Fatigue Safety Factors for Deepwater Risers

2002 ◽  
Author(s):  
B. Stahl ◽  
H. Banon
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Safety Factor ◽  
Damage Index ◽  
Rational Approach ◽  
Fatigue Reliability ◽  
Safety Factors ◽  
Fatigue Design ◽  
Uncertainty Parameters ◽  
Deepwater Risers

Fatigue life is governed by a number of variables that are highly uncertain. The safety factor on fatigue life is used in a deterministic way to account for the estimated fatigue damage uncertainty. High uncertainties lead to high fatigue safety factors, and vice versa. Evaluation of the uncertainties in the variables governing fatigue design provides a grip on what the safety factor should be. This paper addresses riser fatigue using a fatigue reliability model that is relatively simple but still captures the important elements of the fatigue problem. The bias and uncertainty of stress range are extremely important parameters in design against fatigue. This is due not only to the fact that these parameters are highly uncertain, but also to the fact that they are greatly amplified in the fatigue damage equation by the ‘slope’ m of the S-N curve. The Palmgren-Miner fatigue damage index and the intercept value of the S-N curve are additional important variables in fatigue design. A model for combining wave-induced and vortex-induced vibration (VIV) is introduced together with the best available data and reference to industry work in this technology area. A recently completed joint industry project on riser reliability provides good calibration points for the critical fatigue reliability variables. Reliability and sensitivity studies are performed to demonstrate the effect of the uncertainty parameters. An approach to selecting deterministic fatigue design factors that yield specified reliability targets is developed and illustrated. The study provides a rational approach to selecting safety factors for design of deepwater risers, taking into account both wave and VIV-induced fatigue damage.

Probabilistic Fatigue Damage Analysis of Long Span Suspension Bridge Due to Wind Induced Buffeting

2020 ◽  
Vol 980 ◽  
pp. 275-281
Author(s):  
Hu Jun
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Time History ◽  
Suspension Bridge ◽  
Wind Load ◽  
Strong Wind ◽  
Fatigue Reliability ◽  
Long Span ◽  
Fatigue Damage Analysis ◽  
Fluctuating Wind

In order to consider the fluctuating wind load induced fatigue problem of long span suspension bridge, fatigue reliability formula is modified by assuming the fatigue life is accord with the weibull distribution. Based on the accurate bridge buffeting analysis of time history, the stress time history of components of a suspension bridge in east sea China is simulated, and then the fatigue damages and reliabilities are calculated. The results indicate that the main cables and hangers have enough fatigue reliability under the fluctuating wind load, the fatigue failure will not occur; the stiffening girder has larger fatigue damage, under 40 / (m.s-1) mean wind speed action, the girder of mid-support section’s average fatigue life is only 3.103 years, so the girder’s damage under strong wind action should be taken seriously.

The Iterative Method for Reliability Estimation of Fatigue Life

2012 ◽  
Vol 249-250 ◽  
pp. 628-631
Author(s):  
Xin Li Bai ◽  
Peng Xu ◽  
Jiang Yan Li
Keyword(s):  
Fatigue Life ◽  
Design Method ◽  
Estimation Method ◽  
Engineering Application ◽  
Reliability Estimation ◽  
Fatigue Reliability ◽  
Reliability Design ◽  
Fatigue Design ◽  
Machine Parts ◽  
Stress Cycles

The expression of reliability estimation method for fatigue life of machine parts was derived, and two kinds of stress cycles (reversed cycle and un-symmetric reversed cycle) were considered. An iteration method is presented and the corresponding computer program named STRENGTH-2 is developed for estimating reliable life of machine parts. The engineering application results show that the calculated results are close to experimental results. The proposed method can be convenient to carry out the fatigue reliability design for machine parts under the action of uni-axial and multi-axial loadings, and promote the popularization and application of existing anti-fatigue design method. It has the high value of engineering application.

scholarly journals Prediction of Fatigue Life of a Continuous Bridge Girder Based on Vehicle Induced Stress History

2003 ◽  
Vol 10 (5-6) ◽  
pp. 325-338 ◽  
Author(s):  
V.G. Rao ◽  
S. Talukdar
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Fatigue Testing ◽  
Damage Index ◽  
Time History ◽  
Stress Range ◽  
Frequency Histogram ◽  
Bridge Span ◽  
History Of ◽  
Bridge Girder

The fatigue damage assessment of bridge components by conducting a full scale fatigue testing is often prohibitive. A need, therefore, exists to estimate the fatigue damage in bridge components by a simulation of bridge-vehicle interaction dynamics due to the action of the actual traffic. In the present paper, a systematic method has been outlined to find the fatigue damage in the continuous bridge girder based on stress range frequency histogram and fatigue strength parameters of the bridge materials. Vehicle induced time history of maximum flexural stresses has been obtained by Monte Carlo simulation process and utilized to develop the stress range frequency histogram taking into consideration of the annual traffic volume. The linear damage accumulation theory is then applied to calculate cumulative damage index and fatigue life of the bridge. Effect of the bridge span, pavement condition, increase of vehicle operating speed, weight and suspension characteristics on fatigue life of the bridge have been examined.

A Probabilistic Approach to Fatigue Safety and Integrity of TTRs

2014 ◽  
Author(s):  
Mir Emad Mousavi ◽  
Sanjeev Upadhye ◽  
Vishnu Vijayaraghavan ◽  
Kevin Haverty
Keyword(s):  
Fatigue Damage ◽  
Probabilistic Method ◽  
Probabilistic Approach ◽  
Probabilistic Methods ◽  
Fatigue Reliability ◽  
Fatigue Design ◽  
Integrity Index ◽  
Biased Estimators ◽  
Integrity Analysis

Probabilistic methods can improve the reliability of fatigue damage evaluation in top tensioned (production) risers because they tend to provide less biased estimators on their safety, which can be used for more reliable decision making concerning their design. Such methods consider the collective impact of uncertainties in the riser system, which is not accurately assessed in conventional fatigue analysis. The large factors of safety that are commonly used in deterministic-based fatigue damage assessment tend to assure the high safety of the design, still they are generic factors that do not take advantage of available data for accurate quantification of system safety. This paper presents a probabilistic method toward fatigue reliability and integrity analysis of TTR systems. By using rules of probability, a simplified method is developed to estimate the probability of failure of the TTR system in its lifetime, considering the uncertainties with the Palmgren-Miner rule, the cyclic loads, and the fatigue strength of the components, and other analysis approximations. The method is then used for a comparative assessment on the fatigue reliability of the TTR components and calculating its fatigue Integrity Index. The method is illustrated in a case study and is used to provide recommendations that could possibly improve the TTR fatigue design by reducing its cost, increasing its safety, and maximizing its integrity.

Reliability Estimation of Fatigue Life for Machine Parts under Uniaxial Constant Amplitude Load

2012 ◽  
Vol 249-250 ◽  
pp. 632-635
Author(s):  
Yu He Li ◽  
Xin Li Bai ◽  
Ying Fang Zhang
Keyword(s):  
Fatigue Life ◽  
Design Method ◽  
Engineering Application ◽  
Reliability Estimation ◽  
Estimation Methods ◽  
Fatigue Reliability ◽  
Constant Amplitude ◽  
Reliability Design ◽  
Fatigue Design ◽  
Machine Parts

Two methods acquiring p-S-N curve for machine parts are given, namely directly searching out the p-S-N curve of the material from material database and using the idealized p-S-N curve. Reliability estimation methods of fatigue life of machine parts are derived under uniaxial constant amplitude load. Two kinds of circumstances (fixed stress and probabilistic stress) and two kinds of stress cycles (reversed cycle and unsymmetric reversed cycle) are considered. An iteration method is presented and the corresponding computer program is developed for estimating reliable life of machine parts. The engineering application results show that the calculated results are closer to experimental results. The suggested method can be convenient to fatigue reliability design of machine parts. It has good stimulative effect on popularization and application of existing anti-fatigue design method for machine parts, and high value of engineering application.

Calibration of Safety Factors for DNV RP-F105 Free Spanning Pipelines

2006 ◽  
Author(s):  
Gudfinnur Sigurdsson ◽  
Kim Mo̸rk ◽  
Olav Fyrileiv
Keyword(s):  
Fatigue Damage ◽  
Structural Reliability ◽  
Uncertainty Modeling ◽  
Submarine Pipeline ◽  
Safety Factors ◽  
Sources Of Uncertainty ◽  
Fatigue Design ◽  
Vortex Induced Vibrations ◽  
Stochastic Parameters ◽  
Pipeline Design

Free spans often become a significant challenge in pipeline design and operation due to uneven seabed or seabed scouring effects. The trend towards deeper waters, harsher environment and installation of pipelines at very uneven seabed often implies a high number of free spans. High costs related to span intervention puts focus on minimizing these costs and still ensure integrity of the pipeline with respect to vortex induced vibrations (VIV) and associated fatigue damage. On the other hand the potential costs related to fatigue failure of a pipeline (recovery costs and economical loss) are enormous. Therefore it is essential to ensure that the probability of failure for free spans is within acceptable limits, e.g. as required by DNV-OS-F101 “Submarine Pipeline Systems”. This paper describes the structural reliability analysis performed to obtain the safety factors for free span fatigue design. Accumulation of fatigue damage due to VIV of free spans is associated with various sources of uncertainty. The important stochastic parameters are described, and the basis for the uncertainty modeling given. The calibration scope defined from a set of different pipeline cases, span scenarios, and environmental conditions is presented from which calibration results and sensitivities will be discussed.

scholarly journals New Damage Evolution Law for Steel–Asphalt Concrete Composite Pavement Considering Wheel Load and Temperature Variation

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3723 ◽  
Author(s):  
Xunqian Xu ◽  
Xiao Yang ◽  
Wei Huang ◽  
Hongliang Xiang ◽  
Wei Yang
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Damage Evolution ◽  
Steel Bridge ◽  
Wheel Load ◽  
Evolution Law ◽  
Long Span ◽  
Fatigue Design ◽  
Epoxy Asphalt

Epoxy asphalt (EA) concrete is widely used in constructing long-span steel bridge pavements (SBDPs). This study aims to derive a fatigue damage evolution law, conducting an experimental investigation of SBDP. First, a general theoretical form of the fatigue damage evolution law of materials is established based on the thermal motion of atoms. Then, fatigue experiments demonstrate that this evolution law well represents the known damage–life relationships of SBDP. Taking into account the experimental relationships between damage and fatigue life under symmetrical cyclic loadings with different overload amplitudes and temperature variations, a detailed damage evolution law is deduced. Finally, the role of damage accumulation is discussed on the basis of the proposed damage evolution law for the extreme situation of heavy overload and severe environments. The results show that both heavy loading and falling temperatures increase the fatigue damage of SBDP considerably. EA shows a fatigue life two to three times longer than that of modified matrix asphalt (SMA) or guss asphalt (GA). For the same thickness, EA pavement is demonstrated to be more suitable for an anti-fatigue design of large-span SBDP under high traffic flows and low temperatures.

scholarly journals Loading regimes and designing helical coiled springs for safe fatigue life

2012 ◽  
Vol 51 (No. 2) ◽  
pp. 50-55 ◽  
Author(s):  
M. Růžička ◽  
K. Doubrava
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fatigue Damage ◽  
Safety Factor ◽  
Stress Concentration Factor ◽  
Fe Method ◽  
Helical Springs ◽  
Damage And Failure ◽  
Spring Wire ◽  
Inner Diameter

Springs are loaded by harmonic forces very often. High cycles fatigue damage and failure can be found during its service loading. This paper shortly describes stress concentration factor for helical springs on the inner diameter of the spring wire and its evaluation by using FE Method. These results have been compared with correction functions published in the literature. The fatigue safety factor has been derived for three typical loading regimes of springs. All cases are demonstrated in the Haigh diagram. It has been showed that loading cases with constant operational prestress give lowest safety factor then the proportional or constant middle stress regimes.

Fatigue Reliability Evaluation Model of Drillstring in Bending Section of Horizontal Well

2012 ◽  
Vol 490-495 ◽  
pp. 2295-2299
Author(s):  
Yi Fei Yan ◽  
Lu Feng Cheng
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Horizontal Well ◽  
Evaluation Model ◽  
Reference Value ◽  
Reliability Evaluation ◽  
Fair Use ◽  
Bending Stress ◽  
Fatigue Reliability ◽  
Alternating Bending

When drillstring rotates through the bending section of horizontal well, the fatigue damage of drillstring will be caused by alternating bending stress. Therefore, a thought to solve the fatigue reliability problem of drillstring in bending section of horizontal well is proposed. The variable amplitude alternating stress is transformed into equivalent fatigue stress, and the fatigue damage of drillstring is analyzed. Considering Palmgren-Miner rule and S-N curve, the fatigue life and reliability evaluation model of drillstring in bending section of horizontal well is established according to the fatigue reliability theory and probabilistic fracture mechanics. This model can calculate the fatigue damage, fatigue life and reliability of drillstring in the process of drilling and the maximum allowable dogleg angle where the drillstring is under compression and tension. And it has the important reference value for the fair use of drillstring and casing program design.

Application of DNV-RP-F204 for Determining Riser VIV Safety Factors

2005 ◽  
Author(s):  
Muthu Chezhian ◽  
Kim Mo̸rk ◽  
Marit Ronæss ◽  
Trond Stokka Meling
Keyword(s):  
Case Studies ◽  
Fatigue Damage ◽  
Safety Factor ◽  
Lift Coefficient ◽  
Environmental Modeling ◽  
Optimal Choice ◽  
Analysis Model ◽  
Safety Factors ◽  
Acceptance Criterion ◽  
Uncertain Input

Fatigue is often the governing criterion for deepwater riser design. Fatigue assessment methods based on SN curves typically use fatigue safety factors and there is a lack on consensus about the appropriate Design Fatigue Factor (DFF) for VIV that should be applied. A DFF of 20 is commonly used in project specifications to account for a larger uncertainty in prediction of fatigue damage due to VIV, i.e. fatigue life due to VIV should be at least 20 times more than the service life of the riser. Recent case studies and benchmarking assessments, have confirmed that the DFF of 20 for VIV is not always an optimal choice. Owing to the complexity of the VIV problem, often semi-empirical solutions are adopted in the riser VIV analysis. The implicit uncertainty and bias associated with the VIV analysis model, needs to be considered along with the VIV fatigue safety factor, in order to establish the adequate acceptance criterion for VIV induced fatigue. The stochastic variables governing the VIV and their associated uncertainties can vary widely from case to case and this in turn will influence the VIV safety factor. Different stochastic variables may be relevant based on the floater type, riser type, environmental modeling, analysis methodology etc. In addition to these stochastic variables, the uncertainty in the VIV specific variables, such as Strouhal number, bandwidth parameters, damping effects, lift coefficient, response models (Amplitude /Diameter ratio), etc also need to be considered in the evaluation of the VIV safety factor. In this paper, guidance is provided by means of case studies for establishing case specific VIV safety factors. By performing a set of dedicated analyses for the prevailing uncertain input parameters, the resulting uncertainty in the VIV fatigue damage is estimated. The enhanced risk based criterion presented in DNV Recommended Practice RP-F204 [7], developed as part of the Norwegian Deepwater Programme (NDP) is applied for these case studies to calculate the required VIV fatigue safety factors. This project was sponsored by NDP, whose contribution and support is gratefully acknowledged.

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