Evaluation of Alternate Interpretations Regarding the Conditions for Exclusion of Thermal Bending Stresses in Simplified Elastic-Plastic Stress Analyses

2006 ◽  
Author(s):  
Robert B. Keating ◽  
Richard O. Vollmer
Keyword(s):  
Finite Element Analyses ◽  
Sample Problem ◽  
Secondary Stress ◽  
Elastic Plastic ◽  
Thermal Ratcheting ◽  
Plastic Analysis ◽  
Thermal Bending ◽  
Asme Code ◽  
Bending Stresses ◽  
Simplified Analysis

The ASME Code permits the range of primary plus secondary stress to exceed the stress limit of 3Sm, provided that several key conditions are satisfied. These conditions are provided in Paragraph NB-3228.5, “Simplified Elastic-Plastic Analysis”. The first condition is that the range of primary plus secondary stress intensity, excluding thermal bending stresses, shall be less than 3Sm. The term “thermal bending” is not clearly defined in the Code and at least two Code Interpretations have been issued with differing viewpoints. The first interpretation is that only those stresses due to the radial through-wall temperature distribution may be excluded; the second is that all thermal bending stresses, including thermal discontinuity stresses, may be excluded. In order to investigate the suitability of these two interpretations, elastic-plastic analyses are conducted of a highly restrained sample geometry. First, the sample problem is evaluated using the ASME Code rules for simplified elastic-plastic analysis for thermal ratcheting and fatigue, as required by NB-3228.5. Subsequently, cyclic elastic-plastic finite element analyses are conducted to determine if the simplified analysis rules provide adequate protection with regard to thermal ratcheting and fatigue. These analyses are performed using both interpretations to determine if adequate designs can be achieved for the sample problem selected.

On the Interaction of Thermal Membrane and Thermal Bending Stress in Shakedown Analysis

2008 ◽  
Author(s):  
Wolf Reinhardt
Keyword(s):  
Thermal Stress ◽  
Bending Stress ◽  
Membrane Stress ◽  
Secondary Stress ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Thermal Bending ◽  
Asme Code ◽  
The Impact ◽  
Current Code

When the primary plus secondary stress range exceeds 3 Sm, the current ASME Code rules on simplified elastic-plastic analysis impose two separate requirements to evaluate the potential for ratcheting. The range of primary plus secondary stress excluding thermal bending must be less than 3 Sm, and the thermal stress must satisfy the Bree criterion for thermal stress ratchet. It has been shown previously that this method can be unconservative, i.e. predict shakedown when elastic-plastic analysis shows ratcheting. This paper clarifies the interaction between thermal membrane and bending stress in the presence of a primary membrane stress. An analytical model is used to derive the closed-form ratchet boundary for combined uniform loading of this type. The impact of having stress gradients along the wall that are typical for discontinuities is studied numerically. Simple modifications of the current Code methods are suggested that would achieve a clearer and better-justified set of rules.

Elastic-Plastic Analysis of Hydride Blisters in Zircaloy-2 Pressure Tubes

1988 ◽  
Vol 110 (3) ◽  
pp. 276-282 ◽  
Author(s):  
Y. J. Kim ◽  
M. L. Vanderglas
Keyword(s):  
Finite Element ◽  
Physical Properties ◽  
Volume Expansion ◽  
Zirconium Hydride ◽  
Finite Element Analyses ◽  
Elastic Plastic ◽  
Pressure Tubes ◽  
Plastic Analysis

The possibility that stresses might be produced as a consequence of expansion resulting from the transformation of zirconium to zirconium hydride in the form of blisters was investigated. Parametric elastic-plastic finite element analyses were performed because the physical properties near the blister were not clearly defined. Results show that significant stresses can arise from the volume expansion of hydride blisters, being largely compressive within the blister, tensile outside.

Meaning of Ke in Design-by-Analysis Fatigue Evaluation

2005 ◽  
Vol 128 (1) ◽  
pp. 8-16 ◽  
Author(s):  
Gerry C. Slagis
Keyword(s):  
Stress Range ◽  
Elastic Plastic ◽  
Maximum Value ◽  
Penalty Factor ◽  
Plastic Analysis ◽  
Thermal Bending ◽  
Complex Procedure ◽  
Fatigue Evaluation ◽  
Technical Basis

The ASME Section III Design-by-Analysis rules for pressure-retaining components include a detailed fatigue evaluation based on elastically predicted primary, secondary, and peak stresses. A prerequisite for the fatigue analysis is that the primary-plus-secondary stress range does not exceed 3Sm. If this limit is exceeded, the code provides “Simplified Elastic-Plastic Analysis” rules for the fatigue evaluation. A Ke penalty factor is applied to the elastically predicted alternating stress. The maximum value of Ke (3.3 or 5) is a severe design limitation. Test data indicate that the code specified maximum value of Ke is very conservative. The simplified elastic-plastic rules were originally developed for piping and published in B31.7. When the piping rules were incorporated into Section III in 1971, the B31.7 procedure was replaced by a less complex procedure. The development of the simplified elastic-plastic analysis approach is reviewed to establish the technical basis for the present code rules. The concepts of fatigue, shakedown to elastic action, thermal bending, elastic follow-up, notch factor, and strain redistribution are discussed. Recommendations for changes to the plastic strain correction factor are provided.

Meaning of Ke in Design-by-Analysis Fatigue Evaluation

2005 ◽  
Author(s):  
Gerry C. Slagis
Keyword(s):  
Stress Range ◽  
Elastic Plastic ◽  
Maximum Value ◽  
Penalty Factor ◽  
Plastic Analysis ◽  
Thermal Bending ◽  
Complex Procedure ◽  
Fatigue Evaluation ◽  
Technical Basis

The ASME Section III Design-by-Analysis rules for pressure-retaining components include a detailed fatigue evaluation based on elastically-predicted primary, secondary, and peak stresses. A pre-requisite for the fatigue analysis is that the primary-plus-secondary stress range does not exceed 3Sm. If this limit is exceeded, the code provides “Simplified Elastic-Plastic Analysis” rules for the fatigue evaluation. A Ke penalty factor is applied to the elastically-predicting alternating stress. The maximum value of Ke (3.3 or 5) is a severe design limitation. Test data indicate that the code specified value of Ke is very conservative. The simplified elastic-plastic rules were originally developed for piping and published in B31.7. When the piping rules were incorporated into Section III in 1971, the B31.7 procedure was replaced by a less complex procedure. The development of the simplified elastic-plastic analysis approach is reviewed to establish the technical basis for the present code rules. The concepts of fatigue, shakedown to elastic action, thermal bending, elastic follow-up, notch factor, and strain redistribution are discussed. Recommendations for changes to the plastic strain correction factor are provided.

Elastic-Plastic Shakedown Evaluation Using ASME Code Section III and Section VIII Methods

2010 ◽  
Author(s):  
David P. Molitoris ◽  
John V. Gregg ◽  
Edward E. Heald ◽  
David H. Roarty ◽  
Benjamin E. Heald
Keyword(s):  
Elastic Analysis ◽  
Acceptance Criteria ◽  
Elastic Plastic ◽  
Division 1 ◽  
Plastic Analysis ◽  
Asme Code ◽  
Section Viii ◽  
American Society ◽  
Plastic Shakedown ◽  
Division 2

Section III, Division 1 and Section VIII, Division 2 of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code provide procedures for demonstrating shakedown using elastic-plastic analysis. While these procedures may be used in place of elastic analysis procedures, they are typically employed after the elastic analysis and simplified elastic-plastic analysis limits have been exceeded. In using the Section III, Division 1 and Section VIII, Division 2 procedures for elastic-plastic shakedown analyses, three concerns are raised. First, the Section III, Division 1 procedure is vague, which can result in inconsistent results between analysts. Second, the acceptance criteria contained in both procedures are vague, which can also result in inconsistent results between analysts. Lastly, differences in the procedures and acceptance criteria can result in demonstration of component elastic-plastic shakedown under Section III, Division 1 but not under Section VIII, Division 2. The authors presume that the ASME Code intends to provide similar design and analysis conclusions, which may not be a correct assumption. To demonstrate these concerns, a nozzle benchmark design subject to a representative thermal and pressure transient was evaluated using the two Code elastic-plastic shakedown procedures. Shakedown was successfully demonstrated using the Section III, Division 1 procedure. However, shakedown could not be demonstrated using the Section VIII, Division 2 procedure. The conflicting results seem to indicate that, for the nozzle design evaluated, the Section VIII, Division 2 procedure is considerably more conservative than the Section III, Division 1 procedure. To further assess the conservative nature of the Section VIII, Division 2 procedure, the nozzle benchmark design was evaluated using the same thermal transient, but without a pressure load. While shakedown was technically not observed using the Section VIII, Division 2 acceptance criteria, engineering judgment concluded that shakedown was demonstrated. Based on the results of all the evaluations, recommendations for modifications to both procedures were presented for consideration.

Alternative Approaches for ASME Code Simplified Elastic-Plastic Analysis

2017 ◽  
Author(s):  
Sampath Ranganath ◽  
Nathan A. Palm
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Correction Factor ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Asme Code ◽  
Alternative Approaches ◽  
Fatigue Evaluation ◽  
Technical Basis

Subsection NB, Section III of the ASME Code provides rules for the fatigue evaluation of nuclear pressure vessel and piping components. The stress analysis in ASME code evaluation is generally based on linear elastic analysis. Simplified rules using an elastic-plastic strain correction factor, Ke, are provided in Section III to account for plastic yielding when the primary plus secondary stress intensity range exceeds the 3Sm limit. While the simplified elastic-plastic analysis rules are easy to apply and do not require nonlinear analysis, the application of the Ke correction factor can produce extremely conservative results. This paper investigates different analytical methods that are available for simplified elastic-plastic analysis and proposes an alternative method that is not overly conservative (compared to the Code Ke) and offers a more realistic approach to simplified elastic-plastic analysis. The proposed methodology is applicable for both vessel (NB-3200), core support structures (NG-3200) and piping components (NB-3600) and does not require new finite element analysis. Information in existing ASME Code stress reports should be sufficient to determine the new Ke factor. The proposed methodology is applicable to structural materials including austenitic stainless steel and nickel based alloys, carbon steel and low alloy steel. Comparison of the proposed methodology with detailed elastic-plastic finite element analysis shows that the new Ke factors are conservative but offer relief from the excessive conservatism in the Code Ke values. This paper provides the technical basis for an ASME draft Code Case for Alternative Approaches for ASME Code Simplified Elastic-plastic Analysis being pursued through the Section III ASME Code Committees.

Elastic-Plastic Shakedown Assessment of Piping Using a Non-Cyclic Method

2007 ◽  
Author(s):  
Wolf Reinhardt
Keyword(s):  
Boundary Conditions ◽  
Pressure Vessel ◽  
The Other ◽  
Plastic Model ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Class 1 ◽  
Thermal Bending ◽  
Computationally Expensive ◽  
Plastic Shakedown

The analysis for shakedown in nuclear Class 1 piping following NB-3600 of the ASME Boiler and Pressure Vessel Code contains several simplifications and can be overly conservative in some cases and potentially non-conservative in some others. A detailed elastic-plastic analysis following NB-3228.4, on the other hand, is computationally expensive and time consuming because an elastic-plastic model needs to be cycled to stabilization. A non-cyclic method to assess elastic plastic shakedown (absence of ratcheting) has been proposed and is applied to the analysis of some simple straight piping scenarios. Interaction diagrams similar to the Bree diagram are derived for other loading situations, such as thermal bending in conjunction with primary bending. The effect of piping boundary conditions on the ratchet boundary is explored.

ASME III Fatigue Assessment Plasticity Correction Factors for Austenitic Stainless Steels

2014 ◽  
Author(s):  
Julian Emslie ◽  
Chris Watson ◽  
Keith Wright
Keyword(s):  
Preliminary Investigation ◽  
Austenitic Stainless Steels ◽  
Strain Range ◽  
Equivalent Strain ◽  
Elastic Analysis ◽  
Correction Factors ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Asme Code ◽  
Ratio Correction

ASME III NB-3200 provides a method for carrying out fatigue calculations using a simplified elastic-plastic analysis procedure. This allows a correction to elastic analysis to be performed in place of a full elastic-plastic analysis. Two mutually exclusive factors are described: the Poisson’s ratio correction accounts for surface stress exceeding the yield strength of the material and the Ke factor accounts for gross section plasticity. The recently released ASME Code Case N-779 provides a more complex but less onerous calculation of the Ke factor. Correction factors from the JSME and RCC-M codes have also been considered in this paper. The conservatism of different plasticity correction factors has been examined by calculating a ratio between the equivalent strain range from elastic-plastic Finite Element (FE) models and the strain range from elastic FE models and comparing this to calculated plasticity correction factors. Results show the potential for both the current ASME and Code Case Ke corrections to under-predict the strains when compared to those from an elastic-plastic FE assessment. A preliminary investigation has been carried out into an alternative correction factor based on linearised stress and local thermal stress ranges. This addresses the discontinuity between the two correction methods for surface and sectional plasticity which has been identified as a feature of the ASME correction methodology.

Assessment of Flaw Interaction Under Combined Tensile and Bending Stresses: Suitability of ASME Code Case N877-1

2020 ◽  
Author(s):  
Pierre Dulieu ◽  
Valéry Lacroix ◽  
Kunio Hasegawa
Keyword(s):  
Applied Stress ◽  
Three Dimensional ◽  
Stress Fields ◽  
Surface Flaws ◽  
Close Proximity ◽  
Thermal Bending ◽  
Asme Code ◽  
Bending Stresses ◽  
Stress Profiles ◽  
Flaw Characterization

Abstract In the case of planar flaws detected in pressure components, flaw characterization plays a major role in the flaw acceptability assessment. When the detected flaws are in close proximity, proximity rules given in the Fitness-for-Service (FFS) Codes require to combine the interacting flaws into a single flaw. ASME Code Case N877-1 provides alternative proximity rules for multiple radially oriented planar flaws. These rules are applicable for large thickness components and account for the influence of flaw aspect ratio. They cover the interaction between surface flaws, between subsurface flaws and between a surface flaw and a subsurface flaw. The calculations of flaw interaction have been performed under pure membrane stress. However, actual loading conditions induce non-uniform stresses in the component thickness direction, such as thermal bending or welding residual stresses. Non-uniform stress fields can lead to variations in the Stress Intensity Factors of closely spaced flaws, affecting their mutual interaction. The objective of this paper is to assess the suitability of ASME Code Case N877-1 with regards to the presence of a bending part in the applied stress distribution. For that purpose, various applied stress profiles and flaw configurations are covered. The effect on flaw interaction is assessed through three-dimensional XFEM analyses.

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