Fatigue Safety Factors for the Tensile and Pressure Armours of Flexible Risers

2007 ◽  
Author(s):  
Bernt J. Leira ◽  
Ragnar T. Igland ◽  
Naiquan Ye ◽  
Elizabeth A. Passano
Keyword(s):  
Limit State ◽  
State Function ◽  
Flexible Riser ◽  
Safety Factors ◽  
Fatigue Lifetime ◽  
Statistical Variation ◽  
Parametric Studies ◽  
Flexible Risers ◽  
Corrosive Environments ◽  
Wave Induced

In the present paper, fatigue safety factors for metallic layers of 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. Example of calculation of such safety factors for the tensile and pressure armours of some specific flexible riser configurations are given. 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.

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.

A Framework for Reliability-Based Fatigue Safety Factors for Flexible Risers

2007 ◽  
Author(s):  
B. J. Leira ◽  
K. A. Farnes ◽  
R. T. Igland ◽  
J. Martin ◽  
D. Percy ◽  
...  
Keyword(s):  
Reliability Analysis ◽  
Safety Factors ◽  
Fatigue Lifetime ◽  
Specific Target ◽  
Parametric Studies ◽  
Flexible Risers ◽  
Corrosive Environments ◽  
Wave Induced

In the present paper, a procedure for reliability analysis of wave-induced fatigue in the tensile and pressure armours of flexible risers is 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. Different SN-curves which correspond to different corrosive environments are considered.

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.

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.

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.

Corrosion Fatigue Testing of Flexible Riser Armour: Procedures for Testing and Assessment of Design Criteria

2003 ◽  
Author(s):  
Stig Berge ◽  
Erik Bendiksen ◽  
Jonas Gudme ◽  
Richard Clements
Keyword(s):  
Corrosion Fatigue ◽  
Fatigue Testing ◽  
Design Criteria ◽  
Flexible Riser ◽  
Test Procedures ◽  
Fatigue Design ◽  
Flexible Risers ◽  
Corrosive Environments

Fatigue design of armour wires in flexible risers is reviewed, with particular emphasis on effects of corrosive environments in pipe annulus. Test procedures for corrosion fatigue testing of armour wire and assessment of fatigue design criteria are described.

scholarly journals Dimensioning of silicone adhesive joints: Eurocode-compliant, mesh-independent approach using the FEM

2020 ◽  
Vol 5 (3) ◽  
pp. 349-369 ◽  
Author(s):  
Micheal Drass ◽  
Michael A. Kraus
Keyword(s):  
Finite Element ◽  
Safety Factor ◽  
Limit State ◽  
Adhesive Joints ◽  
State Function ◽  
Limit State Function ◽  
Element Calculation ◽  
Safety Factors ◽  
Silicone Adhesive ◽  
Level I

Abstract This paper deals with the application of the semi-probabilistic design concept (level I, DIN EN 1990) to structural silicone adhesives in order to calibrate partial material safety factors for a stretch-based limit state equation. Based on the current legal situation for the application of structural sealants in façades, a new Eurocode-compliant design concept is introduced and compared to existing design codes (ETAG 002). This is followed by some background information on semi-probabilistic reliability modeling and the general framework of the Eurocode for the derivation of partial material safety factors at Level I. Within this paper, a specific partial material safety factor is derived for DOWSIL 993 silicone on the basis of experimental data. The data were then further evaluated under a stretch-based limit state function to obtain a partial material safety factor for that specific limit state function. This safety factor is then extended to the application in finite element calculation programs in such a way that it is possible for the first time to perform mesh-independent static calculations of silicone adhesive joints. This procedure thus allows for great optimization of structural sealant design with potentially high economical as well as sustainability benefits. An example for the static verification of a bonded façade construction by means of finite element calculation shows (i) the application of EC 0 to silicone adhesives and (ii) the transfer of the EC 0 method to the finite element method with the result that mesh-independent ultimate loads can be determined.

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.

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

2003 ◽  
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 ◽  
Input Parameters ◽  
Steel Catenary Risers ◽  
The Relationship ◽  
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: • Case I and II: Vertical tensioned 12” risers suspended from a spar buoy at water depths of 500m and 1500m. • Case III and IV: Steel catenary risers suspended from a spar buoy, both at 1000m. For Case III, the riser diameter is 12”, while for Case IV it is 30”. For each riser configuration, relevant design and analysis parameters which are subject to uncertainty are identified. For these quantities, random variables are established including 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, the relationship between the fatigue safety factor and the failure probability is established for each riser configuration.

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