A Procedure for the Assessment of the Structural Integrity of Nuclear Pressure Vessels

1983 ◽  
Vol 105 (1) ◽  
pp. 28-34 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Structural Integrity ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Plastic Collapse ◽  
Failure Assessment Diagram ◽  
Linear Elastic ◽  
Failure Assessment ◽  
Deformation Plasticity ◽  
Margin Of Safety ◽  
Two Parameters

This paper presents a simple engineering procedure that the utility industry can use to assess the integrity of typical nuclear-grade pressure vessels. The procedure recognizes both brittle fracture and plastic collapse and is based on a set of proposed failure assessment curves which make up a safety/failure plane. The plane is defined by the stress intensity factor/fracture toughness ratio as the ordinate and the applied stress/reference plastic collapse stress ratio as the abscissa. The failure assessment procedure is based in part on the British Central Electricity Generating Board’s R-6 failure assessment diagram and the deformation plasticity solutions of the General Electric Company. Two parameters, a plastic collapse parameter (Sr′) and linear elastic fracture mechanics parameter (Kr′) are calculated by the user. The point (Sr′, Kr′) is plotted on the appropriate failure assessment diagram. If the point lies inside the respective curve, the structure is safe from failure. Moreover, for a given pressure and a postulated or actual flaw size, the margin of safety of the structure can be simply determined. Consistent with Appendix A of Section XI, (Division 1) of the ASME Boiler and Pressure Vessel Code the procedure presented in this paper is limited to ferritic materials 4 in. (102 mm) and greater in thickness. Details of the derivation of the proposed set of failure assessment curves are provided along with a sample problem illustrating the use of these curves.

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.

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.

A New Method for Preventing Plastic Collapse of Ellipsoidal Head Under Internal Pressure

2020 ◽  
Author(s):  
Keming Li ◽  
Jinyang Zheng ◽  
Zekun Zhang ◽  
Chaohua Gu ◽  
Ping Xu
Keyword(s):  
Internal Pressure ◽  
Pressure Vessel ◽  
Pressure Vessels ◽  
Design Methods ◽  
New Method ◽  
Plastic Collapse ◽  
Element Analysis ◽  
Linear Elastic ◽  
Perfectly Plastic ◽  
Margin Of Safety

Abstract Ellipsoidal head is a common end closure of pressure vessel. Plastic collapse is a crucial failure mode considered in the design of ellipsoidal head subjected to internal pressure. Internally pressurized ellipsoidal head tends to be hemisphere (geometric strengthening) due to the effect of material hardening before plastic collapse occurs, which enhances load carrying capacity of ellipsoidal head. However, in the current pressure vessel codes such as ASME BPVC.VIII.1 and BPVC.VIII.2, EN 13445-3, and Chinese codes GB/T 150.3 and JB 4732, design methods based on linear elastic or perfectly-plastic theory are used to prevent plastic collapse of ellipsoidal head, leading to conservative design. Therefore, we developed a new method for preventing plastic collapse of ellipsoidal head under internal pressure, considering the effects of material hardening and geometric strengthening. The new method was developed on basis of our previous extensive work on finite element analysis and experiments for plastic collapse of internally pressurized ellipsoidal heads. The new method provides sufficient margin of safety by checking against the experimental bursting results of full-scale ellipsoidal heads with various geometries, various material types and various manufacturing methods. Compared with the design methods in the current pressure vessel codes, the new method shows an advantage of economy. This new method had been approved by China Standardization Committee on Boilers and Pressure Vessels, and at present it has been introduced into the Chinese pressure vessel code.

Elastic-Plastic J-Estimation for Circumferentially Cracked Pipes Under Combined Mechanical and Thermal Loadings

2013 ◽  
Author(s):  
Chang-Young Oh ◽  
Yun-Jae Kim ◽  
R. A. Ainsworth
Keyword(s):  
Finite Element ◽  
Thermal Gradient ◽  
Order Effects ◽  
Assessment Procedure ◽  
Element Analysis ◽  
Elastic Plastic ◽  
Defect Assessment ◽  
Failure Assessment ◽  
Two Parameters ◽  
J Estimation

This paper addresses load order effects on elastic-plastic J estimation under combined mechanical and thermal loads for circumferentially cracked pipes. The load order effects, for various thermal gradient types and mechanical loading, are evaluated for a range of magnitudes of the loadings, crack sizes and material hardening. Variations of elastic-plastic J obtained by finite element analysis are compared with existing and proposed methods for use with the R6 defect assessment procedure. The load order effects are presented on the R6 failure assessment diagram (FAD) by calculating the two parameters Kr and Lr from the finite element results. It is shown that there are significant load order effects at large secondary stress cases but these are successfully treated by simplified methods proposed for use with R6.

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.

Validity of Assessment Procedure in p-M Method for Multiple Volumetric Flaws

2008 ◽  
Author(s):  
Shinji Konosu ◽  
Masato Kano ◽  
Norihiko Mukaimachi ◽  
Shinichiro Kanamaru
Keyword(s):  
Internal Pressure ◽  
Yield Stress ◽  
Bending Moment ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Plastic Collapse ◽  
Storage Tanks ◽  
Collapse Load ◽  
The Status ◽  
Single Flaw

General components such as pressure vessels, piping, storage tanks and so on are designed in accordance with the construction codes based on the assumption that there are no flaws in such components. There are, however, numerous instances in which in-service single or multiple volumetric flaws (local thin areas; volumetric flaws) are found in the equipment concerned. Therefore, it is necessary to establish a Fitness for Service (FFS) rule, which is capable of judging these flaws. The procedure for a single flaw or multiple flaws has recently been proposed by Konosu for assessing the flaws in the p–M (pressure-moment) Diagram, which is an easy way to visualize the status of the component with flaws simultaneously subjected to internal pressure, p and external bending moment, M due to earthquake, etc. If the assessment point (Mr, pr) lies inside the p–M line, the component with flaws is judged to be safe. In this paper, numerous experiments and FEAs for a cylinder with external multiple volumetric flaws were conducted under (1) pure internal pressure, (2) pure external bending moment, and (3) subjected simultaneously to both internal pressure and external bending moment, in order to determine the plastic collapse load at volumetric flaws by applying the twice-elastic slope (TES) as recommended by ASME. It has been clarified that the collapse (TES) loads are much the same as those calculated under the proposed p–M line based on the measured yield stress.

Estimation of Through-Wall Cracking Frequency of RPV Under PTS Events Using PFM Analysis Method for Identifying Conservatism Included in Current Japanese Code

2014 ◽  
Author(s):  
Kazuya Osakabe ◽  
Koichi Masaki ◽  
Jinya Katsuyama ◽  
Genshichiro Katsumata ◽  
Kunio Onizawa
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Structural Integrity ◽  
Probabilistic Approach ◽  
Pressure Vessels ◽  
Assessment Procedure ◽  
Analysis Method ◽  
Integrity Assessment ◽  
The U.S

To assess the structural integrity of reactor pressure vessels (RPVs) during pressurized thermal shock (PTS) events, the deterministic fracture mechanics approach prescribed in Japanese code JEAC 4206-2007 [1] has been used in Japan. The structural integrity is judged to be maintained if the stress intensity factor (SIF) at the crack tip during PTS events is smaller than fracture toughness KIc. On the other hand, the application of a probabilistic fracture mechanics (PFM) analysis method for the structural reliability assessment of pressure components has become attractive recently because uncertainties related to influence parameters can be incorporated rationally. A probabilistic approach has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. According to the PFM analysis method in the U.S., through-wall cracking frequencies (TWCFs) are estimated taking frequencies of event occurrence and crack arrest after crack initiation into consideration. In this study, in order to identify the conservatism in the current RPV integrity assessment procedure in the code, probabilistic analyses on TWCF have been performed for certain model of RPVs. The result shows that the current assumption in JEAC 4206-2007, that a semi-elliptic axial crack is postulated on the inside surface of RPV wall, is conservative as compared with realistic conditions. Effects of variation of PTS transients on crack initiation frequency and TWCF have been also discussed.

Some Fundamental Aspects of High Temperature Defect Assessment

2005 ◽  
Vol 297-300 ◽  
pp. 428-434 ◽  
Author(s):  
Shan Tung Tu ◽  
Fu Zhen Xuan
Keyword(s):  
High Temperature ◽  
Assessment Method ◽  
Damage Effect ◽  
Assessment Procedure ◽  
Continuum Damage ◽  
Creep Failure ◽  
Failure Assessment Diagram ◽  
Defect Assessment ◽  
Failure Assessment ◽  
Dependent Failure

Current research efforts in the development of high temperature defect assessment procedure are summarized. Creep exemption criteria are proposed for the assessment of defective structures at high temperature in consideration of the effects of loadings, operating temperature and service time. Time-dependent failure assessment diagram (TDFAD) is developed that covers major failure mechanisms of defective high temperature structures. Challenges due to the welding effect are discussed. TDFAD for weldments is derived for various combinations of materials. In order to develop a unified assessment method to cope with material and loading complexity, a new failure assessment diagram based on continuum damage concept is proposed to reflect the damage effect on ductile creep failure and brittle creep fracture.

Deformation Plasticity Failure Assessment Diagram (DPFAD) for Materials With Non-Ramberg-Osgood Stress-Strain Curves

1995 ◽  
Vol 117 (4) ◽  
pp. 346-356 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Tensile Stress ◽  
Manganese Steel ◽  
Uniaxial Tensile ◽  
J Integral ◽  
Stress Strain ◽  
Failure Assessment Diagram ◽  
Failure Assessment ◽  
Strain Data ◽  
Deformation Plasticity ◽  
Uniaxial Tensile Stress

This paper presents a brief history of the evolution of the Central Electricity Generating Board’s (CEGB) R-6 failure assessment diagram (FAD) procedure used in assessing defects in structural components. The reader is taken from the original CEGB R-6 FAD strip yield model to the deformation plastic failure assessment diagram (DPFAD), which is dependent on Ramberg-Osgood (R-O) materials to general stress-strain curves. An extension of the DPFAD approach is given which allows the use of material stress-strain data which do not follow the R-O equation such as stainless steel or carbon manganese steel. The validity of the new approach coined piecewise failure assessment diagram (PWFAD) is demonstrated through comparisons with the J-integral responses (expressed in terms of failure assessment diagram curves) for several cracked configurations of non-R-O materials. The examples were taken from both finite element and experimental results. The comparisons with these test cases demonstrate the accuracy of PWFAD. The use of PWFAD requires the availability of deformation plasticity J-integral solutions for several values of the strain-hardening exponent as well as uniaxial tensile stress-strain data at the temperature of interest. Lacking this information, the original R-O DPFAD approach using known engineering yield and ultimate strengths would give the best available approximation. However, it is strongly recommended that actual uniaxial tensile stress-strain data be used when available.

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