Simplified Approaches to Modeling of Lateral Wire Buckling in the Tensile Armour of Flexible Pipes

2012 ◽  
Author(s):  
Niels H. Østergaard ◽  
Anders Lyckegaard ◽  
Jens H. Andreasen
Keyword(s):  
Structural Integrity ◽  
The Other ◽  
Computational Time ◽  
Flexible Pipe ◽  
Deep Waters ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Load Carrying ◽  
Present Context ◽  
Deformation Patterns

In the present paper, simplifications of methods developed for modeling of lateral wire buckling in the tensile armour layers of flexible pipes are proposed. Lateral wire buckling may occur during pipe laying in ultra-deep waters. In this scenario a flexible pipe is subjected to repeated bending and axial compression due to hydrostatic pressure on the end cap of an empty pipe. If the outer sheath is breached, these loads may cause wire slippage towards states in which the load carrying ability is reduced and wire buckling in the circumferential pipe direction occurs. This leads to characteristic deformation patterns, which may compromise the structural integrity of the entire pipe structure. On the other hand, these loads may cause overstressing of the wires, if the outer sheath is intact. Simplifications of established models for calculation of the load carrying ability are in the present context proposed in a manner, by which the effect of adjacent pipe layers on the postbuckled response can be estimated. The simplifications enables significant reduction of the computational time, which is necessary to calculate the load carrying ability of a given pipe structure.

Polyamide 11: A High Tenacity Thermoplastic, Its Material Properties and the Influence of Ageing in Offshore Conditions

2002 ◽  
Author(s):  
Michael Werth ◽  
Gilles Hochstetter ◽  
Patrick Dang ◽  
Nathalie Chedozeau
Keyword(s):  
Material Properties ◽  
Mechanical Response ◽  
Sea Water ◽  
Flexible Pipe ◽  
Polyamide 11 ◽  
Water Ingress ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Operating Limits ◽  
Sheath Material

Polyamide 11 is a key material in the fabrication of offshore flexible pipes. It is mainly used as the flexible pressure layer assuring the impermeability of the fluid and gas carrying flexible pipe. A further important use is as outer sheath material where it protects efficiently the metal strip structure from sea water ingress even in highly dynamic applications. Given these important functions of polyamide 11 the knowledge of its precise material properties is essential for the design and the operating limits of flexible pipes. This paper aims to give a detailed understanding of the scope of the material properties such as fracture toughness, fatigue resistance and the mechanical response function. In a further step the influence of ageing on these properties is outlined with the aid of aged model specimen studies.

A Simple Alternative Method to Estimate the Collapse Pressure of Flexible Pipes

2010 ◽  
Author(s):  
Victor Pinheiro Pupo Nogueira ◽  
Theodoro Antoun Netto
Keyword(s):  
Structural Integrity ◽  
Plastic Material ◽  
Numerical Models ◽  
Gas Production ◽  
Material Behavior ◽  
Flexible Pipe ◽  
Collapse Pressure ◽  
Operational Conditions ◽  
Alternative Method ◽  
Flexible Pipes

Offshore oil and gas production worldwide constantly moves to deeper water with increasing flexible pipe operational severity. Failure mechanisms, i.e., sequences of events which may lead to failure, are nowadays more likely to happen. Therefore, it is important to develop reliable numerical tools that can be used in the design stages or during service-life to assess the structural integrity of pipes under specific operational conditions. This work presents a methodology to develop simple finite element models capable to reproduce the behavior of structural layers of flexible pipes under hydrostatic pressure up to the onset of collapse. The models use beam elements and include contact between layers, nonlinear kinematics and material behavior. Different configurations were analyzed: carcass-only, and carcass plus pressure armor with dry and wet annular. The dependability of the numerical models is assessed in light of experimental tests on flexible pipes with 4 and 8 inch nominal internal diameters. Relevant geometric parameters and material properties of each specimen were measured and subsequently used in the models to reproduce the physical experiments. The metallic inner carcass and pressure armor layer manufacturing processes cause a high degree of stress-induced material anisotropy. Due to the inherent difficulty to determine the non-homogeneous elastic-plastic material behavior of the wires’ cross-sections, a novel alternative method was used to estimate their average stress-strain curves up to moderate strains (2%). Good correlation was obtained between experimental and numerical results. The applied methodology proved to be simple and yet efficient and reliable for the estimation of the collapse pressure of flexible pipes.

H2S Consumption and the Derivation of a New Annulus Prediction Model for Offshore Flexible Pipes

2016 ◽  
Author(s):  
Marie Haahr ◽  
Jonas Gudme ◽  
Jacob Sonne ◽  
Sten Overby ◽  
Torben Nielsen ◽  
...  
Keyword(s):  
Prediction Model ◽  
Scale Validation ◽  
Cost Savings ◽  
Small Scale ◽  
Annular Space ◽  
Flexible Pipe ◽  
Independent Verification ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Sour Service

This paper presents the outcome of investigations on the effects of H2S consumption in the annulus of a flexible pipe. Low-molecular gases, such as CH4, H2S, H2O and CO2, permeate slowly from the bore through the inner liner into the annular space between the inner liner and outer sheath of a flexible pipe. This space is densely packed with carbon steel armour wires leaving a very limited free volume. In the presence of water, a corrosive environment for the armour wires is generated and a risk of sour service cracking is introduced. H2S concentration in the annulus is traditionally calculated by balancing the inflow through inner liner and the outflow through outer sheath and vent valve. In order to assure H2S resistance of the armour wires towards calculated H2S concentrations, pipes for sour service are typically designed with lower strength wire grades of larger dimensions compared to the possibilities of sweet service pipes. Over the last decade, more and more offshore data has been obtained indicating considerably less H2S in the annulus than predicted by the traditional annulus models. This observation has triggered in-depth investigations of the complex corrosive H2S environment inside a flexible pipe annulus exposed to sour service conditions. An extensive small-scale test program has been conducted and showed that at permeation rates typical for flexible pipes, the consumption of H2S in the corrosion processes occurring in the annular space lowers the concentration and hence criticality of the H2S so significantly that it leaves the traditional models overly conservative to an extreme extent. Using this knowledge of consumption of the corrosive gases in the annulus has become an increasingly important topic with the focus on deeper waters, cost savings and service life extensions without compromising flexible pipe integrity. Based on experimental data obtained, a new annulus model for prediction of H2S pressure in annulus has been derived. Data is presented in this paper to illustrate the methodology for an annulus prediction where the consumption of H2S is included. The data presented covers laboratory tests with variations and effects of gas flux, H2S concentration and total pressure. A full-scale validation, led to an Independent Verification Agency certification of the model. With the introduction of this new annulus prediction model, a wider range of wire products becomes available for the pipe designers. Lower weight pipes with stronger armour wires render optimizations for both cost savings and applications at deeper waters possible.

Development and Experimental Calibration of Numerical Model Based on Beam Theory to Estimate the Collapse Pressure of Flexible Pipes

2015 ◽  
Author(s):  
Jefferson Lacerda ◽  
Marcelo I. Lourenço ◽  
Theodoro A. Netto
Keyword(s):  
Structural Integrity ◽  
Oil And Gas ◽  
Numerical Models ◽  
Beam Theory ◽  
Gas Production ◽  
Operating Conditions ◽  
Flexible Pipe ◽  
Experimental Calibration ◽  
Collapse Pressure ◽  
Flexible Pipes

The constant advance of offshore oil and gas production in deeper waters worldwide led to increasing operational loads on flexible pipes, making mechanical failures more susceptible. Therefore, it is important to develop more reliable numerical tools used in the design phase or during the lifetime to ensure the structural integrity of flexible pipes under specific operating conditions. This paper presents a methodology to develop simple finite element models capable of reproducing the behavior of structural layers of flexible pipes under external hydrostatic pressure up to collapse. These models use beam elements and, in multi-layer analyses, include nonlinear contact between layers. Because of the material anisotropy induced by the manufacturing process, an alternative method was carried out to estimate the average stress-strain curves of the metallic layers used in the numerical simulations. The simulations are performed for two different configurations: one where the flexible pipe is composed only of the interlocked armor, and another considering interlocked armor and pressure armor. The adequacy of the numerical models is finally evaluated in light of experimental tests on flexible pipes with nominal internal diameters of 4 and 6 in.

Proposals for Integrity Management of Flexible Pipe

2013 ◽  
Author(s):  
Shuai Yuan ◽  
Gao Tang ◽  
Jie Bai ◽  
Mohd Fauzi Badaruddin
Keyword(s):  
Research Work ◽  
Management Program ◽  
The Other ◽  
Flexible Riser ◽  
Flexible Pipe ◽  
Whole Process ◽  
Practical Project ◽  
Flexible Pipes ◽  
High Pressure High Temperature ◽  
Integrity Management

The increasing use of flexible pipes in subsea with high pressure/high temperature brings about much more challenges, for example flexible riser fatigue, bird-caging and armour wire disorganization, development of flexible pipes with smooth bore and ones with anti-H2S layer, which demand operators to adopt an effective integrity management program including every phase of flexible pipe industry to avoid reduction of production. To date, much research work has been carried out on this topic. In this paper, the applicable inspection and monitoring measures are presented as proposals to develop the integrity management of flexible pipes. Meanwhile, this paper takes a practical project as an example to show the whole process of integrity management study clearly. The process can be used as reference for the other similar integrity management projects.

Repair Techniques for Flexible Pipe External Sheath

2008 ◽  
Author(s):  
T. A. Netto ◽  
J. M. Touc¸a ◽  
M. Ferreira ◽  
V. Gonc¸alez ◽  
R. Marnet
Keyword(s):  
Sea Level ◽  
Structural Integrity ◽  
Annular Region ◽  
Annular Space ◽  
Flexible Pipe ◽  
Flexible Pipes ◽  
Cutting Out ◽  
Inspection Techniques ◽  
Repair Techniques

During installation or service, the external sheath of flexible pipes can suffer damages that may result in loss of sealing and exposure of the annular region to the external environment. Additionally, visual inspection of the armor layers is sometimes necessary to assess their structural integrity. Such procedure requires cutting out a small segment (window) of the external sheath. One of the most effective inspection techniques to detect problems in the topside relief valves, damages on the external sheath, or pressure barrier failure is the surface monitoring of the pressure in the annular region. Therefore, in the event of sheath damage or inspection windows, in situ repair techniques that guarantee the recovery of its sealing properties are important, particularly in the regions above sea level and water depths usually up to 30 meters. When the pipes are below this level, repairs are in general done on board of an installation vessel. Due to the inherent complexities of each region, specific repair techniques have been developed by PETROBRAS to date. Nevertheless, these techniques do not guarantee the annular space sealing, therefore hampering pressure monitoring. The objective of this work was to develop an external sheath repair technique using light, resistant, and easy-to-install materials for the areas above sea level and small depths (up to 30 m) capable to provide the necessary sealing for annular space monitoring.

Frictional Flexible Pipe Model Using Macroelements

2020 ◽  
Author(s):  
Rodrigo Provasi ◽  
Fernando Geremias Toni ◽  
Clovis de Arruda Martins
Keyword(s):  
Structural Behavior ◽  
Computational Time ◽  
Memory Usage ◽  
Relative Movement ◽  
Flexible Pipe ◽  
Finite Element Software ◽  
Geometrical Characteristics ◽  
Pipe Model ◽  
Contact Formulation ◽  
Flexible Pipes

Abstract Flexible pipes are structures composed by many layers varying in composition and shapes, in which the structural behavior is defined by the role it must play. Flexible pipes construction is such that layers are unbounded, allowing relative movement between them and modifying its behavior. Many approaches are used to model such cables, both analytical and numerical, such as the macroelements model. This sort of model consists in finite elements where geometrical characteristics are taken into account by the formulation and is under development by the authors. Previous works have shown in detail the modeled cylindrical and helical elements, as well node-to-node connection elements (bounded, frictionless and frictional), which have allowed simplified flexible pipe with bonded elements simulations. This article will focus on modeling a simplified cable consisting in an external sheath, two armor layers and a polymeric core, since recent advances in the contact formulation opens the possibility to incorporate friction between the layers. Taking into consideration accuracy, computational time and memory usage, results from macroelements are compared to commercial finite element software.

scholarly journals Burst pressure prediction of fiber-reinforced flexible pipes with arbitrary generatrix

2021 ◽  
Vol 16 ◽  
pp. 155892502199081
Author(s):  
Guo-min Xu ◽  
Chang-geng Shuai
Keyword(s):  
Transfer Matrix ◽  
Linear Equations ◽  
Burst Pressure ◽  
Fiber Reinforced ◽  
Flexible Pipe ◽  
Theoretical Derivation ◽  
Design And Optimization ◽  
Flexible Pipes ◽  
Novel Method ◽  
Winding Angle

Fiber-reinforced flexible pipes are widely used to transport the fluid at locations requiring flexible connection in pipeline systems. It is important to predict the burst pressure to guarantee the reliability of the flexible pipes. Based on the composite shell theory and the transfer-matrix method, the burst pressure of flexible pipes with arbitrary generatrix under internal pressure is investigated. Firstly, a novel method is proposed to simplify the theoretical derivation of the transfer matrix by solving symbolic linear equations. The method is accurate and much faster than the manual derivation of the transfer matrix. The anisotropy dependency on the circumferential radius of the pipe is considered in the theoretical approach, along with the nonlinear stretch of the unidirectional fabric in the reinforced layer. Secondly, the burst pressure is predicted with the Tsai-Hill failure criterion and verified by burst tests of six different prototypes of the flexible pipe. It is found that the burst pressure is increased significantly with an optimal winding angle of the unidirectional fabric. The optimal result is determined by the geometric parameters of the pipe. The investigation method and results presented in this paper will guide the design and optimization of novel fiber-reinforced flexible pipes.

Integrity Assessment of a Free-Fall Lifeboat Launched From a FPSO

2015 ◽  
Author(s):  
Guomin Ji ◽  
Nabila Berchiche ◽  
Sébastien Fouques ◽  
Thomas Sauder ◽  
Svein-Arne Reinholdtsen
Keyword(s):  
Finite Element ◽  
Pressure Distribution ◽  
Structural Integrity ◽  
Dynamic Effect ◽  
Sensitivity Study ◽  
Computational Time ◽  
Load Factor ◽  
Time Varying ◽  
Integrity Assessment

The paper addresses the structural integrity assessment of lifeboat launched from floating production, storage and offloading (FPSO) vessels. The study is based on long-term drop lifeboat simulations accounting for more than 50 years of hindcast data of metocean conditions and corresponding FPSO motions. Selection of the load cases and strength analyses with high computational time is a challenge. The load cases analyzed are those corresponding to the 99th percentile of long term distribution of indicators for large slamming loads (CARXZ) or large submergence (Imaxsub). For six selected cases, the time-varying pressure distribution on the lifeboat hull during and after water impact is calculated by CFD simulations using StarCCM+. The finite element model (FEM) of the composite structure of the lifeboat is modelled by ABAQUS. Quasi-static finite element (FE) analyses are performed for the selected load cases. The structural integrity is assessed by the maximum stress and Tsai-Wu failure measure. In the present study, the load and resistance factors are combined and applied to the response. A sensitivity study is performed to investigate the non-linear load/response effects when the load factor is applied to the load. In addition, dynamic analysis is performed with the time-varying pressure distribution for selected case and the dynamic effect is investigated.

Cathodic Protection Design Consideration for an Offshore Flexible Riser Connected to an Impressed Current System

2021 ◽  
Author(s):  
Thierry Dequin ◽  
Clark Weldon ◽  
Matthew Hense
Keyword(s):  
Cathodic Protection ◽  
Sacrificial Anode ◽  
Flexible Riser ◽  
Flexible Pipe ◽  
Linear Resistance ◽  
Flexible Pipes ◽  
Flexible Risers ◽  
Impressed Current ◽  
Host Structure ◽  
Impressed Current Cathodic Protection

Abstract Flexible risers are regularly used to produce oil and gas in subsea production systems and by nature interconnect the subsea production system to the floating or fixed host facilities. Unbonded flexible pipes are made of a combination of metallic and non-metallic layers, each layer being individually terminated at each extremity by complex end fittings. Mostly submerged in seawater, the metallic parts require careful material selection and cathodic protection (CP) to survive the expected service life. Design engineers must determine whether the flexible pipe risers should be electrically connected to the host in order to receive cathodic protection current or be electrically isolated. If the host structure is equipped with a sacrificial anode system, then electrical continuity between the riser and the host structure is generally preferred. The exception is often when the riser and host structure are operated by separate organizations, in which case electrical isolation may be preferred simply to provide delineation of ownership between the two CP systems. The paper discusses these interface issues between hull and subsea where the hull is equipped with an impressed current cathodic protection (ICCP) system, and provides guidance for addressing them during flexible pipe CP design, operation, and monitoring. Specifically, CP design philosophies for flexible risers will be addressed with respect to manufacturing, installation and interface with the host structure’s Impressed Current Cathodic Protection (ICCP) system. The discussion will emphasize the importance of early coordination between the host structure ICCP system designers and the subsea SACP system designers, and will include recommendations for CP system computer modeling, CP system design operation and CP system monitoring. One of the challenges is to understand what to consider for the exposed surfaces in the flexible pipes and its multiple layers, and also the evaluation of the linear resistance of each riser segment. The linear resistance of the riser is a major determinant with respect to potential attenuation, which in turn largely determines the extent of current drain between the subsea sacrificial anode system and the hull ICCP system. To model the flexible riser CP system behavior for self-protection, linear resistance may be maximized, however the use of a realistic linear resistance is recommended for evaluation of the interaction between the host structure and subsea system. Realistic flexible linear resistance would also reduce conservatism in the CP design, potentially save time during the offshore campaign by reducing anode quantities, and also providing correct evaluation of drain current and stray currents.

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