The high-temperature performance of nickel-based transition joints

Parker, J.D.; Stratford, Gavin C.

doi:10.1016/s0921-5093(00)01375-7

Cited by 22 publications

(27 citation statements)

References 8 publications

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“…Numerous investigations have been conducted of both service and laboratory-induced failures of DMWs 1,14,15,16,18,20,32,33,34,35,36,37,42,43,44,45,46,47,48,49,50,51,52,53,54 and the failure mechanism is now largely understood. There are generally four factors that contribute to premature failure of DMWs during high temperature service:…”

Section: Failure Mechanism Of Dmwsmentioning

confidence: 99%

“…For DMWs made with stainless steel filler metals, cracking typically occurs along the prior austenite grain boundaries (PAGBs) in the ferritic HAZ at a location of about one or two grains away from the fusion line. Figure 21 shows examples that highlight various features of DMW failures 15,35,55 . From a macroscopic view, failures occur at the fusion line on the ferritic side of the joint (Figure 21a).…”

Section: Failure Mechanism Of Dmwsmentioning

confidence: 99%

“…Schematic illustration of variation in composition in the as-welded and PWHT condition for a weld between 2.25Cr-1Mo steel and 309L stainless steel. 12 It is now recognized 15,16,20,34,35,36 that two distinct carbide morphologies will evolve in DMWs during aging. Examples of these are shown in Figure 16.…”

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confidence: 99%

“…16 c) Type II carbides that form as a wide band associated with the martensite region. 17 As discussed in more detail in the next section, examinations of service and laboratory induced failures 15,16,20,34,35,36,37 have shown that premature failure of DMWs made with Ni base filler metals is associated with formation of creep cavities around the Type I carbides. Thus, the nucleation, growth and morphological changes that occur in Type I carbides have received considerable attention, and several kinetic studies have been reported 17,38,39 .…”

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Review of Dissimilar Metal Welding for the NGNP Helical-Coil Steam Generator

DuPont¹

2010

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EXECUTIVE SUMMARYThe U.S. Department of Energy (DOE) is currently funding research and development of a new high-temperature gas-cooled reactor (HTGR) that is capable of providing high-temperature process heat for industry. The steam generator of the HTGR will consist of an evaporator-economizer section in the lower portion and a finishing superheater section in the upper portion. Alloy 800H is expected to be used for the superheater section, and 2.25Cr-1Mo steel is expected to be used for the evaporator-economizer section. Dissimilar metal welds (DMW) will be needed to join these two materials. It is well known that failure of DMWs can occur well below the expected creep life of either base metal and well below the design life of the plant. The failure time depends on a wide range of factors related to service conditions, welding parameters, and alloys involved in the DMW. The overall objective of this report is to review factors associated with premature failure of DMWs operating at elevated temperatures and identify methods for extending the life of the 2.25Cr-1Mo steel-to-alloy 800H welds required in the new HTGR. Information is provided on a variety of topics pertinent to DMW failures, including microstructural evolution, failure mechanisms, creep rupture properties, aging behavior, remaining-life estimation techniques, effect of environment on creep rupture properties, best practices, and research in progress to improve DMW performance.The microstructure of DMWs in the as-welded condition consists of a sharp chemical concentration gradient across the fusion line that separates the ferritic and austenitic alloys. Upon cooling from the weld thermal cycle, a band of martensite forms within this concentration gradient due to high hardenability and the relatively rapid cooling rates associated with welding. Upon aging, during post-weld heat treatment (PWHT), and/or during high-temperature service, C diffuses down the chemical potential gradient from the ferritic 2.25Cr-1Mo steel toward the austenitic alloy. This can lead to formation of a soft C denuded zone near the interface on the ferritic steel, and nucleation and growth of carbides on the austenitic side that are associated with very high hardness. These large differences in microstructure and hardness occur over very short distances across the fusion line (~ 50-100 m). A band of carbides also forms along the fusion line in the ferritic side of the joint. The difference in hardness across the fusion line increases with increasing aging time due to nucleation and growth of the interfacial carbides.Premature failure of DMWs is generally attributed to several primary factors, including: the sharp change in microstructure and mechanical properties across the fusion line, the large difference in coefficient of thermal expansion (CTE) between the ferritic and austenitic alloys, formation of interfacial carbides that lead to creep cavity formation, and preferential oxidation of the ferritic steel near the fusion line. In general, the large gradient in mechanical...

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Section: Failure Mechanism Of Dmwsmentioning

confidence: 99%

Section: Failure Mechanism Of Dmwsmentioning

confidence: 99%

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Review of Dissimilar Metal Welding for the NGNP Helical-Coil Steam Generator

DuPont¹

2010

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“…81 The deleterious effects of PWHT cited to date were the result of data generated from higher stress tests with failure mechanisms that were not representative of service failures. More recent results of well-controlled studies have shown the use of a PWHT does not significantly impact the creep life, 82,83 having a minor effect on carbide size and distribution compared to subsequent 84,85 Since the PWHT provides relief of residual stresses that form in the DMW during welding, it provides a net benefit.…”

Section: Idaho National Laboratory Next Generation Nuclear Plant Steamentioning

confidence: 99%

Next Generation Nuclear Plant Steam Generator and Intermediate Heat Exchanger Materials Research and Development Plan

Wright¹

2010

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SUMMARYThe U.S. Department of Energy (DOE) has selected the high temperature gas-cooled reactor (HTGR) design for the Next Generation Nuclear Plant (NGNP) Project. The NGNP will demonstrate the use of nuclear power for process heat, hydrogen and electricity production. The reactor will be graphite moderated with helium as the primary coolant. Final design features have not been determined and the reactor may be either prismatic or pebble-bed. It will use low-enriched uranium tri-isotopic (TRISO)-coated fuel. It is likely to have an outlet gas temperature of 750°C with a steam generator (SG) and a design service life of 60 years. The plant size, reactor thermal power, and core configuration will ensure passive decay heat removal without fuel damage or radioactive material releases during accidents. Follow-on HTGRs may have outlet temperatures up to 950°C and will incorporate a gas-to-gas intermediate heat exchanger (IHX).The revisions incorporated into this research and development (R&D) plan reflect technical issues associated with the SG that were not considered for application in the NGNP when the plan was initially developed. This R&D plan describes work that is necessary for the first-of-a-kind NGNP and follow-on reactors that might have different design parameters. The fundamental challenge for NGNP is to achieve a significant advancement in nuclear technology while setting the stage for an economically viable deployment of the new technology in the commercial sector soon after 2020.Alloy 800H is approved in the American Society of Mechanical Engineers (ASME) Codes for nuclear applications up to 760°C with a maximum design life of 300,000 h. An SG for 750°C service may require longer service life than the currently allowed 300,000 h. Testing and constitutive model development to support extension of the allowable temperature for this alloy and the allowable lifetime to 500,000 h (~60 years with 95% of availability) are included in this plan. Due to the high design temperature, the requirements of materials for the IHX are among the most demanding. In addition to the SG, this R&D plan focuses on tasks that will be required to generate sufficient understanding of materials for successful design and operation of the NGNP IHX for which the prime candidate material is Alloy 617. Requirements for other core internals (e.g., the core barrel or control rod sleeves) are described in less detail in Appendix C.A number of solid solution strengthened nickel-and iron-based alloys have been considered for application in the NGNP. The primary candidates were Alloy 617, Alloy 230, Alloy 800H and Alloy X. Based on the technical maturity, availability in required product forms, experience base, and high temperature mechanical properties, all of the pre-conceptual design studies prepared by potential reactor vendors have specified Alloy 617 as the material of choice for heat exchangers. Also a draft ASME Code case for Alloy 617 was developed previously. Although action was suspended before the Draft Alloy 617 Code Case was ac...

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