Fatigue Reliability Assessment of Marine Risers in Deep Offshore Fields in Indian Ocean

2010 ◽  
Author(s):  
Rizwan A. Khan ◽  
Suhail Ahmad
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Deep Sea ◽  
Failure Modes ◽  
New Ventures ◽  
Limit State ◽  
Published Data ◽  
Unstable Fracture ◽  
Fatigue Reliability

Depleting oil reserves in shallow water are opening the avenues of new ventures in deep sea conditions. India is no exception; deep sea explorations are highly recommended and exercised. As part of the design process, there are requirements of structural strength based on criteria referring to failure modes, such as rupture by over loading, fatigue failures, buckling or an unstable fracture. 3D Nonlinear dynamic analysis of riser is obtained in the time domain using finite element solver ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue reliability analysis of riser. It is based on a bi-linear relationship to model fatigue crack growth and incorporates a failure criterion to describe the interaction between fracture and plastic collapse. Uncertainty modeling, especially on fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using Monte Carlo Simulation. The bi-linear S-N curve and crack growth models are found to lead to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has been thoroughly investigated. These findings implicate inspection schemes for components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment.

Nonlinear Dynamic and Bilinear Fatigue Performance of Composite Marine Risers in Deep Offshore Fields

2020 ◽  
Author(s):  
Rizwan A. Khan ◽  
Suhail Ahmad
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Failure Modes ◽  
Thermal Protection ◽  
Growth Models ◽  
Limit State ◽  
Design Procedure ◽  
Crack Size ◽  
Unstable Fracture ◽  
Fatigue Reliability

Abstract Composite materials have drawn considerable consideration from the offshore business, basically because of their high explicit quality. Notwithstanding weight decrease, composites offer extra advantages, for example, fatigue resistance, damping, and thermal (protection) properties, and high erosion resistance. As a part of design procedure there are requirements of mechanical strength based on criteria referring to failure modes, such as rupture by over loading, fatigue failures, buckling or an unstable fracture. Three dimensional nonlinear assessment of riser is carried out in time domain using ABAQUS/Aqua. The response time histories so obtained are used for the study of fatigue safety assessment of riser. It is based on a bi-linear approach to model fatigue crack growth and incorporates a failure limit to describe the interaction between rupture and plastic failure. Using Monte Carlo Simulation, tests of fatigue reliability and fatigue crack size evolution are obtained. It is observed that bilinear S-N curve and crack growth models leads to higher estimate of fatigue life. Sensitivity behavior pertinent to limit state adopted has been thoroughly examined. These outcomes implicate assessment of components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment.

Fatigue Reliability Evaluation of Marine Risers Under Vortex Induced Vibration

2013 ◽  
Author(s):  
Rizwan A. Khan ◽  
Suhail Ahmad
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Deep Sea ◽  
New Ventures ◽  
Limit State ◽  
Fatigue Reliability ◽  
Marine Riser ◽  
Vortex Induced Vibration ◽  
Finite Element Software ◽  
Bending Mode

Depleting oil reserves in shallow waters, off-shore oil fields are opening the avenues of new ventures in deep sea conditions. A marine riser is a major component of an offshore drilling and production system that are either fixed or floating in nature. Deepwater risers are quite long and significant currents usually excite natural bending mode that is much higher than the fundamental bending mode. In ultra deep environment currents usually change in magnitude and direction with depth, thereby inducing possibility of exciting multiple modes of the riser vibration due to VIV. Vortex induced vibration analysis has been carried out of a long marine riser in a probable deep sea location. To improve the understanding under deepwater harsh environments, the behavior of the riser under these forces is thoroughly investigated. 3D Nonlinear dynamic analysis of riser is obtained in the time domain using finite element software package ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue reliability analyses of riser. Uncertainty modeling, especially of fatigue crack growth parameters, is undertaken using bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using Monte Carlo Simulation. The bi-linear crack growth models are found to lead to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has been thoroughly investigated. These findings implicate inspection schemes for components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment.

Reliability Analysis of Fatigue Crack Growth with JC Method Based on Scientific Materials

2011 ◽  
Vol 63-64 ◽  
pp. 882-885 ◽  
Author(s):  
Xiao Li Zou
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Normal Distribution ◽  
Crack Growth ◽  
Reliability Index ◽  
Limit State ◽  
State Equation ◽  
Fatigue Reliability ◽  
Crack Propagation Process ◽  
Log Normal

Since the fatigue crack propagation process from initial size till final fracture is affected by lots of random factors, it is difficult to evaluate the fatigue reliability. Based on reliability theory, the first order second moment method ( JC method) is adopted to analyze and compute the fatigue reliability. To account for the uncertainties of material resistance, the parameters in the deterministic fatigue crack growth rate equation and material fracture toughness are taken as random variables with Normal distribution or Log-Normal distribution. Consequently, the limit state equation of fatigue crack growth is derived. The fatigue reliability index at any moment is calculated iteratively through JC method. As a computation example, the curve of fatigue crack growth reliability index with time is presented.

Bi-Linear Fatigue and Fracture Approach for Safety Analysis of an Offshore Structure

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Rizwan A. Khan ◽  
Suhail Ahmad
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Parameters ◽  
Limit State ◽  
Steel Structures ◽  
Published Data ◽  
Offshore Structure ◽  
Structure Degradation

The design of welded structures for the fatigue limit state is normally carried out by means of either linear or bilinear S-N curves, which have been found adequate to predict crack initiation only. To properly assess the effects of the design, fabrication, inspection, and repair strategy for structure degradation due to crack growth, fracture mechanics (FM) models need to be applied. In this paper, alternative S-N and FM formulations of fatigue are investigated. The probabilistic fracture mechanics approach predicts the fatigue life of welded steel structures in the presence of cracks under random spectrum loading. It is based on a recently proposed bi-linear relationship to model fatigue crack growth. Uncertainty modeling, especially on fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bilinear crack growth relationship. Results pertaining to the fatigue reliability and fatigue crack size evolution are presented using the Monte Carlo simulation technique and the emphasis is placed on a comparison between the linear and bilinear crack growth models. Variations in the system configuration, service life, and coefficients of crack growth laws have been studied on the parametric basis

Probabilistic Fatigue Safety Analysis of Oil and Gas Risers Under Random Loads

2010 ◽  
Author(s):  
Rizwan A. Khan ◽  
Suhail Ahmad
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Oil And Gas ◽  
Growth Parameters ◽  
Limit State ◽  
Nonlinear Dynamic Analysis ◽  
Fatigue Reliability ◽  
Gas Drilling ◽  
Finite Element Software

Marine riser is an important component of oil and gas drilling and production system. It is essentially a slender pipe conveying fluid between well-head and floating production unit. They are formed out of three basic types of configuration namely, free hanging, “lazy-wave (SWLR)” riser. Risers are subjected to varied static, quasi-static and dynamic forces. For the safety of design, the behavior of the riser under these forces is thoroughly investigated. 3D Nonlinear dynamic analysis of riser is obtained in the time domain using finite element software package ABAQUS/Aqua. The response histories so obtained are employed for the study of fatigue reliability analyses of riser. It is based on a bi-linear relationship to model fatigue crack growth and incorporates a failure criterion to describe the interaction between fracture and plastic collapse. Uncertainty modeling, especially of fatigue crack growth parameters, is undertaken using bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using Monte Carlo Simulation. The bi-linear crack growth models are found to lead to higher fatigue life estimation. Sensitivity behavior pertinent to limit state adopted has been thoroughly investigated. These findings implicate inspection schemes for components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment.

Effect of Bi-Linear S-N Curve and Crack Growth Law on the Safety Analyses of Welded Joints of an Offshore Structure

2008 ◽  
Author(s):  
Rizwan A. Khan ◽  
Suhail Ahmad
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Limit State ◽  
Published Data ◽  
Offshore Structure ◽  
Structure Degradation ◽  
Crack Growth Model

Design of welded structures for fatigue limit state is normally carried out by means of either linear or bilinear S-N curves which have been found adequate to predict crack initiation only. To properly assess the effects of design, fabrication, inspection and repair strategy for structure degradation due to crack growth, Fracture mechanics (FM) models need to be applied. In this paper, alternative S-N and FM formulations of fatigue are investigated. Probabilistic fracture mechanics approach predicts the fatigue life of welded steel structure in the presence of cracks under random spectrum loading. It is based on a recently proposed bi-linear relationship to model fatigue crack growth and incorporates a failure criterion to describe the interaction between fracture and plastic collapse. Uncertainty modeling, especially on fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bilinear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using the Monte Carlo Simulation Technique, and emphasis is placed on a comparison between linear and bi-linear crack growth models. The bi-linear S-N curve and crack growth model are found to lead to higher fatigue life estimates and shows sensitivity to many other parameters in addition to the stress state of the component. These findings implicate inspection schemes for components of the marine structures to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment. Variations in system configuration, service life and coefficients of crack growth laws have been studied on the parametric basis.

Probabilistic Fracture Mechanics Assessment of Welded Joints of Offshore Structure Using a Bilinear Crack Growth Law

2008 ◽  
Author(s):  
Rizwan A. Khan ◽  
Suhail Ahmad
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Limit State ◽  
Published Data ◽  
Offshore Structure ◽  
Probabilistic Fracture Mechanics ◽  
Crack Growth Model

Design of welded structures for fatigue limit state is normally carried out by means of either linear or bilinear S-N curves approaches. To properly assess the effects of design, fabrication, inspection and repair strategy for structures degradation due to crack growth, Fracture mechanics (FM) models need to be applied. This paper deals with the application of a probabilistic fracture mechanics approach to predict the fatigue life of welded steel structure in the presence of cracks under random spectral loading. It is based on a BS7910 [1] proposed bi-linear relationship to model fatigue crack growth and incorporates a failure criterion to describe the interaction between fracture and plastic collapse. Uncertainty modeling, especially of fatigue crack growth parameters, is undertaken with the aid of recently published data in support of the bi-linear crack growth relationship. Results pertaining to fatigue reliability and fatigue crack size evolution are presented using the Monte Carlo Simulation technique, and emphasis is placed on a comparison between linear and bi-linear crack growth models. The bi-linear crack growth model is found to lead to higher fatigue life estimates and shows sensitivity to many other parameters in addition to the state of stress of the component. This leads to implications on inspection schemes for components of the marine structures and to ensure minimization of the surprises due to wide scatter of the fatigue phenomenon in marine environment. Variations in the system configuration, service life and coefficients of crack growth laws have been studied on the parametric basis.

scholarly journals Multiple Failure Modes Reliability Modeling and Analysis in Crack Growth Life Based on JC Method

2017 ◽  
Vol 2017 ◽  
pp. 1-5 ◽  
Author(s):  
YuanTao Sun ◽  
Chao Liu ◽  
Qing Zhang ◽  
XianRong Qin
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Normal Distribution ◽  
Crack Growth ◽  
Failure Probability ◽  
Failure Modes ◽  
Limit State ◽  
State Equations ◽  
Multiple Failure Modes ◽  
Joint Failure

The fatigue crack growth (FCG) phenomenon generally exists in large mechanical structures. Due to the influences of varied kinds of random factors, the safety evaluation of structure in FCG is under great uncertainty. In this paper, based on the reliability theory, the limit state equations of fracture failure and static strength failure were derived firstly, and the parameters in those equations were regarded as random variables that follow the normal distribution or log-normal distribution. According to the limit state equations, the JC method (equivalent normalizing method) was used to calculate the reliability indexes under the different failure modes of structure in every stress cycle. Based on the reliability indexes and correlation of the two failure modes, the joint failure probability was obtained. In the end, a specific computation example was given, and the curve of joint failure probability in multiple failure modes was used for comparison with the result of single failure mode. The results indicated that the reliability analysis based on multiple failure modes was more reasonable, and the evaluation of reliability could be obtained in fatigue crack growth process.

Probabilistic Inspection Optimization of Free-Span Surveys for Subsea Gas Pipelines

2002 ◽  
Author(s):  
Jens P. Tronskar ◽  
Gudfinnur Sigurdsson ◽  
Olav Fyrileiv ◽  
Olav Forli ◽  
Joseph H. Kiefer ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Probabilistic Methods ◽  
Material Strength ◽  
Pipeline System ◽  
Unstable Fracture ◽  
Girth Welds ◽  
The Impact

Probabilistic methods have been used to develop the basis for free-span inspection of a gas pipeline system in the South China Sea. The objective of the probabilistic analysis was to study the probability of fatigue failure associated with postulated planar flaws in the HAZ of repair welds performed on some of the girth welds. The impact of flaws on the fatigue life under different free-span conditions were studied. Conventional free-span analysis involves computation of allowable free-span lengths based on onset of in-line vibrations and does not normally consider fatigue crack growth. To consider the effect of the weld flaws on the failure probability a combined probabilistic fatigue and fracture model is required. For the particular pipelines analysed automatic ultrasonic testing (AUT) was used replacing the conventional radiography of the girth welds. Conservatism in the free-span assessment can then be significantly reduced by taking into account detailed flaw sizing information from the AUT. The inspection records provide distribution of flaw height, length and position. Combined with information on current distribution, material strength and fracture toughness distribution, a detailed probabilistic fatigue crack growth and unstable fracture assessment can be conducted as per the Det Norske Veritas (DNV) 2000 Rules for Submarine Pipeline Systems [1] using the response models of the DNV Guideline 14 for free-span analyses [2]. The objective of this analysis is to estimate the critical free-span lengths and the time for fatigue cracks to penetrate the pipe wall.

Corrosion Fatigue of Steel Catenary Risers in Sweet Production

2008 ◽  
Author(s):  
Richard Pargeter ◽  
David Baxter ◽  
Briony Holmes
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Corrosion Fatigue ◽  
Fatigue Testing ◽  
Published Data ◽  
Aqueous Environment ◽  
Steel Catenary Risers ◽  
Mn Steel

Steel catenary risers (SCRs) are commonly used for deepwater oil and gas developments and the most economic material of construction is generally carbon manganese (C-Mn) steel. These risers suffer cyclic loading principally due to vessel movements, and vortex induced vibration (VIV) from passage of marine currents. For this reason, close attention is paid to fatigue design and girth weld quality, and fatigue testing is commonly carried out on procedure test welds. A further advantage of C-Mn steel is that good quality welds can readily be made, and more importantly, freedom from defects can be assured by reliable ultrasonic inspection. In sweet corrosive environments, when significant hydrogen effects would not be anticipated, a range of environmental effects on fatigue could be envisaged under different conditions, and at different stages of fatigue crack growth. For example, in early stages of growth, corrosion could blunt crack tips, and therefore slow the growth rate, whereas under other circumstances, or later in life, corrosion could provide additional crack extension, and accelerate growth. It has been demonstrated in this programme of fatigue crack growth rate and endurance testing that the most aggressive conditions in terms of corrosivity may not give shortest fatigue lives in testing. The results of tests comparing behaviour in air and in a very highly corrosive aqueous environment at 60°C saturated with CO2 (conditions which could not be sustained in production) have been explained by reference to competing effects of fatigue and corrosion. Comparison has been made with other published data. Important safety implications surrounding conditions for project-specific corrosion fatigue testing for riser design are considered.

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