Generation of surface degraded layer on austenitic stainless steel piping exposed to flowing sodium in a loop: intercomparison of long-term exposure data

Japan Nuclear Energy Safety Organization (JNES) has been carrying out the research program entitled “Nondestructive Inspection Technologies for the Cast Stainless Steel Piping” since 2009FY to comprehend the unique ultrasonic wave propagation in the Cast Austenitic Stainless Steel (CASS) and to confirm detection and sizing capability for cracks in the material by currently available ultrasonic testing techniques. The research is also intended to provide inspection staff with the fundamental information of ultrasonic wave propagation in CASS, for educational purpose. In this research program, specimens whose material, size, dimension and welding method are identical to the main coolant piping system in Japanese pressurized water reactors (PWRs) are examined. Results from the study on the capability for inspection of CASS and the unique wave propagation phenomena such as beam skewing are discussed in this paper.

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Prediction of Properties in Type 347 Austenitic Stainless Steel after Long-Term Service at High Temperatures

THERMEC 2006 - Materials Science Forum ◽

10.4028/0-87849-428-6.4920 ◽

2007 ◽

pp. 4920-4925

Author(s):

Jan Olof Nilsson

Keyword(s):

Stainless Steel ◽

Austenitic Stainless Steel ◽

High Temperatures ◽

Prediction Of Properties

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Probabilistic Models of Reliability of Cast Austenitic Stainless Steel Piping

ASME 2011 Pressure Vessels and Piping Conference: Volume 6, Parts A and B ◽

10.1115/pvp2011-57270 ◽

2011 ◽

Cited By ~ 1

Author(s):

Haiyang Qian ◽

David Harris ◽

Timothy J. Griesbach

Keyword(s):

Fracture Toughness ◽

Stainless Steel ◽

Austenitic Stainless Steel ◽

Tensile Properties ◽

Nuclear Power ◽

Power Plants ◽

Probabilistic Models ◽

Probabilistic Approach ◽

Delta Ferrite ◽

Steel Piping

Thermal embrittlement of cast austenitic stainless steel piping is of growing concern as nuclear power plants age. The difficulty of inspecting these components adds to the concerns regarding their reliability, and an added concern is the presence of known defects introduced during the casting fabrication process. The possible presence of defects and difficulty of inspection complicate the development of programs to manage the risk contributed by these embrittled components. Much work has been done in the past to characterize changes in tensile properties and fracture toughness as functions of time, temperature, composition, and delta ferrite content, but this work has shown a great deal of scatter in relationships between the important variables. The scatter in material correlations, difficulty of inspection and presence of initial defects calls for a probabilistic approach to the problem. The purpose of this study is to describe a probabilistic fracture mechanics analysis of the maximum allowable flaw sizes in cast austenitic stainless steel piping in commercial power reactors. Attention is focused on fully embrittled CF8M material, and the probability of failure for a given crack size, load and composition is predicted considering scatter in tensile properties and fracture toughness (fracture toughness is expressed as a crack growth resistance relation in terms of J-Δa). Random loads can also be included in the analysis, with results generated by Monte Carlo simulation. This paper presents preliminary results for CF8M to demonstrate the sensitivity of key input variables. The outcome of this study is the flaw sizes (length and depth) that will fail with a given probability when a given load is applied.

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Development of New Design Fatigue Curves in Japan: Discussion of Fatigue Crack Growth Based on Fatigue Test Data With Large Scale Piping

Volume 3: Design and Analysis ◽

10.1115/pvp2019-93272 ◽

2019 ◽

Cited By ~ 1

Author(s):

Masaru Bodai ◽

Yuichi Fukuta ◽

Seiji Asada ◽

Kentaro Hayashi

Keyword(s):

Stainless Steel ◽

Fatigue Crack ◽

Austenitic Stainless Steel ◽

Crack Growth ◽

Large Scale ◽

Fatigue Tests ◽

Surface Finishing ◽

Mean Stress ◽

Best Fit ◽

Steel Piping

Abstract In order to develop new design fatigue curves for carbon steels & low alloy steels and austenitic stainless steels and a new design fatigue evaluation method that are rational and have clear design basis, Design Fatigue Curve (DFC) Phase 1 subcommittee and Phase 2 subcommittee were established in the Atomic Energy Research Committee in the Japan Welding Engineering Society. The study on design fatigue curves was actively performed in the subcommittees. In the subcommittees, domestic and foreign fatigue data of small test specimens in air were collected and a comprehensive fatigue database was constructed. Using this fatigue database, the accurate best-fit curves of carbon steels & low alloy steels and austenitic stainless steels were developed by applying tensile strength to a parameter of the curve. Regarding design factors on design fatigue curves, data scatter, mean stress correction, surface finishing effect, size effect and variable loading effect were investigated and each design factor was decided to be individually considered on the design fatigue curves. A Japanese utility project performed large scale fatigue tests using austenitic stainless steel piping and low-alloy-steel flat plates as well as fatigue tests using small specimens to obtain not only basic data but also fatigue data of mean stress effect and surface finishing effect. Those test results were provided to the subcommittee and utilized the above studies. In the last PVP Conference, the large scale fatigue tests using austenitic stainless steel piping were discussed for the best-fit curve of austenitic stainless steel (PVP2018-84436). In this paper, further studies are performed based on fatigue crack growth of the large scale fatigue tests using austenitic stainless steel piping. From the obtained crack growth data of the tested piping, the number of cycles at 3-mm-deep crack depth and through-wall crack of piping compares with the best-fit curve developed by the DFC1 subcommittee with considering the confidence lower bounds to survey the fatigue life of piping, and size effect for fatigue lives is discussed. The relations between the fatigue crack growths and the number of cycles and the aspect ratios are surveyed including mean stress effect.

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