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seipp2014 | Buckling | Finite Element Method
Uploaded by Andres Vallebella
125760133 Buckling of Thin Metal Shells 38
Laterally supported aluminum flexural members with symmetric cross sections
classical stress
Arcade Asce 2005
Proceedings of the ASME 2014 Pressure Vessels & Piping Conference
July 20-24, 2014, Anaheim, California, USA
PVP2014-28958
Writing and Reviewing FEA Reports Supporting ASME Section VIII, Division 1 and 2 Designs Practical Considerations and Recommended Good Practice
Becht Engineering Canada Ltd.
110-259 Midpark Way, S.E.
Tel: 403-668-7274
Fax: 403-256-3520
Email: tseipp@becht.com
Tel: 403-668-8675
Email: mstonehouse@becht.com
Section VIII, Division 2 for the type of analysis being
performed, then those rules must be followed.
The FEA is not complete without a detailed report
describing the work performed, details of the loads,
boundary conditions, mesh discretization, material
properties, and compliance with all Part 5 requirements.
Since ASME Section VIII, Division 2, Part 5
approaches the design-by-analysis requirements from a
‘protection against failure modes’ perspective, it is
imperative that the analyst determine all reasonably
possible failure modes, create a modeling approach that
will be appropriate for each failure mode, and ensure that
an appropriate margin against failure is maintained.
Finite element analysis (FEA) is used, with increasing
frequency, to supplement or justify the design of an ASME
Section VIII, Division 1 or 2 pressure vessel. When this
occurs, good engineering practice indicates that a
competent engineer should review the finite element
analysis report. In some jurisdictions, it is required that a
Professional Engineer review and certify the report.
This paper discusses some of the practical aspects of
both writing and reviewing a good quality FEA report both in the context of the technical perspective and in the
context of Code compliance. This paper will serve as a
practical assistant to an engineer reviewing an FEA
report, as well as a guide to an engineer preparing an FEA
report. Aspects such as properly following Code
requirements, following appropriate Design By Analysis
methodologies, and applying good design practices will
The goal of the report writer should be to clearly
describe the work performed with sufficient detail that
another analyst could, with applicable referenced
drawings and documentation, independently duplicate the
A quality FEA report consists of the following detailed
FEA can be used to support pressure equipment
design where the configuration is not covered by the
applicable rules in the ASME code. Whether the pressure
vessel design is considered an ASME Section VIII
Division 1 [1] or a Division 2 [2] vessel, all finite element
analysis for pressure vessels should follow the
methodology in ASME Section VIII, Division 2, Part 5 (it is
recommended to use the latest Edition, as improvements
are continually being made) unless that type of analysis
is not covered in Part 5. If specific rules exist in ASME
This should be standard practice and should briefly
describe how the FEA was used to support the design,
the FEA model, the results and conclusions. This section
should be no more than one page, and should be written
primarily for the non-technical reader.
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the software used. justification for using FEA. stress plot with an appropriate color contour to establish some sense of the magnitude of the stress profile of the model with respect to an allowable stress. When contact is included in the analysis. The source for these material properties should also be provided. with an explanation of how the “as safe as” provision is accomplished. axisymmetric.org/ on 04/27/2015 Terms of Use: http://asme. justified. Part 5. then a description of how the different elements are connected together should be provided. should be indicated. On the contrary. it is highly recommended that both the Revision Numbers and the dates of all reference material be included in the list. thermal diffusivity. Analysis of Results and Conclusion This section of the report should follow the approach in ASME Section VIII. Material Properties A complete description of the material properties used in the analysis should be provided. Simply referring to the material specification is not sufficient. if the report is in support of a Division 1 vessel. Model Description Dimensional descriptions should be provided from the referenced drawings. Hundreds of pages of stress plots need not be presented. If there are any geometric simplifications used. such that the rationale for the partial model is described with an explanation of the boundary conditions used to compensate for the missing model sections. particularly the mesh size. It is recommended that symmetry models NOT be used when performing buckling calculations. All physical properties. Division 2. The type (2D. and other supplemental information referenced in the report should be detailed in the References section. Boundary conditions. When symmetry is used. deformed shape with un-deformed shape superimposed. Division 2. There should be a significant description of the mesh. When available. loads and other similar interactions must also be detailed.). such as: Young’s Modulus. the variation of the material properties should be presented either in tabular form or in a graph that demonstrates that variation.Introduction A good introduction should lay out the scope of the FEA. Some critical dimensions should also be explicitly described in the report. Since significant changes can occur in drawings after the FEA report is prepared.asme. Part D [3]. For example. elastic-plastic. the type of analysis (linear elastic. When the material properties vary with temperature. it may be not current by several years. and restraints are described and shown graphically. supports. Since the Edition of the Code of Construction is dictated by the fabrication contract. The method of restraining the model against rigid-body motion should be described and Presentation of Results Depending on the type of analysis being performed the results that need to be presented may vary. The authors’ experience as reviewers has shown that it is useful to provide some basic dimensional details – if for no other reason than to provide the reviewer something to verify from the drawings. etc. The authors recommend that a mixture of tabular data as well as graphical data be used to efficiently provide this data – especially if material properties as a function of temperature are used. then the appropriate monotonic or cyclic elastic-plastic true stress-true strain (either with hardening or perfectly-plastic) should be detailed as functions of temperature. The accuracy of the model. It is most helpful when the loads. Mesh features such as the number of elements on fillet radii should also be reported. When plotting multiple stress contour plots for comparison.asmedigitalcollection. the authors highly recommend that the current Edition of Division 2 be used at all times. industry best practice is to be as concise as possible with 2 Downloaded From: http://proceedings. the results should show enough details to demonstrate an appropriate analysis of the failure modes being checked. As part of generally accepted good practice. calculations. by way of the discretization. and minimum specified yield and ultimate strengths should also be reported as appropriate. those also need to be discussed and justified. References All drawings.org/terms Copyright © 2014 by ASME . A complete description of the material properties should be provided. then reference should be made to article U-2(g). such parameters as the normal and tangential conditions should also be presented and justified. Each Failure Mode must be demonstrated in the results. Despite that. The Edition of the Code of Construction should also be listed. Strength parameters such as the allowable stress. the presentation of the results should be as simple and clear as possible. If the analysis is not linear-elastic. etc. it is most useful when the contour scheme/intervals are identical. 3D. its use must be justified. as should the edition of ASME Section VIII.) and the order of the elements should also be reported. A convergence study is expected – although it is not explicitly required for every FEA. thermal conductivity. density and Poisson’s ration should all be reported. however. The results in most analyses will include displacements. the coefficient of thermal expansion. and the material properties. specific heat capacity. material properties should be obtained from ASME Section II. If different types of elements are used.
A. 5. compliance with the linearization methods in Annex 5.2.2. 5.1.3. Two alternative analysis methods are presented:  Elastic analysis method  Elastic-plastic analysis method FAILURE MODES From a technical perspective.1 shall be detailed. Special attention shall be paid to the cautions in Paragraphs 5. Post-processing of results for the elastic stress analysis method shall be performed in strict accordance to the rules of Paragraph 5. Three alternative analysis methods are presented:  Elastic stress analysis method  Limit-load method  Elastic-plastic stress analysis method The analyst shall describe the method selected. all of the above requirements should be presented in paragraph-form. and the rationale for the selection. 3 Downloaded From: http://proceedings.4.4. All loading scenarios referenced by Paragraph 5.A.3.3 and Annex 5. If this check does not need to be performed. Three alternative methods are presented:  Bifurcation buckling analysis performed using an elastic stress analysis without geometric nonlinearities to determine the pre-stress in the component. If the built-in stress linearization methods of the finite element analysis software are used. even a simple report will likely be 12 pages long. even a long and complicated FEA report should not be longer than 45 pages.1. The appropriate margins for each failure mode depend on the Code of Construction for the component being evaluated. Protection Against Local Failure Paragraph 5. and the rationale for the selection.the results. Division 2 approaches the design-byanalysis requirements from this protection against failure modes perspective.5. and modifications to the default setting must be made. For each failure mode.org/ on 04/27/2015 Terms of Use: http://asme.4. 5.2. If the elastic-plastic analysis method is used. As shown by Seipp [5].3.2. Stress classification lines shall be described in the body of the report and shown graphically.4 discusses the evaluations methods available for protection against buckling failure.4. the analyst is required to present a modeling approach and discuss how it is appropriate. Protection Against Plastic Collapse Paragraph 5. Each step in 5. All figures should be referenced in the text of the report – if they cannot be referenced. and ensure that an appropriate margin against failure is maintained. The analyst shall demonstrate that simplification of the model does not result in exclusion of critical buckling mode shapes. and explicitly considering imperfections. a single statement to that effect needs to be included in the report. Conversely.2 discusses the evaluation methods available for protection against plastic collapse. The report should only present those results specifically relevant to the conclusions.2 (Assessment Procedure) shall be detailed. In general.1. and the rationale for the selection.1. Part 5 of ASME Section VIII.2.A must be demonstrated. extra care must be taken in this failure mode with respect to mesh discretization.  Bifurcation buckling analysis performed using an elastic-plastic analysis with the effects of nonlinear geometry to determine the pre-stress in the component.2. The 2013 Edition provides rules for protection against four critical failure modes. Paragraph 5. and 5.2.2.5 of Part 5.org/terms Copyright © 2014 by ASME . Based on the authors’ experience.2.) The analyst shall describe the method selected.3 discusses the evaluation methods available for protection against local failure.2.asmedigitalcollection. perhaps they are not important/relevant.4. Note that each evaluation method has a particular design factor. Reporting of the results of the limit-load analysis and the elastic-plastic analysis need only consist of a confirmation that a converged solution has been obtained with the required design margins. The analyst shall also describe how the modeling approach will account for axisymmetric as well as non-axisymmetric buckling modes.3. Where appropriate. a plot of the extent of the plastic region should be provided.2. and 5. just to satisfy the requirements listed above and below.asme. Protection Against Buckling Failure This check only needs to be performed when there exists compressive stresses due to the design loads. (Note that the default built-in linearization in some software is NOT compliant with 5. the analyst must evaluate the design for all failure mechanisms in 5. 5.2 shall be evaluated. each step of 5. the same discretization used for Protection Against Plastic Collapse may be inadequate for Protection Against Local Failure.3. The analyst shall describe the method selected.  Non-linear buckling analysis performed in accordance with the elastic-plastic stress analysis method. The analyst is required to create a modeling approach that will be appropriate for each failure mechanism.2. or 5.
2. This is only possible for temperatures not in the creep regime.4 Note 6 need to be used. the required load case combinations from ASME FFS-1/API579 [4] Table B1.5. Table 1 and Table 1A (i. including appropriate references to published recommendations. where no Code rules exist for a given situation. and the rationale for the selection. Where fatigue strength reduction factors (FSRFs) are required in the elastic stress analysis method. and the results of the assessment. applying an RSFa=1. Regardless of whether or not a fatigue assessment is required.e. the rationale for the choice of FSRF shall be detailed.5.5 discusses the evaluation methods that must be performed.2 of Section VIII. there are several considerations that are specific to the application of Division 2. a fatigue assessment in accordance with 5. but consideration of the test condition per UG-22(j) of Section VIII. subject to the acceptance of the Inspector. However. Division 1 is mandatory. Part 5 for a Division 1 vessel that constitute good industry practice. is intended that the Manufacturer. In evaluating load cases involving the pressure term. Evaluation of the test condition per paragraph 4.org/terms Copyright © 2014 by ASME . If the component being evaluated is not covered by a standard detail from Part 4. the allowable stress for all product forms except bolting need to be from Section II. the allowable stress for Section VIII Division 1 construction). can be determined from the current rules in Section VIII Division 2. then an evaluation per 5.6. Otherwise. Where complete details are not given. Division 1. Two alternative methods are provided for protection against ratcheting:  Elastic stress analysis  Elastic-plastic stress analysis The analyst shall describe the method selected.3 is required. shall provide details of design and construction which will be as safe as those provided by the rules of this Division” There exist no other rules currently in ASME Section VIII Division 1 to provide guidance for the performance of FEA. Part D. then the analyst need only report that the screening criteria has been satisfied. Each step in 5. All methods must be fully described. That said. Part D. the analyst is applying Article U-2(g) of Division 1 which states: 4 Downloaded From: http://proceedings. and the rationale for each method must be justified. When elastic-plastic analysis is performed. should be followed. 5.2 shall be detailed. In 5. 5. Bolting material allowable stresses should be determined from Section II. an FEA may be required.4. P. there are many details permitted in Division 1 that are not permitted in Division 2.3 must be performed.5.1. However. The Design By Analysis Rules in ASME Section VIII.3. Division 2.2.2.5. or 5. all components are required to complete the evaluation for protection against ratcheting. When an elastic analysis is performed. and the rationale for the selection.2.3. a component is exempt from the Local Failure Criteria evaluation if the component design is in accordance with the standard details of Part 4.Protection Against Failure From Cyclic Loading Paragraph 5.3. the analyst must ensure that an appropriate margin against failure is maintained.asme. as described above. S. If the component under evaluation has been screened using the screening criteria in paragraph 5. Division 2 is not mandatory. Table 3.5. Three alternative methods are provided for fatigue assessments:  Elastic stress analysis and equivalent stresses  Elastic-plastic stress analysis and equivalent strains  Analysis of welds – elastic stress analysis and structural stress “This Division of Section VIII does not contain the rules to cover all details of design and construction.5. The analyst shall describe the method selected. and 5. All of the load case combinations of the applicable Division 2 assessment procedure need to be considered in addition to any other combinations defined by the User. Protection Against Additional Failure Modes The analyst must also consider all other additional failures modes (such as those that may be described in a UDS).org/ on 04/27/2015 Terms of Use: http://asme.5 of Part 5 need to be evaluated. and provides alternatives for fatigue analysis and protection against ratcheting. Part 5.4. 5. such as fatigue and compressive allowable stresses. or a component of a Division 1 vessel. All of failure mechanisms in 5. SPECIAL CONSIDERATIONS FOR DIVISION 1 An FEA cannot be used to supersede existing rules in ASME Section VIII.asmedigitalcollection. When performing an FEA on a Division 1 pressure vessel. Although no rules for these types of analyses exist in Part 5. the effects of the pressure being equal to zero need to be considered. Limiting values that are not calculated using the allowable stress.
2007 5. New York. Section VIII Division 2. Introduction. Section VIII Division 1. 2013. American Petroleum Institute/American Society of Mechanical Engineers. API 579-1/ASME FFS-1. July 2013.. “An Evaluation of The Protection Against Local Failure in ASME Section VIII.org/terms Copyright © 2014 by ASME . Seipp. New York. ASME. ASME Pressure Vessels and Piping Conference. ASME PVP2013-98028. the foregoing also forms a type of checklist for reviewing and/or certifying any reports. REFERENCES 1. 2013. ASME. NY 2. Section II Part D. NY 3. These guidelines are a good guide for both engineers preparing an FEA report. Fitness For Service. whether performed on an ASME Section VIII Division 1 or 2 vessel. Model Geometry. Results. as well as engineers who are reviewing and/or certifying an FEA report. NY 4.asmedigitalcollection. complete FEA report will include sufficiently detailed sections including an Executive Summary. Therefore. Division 2: Finite Element Model Considerations”. should follow the rules of ASME Section VIII Division 2 Part 5. ASME Boiler and Pressure Vessel Code. ASME Boiler and Pressure Vessel Code. ASME.asme. CONCLUSION The use of FEA for a design implies that the design is different from that typically undertaken in a Design-ByRules context. American Society of Mechanical Engineers. Based on these guidelines. American Society of Mechanical Engineers.org/ on 04/27/2015 Terms of Use: http://asme.REVIEWING AN FEA REPORT The recommendations provided above in this paper represent the authors’ opinions on what constitutes good practice when it comes to preparing an FEA report. References. Analysis of Results and Conclusion. New York. writing a report. The guidelines presented in this paper should be considered as the minimum of such high standards. Trevor G. American Society of Mechanical Engineers. 2013. 5 Downloaded From: http://proceedings. and reviewing that report should adhere to the highest reasonable standard. The absence of any of these essential items represents a deficiency that should be discussed with the author of the FEA report. Performing an FEA. A quality. ASME Boiler and Pressure Vessel Code. An FEA. The report must demonstrate evaluation against all applicable failure modes as defined in Part 5. engineers should hold themselves to a high standard for such Design-ByAnalysis approaches.
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