceptance, and welding practices for metallic materials. Repair options will be identified, including inspection, post-corrosion cleaning, and surface preparation. A new Corrosion in FGD Materials Interest Group will hold a minimum of two meetings a year to provide a forum for ongoing exchange of information, ideas, and performance. Benefits The mitigation and repair of FGD vessels experiencing corrosion are critical issues. Failure of these vessels can result in potential damage to adjoining equipment and lost generation if the FGD system becomes inoperable. Fossil Materials and Repair - Program 87 p. 10

11 Weld Repair of Grade 91 Piping & Components (071850) Background, Objectives, and New Learnings Grade 91 steel is one of a family of creep-strength-enhanced ferritic steels (CSEF). This steel now is routinely installed in both fossil-fuel-fired and combined-cycle units. Recent in-service experience has demonstrated that cracking can occur in CSEF early in life. The reasons include improper heat treatment of welds and components; design or construction practices that result in local stress concentrations; local operating conditions that are unexpectedly severe due to thermal transients r the presence of system loading; and difficulties associated with dissimilar metal welds. Project Approach and Summary This project builds directly on the understanding developed in the life management work. R&D will establish key information on removal of damage and approaches for repair welding. Selected variables and weld processes will be investigated and test programs will link performance to details of how the repair was carried out. This is important because, in contrast to traditional low-alloy steels that are relatively "user friendly" for repairs, CSEF steels introduce an additional complication: the properties and performance of the base metal are critically dependent on the original composition and the full heat treatment history. This aspect is so important that concerns have arisen that the repairability of steels such as Grade 91 will be limited. Many possible variations are associated with making these repairs, including condition of the parent; degree of tempering (i.e., hardness); and level of creep damage present in the weld metal, heat-affected zone (HAZ), and parent. This project will address a number of key questions: What are the most appropriate methods for material removal, and what should be the extent of the excavation What welding process should be used What is the best method of filler metal selection and optimization of bead sequence and welding parameters Can welds be performed using temper bead welding followed by a minimum PWHT Benefits A recent EPRI project has successfully established the background technology necessary for approaches that ensure high-quality components are supplied and installed. In addition, this work delivered a life-management strategy that is both practical and effective in preventing in-service failures. However, large numbers of current components are susceptible to cracking. In the majority of cases, the defects will need to be repaired using fusion welding. The current project will examine key variables involved in repair decisions and quantify which of these variables has the greatest influence on subsequent performance. This knowledge will permit utilities to minimize the time and costs associated with making a repair while maximizing the potential that the repair will provide at least adequate in-service performance. Fossil Materials and Repair - Program 87 p. 11

12 Life Management of Boiler and Piping Components Fabricated from Grade 92 Steels (071851) Background, Objectives, and New Learnings Work to date on Grade 92 steel has demonstrated that this creep-strength-enhanced ferritic (CSEF) steel will be susceptible to many of the problems that have been found in Grade 91. Problems have been identified with incorrectly controlled heat treatment, inadequate quality assurance during fabrication and installation, and Type IV cracking in the heat-affected zone (HAZ) of welds. Additional challenges will significantly influence longerterm damage, including: Very-low-ductility creep failure of base metal samples has occurred, which significantly raises concerns over catastrophic fracture, and Issues associated with creep failure of welds. It appears that creep failure can occur in the weld metal, depending on the post-weld heat treatment conditions used. Project Approach and Summary This project will build directly on the understanding developed in the work performed to date studying the life management of Grade 91 steel. Specifically, work on Grade 92 steel will be undertaken to: Establish key information on how the composition and heat treatment of the parent affects microstructure, strength, and ductility; Establish links between microstructure and development of damage under service conditions; and Examine how key variables associated with weld manufacture influence creep life and in-service failure. The level of work performed will depend on the participation in the project. The following outline shows key potential issues that can be included. The details of the final scope will be established at the project initiation meeting with the sponsors. The work will be considered in two complementary tasks: Task 1: Parent Steel Issues In addition to heat treatment influences, possible metallurgical issues include N:Al ratio and variation of elements that will influence the presence and extent of ferrite. It is anticipated that at least two parent compositions will be selected, and the samples will be renormalized and then tempered. Potential variables include normalizing temperature, cooling rate, tempering temperature, and time. The tempering conditions will be selected to reflect normal tempering and then a range of over-tempers. For each condition, optical metallography and hardness testing will be performed. This will lead to a microstructural atlas and a tempering master curve, linking softening to thermal exposure. Selected samples also will be long-term aged to examine the effects of aging in the absence of applied stress and strain. Creep testing will be carried out on selected samples. The testing conditions will be used so that damage is representative of long-term service. Samples will be taken to failure and also interrupted at known life fractions so that the development of damage can be studied. Creep-tested parent samples available from previous work will be examined metallographically. Task 2: Weld Performance Thick section welds will be manufactured in the selected parent. It is expected that the welds will be manufactured using at least two different processes. For each process, potential variables include consumables, bead size, sequence, and post weld heat treatment. In each case, for all welds made, characterization will include optical metallography, electron microscopy, hardness testing, measurement of mechanical properties, assessment of creep behavior, quantification of damage development, and assessment of factors affecting fracture. Fossil Materials and Repair - Program 87 p. 12

13 Benefits A current EPRI project has successfully established the background technology necessary to underpin significant improvements in approaches for ensuring that high-quality Grade 91 steel components are supplied and installed. This project will deliver a practical life-management strategy for Grade 92 steel, which provides the basis for cost-effectively preventing in-service failures. Fossil Materials and Repair - Program 87 p. 13