Techniques for Fracture Toughness Testing of Offshore Pipelines

2009 ◽  
Author(s):  
Andrea Fonzo ◽  
Giorgio Melis ◽  
Luigi Di Vito ◽  
Gianluca Mannucci ◽  
Philippe Darcis ◽  
...  
Keyword(s):  
Crack Growth ◽  
Structural Integrity ◽  
Element Analysis ◽  
Offshore Pipelines ◽  
Three Point Bending ◽  
Mechanics Model ◽  
Need To Evaluate ◽  
Edge Notch ◽  
Notch Orientation ◽  
Girth Welds

The need to evaluate the significance of flaws in welded pipelines for gas transportation requires the knowledge of the material resistance to ductile tearing. In particular, the fracture resistance of pipe girth welds should be evaluated since they may potentially be critical for structural integrity. Standard toughness Three Point Bending tests (SENB) are too conservative since they are more constrained than actual pipeline. In this case, the adoption of a reduced notch depth, which is considered to reproduce well actual stress-strain conditions at the crack tip of a weld flaw, increases critical toughness values when compared to standard specimen configuration. Alternative solutions may be applied, even if not yet included in toughness standards. In particular, the Single Edge Notch Tensile (SENT) test is a possible solution reducing conservatism. A matter of concern for toughness characterization of weld joint is also represented by the notch orientation, since the weld microstructure is inhomogeneous in nature. The L–R oriented specimen (notch at the pipe inner surface) typically shows CTOD values strongly lower than the ones of L–T oriented specimens (through thickness notch) for both weld metal and heat affected zone. All these issues are discussed within this paper, while an advanced approach is presented to determine the resistance curve by using a single SENT specimen with the compliance method for crack growth evaluation. A relationship between the specimen elastic compliance and actual crack growth was determined through Finite Element Analysis and a Fracture Mechanics model. Such a relationship is presented and compared to other solutions available in scientific literature.

A Modified Engineering Critical Assessment Approach for Offshore Pipelines

2018 ◽  
Author(s):  
Colum Holtam ◽  
Rajil Saraswat ◽  
Ramgopal Thodla ◽  
Feng Gui
Keyword(s):  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Fatigue Loading ◽  
Critical Assessment ◽  
Offshore Pipelines ◽  
Static Crack ◽  
Production Environments ◽  
Assessment Approach ◽  
Girth Welds ◽  
Crack Growth Rates

Environmentally assisted sub-critical static crack growth can occur in offshore pipelines exposed to aggressive production environments. Recent advances in fracture mechanics testing methods have shown that slow static crack growth rates can be reliably measured in sweet and sour environments under constant stress intensity factor (K) conditions. This has potential implications for the engineering critical assessment (ECA) of pipe girth welds subject to low cycle fatigue loading with long periods of operation under constant static load between cycles, e.g. lateral buckling. This paper demonstrates the influence of including static (i.e. time dependent) crack growth as well as fatigue crack growth in a modified pipeline ECA approach.

Validation of Crack Growth for an Finite Element Based ECA Procedure for Reel-Laid Pipelines With Under-Matching Girth Welds

2015 ◽  
Author(s):  
T. Sriskandarajah ◽  
Daowu Zhou ◽  
Lingjun Cao
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Large Scale ◽  
Limit Load ◽  
Bending Test ◽  
Offshore Pipelines ◽  
Reference Stress ◽  
Trial Test ◽  
3D Fea ◽  
Girth Welds

There is a concern on the fracture integrity of the partially over-matching or under-matching weld during reel-lay installation where there is large plastic strain in the pipe. Conventional ECA procedures such as BS7910 and DNV-OS-F101 are applicable for fully over-matching welds only, due to limitations in the reference stress solution (or limit load solutions). The ECA procedure based on 3D finite element (FE) analysis was developed for partially over-matching welds or under-matching. The methodology has been successfully applied to several projects of industry-wide significance, with partially over-matching welds in offshore pipelines. This paper provides a case study validating the crack growth from FE based ECA methodology against the large scale bending trial test where the pipe containing the notched defect was pre-strained under a series of straining cycles. A comparison of the crack growth between 3D FEA and the large scale bending test was presented.

Ductile Damage Study of Defective Girth Welds for Oil and Gas Pipeline: A Tailored Numerical and Finite Element Method Calibration From SENT Fracture Mechanics Test

2017 ◽  
Author(s):  
Roberto Bruschi ◽  
Marco Rossi ◽  
Alex Di Michele ◽  
Daniele Scarsciafratte ◽  
Enrico Torselletti
Keyword(s):  
Finite Element ◽  
Oil And Gas ◽  
Calibration Procedure ◽  
Ductile Damage ◽  
Element Analysis ◽  
Gurson Model ◽  
Offshore Pipelines ◽  
Crack Driving Force ◽  
Girth Welds ◽  
Model Preparation

In this paper, the evolution of ductile damage in pipe girth welds for offshore pipelines application is studied with the use of Finite Element Analysis. To this purpose, the Gurson-Tvergaard-Needlmen (GTN) model is calibrated and applied to different finite element simulations. Saipem internally developed software, written in Matlab® environment, is used to automatically calibrate the Gurson model from experimental data and run several Finite Element Models of the pipe with different flaws in the girth weld. The objective of this paper is to present and discuss this numerical tool, developed by Saipem coupling a Matlab® GUI and the ABAQUS FE solver. The tool allows speeding up and automatizing the calibration procedure of the Gurson model and making a rapid evaluation in terms of the Crack Driving Force (CDF) for defective girth weld. The tool allows also a quick and efficient model preparation, full FE analysis and post-processing, with saving of engineering hours.

Automated Modeling and Crack Growth Simulation in Pressurized Thin Shell Panels With Multi-Site Damage

2003 ◽  
Author(s):  
K. V. N. Gopal ◽  
B. Dattaguru
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Mesh Generation ◽  
Structural Integrity ◽  
Element Analysis ◽  
Automated Modeling ◽  
Growth Simulation ◽  
Crack Growth Simulation ◽  
Piping Systems ◽  
Thin Walled

The residual strength estimation of thin-walled pressurized shell structures is of relevance to pressurized thin piping systems and aged airframes for life extension programs. This requires powerful and efficient computational techniques using finite element method and numerical fracture mechanics for elastic or inelastic stress analysis and crack growth simulation. For this purpose, detailed modeling and finite element mesh generation of built-up structures like stiffened cracked thin shells is necessary and it is a computationally intensive task. Automating the entire process from geometric modeling to stress analysis and crack growth simulation (requires remeshing) vastly improves the efficiency of the computational analysis and reduces the chances of modeling and simulation errors. A geometric primitive based technique has been developed for automated modeling and meshing. The work is carried out primarily on aged fuselage shell panels but the method is applicable to other pressurized thin piping systems. This paper presents a simple and efficient computational procedure using a geometry based logic and surface mesh generation technique for automated modeling and crack growth simulation in pressurized thin-walled shells. The approach has been used to develop a structural integrity evaluator software. Finite element analysis is carried out using a commercial software, and these results are fed to the structural integrity evaluator. Some results of the nonlinear finite element analysis and elastic-plastic stable crack growth simulation in pressurized stiffened fuselage panels using this approach are presented.

Residual Stresses in Strength Mismatched Welded Pipes

2017 ◽  
Author(s):  
Ali Mirzaee-Sisan ◽  
Junkan Wang
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Thermal Stresses ◽  
Structural Integrity ◽  
Welding Residual Stress ◽  
Temperature Fields ◽  
Transient Temperature ◽  
Element Analysis ◽  
Girth Welds ◽  
Welded Pipe

It is commonly understood that residual stresses can have significant effects on structural integrity. The extent of such influence varies and is affected by material properties, manufacturing methods and thermal history. Welded components such as pipelines are subject to complex transient temperature fields and associated thermal stresses near the welded regions. These thermal stresses are often high in magnitude and could cause localized yielding around the deposited weld metal. Because of differential thermal expansion/contraction episodes, misfits are introduced into the welded regions which in turn generate residual stresses when the structure has cooled to ambient temperature. This paper is based on a recently completed Joint Industry Project (JIP) led by DNV GL. It briefly reviews published experimental and numerical studies on residual stresses and strength-mismatched girth welds in pipelines. Several Finite Element Analysis (FEA) models of a reeling simulation have been developed including mapping an initial axial residual stress (transverse to the weld) profile onto a seamless girth-welded pipe. The initial welding residual stress distribution used for mapping was measured along the circumference of the girth welds. The predicted residual stresses after reeling simulation was subsequently compared with experimental measurements.

Numerical Prediction of Constraint Effect of Creep Crack Growth

2009 ◽  
Author(s):  
Masataka Yatomi ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Creep Crack Growth ◽  
Constraint Effect ◽  
Three Point Bending ◽  
Creep Crack ◽  
Reference Stress ◽  
Edge Notch ◽  
Stress And Strain Rate

This paper presents the effect of constraint on creep crack growth (CCG) using FE analysis based on the stress and strain rate state at the crack tip. The comparison is made by modelling C(T) specimen tests under plane stress and plane strain conditions using creep properties of three different steels (C-Mn steel, P91 steel, and 316H austenitic steel). In addition, in order to examine the constraint effect on CCG due to geometry single edge notch specimen (SENT), centre cracked tension specimen (CCT) and three point bending (3PB) specimen have also been analysed. In all cases it is found that when the reference stress under plane strain conditions is higher than the yield stress, there is little difference between CCG rates under plane stress and plane strain.

scholarly journals Finite Element Analysis of Fatigue in Offshore Pipelines with Internal and External Circumferential Cracks

2020 ◽  
Vol 1 (4) ◽  
pp. 193-223
Author(s):  
Ayodeji Olamide ◽  
Abdeldjalil Bennecer ◽  
Stefan Kaczmarczyk
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Structural Integrity ◽  
Numerical Study ◽  
J Integral ◽  
Surface Cracks ◽  
Crack Tip Opening Displacement ◽  
Element Analysis ◽  
Fatigue Lifetime ◽  
Offshore Pipelines

Fatigue lifetime of offshore pipelines with semi-elliptical circumferential surface cracks is often underestimated. An accurate prediction of the pipeline structural integrity is nevertheless important in order to prevent unnecessary and expensive downtime, failures leading to leakage or spillage of pipeline contents to the surrounding environment, and ultimately improve the reliability of the pipeline. The estimation of crack growth in pipelines under varying loads is highly dependent on the calculation of crack driving parameters, such as the stress intensity factor and the crack tip opening displacement (CTOD) using the 3D J-integral or its equivalent. This paper presents a numerical study to predict the fatigue lifetime of cracks in pipes, determining the J-integral that includes first and second derivatives of the displacement field for pipes containing a range of circumferential surface cracks. A pipe segment is structurally loaded and stress intensity factors (SIF) evaluated using the finite element method (FEM). Based on the results, a number-of-cycles to failure curve shows a longer lifetime than previously predicted by about 5% for a pipe with semi-elliptical external surface cracks. In addition, they indicate that the external short cracks are more dangerous than the internal long surface crack hereby requiring earlier assessment.

Prediction of Transient Creep Response Under Combined Primary and Secondary Loading

2010 ◽  
Author(s):  
Hamed Yazdani Nezhad ◽  
Noel P. O’Dowd
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Mechanical Stress ◽  
Structural Integrity ◽  
Creep Behaviour ◽  
Element Analysis ◽  
Stress Effects ◽  
Deformation And Fracture ◽  
Edge Notch ◽  
Cracked Structures

Residual stress effects on creep deformation and fracture play a significant role in structural integrity assessments of engineering components. The focus of the current work is to investigate creep behaviour of mechanically loaded cracked structures in the presence of residual stress fields. Finite-element analyses have been carried out on single edge notch bend, SEN(B), and tension, SEN(T), specimens at different residual stress and mechanical stress levels. The redistribution time and associated stress relaxation for combined primary and secondary (residual) stresses have been determined (from the finite-element analysis) and interpreted using the transient fracture mechanics parameter, C(t). The observed trends are consistent with earlier studies involving combined thermal and mechanical stress.

Tire Bead Overheating in Urban Buses and Trucks Using Drum Brake Systems

1998 ◽  
Vol 26 (1) ◽  
pp. 51-62
Author(s):  
A. L. A. Costa ◽  
M. Natalini ◽  
M. F. Inglese ◽  
O. A. M. Xavier
Keyword(s):  
Heat Transfer ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Thermal Energy ◽  
Structural Integrity ◽  
Experimental Temperature ◽  
Temperature Profiles ◽  
Element Analysis ◽  
Drum Brake ◽  
Fea Model

Abstract Because the structural integrity of brake systems and tires can be related to the temperature, this work proposes a transient heat transfer finite element analysis (FEA) model to study the overheating in drum brake systems used in trucks and urban buses. To understand the mechanics of overheating, some constructive variants have been modeled regarding the assemblage: brake, rims, and tires. The model simultaneously studies the thermal energy generated by brakes and tires and how the heat is transferred and dissipated by conduction, convection, and radiation. The simulated FEA data and the experimental temperature profiles measured with thermocouples have been compared giving good correlation.

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