Prediction of Type IV creep failure of a seam-welded mod. 9Cr-1Mo elbow based on microscopic damage simulation

Fukahori, Takuya; Tokiyoshi, Takumi; Igari, Toshihide; Chuman, Yasuharu; Komai, Nobuyoshi

doi:10.1080/09603409.2017.1289621

Cited by 6 publications

(10 citation statements)

References 17 publications

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“…According to the grain-boundary-resistance modeling simulation results by Fukahori et al (2013Fukahori et al ( , 2017, micro-cracks initiate by the coalescence of creep cavities when the creep cavity density reaches 4,000/mm 2 . Based on this result, the critical value of creep damage variable D cr is defined as below:…”

Section: Definition Of Creep Damagementioning

confidence: 99%

Creep damage analysis of simulated-HAZ notched bar specimens of modified 9Cr-1Mo steel

Honda

Fukahori

Igari

et al. 2017

Mechanical Engineering Journal

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From the standpoint of evaluating Type IV creep damage in the fine-grained heat affected zones (FGHAZ) of welded joints, an analysis method combining continuum damage mechanics (CDM) and a cavity nucleation model is proposed and applied to the creep testing of simulated-FGHAZ notched bars of mod. 9Cr-1Mo steel at 650℃. The Perrin-Hayhurst CDM model is adopted, which considers both softening by precipitate coarsening and damage by creep cavities. For the cavity nucleation model, a proposal by Gonzalez and Cocks is employed, which considers the randomness of grain-boundary-facet orientations in a polycrystalline material and gives a nucleation rate that is a function of the creep strain rate and a tri-axiality factor. The critical value of the damage parameter, corresponding to the initiation of micro cracks due to the coalescence of creep cavities, is expressed in terms of a critical value of the number density of creep cavities as determined from grain-boundary-resistance model simulations by the present authors. Creep rupture experiments have been conducted for circumferentially notched bar specimens with two kinds of notch acuities. The applicability of the combined CDM and cavity nucleation model is demonstrated by comparing the distribution of creep cavities observed experimentally with the simulation results. The final rupture life of the circumferentially notched bar specimens was also predicted to within a factor of two.

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Section: Definition Of Creep Damagementioning

confidence: 99%

Creep damage analysis of simulated-HAZ notched bar specimens of modified 9Cr-1Mo steel

Honda

Fukahori

Igari

et al. 2017

Mechanical Engineering Journal

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“…This number 40000 is derived from the reference [19], in which foursquare shape with an averaged grain size of 5μm is assumed.…”

Section: Void Mechanics and Damage Models For Fghazmentioning

confidence: 99%

“…Critical number density of creep void 4000/mm 2 was determined based on the previous works by the authors. In the reference [19], we carried out a simulation based on random-fracture-resistance model of grain boundaries to predict time-history of creep void density distribution in mod.9Cr-1Mo steel welds. We compared the obtained results with observed results [11] for through-thickness distribution of voids and cracks, in which FGHAZ in the other side of ruptured FGHAZ was observed.…”

Section: Void Mechanics and Damage Models For Fghazmentioning

confidence: 99%

“…Fukahori et al [18,19] carried out damage simulations using a random-fracture-resistance model of grain boundaries to predict the creep void density distribution of large uniaxial welded joints, and predicted final rupture life using a damage mechanics concept. By comparing the observed creep void density and simulation results, they identified a critical value of the creep void density corresponding to micro-crack initiation.…”

Section: Introductionmentioning

confidence: 99%

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Creep damage analysis of mod.9Cr-1Mo steel welds considering void mechanics modeling

Honda

Fukahori

Tokiyoshi

et al. 2021

International Journal of Pressure Vessels and Piping

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“…The critical number density (Nc) of the grain-sized cavities for Type IV failure in P91 ferritic steel has been identified by Igari et al [29] and Fukahori et al [30] to be Nc = 40,000/mm 2 based on the measurement of the average grain size in P91 FGHAZ. Following our previous work [8], we do not further consider the complexity of the effect of cavitation on the creep behavior of HAZ but track and store the ratio N/Nc as a state variable to provide an indication of damage evolution in the HAZ, while a different form of damage accumulates at the interface (considered in the next sub-section) which leads to crack initiation and propagation along the interface.…”

Section: Base Metal and Filler Metal(power-law)mentioning

confidence: 99%

Effect of weld angle on the creep rupture life of ferritic/austenitic dissimilar weld interfaces under remote mode I fracture

Elmukashfi

Fukahori

et al. 2019

Engineering Fracture Mechanics

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Dissimilar metal welded structures (DMWs) used extensively in conventional and nuclear power plants can suffer from in-service failures at the dissimilar interface with a much reduced life compared to similar metal weld counterparts at the same operating stress and temperature. This paper evaluates the effect of weld angle on the interface creep failure mode of two-dimensional DMW plates consisting of a ferritic steel P91 and an Inconel 82 filler metal within a finite element (FE) framework. A physical cavity growth damage zone model is developed to describe the damage accumulation at the interface, which naturally takes into account the local mode mixity. The material parameters are calibrated against standard 90 o weld creep rupture data and used to predict the rupture life of DMWs with a range of axial loads and reduced weld angles (75 o , 60 o , 45 o and 30 o). The predicted results match reasonably well with the limited interface failure data for a 45 o weld angle. This work also provides additional evidence and insights regarding the improvement of interface creep rupture life of DMWs in power plant pipelines, in particular: (1) Compared with a 45 o weld angle, a 60 o weld angle is more detrimental to the creep life and should be avoided in actual components-on the contrary, damage tolerance can be promoted by designing and adopting weld angles smaller than 45 o , which can have lives exceeding that of standard 90 o welded components; (2) A weld interface with alternating weld angles/paths is expected to enable a greater fraction of the creep rupture life to be taken up with crack propagation compared with a flat weld interface, which also increases the probability of damage detection; (3) A fully constrained boundary condition is beneficial to the creep rupture life compared with a free boundary condition; (4) For weld angles less than 90 o , the diversion of the crack into the HAZ is less likely compared with a 90 o weld angle. Type IV failure mode through the FGHAZ is also less likely to occur.

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Prediction of Type IV creep failure of a seam-welded mod. 9Cr-1Mo elbow based on microscopic damage simulation

Cited by 6 publications

References 17 publications

Creep damage analysis of simulated-HAZ notched bar specimens of modified 9Cr-1Mo steel

Creep damage analysis of simulated-HAZ notched bar specimens of modified 9Cr-1Mo steel

Creep damage analysis of mod.9Cr-1Mo steel welds considering void mechanics modeling

Effect of weld angle on the creep rupture life of ferritic/austenitic dissimilar weld interfaces under remote mode I fracture

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