Reliability Analysis of Defect-Containing Structures Using Partial Safety Factors

2009 ◽  
Author(s):  
Liwu Wei
Keyword(s):  
Failure Probability ◽  
Structural Integrity ◽  
General Trend ◽  
Safety Factors ◽  
Integrity Assessment ◽  
Fracture Region ◽  
Failure Assessment ◽  
Elastic Fracture ◽  
Partial Safety Factors ◽  
Collapse Region

Some standards of structural integrity assessment such as BS 7910 and API 579-1/ASME FFS-1 recommend values of partial safety factor (PSF) applied to the deterministic engineering critical assessments of flaw-containing structures to achieve certain reliability levels. However, it is still uncertain as to whether the use of the PSFs can achieve the target reliability level specified in the codes, or excessively exceed the targets (un-conservative) or under-reach the targets (too conservative). This work was undertaken to make investigations into these issues raised from the use of PSFs through case studies involving deterministic fitness-for-service analysis incorporating PSFs and probabilistic fracture mechanics analysis. Two cases, a through-thickness crack and a surface-breaking elliptical crack in a plate subjected to tension, were considered. The results in terms of failure probability from the studied cases have shown a general trend that for each of the four PSFs recommended in BS 7910, the failure probability decreased as the assessments changed from the elastic fracture region to the plastic collapse region in the failure assessment diagram. Some over-conservatism has been found in certain situations from the use of PSFs recommended in BS 7910:2005. Cautions are given for application of the PSFs for integrity assessment of the structures and components containing flaws.

Reliability-Based Derivation of Partial Safety Factor for Structural Integrity Assessment

2008 ◽  
Author(s):  
Shuo Pan ◽  
Jianping Zhao
Keyword(s):  
Safety Factor ◽  
Fracture Mode ◽  
Structural Integrity ◽  
Research Work ◽  
Random Variables ◽  
Assessment Procedure ◽  
Safety Factors ◽  
Integrity Assessment ◽  
Partial Safety Factor ◽  
Partial Safety Factors

When there are uncertainties in the input random variables, or scatter in the material properties, probabilistic assessment is a useful tool for decision making in the field of safety analysis. The partial safety factor (PSF) method was aimed on ensuring that the failure probability did not exceed a target value. In order to be conservative the input value for each random variable during the assessment procedure should be multiplied by the partial safety factors. So it is essentially a deterministic assessment using conservative values of the input random variables and a relatively simple and independent method of assessing failure probabilities using R6 failure assessment diagram. The application of partial safety factors is an important breakthrough of assessment in structures containing defects. In recent years, sets of PSFs for load, defect size, fracture toughness and yield stress had been given in two standards, BS7910 and API579. However, the recommended PSFs in both standards were larger than the original PSFs in PD6493 which was replaced by BS7910. It is therefore a new method of calculating PSFs should be found to prove which is more appropriate and convenient for engineering application. In the case of the partial safety factor method target reliabilities in the range from 0.001 to 0.00001 were considered and new series of PSFs were derived from the results of reliability analysis for the linear elastic fracture mode and elastic-plastic fracture mode. After comparing with the PSFs in BS7910 and API 579, it is concluded that the partial safety factors were generally conservative compared to our research work.

A Comparison of Fracture Assessment Methods in Several Structural Integrity Assessment Procedures

2009 ◽  
Author(s):  
Tiecheng Yang ◽  
Xuedong Chen ◽  
Zhichao Fan
Keyword(s):  
Structural Integrity ◽  
Limit Load ◽  
Assessment Method ◽  
Assessment Methods ◽  
Safety Factors ◽  
Specific Calculation ◽  
Integrity Assessment ◽  
Fracture Assessment ◽  
Partial Safety Factors ◽  
Assessment Procedures

For the fracture assessment method internationally used in different structural integrity assessment procedures, such as R6, BS 7910, FITNET API 579 and GB/T 19624, this paper gives the results of analytical comparisons in combination with specific calculation examples by comparing different assessment options or levels, the partial safety factors (PSFs), limit load solutions, stress intensity factor solutions, residual stress distribution and treatment methods, secondary stresses and ρ factor solutions etc., which provide a basis for improvement of fracture assessment methods.

Structural Integrity for Nuclear Power Plant Against Excessive Load on Design Extension Condition

2013 ◽  
Author(s):  
Daigo Watanabe ◽  
Kiminobu Hojo
Keyword(s):  
Nuclear Power ◽  
Structural Integrity ◽  
Safety Factors ◽  
Design Code ◽  
Acceptance Criteria ◽  
Integrity Assessment ◽  
Current Design ◽  
Factor Design ◽  
Excessive Load ◽  
Load And Resistance Factor

This paper introduces an example of structural integrity evaluation for Light Water Reactor (LWR) against excessive loads on the Design Extension Condition (DEC). In order to assess the design acceptance level of DEC, three acceptance criteria which are the stress basis limit of the current design code, the strain basis limit of the current design code and the strain basis limit by using Load and Resistance Factor Design (LRFD) method were applied. As a result the allowable stress was increased by changing the acceptance criteria from the stress basis limit to the strain basis limit. It is shown that the practical margin of the LWR’s components still keeps even on DEC by introducing an appropriate criterion for integrity assessment and safety factors.

Structural Integrity Assessment of Notched Components

2011 ◽  
Author(s):  
Sergio Cicero ◽  
Virginia Madrazo ◽  
Isidro Carrascal ◽  
Miguel Laporta
Keyword(s):  
Structural Integrity ◽  
Notch Effect ◽  
Single Edge ◽  
Integrity Assessment ◽  
Failure Assessment ◽  
Notched Components ◽  
Notch Analysis

This paper analyzes the notch effect and presents a methodology, based on failure assessment diagrams and the notch analysis approaches based on the theory of critical distances, for the structural integrity assessment of notched components, which allows more accurate structural analyses to be made. The methodology is applied to a set of tests performed on PMMA single edge notched bending (senb) specimens, providing better results than those obtained when the analysis is performed considering that notches behave as cracks.

On the Constraint-Based Failure Assessment of Surface Cracks in T-Plate Welded Joints

2003 ◽  
Author(s):  
X. Wang ◽  
R. Bell ◽  
S. B. Lambert
Keyword(s):  
Lower Bound ◽  
Welded Joints ◽  
Structural Integrity ◽  
Constraint Effect ◽  
Engineering Structures ◽  
Integrity Assessment ◽  
Failure Assessment ◽  
Recent Developments ◽  
Failure Predictions ◽  
Crack Tip Constraint

The loss of crack tip constraint leads to enhanced resistance to both cleavage and ductile tearing. However, conventional failure assessment schemes (CEGB-R6, BS-7910) use lower bound toughness obtained from highly constrained test specimens. Cracks in many real engineering structures are not highly constrained, which makes failure predictions using conventional failure assessment schemes based on lower bound fracture toughness values overly pessimistic. Excessive pessimism in the structural assessment can lead to unwarranted repair or decommissioning of structures, and thus cause unneeded cost and inconvenience. Recent developments on constraint-based fracture mechanics have enabled the practical assessment of defective components including the constraint effect. For example, the recent revision of R6 and the newly developed structural integrity assessment procedures for European industry (SINTAP) have suggested a framework for failure assessments including the constraint effect. In this paper, the constraint-based failure assessment of surface cracked T-plate welded joints under tension load is presented. Different issues including the constraint-based failure assessment diagrams, the treatment of combining primary and the secondary loads, and the calculation of stress intensity factors, limit loads and constraint parameters for surface cracked T-plate joints are discussed. It is demonstrated that when the lower constraint effect is properly accounted for, the maximum allowable tensile stress level increases substantially.

Limits of Applicability of the Notch Failure Assessment Diagram

2018 ◽  
Author(s):  
Anthony J. Horn ◽  
Chris Aird
Keyword(s):  
Structural Integrity ◽  
Notch Root ◽  
Fatigue Cracks ◽  
Mechanical Damage ◽  
Root Radius ◽  
Integrity Assessment ◽  
Failure Assessment Diagram ◽  
Notch Root Radius ◽  
Failure Assessment ◽  
Sharp Crack

Structural integrity assessment codes such as R6 [1] and BS7910 [2] provide guidance on the assessment of flaws that are assumed to be infinitely sharp using the Failure Assessment Diagram (FAD). In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as those associated with lack of fusion, porosity or mechanical damage. Several Notch Failure Assessment Diagram (NFAD) methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. This paper uses mechanistic modelling to define the limits of applicability of the NFAD approach in terms of ρ/a, where ρ is the notch root radius and a is the notch depth. The work concludes that the NFAD can be used to assess notches with ρ/a values of up to unity.

Improvement of Probabilistic Fracture Mechanics Analysis Code PASCAL-SP Regarding Stress Corrosion Cracking in Nickel Based Alloy Weld Joint of Piping System in Boiling Water Reactor

2021 ◽  
Author(s):  
Akihiro Mano ◽  
Yoshihito Yamaguchi ◽  
Jinya Katsuyama ◽  
Yinsheng Li
Keyword(s):  
Fracture Mechanics ◽  
Stress Corrosion Cracking ◽  
Failure Probability ◽  
Weld Joint ◽  
Structural Integrity ◽  
Boiling Water ◽  
Piping System ◽  
Integrity Assessment ◽  
Weld Joints ◽  
Nickel Based Alloy

Abstract In the past few decades, the cracks because of stress corrosion cracking (SCC) have been detected in the dissimilar weld joints welded using nickel based alloy in piping system of boiling water reactors. Thus, the structural integrity assessment for such weld joints has become important. Nowadays, probabilistic fracture mechanics (PFM) analysis is recognized as a rational method for structural integrity assessment because it can consider inherent uncertainties of various influencing factors as probability distributions and quantitatively evaluate the failure probability of a cracked component. The Japan Atomic Energy Agency has developed a PFM analysis code PASCAL-SP for a probabilistic structural integrity assessment of weld joint in pipe in nuclear power plant. This study improves the analysis functions of PASCAL-SP for weld joint welded using nickel based alloy in boiling water reactor susceptible to SCC. As an analysis example of the improved version of PASCAL-SP, the failure probability of a weld joint is quantitatively evaluated. Furthermore, sensitivity analyses are conducted concerning the effect of leak detection and in-service inspection. From the analysis results, it is concluded that the improved version of PASCAL-SP is useful for structural integrity assessment.

Instrumented Indentation Technique to Measure Flow Properties: A Novel Way to Enhance the Accuracy of Integrity Assessment

2003 ◽  
Author(s):  
Jae-Il Jang ◽  
Yeol Choi ◽  
Yun-Hee Lee ◽  
Jung-Suk Lee ◽  
Dongil Kwon ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Crack Detection ◽  
Structural Integrity ◽  
Instrumented Indentation ◽  
Flow Properties ◽  
Integrity Assessment ◽  
Indentation Technique ◽  
Failure Assessment ◽  
Similar Vein ◽  
Non Destructive

While most in-field technologies for structural integrity diagnosis focus on precise crack detection, the instrumented indentation technique has emerged as one of the most practically useful technologies for non-destructive and quantitative in-field measurement of mechanical properties. In a similar vein, here an advanced indentation technique for determining tensile properties and its application to structural integrity assessment are introduced and discussed. This novel indentation technique can enhance the accuracy of fitness-for-service (FFS) assessment by application to failure assessment diagram (FAD) construction.

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