Session: MF-01-01 The Noel O'Dowd Memorial Symposium on Fracture: Application of Fracture Mechanics in Failure Assessment

Paper Number: 152103

152103 - Reference Stress Based J Solution for Pipe With Circumferential Surface Flaw and Its Application to Pipe Fracture Test Under Cyclic Loading 

Abstract: 

Usually, the fatigue crack growth calculation is performed using stress intensity factor K on the assumption of the small scale yielding condition. Since the K-calculation is repeated corresponding to the number of cyclic loadings, simplified K-solutions are used, which have been incorporated into the Codes and Standards, like the JSME Rules on Fitness for Service (FFS) in Japan, or the ASME Section XI in the US. However, beyond the small scale yielding condition, the fatigue crack growth calculation procedure has not been established. Therefore, the FDF-III subcommittee of the Japan Welding Engineering Society has been preparing a simplified J-integral calculation method for a semi-elliptical surface cracked plate and a pipe with an axial flaw or a circumferential flaw in order to finally incorporate into the Codes and Standards for fatigue crack growth evaluation under large cyclic loading conditions beyond the small scale yielding condition. These simplified J solutions are based on the reference stress method adopted in the JSME Rules on FFS, API 579-1/ASME FFS-1 - Fitness-For-Service in the US, R6 in UK, and RCC-M/RSE-M in France. The authors were in charge of preparing a simplified J solution for a pipe with a circumferential semi-elliptical flaw. For this purpose, FE analyses were carried out for 10 cases with the parameters of the crack depth/thickness, a/t, and aspect ratio, a/c, and J values at the deepest point and the surface point were obtained. For the reference stress based J, two fitting parameters α and β, were introduced for the small scale yielding correction term according to the level of σref/σy, referring to the R6 with the small scale yielding correction. The parameters were adjusted so as to approach to the J values by FEA. In order to confirm the applicability of the simplified J solution, the crack growth behavior of the cyclic load test using a pipe with a circumferential surface flaw conducted by other researchers in the preparatory committee of the FDF-III subcommittee was predicted. For the fatigue crack growth analysis, ΔJ by the simplified J solution was calculated using the fatigue crack growth rate obtained by converting the ferritic fatigue crack growth rate in air prescribed in the JSME Rules on FFS to ΔJ basis. The predicted fatigue crack growth behavior was compared with the experimental results. The simplified J solution was currently formulated at the deepest point. The simplified J solution at the surface point will be developed in the next step.                                                                                                                                                                                                                                                                                                                                                    

Presenting Author: Kiminobu Hojo Mitsubishi Heavy Industries Ltd

Presenting Author Biography: Kiminobu Hojo joined Mitsubishi Heavy Industries I in 1983 and now Chief Staff Manager, Managing Expert. He studied local approach at Kernforshungszentrum Karsruhe (KfK) in Germany in 1993 and he has been engaged on structural integrity issues of nuclear power plants like LBB of cast stainless steel and low alloy steel pipes, PTS, thermal aging of CASS, thermal stratification, high cycle thermal fatigue. Now his major interest is constraint effect on fracture.
He is a member of subgroups and a chairman of Flaw Evaluation Working Group of JSME Codes and Standards Committee . He is also a member of working groups and a subgroup and Standard Committee of ASME Sec. XI.

Authors:

Kiminobu Hojo Mitsubishi Heavy Industries Ltd
Satoshi Kumagai Mitsubishi Heavy Industries