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.

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.

Probabilistic Analysis of the Collapse Pressure of Corroded Pipelines

2016 ◽  
Author(s):  
Nara Oliveira ◽  
Helio Bisaggio ◽  
Theodoro Netto
Keyword(s):  
Monte Carlo ◽  
Structural Reliability ◽  
Limit State ◽  
Monte Carlo Integration ◽  
Experimental Program ◽  
Small Scale ◽  
Collapse Pressure ◽  
First Order ◽  
Operational Life ◽  
Corrosion Defects

Oil and gas offshore pipelines are one of the main components of a subsea system. A major accident can have a great economic impact due to loss of revenue and the expenses involving actions to mitigate damages to the environment. Therefore, investment in accident prevention through a carefully designed inspection and maintenance plan is necessary. In this scenario, many companies have changed their procedures to ensure the structural integrity of their pipelines — from a model that incorporates empirical safety factors and periodic inspections to another, based on methods that consider concepts of structural reliability to establish risk based inspections. 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. However, loads and resistance parameters have uncertainties which define the basic reliability problem. These uncertainties are related to the geometric and material parameters of the pipe and the operational conditions. In recent years, many studies have been developed using reliability concepts in order to predict the probability of failure of a corroded pipeline at any given time. The main problem in assuring the integrity and safe operation of pipelines lies in obtaining the necessary accurate prediction of their future condition. 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. Probabilistic failure analyses of pipelines considering different failure mechanisms have been performed by different authors over the last decade. Limit state functions similar to the mentioned above, coupled with reliability algorithms such as the first-order second-moment (FOSM) iterative method, the Monte Carlo integration method, and the first-order and second-order reliability methods (FORM/SORM) are generally used. The analyses take into account the natural spread of material properties, geometric and operational parameters, and the uncertainties associated with the sizing of eventual corrosion defects. In this paper, Netto’s deterministic formulation and the crude Monte Carlo method were used to obtain the reliability of corroded pipelines under external hydrostatic pressure. This approach provides a method to predict the probability of collapse of a corroded pipeline along its operational life. It applies concepts of structural reliability to evaluate the detrimental effect of corrosion damages, giving the basis to develop a risk based maintenance strategy.

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.

On the Effect of Narrow and Long Corrosion Defects on the Collapse Pressure of Pipelines

2007 ◽  
Author(s):  
T. A. Netto
Keyword(s):  
Numerical Models ◽  
Simple Procedure ◽  
Small Scale ◽  
Offshore Pipelines ◽  
Internal Corrosion ◽  
Chemical Contaminants ◽  
Collapse Pressure ◽  
Multi Phase Flow ◽  
Corrosion Defects ◽  
Multi Phase

Internal corrosion in pipelines is often caused by water, sediment, or chemical contaminants present in the multi-phase flow. This normally occurs at the bottom of the pipe and at low points in the pipeline where sediment and water can settle out of the product being transported, therefore creating narrow and long defects. 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. After calibrated in view of the experimental results, the model was used to determine the collapse pressure as a function of material and geometric parameters of different pipes and defects. 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 reports these results which are subsequently used to develop a simple procedure for estimating the collapse pressure of pipes with narrow defects.

Low Cycle Fatigue of Internally Pressurized Corroded Pipes Under Cyclic Bending

2009 ◽  
Author(s):  
Marcos Andre´ Baeta ◽  
Marcelo Igor Lourenc¸o ◽  
Theodoro A. Netto
Keyword(s):  
Cyclic Load ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Experimental Tests ◽  
Small Scale ◽  
Cycle Fatigue ◽  
Cyclic Tests ◽  
Operational Conditions ◽  
Oil Transportation ◽  
Operational Load

Corroded pipes for oil transportation can eventually experience low cycle fatigue failure after some years of operation. The evaluation of the defects caused by corrosion in these pipes is important when deciding for the repair of the line or continuity in operation. Under normal operational conditions, these pipes are subject to constant internal pressure and cyclic load due to bending and/or tension. Under such loading conditions, the region in the pipes with thickness reduction due to corrosion could experience the phenomenon known as ratcheting. The objective of this paper is to present a revision of the available numerical models to treat the ratcheting phenomenon. Experimental tests were developed allowing the evaluation of occurrence of ratcheting in corroded pipes under typical operational load conditions as well as small-scale cyclic tests to obtain the material parameters. Numerical and experimental tests results are compared.

Pipeline Remaining Life Estimation Based on Concepts of Structural Reliability and Bayesian Inference

2014 ◽  
Author(s):  
Helio da Cunha Bisaggio ◽  
Theodoro Antoun Netto
Keyword(s):  
Structural Reliability ◽  
Limit State ◽  
Probability Of Failure ◽  
Operational Parameters ◽  
Simple Method ◽  
Life Estimation ◽  
Predicted Probability ◽  
Operational Life ◽  
Corrosion Defects ◽  
State Functions

In this paper, structural reliability concepts are used in conjunction with DNV Recommended Practice RP-F101 [1] formulation to establish the limit state functions of corroded pipes. The model takes into account the natural spread of material properties, geometric and operational parameters, and the uncertainties associated with the sizing of eventual corrosion defects to determine the probability of failure at a given time. Bayesian and reliability concepts are used to estimate the evolution of a pre-defined distribution of defects obtained, for instance, from an inspection campaign. By comparing the predicted probability of failure with the reliability acceptance criteria the operator can schedule defect repairs and establish inspection intervals with more confidence. Thus, a simple method to predict the probability of failure of a corroded pipeline along its operational life is proposed to provide the basis to develop a risk based maintenance strategy.

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.

Ratcheting of Corroded Pipes

2012 ◽  
Author(s):  
Marcelo Igor Lourenço ◽  
Theodoro A. Netto
Keyword(s):  
Cyclic Load ◽  
Numerical Models ◽  
Experimental Tests ◽  
Small Scale ◽  
Cyclic Tests ◽  
Operational Conditions ◽  
Material Parameters ◽  
Oil Transportation ◽  
Operational Load ◽  
Practical Tool

Corroded pipes for oil transportation can eventually experience Ratcheting after some years of operation. The evaluation of the defects caused by corrosion in these pipes is important when deciding for the repair of the line or continuity in operation. Under normal operational conditions, these pipes are subject to constant internal pressure and cyclic load due to bending and/or tension. Under such loading conditions, the region in the pipes with thickness reduction due to corrosion could experience the phenomenon known as ratcheting. The objective of this paper is to present a revision of the available numerical models to treat the ratcheting phenomenon. Experimental tests were developed allowing the evaluation of occurrence of ratcheting in corroded pipes under typical operational load conditions as well as small-scale cyclic tests to obtain the material parameters. Numerical and experimental tests results are compared. Shakedown models are also investigated as a practical tool for ratcheting prediction.

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.

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