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

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.

The Potential for Non-Conservative Results From the Probabilistic Fracture Mechanics Analyses Is Assessed Based on the Collected Observation of Fatigue Cracks in Offshore Steel Structures

2017 ◽  
Author(s):  
Ole Tom Vårdal
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Structural Integrity ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Lessons Learned ◽  
Probabilistic Methods ◽  
Growth Potential

In structural integrity management, it is essential to know the fatigue crack growth potential. The lessons learned from use of refined fatigue analyses, fracture mechanics and probabilistic methods for platforms in-service are presented. For ageing offshore units of semi-submersible design, the inspection history of more than 20 000 NDT inspections and detection of close to 1000 fatigue cracks, are used in this study. These experience data are used to assess the potential for Non-conservative estimate for the fatigue crack growth potential.

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.

scholarly journals Probabilistic Modeling of Fatigue Crack Growth in Ti-6Al-4V

2000 ◽  
Author(s):  
W. O. Soboyejo ◽  
A. B. O. Soboyejo ◽  
W. Shen
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Parameters ◽  
Experimental Studies ◽  
Fatigue Tests ◽  
Log Normal ◽  
Probabilistic Nature ◽  
Long Fatigue Crack

Abstract This paper presents the results of a combined experimental and analytical study of the probabilistic nature of fatigue crack growth in Ti-6Al-4V. A simple experimental fracture mechanics is presented for obtaining statistical fatigue crack growth parameters from one or two fatigue tests. The experimental studies of long fatigue crack growth show that the variabilities in the long fatigue crack growth rate and the Paris coefficient are well described by the log-normal distribution. The variabilities in the Paris exponent are also shown to be well characterized by a Weibull distribution. The measured statistical distributions are incorporated into a probabilistic fracture mechanics framework for the estimation of material reliability. The implications of the results are also discussed for the probabilistic analysis of fatigue crack growth in engineering components and structures.

A Study on Fatigue Crack Growth Parameters for Fatigue Life Assessment based on Fracture Mechanics

2017 ◽  
Vol 35 (1) ◽  
pp. 61-67
Author(s):  
Hyeon-Su Kim ◽  
Tae-Jong Park ◽  
Dong-Ju Lee ◽  
Sang-Beom Shin ◽  
Myung-Hyun Kim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Parameters ◽  
Life Assessment ◽  
Fatigue Life Assessment

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.

Effective Modeling of Fatigue Crack Growth in Pipelines

2012 ◽  
Author(s):  
Steven J. Polasik ◽  
Carl E. Jaske
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Models ◽  
Critical Parameters ◽  
Operating Pressure ◽  
Mechanics Model ◽  
Key Variables

Pipeline operators must rely on fatigue crack growth models to evaluate the effects of operating pressure acting on flaws within the longitudinal seam to set re-assessment intervals. In most cases, many of the critical parameters in these models are unknown and must be assumed. As such, estimated remaining lives can be overly conservative, potentially leading to unrealistic and short reassessment intervals. This paper describes the fatigue crack growth methodology utilized by Det Norske Veritas (USA), Inc. (DNV), which is based on established fracture mechanics principles. DNV uses the fracture mechanics model in CorLAS™ to calculate stress intensity factors using the elastic portion of the J-integral for either an elliptically or rectangularly shaped surface crack profile. Various correction factors are used to account for key variables, such as strain hardening rate and bulging. The validity of the stress intensity factor calculations utilized and the effect of modifying some key parameters are discussed and demonstrated against available data from the published literature.

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