Welding Grade P-91 and Other CSEF Alloys (Creep Strength Enhanced Ferritic)

The Canadian Welding Association (CWA) is organizing a seminar on welding grade P-91, P92 and other Chrome/Molly/Vanadium Alloys. These material types perform well at elevated temperatures and, as a result, have become more commonplace in power generation applications and in specific applications in refining industries. Special attention must be paid to materials selection and design aspects. The design and selection of welding consumables, welding techniques and pre and post-heating avoid issues such as cracking and even catastrophic failures of components. This seminar will bring greater awareness of what the issues are and provide some solutions on how these challenges may be solved.

CWB Group8260 Parkhill DriveMilton ON L9R 5V7

Date: March 25, 2015Time: 8:00 AM – 4:30 PMRegister at: www.cwa-acs.org/events

CWA SEM

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Grade 91 steel, also known as the modified 9Cr-1Mo-V steel, is widely used in the nuclear and fossil fuel power generation industries, due to its high creep strength and corrosion resistance. A detailed metallurgical microstructure analysis has been conducted on the heat-affected zone (HAZ) of Grade 91 steel pipe welds under three conditions: the as-welded (AW), after a typical post-weld heat-treatment (PWHT, 760°C for 2 hours), and after creep testing (CT). Creep property of the welds has been measured at 650 °C with a stress level of 70 MPa. A type IV creep failure of the weld is identified in the fine grain heat-affected zone (FGHAZ) close to the inter-critical heat-affected zone (ICHAZ). The grain growth and re-distribution of the M23C6 carbides after PWHT are observed by electron back-scattered diffraction (EBSD). The majority of the identified Cr-rich M23C6-type carbides distribute on the tempered martensite or ferrite grain boundaries in FGHAZ. After creep testing, the shear deformation and recrystallization of the ferrite grains in FGHAZ is observed in the creep-damaged area.

Author biographies:Yiyu (Jason) Wang is a PhD candidate and Dr. Leijun Li is a professor in the Department of Chemical and Materials Engineering, University of Alberta. Their research focuses on basic and applied research in microstructure characterization and properties evaluation.

Dr. Li has supervised research students in fusion and solid-state welding, and laser and plasma-enabled additive manufacturing technologies. Dr. Li serves as Principal Reviewer for the Welding Journal and Key Reader for the Metallurgical and Materials Transactions. He is a Fellow of the American Society of Materials and a past chair of the Joining Critical Technologies Committee of ASM.

Microstructural Evolution During Creep of Grade 91 Steel Pipe Weld Leijun Li, Yiyu Wang Department of Chemical and Materials Engineering University of Alberta

Leijun Li

Yiyu Wang

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Procurement of standard, commodity type welding consumables is rather straightforward. However, when weld metal toughness, properties after post weld heat treatment, specified hardness, or other out-of-the-ordinary requirements are needed, communication between the purchaser and supplier becomes critical. In cases where the lowest bid rules, sole sourcing is difficult, or when merely stating the AWS filler metal specification and classification is not adequate to obtain exactly what is needed, frustration can result, deliveries delayed, or inadequate products may be purchased. These factors are especially important where the creep strength-enhanced ferritic steels such as Grade 91 are involved.

Over the last decade, it has become apparent that wire processing is critical to success and defect free welding, especially where automated or orbital gas tungsten arc welding (GTAW) is used. The composition of many alloys, especially the creep strength-enhanced ferritic weld metals are lean on deoxidizing elements because of their detrimental effect on elevated temperature creep strength. Aluminum, silicon, titanium and manganese are traditionally used to deoxidize or “clean” the molten weld pool and assist the escape of gases, thus reducing or eliminating porosity. Any foreign material on or in the wire can jeopardize the cleanliness of the weld. Manual GTAW typically can tolerate more contaminants because the weld pool is somewhat more turbulent and assists the evolution of gases or other contaminants. Remedies and practical examples will be discussed.

Author Biography:Bill Newell is involved in welding engineering applications and consulting in the nuclear and fossil electric power and heavy industrial arenas for over 40 years, both domestic and internationally. Bill graduated from The Ohio State University with a B.S. in Welding Engineering and was also awarded a diploma as an International Welding Engineer by the International Institute of Welding. He holds Professional Engineer licenses in Ohio, North Carolina, South Carolina, Tennessee and Texas, plus Alberta, Canada and holds four patents on welding related technology. Bill is a member on national and international code bodies, a Life Member of the American Welding Society, and a member of AWS A5N, Vice Chair of AWS D10 and Chairman of D10C and D10I; a Member on ISO/TC 44, International Committee on Welding and Allied Processes, plus a member of ASME Standards Committee IX – Welding and Brazing Qualifications, ASME Post Construction Issues – Subcommittee on Materials and Repair, Chair of ASME SCII/IX Subgroup on Strength of Weldments, and a member on the ASME SCII Task Group on CreepStrength-Enhanced Ferritic Steels. He is the President of W. F. Newell & Associates, Inc., a consulting firm that specializes in welding engineering and Co-Founder/Vice President – Engineering of Euroweld, Ltd., a supplier of specialty welding consumables and technology.

Weld Metal Procurement for Grade 91 Welding Bill Newell, P. Eng. Euroweld

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Loss of creep resistance in post-weld P91 alloy occurs mainly due to the change in grain size as well as residual stress from the welding process. Post-weld heat treatments can partially improve the creep life, however it remains important to determine the remaining useful life (RUL) particularly in the heat-affected zone under actual service operating conditions. Most creep damage models have focused on the short term creep response at relatively high temperature and stress, where the deformation mechanism is governed by power-law creep (PLC). However, under the actual service temperature and stress (i.e. about half of the melting point) grain-boundary sliding (GBS) is the dominant deformation mechanism that contributes to the creep life. In this paper, a validated deformation mechanisms map (DMM) using low temperature creep strain accommodation processes i.e. GBS, is developed for P91 alloy that predicts the creep rates over a wide range of temperature and stress including those arising under the actual service conditions. These creep rates are further utilized in a microstructure-based creep damage model for accurate life prediction. A 3D transient computational welding mechanics (CWM) modeling of a pipe in a super-critical water loop, predicts the thermal, microstructure and stress state from welding. It also determines the coarse and fine grain heat affected zone (CGHAZ & FGHAZ). The CWM results are coupled with physics-based creep damage modeling to predict the RUL under the actual service conditions considering the welding residual stress and microstructure states.

Author Biography:Mahyar Asadi received his engineering degree in Material Science and Engineering (1999), and his Master’s degree in Material Science and Engineering, majoring in Welding (2001). He started his career in the automotive industry’s inspection and quality control including a promotion to manager of the engineering department. He was working for many years in the automotive sector before returning to academia (2007) for his PhD in Mechanical and Aerospace Engineering, specializing in Computational Welding Mechanics supervised by the distinguished research professor, Dr. John Goldak. After graduation (2011), he was granted a prestigious Canadian NSERC-PDF award and started post-doctoral position working jointly at the University of Ottawa and at the University of British Colombia in fracture mechanics, creep and fatigue analysis in close collaboration with industry. Together with Dr. John Goldak, he has developed and offers his signature course on welding models and computational welding mechanics at the university graduate level. He is also licensed by the Province of Ontario for practicing as a P. Eng.

A Coupled Computational Welding Mechanics and Physics-Based Damage Modeling for Prediction of Remaining Useful life in Welded P91 Alloy Dr. Mahyar Asadi and Dr. Jun ZhaoLife Prediction Technologies Inc.Leijun Li, Ph.D., FASMUniversity of Alberta

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Experts are suggesting that roughly 90% of material anomalies and premature weld failures in Grade 91 CSEF steels can be attributed to improper Pre and Post Weld Heat Treatment. While the benefits of CSEF steels are well documented and growing in popularity, welding processes and skill sets become more critical than on steels with lower chrome content, and sensitivity to PWHT becomes more significant than ever before.

As an industry leader and innovator in Advanced Industrial Heat Treatment Services, Superheat FGH will attempt to shed light on some of the pitfalls of traditional field service practices and shortcomings of existing weld procedures, code guidelines and specifications that, in many cases, have been established with more forgiving materials in mind.

Topics discussed will include significance of heat treatment in achieving material properties; practical methods of heat treatment in use today; latitude given service providers through non-specific procedural guidelines; insight to implementation pressures, and new technologies available to enhance Quality Control, Process Quality Management and enhanced Oversight capabilities.

Influence of Pre and Post-Weld Heat Treatment on CSEF Steels Gary G. Lewis Superheat FGH Mooresville

Creep strength-enhanced ferritic steels such as 9Cr-1Mo-0.25V grade is used worldwide in power industries as well as petroleum refining and related industries. Today’s combined-cycle power plants and advanced coal-fired plants operate at more demanding operating conditions such as high super heater temperatures, and undergo rigorous cycling (in some countries).

9Cr-1Mo-0.25V alloy, popularly known as Grade-91 steel, is extremely popular amongst designers. Due to higher allowable design stress as well as higher creep strength, such materials offer significant savings in material thicknesses for front-end design of critical boiler tubing and thick-walled piping and other components. Components with thinner wall produce substantially reduced thermal stresses while cycling and thereby improve service life.

The lessons learned thus far with P(T)91 weldments have truly demonstrated that this steel is quite different and requires significantly more detailed attention than the P(T)22 and lesser grade low alloy steel materials used in the utility industry. Grade 91 alloys require a very thorough design analysis, materials and welding consumable selection, a very controlled welding and PWHT requirements to sustain safely and reliably in service.

Grade -91 steel delivers the best mechanical and high temperature creep properties when it’s fabricated with the utmost quality control. In the subsequent pages/presentations the author has tried to develop a detailed roadmap for good welding and fabrication practices for this alloy, for demanding and cyclic services in today’s power industry.

Author’s Biography:Pradip Goswami has over 30 years of versatile experience as a Welding and Metallurgical Engineering Specialist in Power Generation, Oil Refining, Oil and Gas Production, Petrochemical Industries. He has a strong Fundamentals in Welding, Metallurgical Engineering with welding experiences in Cr-Mo-V steels (refinery hydrocrackers), T-91/P-91 Steels, Duplex and Super Duplex Stainless Steels, Super Austenitic Stainless Steels (254SMO). He has a number of publications related to the above alloys in international conferences/journals. The author is quite an active participant and respondent to technical queries in various Professional internet forums, LinkedIn, Eng-Tips, Materials-Welding Group.

Modified 9Cr-1Mo-V (Grade-91) Steel, A Comprehensive Review of Design and Fabrication and Best Industry Practices. Pradip Goswami, P. Eng., IWE Welding & Metallurgical Specialist

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The Electric Power Research Institute (EPRI) has been actively researching the integrity of alternative well-engineered cold weld repair (i.e. no post weld heat treatment, PWHT) and low PWHT weld repair options for Grade 91 steel components. This research has resulted in the incorporation of Welding Method 6 for tube to tube weld repairs into the National Board Inspection Code (NBIC), Part 3 - Repairs and Alterations, proposal of a new Welding Supplement to the NBIC, Part 3 - Repairs and Alterations. It has ignited recent discussion within the American Society of Mechanical Engineers Boiler and Pressure Vessel (ASME B&PV) Code regarding the relaxation of the current minimum allowable PWHT of 1350°F (730°C) to 1250°F (675°C) for new construction of Grade 91 steel weldments. The value of alternative weld repair procedures will be detailed in the context of destructive evaluation testing and application considerations which are discussed in a recently released EPRI Report (3002003833) Best Practice Guideline for Well-Engineered Weld Repair of Grade 91 Steel.

Alternative Well-Engineered Weld Repair Options for Grade 91 Steel John A. Siefert and Jonathan D. Parker Electric Power Research Institute (EPRI)

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Registration: www.cwa-acs.org/eventsMember: $425Nonmember: $525Student: $150(lunch is included)

Seminar Cancellation Policy: The seminar registration fee, less 25% per person, will be refunded if cancellation is made in writing on or before March 12, 2015. There will be no refund for cancellation after this date.

CEU Credits: This seminar qualifies for .5 CEU’s.

Agenda:

8:00 – 9:00 Breakfast and Registrations9:00 – 9:10 Opening remarks and Introductions9:10 – 10:00 Yiyu (Jason) Wang and Dr. Leijun Li - Microstructural Evolution During Creep of Grade 91 Steel Pipe Weld10:00 - 10:20 Morning Break10:20 – 11:10 Bill Newell - Weld Metal Procurement for Grade 91 Welding 11:10 – 12:00 Pradip Goswami - Modified 9Cr-1Mo-V Steel, A Comprehensive Review of Design and Fabrication and Best Industry Practices12:00 – 1:00 Lunch (included)1:00 – 1:50 Gary Lewis - Influence of Pre and Post Weld Heat Treatment on CSEF Steels1:50 – 2:40 John A. Siefert - Alternative Well-Engineered Weld Repair Options for Grade 91 Steel2:40 – 3:00 Afternoon Break3:00 – 3:50 Mahyar Asadi - A Coupled Computational Welding Mechanics and Physics-Based Damage Modeling for Prediction of Remaining Useful life in Welded P91 Alloy3:50 – 4:20 Roundtable discussion with Presenters4:20 – 4:30 Wrap up

Location:CWB Group8260 Parkhill DriveMilton ON L9R 5V7

Date: March 25, 2015Time: 8:00 AM – 4:30 PM

CWA SEM

INAR

Should you require Hotel accommodations, please contact Holiday Inn 2750 High Point Dr. Milton, ON L9T 5G5 Telephone: (905) 876-4955 and request the preferred CWB Group rate of $115 per night. Taxes are extra. The Holiday Inn is located a short 5 minute walk from the CWB Group facility.