Prediction of Creep Void Growth in Heat-Affected Zone of High Chromium Steel Weldments Considering Multiaxial Stress State

2012 ◽  
Author(s):  
Eiji Murakami ◽  
Masamitsu Hashimoto ◽  
Seiji Kikuhara
Keyword(s):  
Stress State ◽  
Heat Affected Zone ◽  
Void Growth ◽  
Stress Triaxiality ◽  
Chromium Steel ◽  
Growth Behavior ◽  
High Chromium ◽  
Multiaxial Stress State ◽  
The Relationship ◽  
Triaxiality Factor

This paper deals with a method for predicting creep void growth in heat-affected zone (HAZ) of high chromium steel weldments. The method has been proposed by authors based on the relationship between creep void density increasing rate and multiaxial stress state. In this study, internal pressure creep tests of ASME grade 91 (9Cr-1Mo-Nb-V) tubes with longitudinal weldments subjected to several internal pressures have been conducted to reveal creep void growth behavior in HAZ. In addition, finite element creep analyses of the specimens at different creep strain rates in base metal, weld metal and HAZ have been carried out to investigate distribution of stresses and stress triaxiality factor in HAZ. A comparison between stress distributions and void distributions revealed that stress triaxiality factor predominantly affects growth behavior of creep voids. From the result, the relationship between creep void density increasing rate and the parameter as a function of principal stress and triaxiality factor was established. It was found that there is a proportional relationship between creep void density increasing rate and the parameter to represent stress multiaxiality on the logarithmic graph. To verify proposed prediction method, the method was applied to the internal pressure creep test specimens at different experimental conditions. As a result, the predicted void distribution and void density increasing rates were in good agreement with experimental results.

Simplified Prediction of Creep Void Density in Heat-Affected Zone of Grade 122 Steel Considering Multiaxial Stress State

2013 ◽  
Author(s):  
Eiji Murakami ◽  
Masamitsu Hashimoto ◽  
Seiji Kikuhara
Keyword(s):  
Stress State ◽  
Void Growth ◽  
Stress Triaxiality ◽  
Prediction Method ◽  
Growth Behavior ◽  
Multiaxial Stress State ◽  
Grade 91 ◽  
The Relationship ◽  
Tubular Specimens ◽  
Triaxiality Factor

This paper deals with a simplified method for approximately predicting creep void growth in heat-affected zone (HAZ) of ASME grade 122 (11Cr-2W-0.4Mo-Cu-Nb-V) steel weldments. Authors have proposed a simplified prediction method based on the relationship between creep void density increasing rate and multiaxial stress state. This method has been applied to prediction of creep void growth behavior for grade 91 (9Cr-1Mo-Nb-V) tubular specimens with longitudinal weldments. In this study, the method has been also applied to grade 122 steel to clarify the applicability of the method. Internal pressure creep tests of grade 122 tubular specimens with longitudinal weldments subjected to several internal pressures have been conducted to reveal creep void growth behavior in HAZ. In addition, finite element creep analyses for the specimens at different creep strain rates in base metal, weld metal and HAZ have been carried out to investigate distribution of stresses and stress triaxiality factor in HAZ. A comparison between stress distributions and creep void distributions revealed that stress triaxiality factor affects growth behavior of creep voids. From the result, the relationship between creep void density increasing rate and the parameter as a function of principal stress and triaxiality factor was established. It was found that the slope of this relationship for 122 steel has a tendency to be slightly small compared with grade 91 steel. To demonstrate the applicability of the proposed simplified prediction method, the method was applied to the internal pressure creep test specimens at different experimental conditions. As a result, the predicted void distribution and void density increasing rates for grade 122 steel were in good agreement with the experimental results.

New Analytical Approach to Predict Creep Void Growth in Heat-Affected Zone of High Cr Steel Weldments

2011 ◽  
Author(s):  
Eiji Murakami ◽  
Takeshi Iwamoto ◽  
Toshiyuki Sawa
Keyword(s):  
Finite Element ◽  
Heat Affected Zone ◽  
Void Growth ◽  
Analytical Approach ◽  
Axial Stress ◽  
Stress Triaxiality ◽  
Growth Behavior ◽  
Damage Level ◽  
The Relationship ◽  
Triaxiality Factor

This paper proposes a new analytical approach to predict creep void growth and remaining creep lifetime in a heat-affected zone (HAZ) of high Cr steel weldments. Concept of the new approach is based on a relationship between creep void growth rate and a parameter to represent multi-axial stress state obtained by finite element analysis. In this study, creep tests of ASME grade 91 (9Cr-1Mo-Nb-V) and grade 122 (11Cr-2W-0.4Mo-Cu-Nb-V) tubes with longitudinal weldments subjected to various internal pressures have been conducted to reveal creep void growth behavior in HAZ. Some specimens were intentionally interrupted before leakage at a damage level from 40 to 70% for clarification of void growth behavior at intermediate damage level. In addition, finite element creep analyses of the specimens at different creep strain rates in base metal, weld metal and HAZ have been carried out to investigate distribution of stress and stress triaxiality factor in HAZ. A comparison between stress distributions and void distributions revealed that stress triaxiality factor predominantly affects growth behavior of creep voids. From the result, the relationship between creep void growth rates and the parameter as a function of principal stress and triaxiality factor was established. Based on the relationship, a new prediction method was proposed. To verify proposed approach, the new method was applied to the elbow pipe with longitudinal weldment. As a result, predicted creep void growth in HAZ showed a good agreement with the results from diffusion simulation reported by literature. Therefore, the results demonstrated that the proposed approach is applicable to predict void distribution and remaining creep lifetime in the HAZ of high Cr steel weldments.

Notch Effects, Stress State, and Ductility

1978 ◽  
Vol 100 (4) ◽  
pp. 348-355 ◽  
Author(s):  
Alice M. Agogino
Keyword(s):  
Stress State ◽  
Stress Triaxiality ◽  
Review Of The Literature ◽  
Simple Criterion ◽  
Short Term ◽  
Notched Specimens ◽  
Tension Tests ◽  
Notch Geometry ◽  
Limiting Value ◽  
Triaxiality Factor

A review of the literature on testing of notched specimens is provided with emphasis on short-term notched bar tension tests. The effects of notch geometry, stress state, and smooth-bar tensile properties on notched ductility, notch sensitivity, and mode of fracture are discussed. For design against failure due to notch weakening, a simple criterion based on a limiting value of notched ductility is proposed. Notched ductility for the metals considered in this study, can be approximated by the reduction in and from a smooth tension test divided by a tensile stress triaxiality factor that is proportional to the ratio of hydrostatic to octahedral shearing stresses associated with the notch.

scholarly journals Effect of Stress Triaxiality on the Strain Concentration Factor

2019 ◽  
Vol 8 (4) ◽  
pp. 3468-3474
Keyword(s):  
Stress State ◽  
Concentration Factor ◽  
Notch Root ◽  
Stress Triaxiality ◽  
Critical Section ◽  
Triaxial Stress ◽  
Triaxial Stress State ◽  
Strain Concentration ◽  
Machine Element ◽  
Triaxiality Factor

Axisymmetric machine element with irregularities such as notches encountered with effects of stress triaxiality on the strain concentration factor (SNCF) at the reduced section. The effect of notch geometries on the triaxial stress state development in the critical section of a notched cylindrical bar is studied here using FEM. In addition, the effect of triaxial stress state (TSS) on the SNCF is evaluated. To this end, a notched cylindrical bars with notch depths from extremely deep notch (do/Do = 0.2) shallow notch (do/Do = 0.95) has been employed. The results show that the notches introduce a TSS at the critical section, which strongly affected by the notch depth as well as the notch radii. In this paper, a new concentration factor is introduced as the ratio of the stress triaxiality factor at the notch root (TFNR) to the average triaxiality on the critical section (), i.e. the triaxiality concentration factor KTF. The numerical results reveal that the variation of the average triaxiality factor with total strain shows the same trend as that of the SNCF. The variation of the elastic values of TFCN, , , and SNCF with do/Do and show that the minimum TFNR leads to the maximum elastic SNCF. It is prominent that elastic TFNR is less that elastic TFCN for 0.2 ≤ do/Do ≤ 0.85, while it is greater for shallow notches. The current results indicate a strong compatibility between the newly defined triaxiality concentration factor and the SNCF up to general yielding.

Creep Damage Assessment Procedure for Weldment Parts of P91 Boiler Piping in USC Plants: Part II—Validation of a Creep Damage Assessment Method Based on Void Growth Simulation

2011 ◽  
Author(s):  
Takashi Ogata ◽  
Takayuki Sakai ◽  
Masatsugu Yaguchi ◽  
Katsuaki Hoshino
Keyword(s):  
Heat Affected Zone ◽  
Void Growth ◽  
Damage Assessment ◽  
Thermal Power ◽  
Creep Damage ◽  
Simulation Method ◽  
Assessment Method ◽  
Growth Behavior ◽  
Assessment Procedure ◽  
Growth Simulation

Clarification of creep damage mechanisms and establishment of remaining life prediction methods of weldment parts of P91 boiler pipings are important subjects to maintain reliable operation of boilers in thermal power plants. In order to develop a creep damage assessment method of weldment parts of P91 pipings, internal pressure creep tests were conducted on P91 steel longitudinally welded tubes and a previously proposed void growth simulation method is applied to predict void growth behavior. Failure occurred at the heat affected zone without significant deformation. It was found from observation of creep damage interrupted specimens that initiation of creep voids concentrated at the mid-thickness region rather than the surface. It was suggested that triaxial stress states caused acceleration of creep damage evolution in the heat affected zone resulting in internal failure of the tube specimens. Void growth behavior in the heat affected zone was well predicted by the previously proposed void growth simulation method. The void growth prediction method is applied to predict creep damage induced by void initiation and growth in a weldment part of an actual P91 pipe. From comparison of void number density between measurement for a weldment part of a retired elbow pipe and prediction by the simulation, good agreement is obtained indicating the void growth simulation method can be applied to creep damage assessment of weldment parts in actual boiler piping.

Modeling of Multiaxial Stress Effects on the Creep Resistance of High Chromium Steel

2013 ◽  
Author(s):  
Luca Esposito ◽  
Nicola Bonora ◽  
Simone Dichiaro
Keyword(s):  
Creep Resistance ◽  
Stress Triaxiality ◽  
Load Condition ◽  
Constant Load ◽  
Chromium Steel ◽  
Creep Model ◽  
Creep Life ◽  
Computational Point ◽  
High Chromium ◽  
State Of Stress

Materials creep resistance is usually determined under uniaxial constant load condition while the state of stress in real components is multiaxial in general. How to correlate multiaxial creep behavior to uniaxial creep data is still an open issue. Most of the theories available in the literature are phenomenological in nature and limited to few classes of metals and stress triaxiality ranges. From the computational point of view, stress field relaxation depends on the creep model formulation. Therefore, it is necessary to use a refined creep model capable to reproduce the effective state of stress in the material. In the present work, a mechanism based creep model proposed by Bonora and Esposito [1] was used to predict creep life of P91 high chromium steel under multiaxial state of stress. This creep model is capable to reproduce all creep stages and was validated for different classes of metals and alloys. The performance of different reference stress definitions (i.e. the principal facet stress, skeletal stress and a new formulation) was investigated. Results were compared with available creep life data obtained on round notched samples at different temperatures.

AISI TYPE 440B

Alloy Digest ◽  
1969 ◽  
Vol 18 (4) ◽  
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Corrosion Resistance ◽  
Heat Treating ◽  
Chromium Steel ◽  
Ball Bearings ◽  
High Carbon ◽  
High Chromium ◽  
Steel Mills ◽  
Aisi Type

Abstract AISI Type 440B is a hardenable high-carbon high-chromium steel recommended stainless for cutlery, valve parts, ball bearings, pivot pins, etc. This datasheet provides information on composition, physical properties, microstructure, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SS-223. Producer or source: Stainless steel mills.

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