Extensions of the Failure Assessment Diagram Approach Semi-Elliptical Flaw in Pressurized Cylinder

1985 ◽  
Vol 107 (1) ◽  
pp. 25-29 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Safety Assessment ◽  
Pressure Vessels ◽  
Failure Assessment Diagram ◽  
The United Kingdom ◽  
Safety Margins ◽  
Failure Assessment ◽  
Assessment Approach ◽  
Model Versus ◽  
Pressurized Cylinder ◽  
Diagram Approach

A simple, viable engineering method for assessing the integrity of nuclear pressure vessels has been developed at Babcock & Wilcox. The method uses results given in a plastic fracture handbook developed by General Electric and which are in the format of the Central Electricity Generation Board of the United Kingdom R-6 failure assessment diagram. The method is currently limited to two-dimensional/axisymmetric structural models with continuous flaws. Failure assessment of nuclear pressure vessels with assumed continuous flaws result in the calculation of overly conservative safety margins. This paper presents the extension of the existing failure assessment approach to include semi-elliptical flaw models, as well as example problems which demonstrate increased safety margins over the continuous flaw assumptions. In particular, failure assessment diagram curves and the corresponding failure assessment point expressions for an axially cracked pressurized cylinder with an ASME Section III, Appendix G semi-elliptical flaw are presented. The results of the example problems considering the less conservative semi-elliptical flaw model versus the continuous flaw model dramatically illustrate increased safety margins of 50 percent when more realistic semi-elliptical flaws are postulated. The results given in this paper are particularly valuable in the safety assessment of PWR vessels which have low toughness welds in their beltline regions.

Validation of the Deformation Plasticity Failure Assessment Diagram (DPFAD) Approach—The Case of an Axial Flaw in a Pressurized Cylinder

1990 ◽  
Vol 112 (3) ◽  
pp. 213-217 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Crack Depth ◽  
Pressure Vessels ◽  
Inside Surface ◽  
Failure Assessment Diagram ◽  
Steel Technology ◽  
Failure Assessment ◽  
Deformation Plasticity ◽  
Structural Tests ◽  
Structural Configurations ◽  
Pressurized Cylinder

The validation of the deformation plasticity failure assessment diagram (DPFAD) approach for application to the prediction of failure pressures for pipes or pressure vessels with axial flaws is addressed in this paper. The DPFAD approach has been extensively documented with regard to its validity in open literature for various configurations of test specimens. For actual structural configurations, however, no such comparisons appear in open literature. In particular, the model of a part-through wall axial flaw in a pressurized cylinder has not been validated through comparisons with actual structural tests results. Two sources of test data from structural tests of axially flawed pressurized cylinders were evaluated. • Heavy-Section Steel Technology (HSST) intermediate test vessels. • Eiber/Battelle Columbus Laboratories (BCL) axially cracked pipes. The DPFAD axial flaw model was developed using finite-element results to generate calibration constants as functions of crack depth to wall thickness and crack depth to crack length for an axially oriented semi-elliptical flaw on the inside surface of a pressurized cylinder. The calibration constants were then used to generate failure assessment curves that can be used to assess or predict failure of pipes or vessels with axial flaws under pressure loading. A key assumption in the analysis was the use of the failure assessment curve for the inside surface flaw in the prediction of outside-surface-flawed cylinder failures. Based on the excellent results from the comparisons with predicted failures to actual vessel and pipe failures, this assumption was found to be reasonable. Furthermore, based on predicted test results of the HSST vessel tests and the Eiber/BCL pipe tests, it was concluded that the DPFAD semi-elliptical axial flaw model can be used reliably in assessing part-through flaws in pressurized vessels and pipes.

Constraint in the Failure Assessment Diagram Approach for Fracture Assessment

1995 ◽  
Vol 117 (3) ◽  
pp. 260-267 ◽  
Author(s):  
R. A. Ainsworth ◽  
N. P. O’Dowd
Keyword(s):  
Crack Size ◽  
Structural Constraint ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
T Stress ◽  
Fracture Assessment ◽  
The Subject ◽  
Constraint Effects ◽  
Two Parameters ◽  
Diagram Approach

This paper presents a framework for including constraint effects in the failure assessment diagram approach for fracture assessment. As parameters for describing constraint are still the subject of development, the framework is illustrated using both the elastic T-stress and the hydrostatic Q-stress. It is shown that constraint effects can be treated by modifying the shape of the failure assessment curve. In their simplest form, the modifications involve only two parameters: one quantifying the magnitude of structural constraint which depends on geometry and crack size; and the second quantifying the influence of constraint on fracture toughness.

Numerical Validation of a Strain-Based Failure Assessment Diagram Approach to Fracture

2009 ◽  
Author(s):  
Peter J. Budden ◽  
Michael C. Smith
Keyword(s):  
Finite Element ◽  
Plastic Strain ◽  
Present Author ◽  
Plastic Relaxation ◽  
Failure Assessment Diagram ◽  
Defect Assessment ◽  
Failure Assessment ◽  
Basic Approaches ◽  
Assessment Procedures ◽  
Diagram Approach

The basic approaches in defect assessment procedures such as R6 consider the stresses on the section containing the flaw. Such approaches can be overly conservative and lead to unacceptably small estimates of limiting defect sizes for cases where the applied loads are due to displacements or strains well in excess of yield, when significant plastic relaxation of stress occurs. The potential for over-conservative assessments has led to a renewed interest in recent years in strain-based assessment methods, in both the power and pipeline industries. Significant levels of plastic strain can be imposed across the flawed section in some cases. Recently, the present author has published a general approach to strain-based fracture that uses a strain-based failure assessment diagram (SB-FAD). This includes a range of Options similar to that of the basic R6 approach. The present paper describes some validation of the SB-FAD approach based on elastic-plastic cracked-body finite element data for plates and cylinders.

Assessment Procedure for Multiple Cracklike Flaws in Failure Assessment Diagram (FAD)

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Shinji Konosu
Keyword(s):  
Body Force ◽  
Pressure Vessels ◽  
The Body ◽  
Assessment Procedure ◽  
Failure Assessment Diagram ◽  
Reference Stress ◽  
Body Force Method ◽  
Failure Assessment ◽  
Common Problems ◽  
Shielding Effects

Assessment of multiple discrete cracklike flaws is one of the most common problems relating to pressure vessels and piping components. Under the current fitness for service (FFS) rules, such as ASME, BS, and so on, multiple cracklike flaws are usually recharacterized as an enveloping crack (defined as a single larger crack), following their assessment rules. The procedure, however, varies significantly in these FFS codes. In this paper, the interaction between nonaligned multiple unequal cracks is clarified by applying the body force method. Based on the interaction that indicates the magnification and shielding effects and the reference stress solutions, a newly developed assessment procedure for multiple discrete cracklike flaws in the failure assessment diagram is proposed.

Revision of ISO 27306 for CTOD Toughness Correction for Constraint Loss

2016 ◽  
Vol 879 ◽  
pp. 54-59
Author(s):  
Fumiyoshi Minami ◽  
Mitsuru Ohata ◽  
Yasuhito Takashima
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Stress Criterion ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Fracture Assessment ◽  
International Standardization ◽  
Diagram Approach ◽  
Weibull Stress

As the result of the international standardization work in Japanese IST project, ISO 27306 were published in 2009 for correction of CTOD fracture toughness for constraint loss in steel components. ISO 27306 employs an equivalent CTOD ratio based on the Weibull stress criterion, which leads to more accurate fracture assessment than the conventional fracture mechanics assessment. On the occasion of the 1st periodical review, the revision of ISO 27306 has been proposed from Japan. This paper describes the key contents of the new ISO 27306. A case study is included on the fracture assessment of a wide plate component according to FAD (failure assessment diagram) approach specified in BS 7910:2013.

Extensions of the Failure Assessment Diagram Approach Semi-Elliptical Flaw in Pressurized Cylinders—Part II

1986 ◽  
Vol 108 (4) ◽  
pp. 485-489 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Closed Form ◽  
Crack Depth ◽  
Strain Hardening Exponent ◽  
J Integral ◽  
Failure Assessment Diagram ◽  
Aspect Ratios ◽  
Failure Assessment ◽  
Deformation Plasticity ◽  
Estimation Scheme ◽  
Pressurized Cylinder

Approximate closed-form J-integral expressions based on the estimation scheme for use in the Deformation Plasticity Failure Assessment Diagram (DPFAD) approach are presented for an axially oriented semi-elliptical flaw in a pressurized cylinder for crack depth to wall thickness ratios, a/t, from 1/4 to 3/4 and aspect ratios, a/l, from 0 to 1/2. The DPFAD approach was used to derive closed-form J-integral expressions from limited elastic-plastic finite element solutions. Results are also presented in terms of the DPFAD curves as functions of a/t and a/l for the strain-hardening exponent of n = 8.6. Curves are given for the calibration constant h1 as a function of a/t and a/l for ease of interpolation. Lastly, discussion is provided as to the applicability of the solutions and a possible interpolation scheme for obtaining h1 values for n other than 8.6.

Critical Crack Sizes of Pressure Vessels Based on Failure Assessment Diagram Under Design Requirements

2019 ◽  
Author(s):  
Yuebing Li ◽  
Weiya Jin ◽  
Mingjue Zhou ◽  
Zengliang Gao
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessels ◽  
Design Standards ◽  
Critical Crack ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Section Viii ◽  
Design Requirements ◽  
Assessment Standards ◽  
Material Fracture

Abstract Standards or codes for defects assessment usually accompany their own design standards, such as, ASME BPVC section VIII and API 579-1/ASME FFS-1, GB 150 and GB/T 19624. The development of defects assessment standards should be adapted to the design requirements of pressure vessels. The consistency between fitness-for-service (FFS) procedures and design requirements of pressure vessels is discussed in this work. As a key link between FFS procedures and design standards, the required material fracture toughness not only depends on the methods of FFS procedures such as failure assessment diagram, but also on the design requirements. A procedure based on failure assessment diagram under design requirements is proposed to calculate critical crack sizes. The result can give some meaningful suggestions for the development of standards or codes.

Evaluation of Bending Limit of 9Cr-1Mo-V Steel by Master Curve and Failure Assessment Diagram Method: Evaluation of Base Metal

2018 ◽  
Author(s):  
Kazuo Oda ◽  
Mitsuyoshi Nakatani ◽  
Tomohiro Tanaka ◽  
Masamitsu Abe ◽  
Yasuhito Takashima ◽  
...  
Keyword(s):  
Brittle Fracture ◽  
Master Curve ◽  
Steel Plate ◽  
Fracture Probability ◽  
Pressure Vessels ◽  
Unstable Fracture ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Bending Process ◽  
Loading Tests

We investigated the bending and rolling limit of 9Cr-1Mo-V steel plate used in pressure vessels for the purpose of improving its manufacturing efficiency. Hereafter in this report, the bending limit refers to bending by press or by roller. It includes acceptable crack size, temperature, introduced plastic strain and other factors. When fracture toughness tests of 9Cr-1Mo-V steel plate were performed at bending temperature in production, unstable fracture rarely occurred. Since fracture probability during the bending process seems to be low, it was not possible to evaluate aspects of the degree of safety factor for brittle fracture. To estimate the bending limit at high temperature where unstable fracture rarely occurs, a method was proposed for estimating fracture probability using master curve and failure assessment diagram (FAD). In order to verify the proposed method, loading tests simulating the bending process were performed. The bending limits obtained from the loading tests were in good agreement with the values predicted by the proposed method. In this study, guidelines such as required toughness value and bending temperature for preventing brittle fracture during the bending process of 9Cr-1Mo-V steel plate were investigated.

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