Prediction Method of Tensile Properties and Fracture Toughness of Thermal Aged Cast Duplex Stainless Steel Piping

Abstract

Cast duplex stainless steels of CF8M and CF8 are used in major components because of their superior characteristics, such as corrosion resistance, weldability, and so on. However, these stainless steels are known to have tendency of thermal aging embrittlement after long term service. Therefore, the mechanical properties have been investigated using tensile test specimens and fracture toughness specimens aged at 300 to 450°C for up to 40,000 hours. From the results, the effects of thermal aging on the mechanical properties of these cast duplex stainless steels were identified. The true stress-true strain curve prediction method (TSS model) and fracture toughness prediction method (H3T model) after long term service were established. These prediction methods are used for the evaluation on the plant life management of nuclear power plants in Japan.

Benchmark analyses of probabilistic fracture mechanics for cast stainless steel pipe

“…It is well known that cast stainless steel (CASS) pipes are susceptible to thermal aging. Many researches have been involved in this issue and material data have been accumulated (Chopra, et al, 1987, 1992, 1994a, 1994b, Sakamoto, et al, 1994, Michaud, et al, 1994, Kawaguchi, 1997, 2005, Ligneau, et al, 2009, Faidy, 2010. Flaw acceptance rules of CASS pipes of the JSME rules on fitness-for-service (JSME ed., 2012) are based on elastic-plastic fracture mechanics method using Z-factor with the conservative assumption of high ferrite number and fully thermal aging condition (Koyama, et al , 1999 andKoyama, 2009).…”

Influence of thermal aging on cast stainless steels used in JAEA's nuclear reactor Fugen

“…The ability to predict the degree of toughness loss suffered during normal and extended reactor service life would be valuable when assessing the soundness of cast stainless steel reactor components. Therefore, models for predicting changes in the mechanical properties of cast stainless steel components due to thermal aging on the basis of an expanded database were established in previous studies [6,7]. However, to establish the toughness of the actual component in service in a reasonable time period, the aging process in the test material must be accelerated for the aging temperature range 300-400…”

Flaw evaluation of cast stainless steel pipe for revision of JSME rules on fitness for service

“…At the same time, applicability of a new fracture criterion for plastic collapse was verified for a shallow flaw. Second, the degradation model presented by Kawaguchi et al, 1997Kawaguchi et al, , 2005 was reinvestigated and a revision of the prediction method for S-S curve was made to improve the prediction accuracy of the curve. Third, the Z-factor for a pipe with an axial flaw by Kamaya et al 2016 was introduced and verified by comparison with FEA results.…”

“…(1) Material properties Two material data from the flat plate specimens' and two materials from Kawaguchi et al 2005 with fully aging condition were chosen. Table 7 shows the measured tensile properties and fracture toughness of each material.…”