Session: OAC-06-03 Continued Safe Operation of Existing Assets - 3

Paper Number: 105293

105293 - Multi-Axial Stress Creep Consumption Part I; Testing and Validation of Ex-Service 347ss 

Unusual cracking damage was found in 347SS flange neck operated at 520 deg.C. In previous report presented in PVP2019-9304, it was concluded that the cracking was due to creep damage from FEM analysis using isochronous curve based on API 579/ASME FFS-1. In this paper, destructive testing and remaining life assessment of the ex-service flange, installed after the cracking problem and operated for 4 years, are conducted to validate the analysis. Factors affecting remaining life assessment through destructive testing, including impact of multiaxial stress condition on the assessment and creep threshold temperatures, are discussed.

From creep testing of samples taken from various locations, the sample from the flange neck shows shortest remaining life, that is consistent with the previous analysis. Omega testing, as well as microstructural observations, revealed life consumption of 10 to 20% after 4 years operation, close to the remaining life by the analysis assuming average creep strength. Remaining life is also assessed using Larson Miller Parameter curve obtained from destructive testing data with reference to API 579/ASME FFS-1 and WRC541, resulting in much longer remaining life, compared to that from Omega testing. From comparison of estimated remaining lives under uniaxial stress state and multiaxial stress condition, differences of remaining lives are largely attributed to effects of multiaxial stress condition in each method. Detail of multiaxial stress consideration in the assessment is further discussed.

This study, as well as the previous analysis, shows creep damage can be significant in 100,000 to 200,000Hrs, at temperature around 520Deg.C, that is slightly lower than creep threshold temperature of TP347SS in API 579/ASME FFS-1, 538Deg.C. Detail creep data analysis using Omega method shows that, when using equivalent stress, apparent rupture stress is reduced in multiaxial stress state compared to that in uniaxial stress sate. It can be lower than elastic allowable stress at given temperature below creep threshold temperature, which means reduction of creep threshold temperatures. Gap between creep threshold temperatures by API 579/ASME FFS-1 and by analysis under multiaxial stress state is most significant in TP347SS and also observed in other materials including TP321SS. Appropriate creep threshold temperatures under multiaxial stress state for each material are further discussed in this paper. This paper is part 1 of 2.

Presenting Author: Teppei Suzuki Idemitsu Kosan Co., Ltd.

Presenting Author Biography: Dr. Teppei Suzuki received ph.D in Material Processing from Tohoku University. From 2003, he has been a Materials and Corrosion Engineer in Idemitsu Kosan about 20 years. Currently he is a Chief Engineering Associate in Technology and Engineering Center, working for materials and corrosion issues, fixed equipment reliability management and fitness for service assessment for refining and petrochemical plants in Idemitsu group. He has been an active member of AMPP Oil and Gas - Downstream standard committee and the Japanese Welding Engineering Society.

Authors:

Teppei Suzuki Idemitsu Kosan Co., Ltd.
Yoichi Ishizaki Idemitsu Kosan Co., Ltd.