Reliability Analysis of Corroded Pipelines Under External Pressure

2017 ◽  
Author(s):  
A. P. Teixeira ◽  
O. G. Palencia ◽  
C. Guedes Soares
Keyword(s):  
Reliability Analysis ◽  
Three Dimensional ◽  
External Pressure ◽  
Design Methods ◽  
Sensitivity Analyses ◽  
Structural Safety ◽  
Small Scale ◽  
Collapse Pressure ◽  
Collapse Probability ◽  
Subsea Pipelines

This paper aims at assessing the reliability of pipelines with corrosion defects subjected to external pressure. Several design methods that explicitly account for the effect of corrosion damages on the collapse pressure of pipelines are considered. In particular, semi-empirical design equations derived from small-scale experiments and three-dimensional non-linear finite element analyses and design code methods currently used in practice are adopted. First, the design methods are analyzed and their predictions compared and then used to formulate the reliability problem of corroded pipelines subjected to external pressure. The reliability analysis adopts the state-of-the art stochastic models to characterize the uncertainty on the main parameters influencing the structural safety of corroded subsea pipelines. Parametric and sensitivity analyses are then performed for different levels of corrosion damages to identify the influence of the various parameters on the collapse probability of corroded pipelines under external pressure.

A Simple Procedure for the Prediction of the Collapse Pressure of Pipelines With Narrow and Long Corrosion Defects: Uncertainty and Sensibility Analysis

2018 ◽  
Author(s):  
Nara Oliveira ◽  
Theodoro Netto
Keyword(s):  
Simple Procedure ◽  
Experimental Tests ◽  
External Pressure ◽  
Experimental Program ◽  
Small Scale ◽  
Test Results ◽  
Collapse Pressure ◽  
Operational Conditions ◽  
Sensibility Analysis ◽  
Corrosion Defects

The collapse pressure of pipelines containing corrosion defects is usually predicted by deterministic methods, either numerically or through empirical formulations. The severity of each individual corrosion defect can be determined by comparing the differential pressure during operation with the estimated collapse pressure. A simple deterministic procedure for estimating the collapse pressure of pipes with narrow and long defects has been recently proposed by Netto (2010). This formulation was based on a combined small-scale experimental program and nonlinear numerical analyses accounting for different materials and defect geometries. However, loads and resistance parameters have uncertainties which define the basic reliability problem. These uncertainties are mailyrelated to the geometric and material parameters of the pipe and the operational conditions. This paper presents additional experimental tests on corroded pipes under external pressure. The collapse pressure calculated using the equation proposed by Netto (2010) is compared with this new set of experiments and also with test results available in open literature. These results are used to estimate the equation uncertainty. Finally, a sensitivity analysis is performed to identify how geometric parameters of the defects influence the reduction of collapse pressure.

Flexible Pipes: Influence of the Pressure Armor in the Wet Collapse Resistance

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clóvis de Arruda Martins
Keyword(s):  
Three Dimensional ◽  
External Pressure ◽  
Flexible Pipe ◽  
3D Fem ◽  
Collapse Pressure ◽  
Flexible Pipes ◽  
Polymeric Layer ◽  
Set Up ◽  
3D Finite Element Method ◽  
Ring Approximation

When submitted to high external pressure, flexible pipes may collapse. If the external sheath is damaged, all the external pressure is directly applied on the internal polymeric layer that transmits the loading to the carcass layer, which can fail due to this effect, leading to wet collapse. This failure mode must be taken into account in a flexible pipe design. A model can be set up neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to include the pressure armor effect in the numerical prediction of wet collapse. The main contribution of the pressure armor to the flexible pipe resistance to collapse is to be a constraint to the radial displacement of the carcass and the internal polymeric layers. Two models were developed to find the wet collapse pressure in flexible pipes. A first study was done using a ring approximation three-dimensional (3D) finite element method (FEM) model. Comparisons are made with more simplified models using a 3D FEM equivalent ring approximation. The aim is to clarify the mechanical behavior of the pressure armor in the wet collapse scenario. Parametric studies of initial ovalization of carcass and initial gaps and interference between polymeric layer and pressure armor are made and discussed.

Propagation of Buckles in Sandwich Pipes Under External Pressure

2005 ◽  
Author(s):  
I. P. Pasqualino ◽  
M. I. Lourenc¸o ◽  
T. A. Netto
Keyword(s):  
Three Dimensional ◽  
Nonlinear Behavior ◽  
Element Model ◽  
External Pressure ◽  
Core Material ◽  
Small Scale ◽  
Ongoing Research ◽  
Scale Models ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element

Sandwich pipes have been considered feasible conceptions for ultra deepwater pipelines, since they are capable to work at low temperatures and withstand high hydrostatic pressures. Sandwich pipelines are composed by inner and outer metallic pipes and a suitable core material which must provide high compression strength and good thermal insulation. The aim of this ongoing research is to study the quasi-static propagation of buckles in sandwich pipes. In this paper, a three-dimensional finite element model considering material and geometric nonlinear behavior is presented. The mesh discretization is determined through a detailed mesh sensitivity analysis. Some experiments with small scale models combining aluminum pipes and polypropylene as core material were carried out to calibrate the numerical model. The propagation pressure is evaluated under different bonding conditions between pipe layers.

Effects of Reeling on Pipe Structural Performance—Part II: Analysis

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Yafei Liu ◽  
Stelios Kyriakides ◽  
Jyan-Ywan Dyau
Keyword(s):  
3D Model ◽  
Kinematic Hardening ◽  
Three Dimensional ◽  
Element Model ◽  
External Pressure ◽  
Structural Performance ◽  
Collapse Pressure ◽  
Reverse Loading ◽  
Tension Loading ◽  
Different Levels

Part II presents two modeling schemes for simulating the reeling/unreeling of a pipeline, with the aim of establishing the degrading effect of the process on the structural performance of the pipeline. A three-dimensional (3D) finite element model of the winding/unwinding of a long section of pipeline onto a rigid reel is presented first. The second model applies the curvature/tension loading history experienced at a point to a section of pipe in contact with a rigid surface of variable curvature. Both models use nonlinear kinematic hardening plasticity to model the loading/reverse loading of the material. The 3D model first demonstrates how the interaction of the problem nonlinearities influences the evolution of deformation and load parameters during reeling/unreeling. The two models are subsequently used to simulate the three-reeling/unreeling cycle experiments under different levels of back tension in Part I. The ovality-tension and axial elongation-tension results are reproduced by both models with accuracy for the first cycle, adequately for the second cycle, and are overpredicted for the third cycle. The two models are also used to simulate the reeling/unreeling followed by collapse of the tubes under external pressure experiments. Both models reproduce the measured ovality-tension results and the corresponding collapse pressures accurately. Since the two-dimensional (2D) model is computationally much more efficient, it is an attractive tool for estimating the effect of reeling on collapse pressure. Questions that require exact tracking of the winding/unwinding history and the interaction of the pipe with the reel are best answered using the 3D model.

Numerical and Experimental Study of Damaged Sandwich Pipe Under External Pressure

2014 ◽  
Author(s):  
João Fabrício Machado de Castilho ◽  
Ilson Paranhos Pasqualino
Keyword(s):  
Experimental Study ◽  
Three Dimensional ◽  
Mechanical Damage ◽  
High Strength ◽  
Good Alternative ◽  
External Pressure ◽  
Small Scale ◽  
Fe Model ◽  
Steel Tubes ◽  
Initiation Pressure

Studies on sandwich pipes, which comprise two concentric high strength steel tubes and a suitable annular material have shown good results due to their improved strength under external pressure and therefore they have been indicated as a good alternative for application in brazilian pre-salt scenario as gas and oil exportation pipelines. After installation on seabed a sandwich pipe can undergo mechanical damage caused by possible impacts of an anchor or some dropped heavy objects. When this happens, its strength under external pressure can be significantly reduced. This paper presents a numerical and experimental study of the reduced strength under external pressure (initiation pressure) of a damaged sandwich pipe. To this end, small scale sandwich pipe models were manufactured using steel tubes and PVDF in the annular space. Mechanical damages were simulated on the external surface of the models to collapse them under external pressure. The test results were compared to a three dimensional FE model simulating both the initiation pressure and the propagation pressure of the tested samples. A parametric study was carried out to analyze the sandwich pipe performance under damaged conditions.

The Effect of the Reeling Laying Method on the Collapse Pressure of Steel Pipes for Deepwater

2004 ◽  
Author(s):  
Ilson P. Pasqualino ◽  
Silvia L. Silva ◽  
Segen F. Estefen
Keyword(s):  
Numerical Model ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Element Model ◽  
External Pressure ◽  
Test Facility ◽  
Collapse Pressure ◽  
Steel Pipes ◽  
Custom Made ◽  
Nonlinear Finite Element Model

This work deals with a numerical and experimental investigation on the effect of the reeling installation process on the collapse pressure of API X steel pipes. A three-dimensional nonlinear finite element model was first developed to simulate the bending and straightening process as it occurs during installation. The model is then used to determine the collapse pressures of both intact and plastically strained pipes. In addition, experimental tests on full-scale models were carried out in order to calibrate the numerical model. Pipe specimens are bent on a rigid circular die and then straightened with the aid of a custom-made test facility. Subsequently, the specimens are tested quasi-statically under external pressure until collapse in a pressure vessel. Unreeled specimens were also tested to complete the database for calibrating the numerical model. The numerical model is finally used to generate collapse envelopes of reeled and unreeled pipes with different geometry and material.

Modeling of the Collapse and Propagation Behavior of UOE SAW Pipes Under External Pressure: Influence of Thermal Treatments for Typical Coating Applications

2012 ◽  
Author(s):  
Luciano O. Mantovano ◽  
Santiago Serebrinsky ◽  
Hugo A. Ernst ◽  
Teresa Perez ◽  
Martin Valdez ◽  
...  
Keyword(s):  
Finite Element ◽  
Experimental Testing ◽  
Large Diameter ◽  
Model Development ◽  
External Pressure ◽  
Sensitivity Analyses ◽  
Thermal Treatments ◽  
Collapse Pressure ◽  
Collapse Resistance ◽  
Comparison Of The Results

Large diameter UOE pipes are being increasingly used for the construction of offshore pipelines. Since oil discoveries are moving towards ultra deep water areas, collapse resistance is a key factor in the design of the pipelines. It has been demonstrated in previous works that the application of typical coating thermal treatments increases the collapse resistance of the pipes recovering the original strength of the plate. To improve the understanding of these effects, the Tenaris has embarked on a program of both, experimental testing and finite element modeling. Previous phases of this work formulated the basis for model development and described the 2D approach taken to model the various stages of manufacture, from the plate to the final pipe and the collapse test. More recent developments included some modeling enhancements, sensitivity analyses, and comparison of predictions to the results of full scale collapse testing. In the present work, 3D finite element analyses of collapse were performed and compared with the latest collapse and propagation tests performed by Tenaris, where the effect of typical coating thermal treatments was studied and significant increments in the collapse pressure of pipes were obtained. The numerical results show a good agreement with the experimental ones and could predict the increment produced in the collapse pressure by the effect of the thermal treatments. Comparison of the results with the predictions from API RP 1111 and DNV OS-F101 equations was also performed. The outcomes of this study will be employed to further optimize the collapse resistance of subsea linepipe in order to reduce material and offshore installation costs through the increment of the fabrication factor as stated in the DNV OSF101 standard.

Residual Strength of Corroded Pipelines Under External Pressure: A Simple Assessment

2006 ◽  
Author(s):  
T. A. Netto ◽  
U. S. Ferraz ◽  
A. Botto
Keyword(s):  
Numerical Models ◽  
Simple Procedure ◽  
External Pressure ◽  
Small Scale ◽  
The Finite Element Method ◽  
Offshore Pipelines ◽  
Collapse Pressure ◽  
Irregular Shapes ◽  
Internal Surfaces ◽  
Corrosion Defects

The loss of metal in a pipeline due to corrosion usually results in localized pits with various depths and irregular shapes on its external and internal surfaces. The effect of corrosion defects on the collapse pressure of offshore pipelines was studied through combined small-scale experiments and nonlinear numerical analyses based on the finite element method. An extensive parametric study using 2-D and 3-D numerical models was carried out encompassing different defect geometries and their interaction with pipe ovalization. This paper briefly summarizes these results, which are subsequently used to develop a simple procedure for estimating the collapse pressure of pipes with narrow defects.

Collapse Experiments and Reliability Analyses of Corroded Pipes for Offshore Applications

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
N. Oliveira ◽  
T. A. Netto
Keyword(s):  
Structural Reliability ◽  
Simple Procedure ◽  
Experimental Tests ◽  
External Pressure ◽  
Experimental Program ◽  
Small Scale ◽  
Collapse Pressure ◽  
Operational Conditions ◽  
Operational Life ◽  
Corrosion Defects

Abstract The collapse pressure of subsea pipelines containing corrosion defects is usually predicted by deterministic methods, either numerically or through empirical formulations. A simple deterministic procedure for estimating the collapse pressure of pipes with narrow and long defects has been recently proposed by Netto, T. A. (2009, “On the Effect of Narrow and Long Corrosion Defects on the Collapse Pressure of Pipelines,” Appl. Ocean Res., 31(2), pp. 75–81) and Netto, T. A. (2010, “A Simple Procedure for the Prediction of the Collapse Pressure of Pipelines With Narrow and Long Corrosion Defects—Correlation With New Experimental Data,” Appl. Ocean Res., 32(1), pp. 132–134). The formulation was based on a combined small-scale experimental program and nonlinear numerical analyses accounting for different materials and defect geometries. This paper presents additional experimental tests on corroded pipes under external pressure. The collapse pressure calculated using the equation proposed by Netto is compared with this new set of experiments and also with test results available in open literature. These results are used to estimate the equation uncertainty. A sensitivity analysis is also performed to identify how geometric parameters of the defects influence the reduction of collapse pressure. However, loads and resistance parameters have uncertainties. These uncertainties are related to the geometric and material parameters of the pipe and the operational conditions. To account for these uncertainties, a method to predict the probability of collapse of a corroded pipeline along its operational life is proposed. The methodology is illustrated through a case study in which concepts of structural reliability are used to evaluate the detrimental effect of corrosion damages in a pipeline, providing the basis to develop a risk-based maintenance strategy.

Collapse Failure Analysis of Subsea Corroded Pipeline Under Combined External Pressure and Axial Force

2020 ◽  
Author(s):  
Yanfei Chen ◽  
Guoyan He ◽  
Shaohua Dong ◽  
Fuheng Hou ◽  
Shang Ma ◽  
...  
Keyword(s):  
Axial Force ◽  
External Pressure ◽  
Combined Loading ◽  
Engineering Practice ◽  
Regression Equations ◽  
Collapse Pressure ◽  
Corrosion Depth ◽  
Integrity Assessment ◽  
Collapse Failure ◽  
Subsea Pipelines

Abstract The subsea pipelines are usually located in a corrosive external and internal environment. Corrosion presents to be the most common defect type in subsea pipelines, and it is regarded to be one of the main causes of subsea pipeline failure. Due to subsea subsidence, mudslides, and seismic activities, the pipeline is presented under combined external pressure, bending moments and axial force combined loading cases. The accurate determination of the collapse pressure of corroded pipelines under combined loading is important in engineering practice. On the basis of the finite element method, collapse failure of subsea corroded pipelines under combined loads is investigated. The influence of corrosion length, corrosion width, corrosion depth and diameter-thick ratio on the collapse failure pressure is studied. It is observed that corrosion depth has the most significant impact on pipelines’ collapse capacity. Furthermore, regression equations for predicting the collapse pressure of subsea corroded pipelines are proposed based on numerical results. The solution can be referred to in structural integrity assessment of subsea corroded pipelines.

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