scholarly journals Creep-Fatigue Crack Initiation Simulation of a Modified 12% Cr Steel Based on Grain Boundary Cavitation and Plastic Slip Accumulation

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6565
Author(s):  
Xin Jin ◽  
Run-Zi Wang ◽  
Yang Shu ◽  
Jia-Wen Fei ◽  
Jian-Feng Wen ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Grain Boundary ◽  
Power Plants ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Local Stress ◽  
Average Grain Size ◽  
Creep Fatigue ◽  
Creep Fatigue Crack

High-temperature components in power plants may fail due to creep and fatigue. Creep damage is usually accompanied by the nucleation, growth, and coalescence of grain boundary cavities, while fatigue damage is caused by excessive accumulated plastic deformation due to the local stress concentration. This paper proposes a multiscale numerical framework combining the crystal plastic frame with the meso-damage mechanisms. Not only can it better describe the deformation mechanism dominated by creep from a microscopic viewpoint, but also reflects the local damage of materials caused by irreversible microstructure changes in the process of creep-fatigue deformation to some extent. In this paper, the creep-fatigue crack initiation analysis of a modified 12%Cr steel (X12CrMoWvNBN10-1-1) is carried out for a given notch specimen. It is found that creep cracks usually initiate at the triple grain boundary junctions or at the grain boundaries approximately perpendicular to the loading direction, while fatigue cracks always initiate from the notch surface where stress is concentrated. In addition to this, the crack initiation life can be quantitatively described, which is affected by the average grain size, initial notch size, stress range and holding time.

Creep-Fatigue Damage and Crack Initiation for a Mod 9Cr-1Mo Structure With Weldments

2007 ◽  
Author(s):  
Hyeong-Yeon Lee ◽  
Se-Hwan Lee ◽  
Jong-Bum Kim ◽  
Jae-Han Lee
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Hold Time ◽  
Fatigue Crack Initiation ◽  
Creep Damage ◽  
Steel Specimen ◽  
Structural Test ◽  
Creep Fatigue ◽  
Creep Fatigue Crack

A structural test and evaluation on creep-fatigue damage, and creep-fatigue crack initiation have been carried out for a Mod. 9Cr-1Mo steel structural specimen with weldments. The conservatisms of the design codes of ASME Section III subsection and NH and RCC-MR codes were quantified at the welded joints of Mod.9Cr-1Mo steel and 316L stainless steel with the observed images from the structural test. In creep damage evaluation using the RCC-MR code, isochronous curve has been used rather than directly using the creep law as the RCC-MR specifies. A y-shaped steel specimen of a diameter 500mm, height 440mm and thickness 6.35mm is subjected to creep-fatigue loads with two hours of a hold time at 600°C and a primary nominal stress of 30MPa. The defect assessment procedures of RCC-MR A16 guide do not provide a procedure for Mod.9Cr-1Mo steel yet. In this study application of σd method for the assessment of creep-fatigue crack initiation has been examined for a Mod. 9Cr-1Mo steel structure.

Creep-Fatigue Crack Initiation Assessments of an Instrument Guide Tube Within a Superheater Header

2014 ◽  
Author(s):  
Jinhua Shi ◽  
Hassam Dodia
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Material Properties ◽  
Fatigue Crack Initiation ◽  
Guide Tube ◽  
New Approach ◽  
Weld Material ◽  
Creep Fatigue ◽  
Creep Fatigue Crack

In order to extend the boiler lives at Advanced Gas-Cooled Reactor (AGR) nuclear power stations in the UK, new temperature measuring instrumentation to monitor reactor gas temperature has been proposed to install on the bore of an intact boiler tube to provide additional boiler operating data to support the station lifetime extension. This paper details a creep-fatigue crack initiation assessment of the proposed installation of an instrument guide tube within the superheater header using the latest R5 high temperature assessment procedures based on detailed finite element thermal transient stress analysis values for a bounding start-up and shutdown cycle. The fatigue damage at welds has been calculated based on both weld and parent material properties. The new approach for assessing weldments has been used in this paper. This new approach involves splitting the existing Fatigue Strength Reduction Factor (FSRF) into a Weldment Endurance Reduction (WER), which accounts for reduced fatigue endurance due to weld imperfections, and a Weldment Strain Enhacement Factor (WSEF), which accounts for material mismatch and local geometry. The creep assessments of the weld material locations have been carried out on both parent and weld material properties including the welding residual stress. The total creep-fatigue damage is then obtained as the sum of fatigue damage, Df, and creep damage, Dc.

Characterizations of Creep-fatigue Crack Initiation and Growth Life for P92 using Circular Notched Round Bar Specimen

2012 ◽  
Vol 9 (1) ◽  
pp. 103956
Author(s):  
R. Sugiura ◽  
A.T. Yokobori ◽  
T. Nakagawa ◽  
T. Adachi ◽  
I. Nonaka ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Round Bar ◽  
Creep Fatigue ◽  
Creep Fatigue Crack

A Structural Integrity Assessment of a Nuclear Boiler Superheater Bifurcation at High Temperature

2018 ◽  
Author(s):  
Brahim Nadri ◽  
Robert X. Wang
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Structural Integrity ◽  
Fatigue Crack Initiation ◽  
Metal Loss ◽  
Term Operation ◽  
Creep Fatigue ◽  
Safety Case ◽  
Creep Fatigue Crack

Steam generating boilers in gas cooled nuclear reactors in the UK operate at high temperatures and some of them have been in service for more than 30 years and are now facing the challenges from long term operation extension demand. The tubular components experience surface metal losses due to exposure to oxidation and corrosive environment and as a result, some tubes suffer from restricted flow which may lead to an increased creep-fatigue crack initiation damage. To maintain or recover boiler heat transfer efficiency, internal chemical cleaning of selected boiler tubes is carried out, which introduces additional metal loss in the tube wall, weakening its load bearing capacity. Some boiler components are subject to high temperature, pressure and mechanical loadings in large number of operating cycles through life, introducing creep in addition to cyclic fatigue damage. In support of an operational safety case and plant long term operation extension requirements, structural integrity assessments have been carried out on a critical boiler component — bifurcation, taking into account tube wall metal loss for extended long term services, including the effects of possible future chemical cleaning operations. This paper presents the finite element analyses and R5 Volume 2/3 assessment work carried out for the structural integrity substantiation of a stainless steel boiler tube bifurcation. The bifurcation is a tubular component subject to significant applied displacement due to long range thermal expansion of the neighbouring components. The initial study following normal industry practice using a decoupled analysis approach showed that the strain ranges obtained would exceed the creep-fatigue crack initiation capacity and plastic ratchetting would occur which would lead to short term, incremental plastic collapse, hence a safety case could not be made. To meet the challenge, the analysis and assessment processes have been examined. A coupled FE analysis approach was used to remove the pessimism associated with the decoupled analysis approach. This approach captures the displacement-controlled nature of the system loads and allows a more realistic assessment. In addition, the plant life has been divided into a number of assessment periods such that the more realistic metal loss appropriate for each period could be used. Furthermore, segregated temperature zones have been considered in the assessment, leading to a significant reduction in the creep-fatigue crack initiation damage and a satisfactory extended long term operation safety case.

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