Partial Safety Factors Assessment of Pipes With a Circumferential Surface Flaw

2010 ◽  
Author(s):  
Hideo Machida ◽  
Hiromasa Chitose ◽  
Manabu Arakawa
Keyword(s):  
Fracture Resistance ◽  
Design Method ◽  
Limit State ◽  
Surface Flaw ◽  
Flaw Size ◽  
Material Strength ◽  
State Function ◽  
Safety Factors ◽  
Related Parameter ◽  
Partial Safety Factors

This paper describes the evaluation of partial safety factors (PSF’s) for parameters related to flaw evaluation of pipes which have a circumferential surface flaw, and proposes the important matter which should be pay attention in the setup of the safety factors used in flaw evaluation. PSF’s were evaluated considering randomness of flaw size, a fracture resistance curve (J-R curve) and applied loads using load and resistance factor design method (LRFD). The limit state function is expressed by fracture resistance (resistance-related parameter) and applied J integral (load-related parameter). The measure parameters in the reliability assessment are the flaw size and the J-R curve, and PSF’s of them are larger than those of applied loads. Since the material properties used in the flaw evaluation are generally set to the engineering lower limit of their variation (e.g., 95% lower confidence limit), variation of the flaw size is considered to have important role on flaw evaluation. Therefore, when setting up the safely factors used in Rules on Fitness-for-Service (FFS), it is necessary to take into consideration not only the influence of variation of loads or material strength but the influence of variation of flaw size.

Fatigue Design Margin Evaluation for Carbon and Low-Alloy Steels by Reliability-Based Load and Resistance Factor Method

2011 ◽  
Author(s):  
Masahiro Takanashi ◽  
Makoto Higuchi ◽  
Junki Maeda ◽  
Shinsuke Sakai
Keyword(s):  
Applied Stress ◽  
Limit State ◽  
State Function ◽  
Low Alloy Steels ◽  
Limit State Function ◽  
Safety Factors ◽  
Fatigue Data ◽  
Alloy Steels ◽  
Partial Safety Factors ◽  
Two Parameters

This paper discusses the margins of the design fatigue curve in the ASME Boiler and Pressure Vessel Codes Section III from a reliability analysis point of view. It is reported that these margins were developed so as to cover uncertainties of fatigue data scatter, size effect, and surface condition[1], but the reasons for them remain unclear. In order to investigate the physical implications of the design margin, a probabilistic approach is taken for the collected fatigue data of carbon and low-alloy steels. In this approach, these three parameters are treated as random variables, and an applied stress is also taken into consideration as a random variable. For the analysis, to begin with, a limit state function for fatigue is proposed. Next, reliability index contours of the design fatigue curves for carbon and low-alloy steels are obtained based on the proposed limit state function. The contours indicate that the margins 2 on stress and 20 on life do not provide equal reliability. The margin 20 on life is more conservative and the margin became a minimum near intersections of the design curves with margins 2 on stress and 20 on life. For practical applications, the partial safety factors (PSF) for the target reliability are computed for all materials and several levels of coefficients of variation (COV) of the applied stress. A sensitivity analysis of the PSFs clarifies that only two parameters, the strength (or the life) and the applied stress, are predominant. Thus, the partial safety factors for these two parameters are proposed in a tabular form.

Application of Partial Safety Factors for Fitness-for-Service Assessment of Pressure Equipment With Local Metal Loss

2017 ◽  
Author(s):  
Takuyo Kaida ◽  
Shinsuke Sakai
Keyword(s):  
Reliability Analysis ◽  
Limit State ◽  
Probability Of Failure ◽  
Pressure Vessels ◽  
Metal Loss ◽  
State Function ◽  
Safety Factors ◽  
Loss Assessment ◽  
Reliability Method ◽  
Partial Safety Factors

Reliability analysis considering data uncertainties can be used to make a rational decision as to whether to run or repair a pressure equipment that contains a flaw. Especially, partial safety factors (PSF) method is one of the most useful reliability analysis procedure and considered in a Level 3 assessment of a crack-like flaw in API 579-1/ASME FFS-1:2016. High Pressure Institute of Japan (HPI) formed a committee to develop a HPI FFS standard including PSF method. To apply the PSF method effectively, the safety factors for each dominant variable should be prepared before the assessment. In this paper, PSF for metal loss assessment of typical pressure vessels are derived based on first order reliability method (FORM). First, a limit state function and stochastic properties of random variables are defined. The properties of a typical pressure vessel are based on actual data of towers in petroleum and petrochemical plants. Second, probability of failure in several cases are studied by Hasofer-Lind method. Finally, PSF’s in each target probability of failure are proposed. HPI published a new technical report, HPIS Z 109 TR:2016, that provide metal loss assessment procedures based on FORM and the proposed PSF’s described in this paper.

Applicability of FFS Assessment Using Partial Safety Factors Evaluated by Infinite Plate

2013 ◽  
Author(s):  
Qiang Qu ◽  
Satoshi Izumi ◽  
Shinsuke Sakai
Keyword(s):  
Limit State ◽  
Infinite Plate ◽  
Safety Margin ◽  
Simulation Method ◽  
State Function ◽  
Monte Carlo Simulation Method ◽  
Safety Factors ◽  
Failure Assessment ◽  
Partial Safety Factors ◽  
Load Types

This paper investigates the applicability of a Fitness-For-Service (FFS) assessment of crack-like flaws using the Partial Safety Factors (PSFs) calculated from the infinite plate model. Procedures of FFS assessment using PSFs are provided in API579-1, and several PSFs calculated from an infinite plate are given to evaluate structures approximately for simplification. However, the applicability of these PSFs is not clear, and the safety margin cannot be evaluated precisely. To clarify the applicable region of these infinite plate PSFs in this paper, we calculate PSFs of various structures, crack geometries and load types and compare with those of the infinite plate. We also examine whether the target reliability is satisfied when infinite plate PSFs are applied to the concrete structures. In addition, we used sensitivity analysis to show the dependence of probabilistic properties on the safety margin. Both the limit state function method and the Monte Carlo simulation method are used for the analysis, and the limit state is defined by the Failure Assessment Diagram (FAD) curve. Finally, the relation between infinite plate PSFs’ applicability and probabilistic properties of structure, and crack geometries are discussed.

Research on Design Reference Period and Structural Design Method

2011 ◽  
Vol 368-373 ◽  
pp. 2364-2368
Author(s):  
Jia Nian He ◽  
Zhan Wang
Keyword(s):  
Structural Design ◽  
Reliability Index ◽  
Design Method ◽  
Structure Design ◽  
Reference Period ◽  
Building Structure ◽  
Safety Factors ◽  
Importance Factor ◽  
Partial Safety Factors

In structure design, for expressions with partial safety factors, partial safety factors and nominal value of loads are calculated based on the presupposition that the design reference period is 50 years. When the design reference period is not 50 years, it would cause unclear reliability of building structure by using expressions with partial safety factors following correlative codes yet. It may lead to hidden dangers in that way. In order to derive expressions with partial safety factors suitable for any design reference period, two useful methods are shown in this paper, modification of partial safety factors and modification of importance factor of structures. From results of analysis, we get the conclusions that it can assure the reliability index of the expression using the method of modification of partial safety factors, and the method of modification of importance factor of structures is very simple, but cannot assure the reliability index of the expression.

Assessment of Fatigue Safety Factors for Deep-Water Risers in Relation to VIV

2005 ◽  
Vol 127 (4) ◽  
pp. 353-358 ◽  
Author(s):  
Bernt J. Leira ◽  
Trond Stokka Meling ◽  
Carl M. Larsen ◽  
Vidar Berntsen ◽  
Bernie Stahl ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Limit State ◽  
Random Variables ◽  
Response Surfaces ◽  
State Function ◽  
Safety Factors ◽  
Parameter Variations ◽  
Input Parameters ◽  
Steel Catenary Risers ◽  
Analytical Expressions

Safety factors required to control fatigue damage of deepwater metallic risers caused by vortex-induced vibration (VIV) are considered. Four different riser configurations are studied: Cases I and II: Vertical tensioned 12in. risers suspended from a spar buoy at water depths of 500 and 1500m. Cases III and IV: Steel catenary risers suspended from a spar buoy, both at 1000m. For Case III, the riser diameter is 12in., while for Case IV it is 33in. For each riser configuration, relevant design and analysis parameters which are subject to uncertainty are identified. For these quantities, random variables are established also representing model uncertainties. Subsequently, repeated analyses of fatigue damage are performed by varying the input parameters within representative intervals. The results are applied to fit analytical expressions (i.e., so-called response surfaces) utilized to describe the limit state function and to develop the probabilistic model for reliability analysis of the risers. By combining the random variables for the input parameters with the results from the parameter variations, a relationship between the fatigue safety factor and the failure probability is established for each riser configuration.

Fatigue Safety Factors for Flexible Risers Based on Case Specific Reliability Analysis

2005 ◽  
Author(s):  
Bernt J. Leira ◽  
Ragnar T. Igland ◽  
Gro S. Baarholm ◽  
Knut A. Farnes ◽  
Dick Percy
Keyword(s):  
Reliability Analysis ◽  
Limit State ◽  
State Function ◽  
Safety Factors ◽  
Fatigue Lifetime ◽  
Statistical Variation ◽  
Parametric Studies ◽  
Flexible Risers ◽  
Corrosive Environments ◽  
Wave Induced

In the present paper, fatigue safety factors for flexible risers are assessed. A procedure for reliability analysis of wave-induced fatigue is first described. The procedure is based on performing a number of parametric studies with respect to variables that influence the fatigue lifetime. The results of these parametric studies are subsequently combined with models describing the statistical scatter of the same parameters. By application of this procedure, the safety factors which are required in order to reach specific target reliability levels can be computed. Such safety factors are computed for three specific flexible riser configurations. Different SN -curves which correspond to different corrosive environments are considered. The percentwise contribution from each parameter to the total statistical variation of the limit state function is also quantified.

scholarly journals Harmonized European Standards for Proof of Competence of Cranes

2018 ◽  
Vol 41 ◽  
pp. 03018
Author(s):  
Stefan VÖth ◽  
Guido Schneider ◽  
Maxim Tyulenev
Keyword(s):  
Limit State ◽  
Safety Factors ◽  
Safety Requirements ◽  
New Concepts ◽  
Partial Safety Factors ◽  
State Method ◽  
European Standards ◽  
Structural Parts ◽  
Major Argument ◽  
Distribution Class

With EN 13001-1 ff. a harmonized set of standards for safety of cranes was and is established. Due to harmonization the use of the standards leads to the assumption of conformity with the safety requirements of the machinery directive. A major argument for the application of the standards. The standards comprise new concepts of proof of competence in comparison to previous standards. Keywords of these new concepts are “Classification”, “Limit state method”, “Mass Distribution Class” and “Partial safety factors”. The article gives an overview to EN 13001-1, EN 13001-2 and EN 13001-3-1. This is the set of standards for proof of the structural parts of a crane. The main aspects of the standards are shown and discussed with regard to their impact on calculation.

Partial Safety Factors for Vertical Bending Loads on Containerships

1992 ◽  
Vol 114 (2) ◽  
pp. 129-136 ◽  
Author(s):  
C. O¨stergaard
Keyword(s):  
Probability Density ◽  
Reliability Analysis ◽  
Limit State ◽  
Bending Moment ◽  
Bending Moments ◽  
Wave Loads ◽  
Safety Factors ◽  
The North ◽  
Design Values ◽  
Partial Safety Factors

International design codes for seagoing steel ships of today are in the process of testing a new safety format with load factors separately multiplied with nominal (code) values of still water and wave loads. This leads to two design values of these loads, the sum of which must not exceed a design value of the strength of the ship structure, which is again a nominal (code) value of strength, this time divided by a strength factor. Such load and strength factors are generally termed partial safety factors. In the paper, vertical still water and wave bending moments of containerships are considered as loads. The partial safety factors are determined on the basis of reliability analysis, i.e., the sum of the design values of the loads will not exceed a design serviceability limit state of the ship’s structure with given probability. To enable reliability analysis, distribution density of the ship’s strength to resist bending moments is based on a stochastic interpretation of nominal (code) values used in the conventional safety format. The probability density of the still water bending moment is obtained from recently published statistical data. The probability density of the wave bending moment is calculated using advanced hydrodynamic and spectral analysis, including long-term statistics of the (North Atlantic) seaway. Reliability and related design values are estimated using the FORM algorithm with due consideration of the different repetition numbers for which the stochastic models of the two bending moments are valid. The results are presented as nonlinear regression formulas and as diagrams that specify partial safety factors related to length and beam of containerships. The nominal values of bending moments to be used with these partial safety factors are given as functions of length, beam, and block coefficient of those ships.

Reliability-Based LRFD Criteria for Unstiffened Panel of Ship Structures

2013 ◽  
Author(s):  
Yong Bai ◽  
Miao-hua Qian
Keyword(s):  
Limit State ◽  
State Equation ◽  
Safety Factors ◽  
Ship Structures ◽  
Future Design ◽  
Practical Project ◽  
Safety And Reliability ◽  
Partial Safety Factors ◽  
Factor Design ◽  
Load And Resistance Factor

It is of significance to do the research of safety and reliability for ship structures, especially for marine structures because of the poor conditions and high risks, future design for ship structures will move toward a more rational and probability-based design. This paper chooses the unstiffened panel of ship structures as the research subject. Based on the MATLAB software, this paper develops the procedures and calculates one limit state equation of the panel, derives partial safety factors (PSF) for the Load and Resistance Factor Design (LRFD) of the panel under different reliability index levels. The PSF may provide a reference for the practical project design.

Gear Reliability Design Using Probability Finite Element Method Based on Response Surface

2010 ◽  
Vol 34-35 ◽  
pp. 7-12 ◽  
Author(s):  
Shu Xia Sun ◽  
Ming Yan ◽  
Ping Bai ◽  
Li Han
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Response Surface ◽  
Design Method ◽  
Limit State ◽  
General Purpose ◽  
State Function ◽  
Limit State Function ◽  
Reliability Design ◽  
Element Method

The paper studies on the gear reliability design method using probability finite element method based on response surface and it indicates that the reliability sensibility calculation method of function in response surface can be used when limit state function is unknown. The limit state function established on response function is quadratic polynomial with simple form and it makes the calculation of variance and deviation very convenient, which realizes the simple and easy calculation of reliability sensitivity and largely increases calculation velocity and precision. The method can be applied for general purpose with certain standard, which is easy for programming and accomplishing gear reliability design in a rapid and precise way.

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