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.

Simplified Finite Element Models to Study the Wet Collapse of Straight and Curved Flexible Pipes

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clóvis de Arruda Martins ◽  
Eduardo Ribeiro Malta ◽  
Rafael Loureiro Tanaka ◽  
Carlos Alberto Ferreira Godinho
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
3D Models ◽  
External Pressure ◽  
Finite Element Models ◽  
Flexible Pipe ◽  
Collapse Pressure ◽  
Flexible Pipes ◽  
Polymeric Layer ◽  
Collapse Failure

When the external sheath of flexible pipes experiences damage, seawater floods the annulus. Then, the external pressure is applied directly on the internal polymeric layer, and the load is transferred to the interlocked carcass, the innermost layer. In this situation, the so-called wet collapse failure of the interlocked carcass can occur. Simplified methodologies to address such a scenario, using restricted three-dimensional (3D) finite element models, are presented in this work. They are compared with full 3D models, studying both straight and curved flexible pipes scenarios. The curvature of the flexible pipe is shown to be important for wet collapse pressure predictions.

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

2011 ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clo´vis de Arruda Martins
Keyword(s):  
External Pressure ◽  
Flexible Pipe ◽  
3D Fem ◽  
Collapse Pressure ◽  
Flexible Pipes ◽  
External Pressures ◽  
Complete Study ◽  
Polymeric Layer ◽  
Equivalent Ring ◽  
Comparison Of The Results

When subjected to large valued external pressures, flexible pipes may collapse. If the external sheath is damaged, all the external pressure is directly applied to the internal polymeric layer that transmits the loading to the carcass layer. When the carcass layer fails due to this effect, the wet collapse occurs. This failure mode must be taken into account in the flexible pipe design. The study for this problem can be done neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to study 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 and compared with the purpose of calculating the critical value of the external pressure that causes carcass layer to collapse. The first and most complete study is done using a ring 3D FEM model that takes into account both the real pressure armor and carcass real profiles. In the second model, the pressure armor is considered adopting an equivalent ring simplification. The comparison of the results of both the models clarifies how the behavior of the pressure armor in the wet collapse situation is. Parametric studies of initial ovalization of the carcass and initial gaps in manufacturing of flexible pipes are made and discussed.

A Comparative Buckling Study for the Carcass Layer of Flexible Pipes

2009 ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clo´vis de Arruda Martins
Keyword(s):  
Numerical Models ◽  
External Pressure ◽  
Plastic Layer ◽  
Internal Diameter ◽  
Flexible Pipe ◽  
Equivalent Thickness ◽  
Flexible Pipes ◽  
Buckling Behavior ◽  
Numerical Finite Element ◽  
Ring Approximation

When there are some failures on the external plastic layer of a flexible pipe, a high value of hydrostatic pressure can be transferred to its interlocked carcass layer, maybe causing a collapse. So it is necessary to predict on the design of a flexible pipe the maximum value of pressure that would be acceptable to avoid collapse of the carcass layer. That value depends on the imperfections on the internal diameter due to fabrication uncertainties. To study that problem, two numerical finite element models were created and used to simulate external pressure loading condition. The first model is a full 3D approximation, composed by solid elements. The second one is a 3D ring approximation, still made by solids. An analytical model using an equivalent thickness approach for carcass was done. A good correlation between analytical and numerical models was achieved for pre-buckling behavior, but analytical buckling behavior was not the same as numerical values predictions. Discussions about these differences are done.

Simplified Finite Element Models to Study the Dry Collapse of Straight and Curved Flexible Pipes

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Alfredo Gay Neto ◽  
Clóvis de Arruda Martins ◽  
Eduardo Ribeiro Malta ◽  
Rafael Loureiro Tanaka ◽  
Carlos Alberto Ferreira Godinho
Keyword(s):  
Finite Element ◽  
Failure Modes ◽  
Computational Cost ◽  
Three Dimensional ◽  
Element Model ◽  
External Pressure ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Simplified Modeling ◽  
Good Agreement

Dry collapse is one of the possible failure modes of flexible pipes. It refers to the situation in which no damage occurs in the flexible pipe external sheath. In this scenario, all layers of the pipe withstand the external pressure loading in a deep-water application. Such a situation is addressed in this work, which proposes some simplified modeling techniques to represent straight and curved flexible pipes subjected to external pressure, undergoing dry collapse during simulation procedure. The results of the proposed models are compared to other reference results, from a fully three-dimensional (3D) finite element model. Good agreement has been got, even with the proposed simplifications with a large reduction in computational cost when compared to full 3D model.

Investigation on Mechanical Properties of Fibreglass Reinforced Flexible Pipes Under Torsion

2018 ◽  
Author(s):  
Pan Fang ◽  
Yuxin Xu ◽  
Shuai Yuan ◽  
Yong Bai ◽  
Peng Cheng
Keyword(s):  
Mechanical Behavior ◽  
Torsion Angle ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Load Condition ◽  
Element Model ◽  
Flexible Pipe ◽  
Torsional Load ◽  
Flexible Pipes ◽  
The Impact

Fibreglass reinforced flexible pipe (FRFP) is regarded as a great alternative to many bonded flexible pipes in the field of oil or gas transportation in shallow water. This paper describes an analysis of the mechanical behavior of FRFP under torsion. The mechanical behavior of FRFP subjected to pure torsion was investigated by experimental, analytical and numerical methods. Firstly, this paper presents experimental studies of three 10-layer FRFP subjected to torsional load. Torque-torsion angle relations were recorded during this test. Then, a theoretical model based on three-dimensional (3D) anisotropic elasticity theory was proposed to study the mechanical behavior of FRFP. In addition, a finite element model (FEM) including reinforced layers and PE layers was used to simulate the torsional load condition in ABAQUS. Torque-torsion angle relations obtained from these three methods agree well with each other, which illustrates the accuracy and reliability of the analytical model and FEM. The impact of fibreglass winding angle, thickness of reinforced layers and radius-thickness ratio were also studied. Conclusions obtained from this research may be of great practicality to manufacturing engineers.

On the Structural Response of a Flexible Pipe With Damaged Tensile Armor Wires

2011 ◽  
Author(s):  
Jose´ Renato M. de Sousa ◽  
George C. Campello ◽  
Antoˆnio Fernando B. Bueno ◽  
Eduardo Vardaro ◽  
Gilberto B. Ellwanger ◽  
...  
Keyword(s):  
Mechanical Response ◽  
High Stress ◽  
Three Dimensional ◽  
Structural Response ◽  
Experimental Tests ◽  
Element Model ◽  
Axial Stiffness ◽  
Stress Concentrations ◽  
Flexible Pipe ◽  
Flexible Pipes

This paper studies the structural response of a 6.0″ flexible pipe under pure tension considering two different situations: the pipe is intact or has five wires broken in its outer tensile armor. A three-dimensional nonlinear finite element model devoted to analyze the local mechanical response of flexible pipes is employed in this study. This model is capable of representing each wire of the tensile armors and, therefore, localized defects, including total rupture, may be adequately represented. Results from experimental tests are also presented in order to validate the theoretical estimations. The theoretical and experimental results indicate that the imposed damage reduced the axial stiffness of the pipe. High stress concentrations in the wires near the damaged ones were also observed and, furthermore, the stresses in the inner carcass and the pressure armor are affected by the imposed damage, but, on the other hand, the normal stresses in the wires of the inner tensile armor are not.

A KNN Based Collapse Methodology and Recent Qualification of Flexible Pipes in Deepwater Application

2020 ◽  
Author(s):  
Linfa Zhu ◽  
Victor Pinheiro Pupo Nogueira ◽  
Zhimin Tan
Keyword(s):  
Structural Characteristics ◽  
Design Guidelines ◽  
Flexible Pipe ◽  
Collapse Pressure ◽  
Collapse Strength ◽  
Flexible Pipes ◽  
Collapse Model ◽  
Testing Data ◽  
Collapse Prediction ◽  
Current Design

Abstract As the flexible pipe industry targets more on deepwater applications, collapse performance of flexible pipes becomes a key challenge due to the huge hydrostatic pressure during installation and service. The collapse strength of flexible pipes largely depends on the structural characteristics of carcass, pressure sheath and pressure armor layers. Therefore, the collapse prediction methodology involving a sound modeling of these layers is essential. Over the years, Baker Hughes have collected a large amount of collapse testing data. The prediction tool needs to be validated and calibrated against all the collapse tests for best accuracy. In this paper, the latest progress of the collapse prediction methodology and qualification tests are presented. A generalized collapse model was developed to predict the collapse pressure of flexible pipes. This model incorporates the advantages of both the weighted kNN regression technique and an analytical collapse model. It is able to reproduce the exact collapse pressure on the pipes tested and can predict the collapse pressure of other pipe designs not tested. As part of the qualification process, the capacity to prevent collapse must be demonstrated. Several flexible pipes were designed based on this generalized prediction methodology for deep water application, and pipe samples were manufactured using industrial production facilities for collapse tests. The results show that flexible pipes following current design guidelines are suitable for deepwater applications.

Prediction and Qualification of Radial Birdcage and Lateral Buckling of Flexible Pipes in Deepwater Applications

2015 ◽  
Author(s):  
Linfa Zhu ◽  
Zhimin Tan ◽  
Victor Pinheiro Pupo Nogueira ◽  
Jian Liu ◽  
Judimar Clevelario
Keyword(s):  
Failure Modes ◽  
Local Buckling ◽  
External Pressure ◽  
Design Guidelines ◽  
Prediction Theory ◽  
Flexible Pipe ◽  
Lateral Buckling ◽  
Operation Conditions ◽  
Flexible Pipes ◽  
Compressive Loads

Increasing oil exploitation in deepwater regions is driving the R&D of flexible pipes which are subjected to high external pressure loads from the hydrostatic head during their installation and operation. One of the challenges of flexible pipe design for such applications is to overcome the local buckling failure modes of tensile armor layers due to the combination of high external pressure, compressive loads and pipe curvature. This paper presents the latest progress in local buckling behavior prediction theory and the qualification process of flexible pipes. First, the mechanisms of two types of buckling behaviors, radial birdcage buckling and lateral buckling, are described. For each failure mode, the analytical buckling prediction theory is presented and the driving parameters are discussed. As part of the qualification process, the ability to resist radial birdcage and lateral buckling must be demonstrated. Suitable test protocols are required to represent the installation and operation conditions for the intended applications by deep immersion performance (DIP) tests. Several flexible pipes were designed based on radial birdcage and lateral buckling prediction theory, and pipe samples were manufactured using industrial production facilities for DIP tests. The results clearly show that flexible pipes following current design guidelines are suitable for deepwater applications. An alternative in-air rig was developed to simulate the DIP tests in a controlled laboratory environment to further validate the model prediction as a continuous development.

Numerical Analysis of a Flexible Pipe With Damaged Tensile Armor Wires

2009 ◽  
Author(s):  
Jose´ Renato M. de Sousa ◽  
Aline Nacif Pinho ◽  
Gilberto Bruno Ellwanger ◽  
Edison C. P. Lima
Keyword(s):  
Mechanical Response ◽  
High Stress ◽  
Three Dimensional ◽  
Element Model ◽  
Axial Rotation ◽  
Flexible Pipe ◽  
High Stress Concentration ◽  
Flexible Pipes ◽  
Localized Defects ◽  
Nonlinear Finite Element Model

This paper focus on the structural analysis of a 2.5″ flexible pipe with one up to five broken wires in its outer tensile armor. The pipe is supposed to be under pure tension and the effect of the number of ruptured wires on its response is discussed. A three-dimensional nonlinear finite element model devoted to analyze the local mechanical response of flexible pipes is proposed and employed in all performed analyses. This model is capable of representing each wire of the tensile armors and, therefore, localized defects, including total rupture, may be adequately represented. The obtained results pointed to high stress concentration in the wires near the damaged ones as well as a significant increase in the axial rotation of the pipe. Moreover, the stresses in the inner carcass and the pressure armor are also affected by the rupture of wires in the outer tensile armor.

Controlling Factors of Carcass Fatigue in Unbonded Flexible Pipes

2019 ◽  
Author(s):  
Upul S. Fernando ◽  
Andrew P. Roberts ◽  
Michelle Davidson
Keyword(s):  
Fatigue Failure ◽  
Failure Modes ◽  
Dynamic Stress ◽  
External Pressure ◽  
Controlling Factors ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Innermost Layer ◽  
Key Features ◽  
Unbonded Flexible Pipes

Abstract Carcass, the innermost layer of a flexible pipe structure is designed to prevent the collapse of the pressure sheath due to external pressure. Weakness, damage or failure of the carcass layer can result in collapse with associated loss of production and potentially serious risk to pipe integrity and hydrocarbon leakage to the environment. Avoiding carcass failure in service is therefore an essential consideration during the design of unbonded flexible pipes. Carcass failure is rare in service. This paper highlights the three possible failure modes and presents further analysis on the fatigue failure mode, relevant to dynamic service. Two key features of carcass manufacture are identified as causes for dynamic stress; locking of the carcass profile due to extended pitch and polymer ingress within the carcass cavity. Guidelines for the design of carcass profiles, setting safe pitch limits and appropriate barrier profile controls to mitigate carcass fatigue failure in dynamic service are presented.

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