Critical review of subsea structures in the Gulf of Guinea : “Finite element analysis to predict the behaviour of a multi-layer non-bonded flexible pipe under hydrate plug in a static application”

The concept of blockages in a non-bonded flexible pipe during oil and gas mining operations have over the years shown to be a persistent problem, and the need for a standardized remediation approach is paramount. This research work studies the behaviour of non-bonded flexible pipes with methane hydrate blockage under the influence of diverse loading conditions. Nonlinear tridimensional finite element models were used on two (2) scenarios, blocked and unblocked conditions. These models recreate a seven-layer flexible pipe with two tensile armour layers, an external polymeric sheath, high strength tape, orthotropic equivalent carcass, and pressure armour layers with an internal polymetric sheath. With these models, several studies were conducted to verify the influence of key parameters on the instability phenomenon when the flexible pipe is under hydrate blockage. The internal pressure and compressive loads can be considered one of these parameters, and their variation causes a significant change in the stability response of the pipe layers. This work includes a detailed description of the finite element model and a case study where the non-bonded flexible pipe is blocked by methane hydrate. The procedure of this analysis is here described, along with the results. For in-depth knowledge of hydrate formation and its consequences in flexible pipes, this thesis used ABAQUS, a standard finite element (FE), in modelling, simulating, and investigating a hydrate blocked and unblocked non-bonded flexible pipe. It is divided into two Samples, A and B, respectively, under the influence of various load conditions. FE model was adopted to investigate the effects of hydrate on the layers as were not detailed in America Petroleum Institute codes [1]. This was carried out under various conditions such as pipe with and without blockage at various pressure, forces (longitudinal and compressive) values, different hydrate lengths, coefficients of friction and stiffness constants. In addition to the FE analysis, an experimental investigation was carried out on the samples and where necessary mathematical analyses were undertaken to reverify results. The studies carried out were to determine the non-bonded flexible pipes responses under certain load conditions. This determines the deformation, stress concentration on individual layers, making sure the results are within the recommended API standards, hoop, axial and radial stresses, reactive force, and contact pressure between the layers. A simplified model was employed and a finer mesh to resolve the issue with the FE model. And progress the effect of the hydrate on the pipe layers. Importantly, this present work considered and investigated a 7-layers 6” diameter non-bonded flexible pipe as a case study. The results were obtained from the numerical and experimental investigations, analysed, and presented accordingly. Obtained results showed a significant influence of methane hydrate on Sample A, while Sample B behaves normally under various load conditions. The detailed outcome and further research works are presented in this thesis.The concept of blockages in a non-bonded flexible pipe during oil and gas mining operations have over the years shown to be a persistent problem, and the need for a standardized remediation approach is paramount. This research work studies the behaviour of non-bonded flexible pipes with methane hydrate blockage under the influence of diverse loading conditions. Nonlinear tridimensional finite element models were used on two (2) scenarios, blocked and unblocked conditions. These models recreate a seven-layer flexible pipe with two tensile armour layers, an external polymeric sheath, high strength tape, orthotropic equivalent carcass, and pressure armour layers with an internal polymetric sheath. With these models, several studies were conducted to verify the influence of key parameters on the instability phenomenon when the flexible pipe is under hydrate blockage. The internal pressure and compressive loads can be considered one of these parameters, and their variation causes a significant change in the stability response of the pipe layers. This work includes a detailed description of the finite element model and a case study where the non-bonded flexible pipe is blocked by methane hydrate. The procedure of this analysis is here described, along with the results. For in-depth knowledge of hydrate formation and its consequences in flexible pipes, this thesis used ABAQUS, a standard finite element (FE), in modelling, simulating, and investigating a hydrate blocked and unblocked non-bonded flexible pipe. It is divided into two Samples, A and B, respectively, under the influence of various load conditions. FE model was adopted to investigate the effects of hydrate on the layers as were not detailed in America Petroleum Institute codes [1]. This was carried out under various conditions such as pipe with and without blockage at various pressure, forces (longitudinal and compressive) values, different hydrate lengths, coefficients of friction and stiffness constants. In addition to the FE analysis, an experimental investigation was carried out on the samples and where necessary mathematical analyses were undertaken to reverify results. The studies carried out were to determine the non-bonded flexible pipes responses under certain load conditions. This determines the deformation, stress concentration on individual layers, making sure the results are within the recommended API standards, hoop, axial and radial stresses, reactive force, and contact pressure between the layers. A simplified model was employed and a finer mesh to resolve the issue with the FE model. And progress the effect of the hydrate on the pipe layers. Importantly, this present work considered and investigated a 7-layers 6” diameter non-bonded flexible pipe as a case study. The results were obtained from the numerical and experimental investigations, analysed, and presented accordingly. Obtained results showed a significant influence of methane hydrate on Sample A, while Sample B behaves normally under various load conditions. The detailed outcome and further research works are presented in this thesis

Nonlinear behaviour of offshore flexible risers

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel UniversityAs the search for exploration of oil and gas moves to deeper waters, flexible unbounded risers have become the main means of extracting hydro carbonates from deep waters. In this context, structural integrity of flexible risers has become a crucial issue for the offshore industry. In this study, experimental tests and detailed finite element analyses were carried out on a scaled down model of a flexible riser pipe. The model used consists of four layers which include two cylindrical polycarbonate tubes and two steel helical layers. One helical layer represents the carcass layer in an actual flexible riser whilst the other represents the riser tendon armour layers, wounded around the pipe assembly. The model was first subjected to a three point bending load in order to study its bending-curvature behaviour experimentally. Then, the specimen was tested under compressive load with different pressure values to investigate the effect of pressure on the pipe deformation. Additionally, the effects of pure axial load and pure pressure with no load on the model were examined. The effects of static load on the deformation of a single helical tendon layer and creep behaviour (Shetty, 2013) of the layer were also studied. The investigation of a single tendon under axial load using finite element based software shows residual strains results are in good agreement with the experiments. The numerical model also shows a non-linear behaviour in bending-moment curvature for flexible pipe which is in a good agreement with the experimental data

A STUDY OF MECHANICAL PROPERTIES AND CRUSHING PERFORMANCE OF CARBON FIBER WOUND TO HDPE PIPE (CFWHP

Carbon fiber-reinforced polymer, is a type of composite polymer which is highly regarded as one of the best alternatives for light weight, strong and anti-corrosion material. Composite polymer consists of 2 main constituent materials which are matrix and reinforcement which are fabricated using the filament winding technique. This material is vastly used in various industries such as the automotive industry, oil and gas industry, aerospace industries and also industries that demands a high strength-to- weight ratio criteria. The focal point of this research is to study the effect of different carbon fiber tow arrangements on the carbon fiber tow wind to HDPE composite pipe (CFWHP) and their mechanical properties. There are 3 types of samples used in this project, both with different carbon fiber tow arrangements. These samples will be then fabricated in SIRIM Permatang Pauh using epoxy resin as the desired matrix to form the composite material. The first sample with an arrangement of 4 fiber tows of 12k carbon fiber (total of 48k) with a winding angle of 57°

A chemical based wet cold flow approach for addressing hydrate flow assurance problems

Current gas hydrate flow assurance methods are becoming less economical and/or practical for deepwater operations, long tiebacks and ageing reservoirs. The industry thus needs novel flow assurance techniques to address these challenging conditions. An alternative approach called HYDRAFLOW, a chemical based wet Cold Flow method, has been presented in this thesis in which gas hydrate management, rather than prevention, is the aim. The idea is to convert most of the gas phase into hydrates and transfer it in the form of hydrate-slurry in the pipeline. This study investigates the concept, i.e. the transportability of hydrate slurries, for different systems (low and high GOR oil systems in the presence and absence of AAs) in different operating conditions, especially in conditions where the other flow assurance solutions either cannot be applied or are not economically viable, e.g. at high watercuts or under very high degree of subcoolings. The experiments involve investigating the rheological behaviour and flow properties of hydrate slurries using the HTI-set up (Helical Tube Impeller, an apparatus designed and build in-house for measuring viscosity of hydrate slurries at high pressures). Additionally, the rate of hydrate formation in low and high oil systems and also at subzero conditions has been measured. Furthermore, the effect of key variables, (e.g. heat transfer, mass transfer, degree of subcooling, salt, anti-agglomerants (AAs) and thermodynamic inhibitors) on the rate of hydrate formation and also on the rheology of hydrate suspensions have been studied in this work. The partitioning of a commercial AA between hydrate, oil and aqueous phases and its performances in each phase have also been determined which can help for decision making about recovering and/or recycling all or part of AAs. And finally, it has been shown that hydrate flow can potentially reducing wax deposition problems in pipeline by abrasion of the deposited wax

Well P&A Tubing Compaction Method Evaluation and Modelling

Master's thesis in Petroleum engineeringThe number of aged fields in the North Sea is increasing, and in few years, and there will be a significant increase in number of wells that need to be permanently plugged and due to low oil prices and other reasons, there is a push from the industry to reduce the cost of P&A operations as much as possible, and using rig-less equipment for P&A has proven to be a reliable alternative to drilling rigs, but this solution requires the development of new technologies to overcome the challenges that come up with it. The presence of tubing in the area where the permeant plug should be set is still a thorny issue for P&A rig-less operation for many reasons. Recently there are many approaches for removing tubing in place without pulling it to surface, one of these alternative ideas is downhole tubing disposal (DHTD). The main scope of this thesis is to give an insight into DHTD method, its advantages and the challenges to translate this idea into practice. In this work as well, different approaches are incorporated to estimate the required tubing crushing force, including FEM, analytical estimation and experimental work. Results are reported for an analytical estimation and FEM (ABAQUS) analysis of a slotted tubular subjected to compression axial load. The results showed different kinds of correlations with experimental test data. On the other hand, they showed that FEM is a powerful method to solve this kind of problems

Book of abstracts of the 15th International Symposium of Croatian Metallurgical Society - SHMD \u272022, Materials and metallurgy

Book of abstracts of the 15th International Symposium of Croatian Metallurgical Society - SHMD \u272022, Materials and metallurgy, Zagreb, Croatia, March 22-23, 2022. Abstracts are organized in four sections: Materials - section A; Process metallurgy - Section B; Plastic processing - Section C and Metallurgy and related topics - Section D

Book of abstracts of the 15th International Symposium of Croatian Metallurgical Society - SHMD \u272022, Materials and metallurgy

Book of abstracts of the 15th International Symposium of Croatian Metallurgical Society - SHMD \u272022, Materials and metallurgy, Zagreb, Croatia, March 22-23, 2022. Abstracts are organized in four sections: Materials - section A; Process metallurgy - Section B; Plastic processing - Section C and Metallurgy and related topics - Section D

The Design and Manufacture of a Glass Fibre Reinforced Polymer (GFRP) Bolted Flange Joint for Oil and Gas Applications

Metallic bolted flange and pipes both have been increasingly replaced by fibre reinforced polymer (FRP) materials in many applications which deal with extreme harsh environments such as oil, gas, marine, chemical etc. However, only a handful of research works have been conducted regarding the bolted flange joint (BFJ) made of FRP materials. Also, the availabilities of standards and codes are very limited for the composite BFJ. Hence, the design guidelines for fabrication methods and dimensional considerations of bolted FRP flange are yet to be optimised fully. For instance, the ASME Boiler and Pressure Vessel Code, Section X, does not include specific rules for the design of bolted FRP flange joints. As a result, it is difficult to understand the consequences of the reliability of FRP flanges made with parametric variations and dimensional alterations. Therefore, the current research aims to produce a bolted GFRP flange joint with high performance through a series of experimentations and numerical simulations. A mould has been designed and manufactured using aluminium, glass, O-ring gasket and bolts. The bolted GFRP flanges have been fabricated using vacuum infusion process, polyester and fibreglass braid sleeves. Various experiments were conducted to solve the faced issues during the manufacturing process. Several experiments were carried out with different strain gauges to measure the bolt load. The GFRP flange has been assembled with other required components to produce the pressure vessel and tested under various bolt and internal pressure loads using different gaskets (Nitrile and Viton), which are suitable for the oil and the gas applications. Numerically, finite element analysis (FEA) of the BFJ comprised of composite flange and pipe, flange-pipe adhesive bonding, gasket and fastener has been conducted using ANSYS Mechanical. The FEA has been performed considering the orthotropic properties of the composite materials and the non-linearity behaviour of the rubber gasket. The FEA also includes the simulation of the fluid pressure penetration (FPP) between the flange and the gasket using the contact element real constant criterion (PPNC). Furthermore, another FEA model has been developed for a metal flange using the same boundary conditions as the GFRP flange. This flange has been investigated experimentally and numerically in published work [1]. The agreements between the obtained results and the previous results are excellent. This confirms the validity of the FEA performed in this project. The BFJ has been tested under various bolt and internal pressure loads experimentally and numerically and the strains in three directions (axial, hoop and radial) have been measured and calculated. The obtained results show that the influence of the bolt load is higher than the pressure load and the leakage pressure increases with increasing the bolt load. The effects of the flange dimensions on the maximum axial, hoop and radial strains, axial displacement, flange rotation and leakage pressure have been investigated using the FEA. The dimensions considered are the flange outer diameter and thickness, hub length and thickness. Most of the flange joint dimensions (within the selected range) have a small effect on the results and that confirms that the flange dimensions should be reduced to save the materials cost. The current flange is very strong and this is due to the good selection of the materials, fabric structure and the fabrication process, which gives high fibre content. In addition, the results show that the gasket materials and thickness has very small influences on the flange strains, axial displacement and rotation. The leakage pressure is affected by the gasket materials more than the thickness.The Higher Committee for Education Development (HCED) in Iraq

Tetraparametric assembly method for the simulation and optimizaction of bolt tightening sequences in ASME ring type joints

211 p.En el sector del Oil&Gas, debido a la gran longitud que suelen tener las tuberías de los oleoductos y gasoductos submarinos, se hace necesario fabricar las tuberías en pequeños tramos para posteriormente unirlos mediante uniones in situ. Además, esto permite abaratar los costes de fabricación ya que hace posible fabricar piezas de carácter general (tramos rectos de tubería, codos, válvulas, etcétera). Entre los diferentes tipos de uniones, las uniones atornilladas son muy utilizadas debido a su fácil desmontaje, ya que hace posible realizar tareas de mantenimiento o acoplar nuevos dispositivos a las tuberías de una manera muy sencilla. No obstante, en este tipo de uniones es necesario obtener una distribución de presiones uniforme en la junta para así evitar o al menos reducir al máximo sus fugas. Para ello, obviamente, es preciso obtener una carga uniforme en todos los tornillos de la unión. Esto no es una tarea sencilla ya que cuando un tornillo es precargado durante la secuencia de atornillado, la unión se comprime y por lo tanto la carga de los tornillos que han sido previamente precargados se reduce. Este fenómeno es conocido como interacción elástica. Debido a la pérdida de carga de los tornillos durante lasecuencia de atornillado, la carga que tienen los tornillos al final de la secuencia de atornillado es diferente de la carga de apriete que se ha aplicado a los tornillos. Además, la magnitud de estas variaciones de carga depende de un gran número de parámetros cuya influencia es muy difícil de prever, como por ejemplo la geometría y el material de los componentes de la unión, el orden de apriete, el espaciado entre tornillos, etcétera. En este sentido, se hace difícil prever las cargas finales en los tornillos, y por lo tanto, también es complicado obtener una distribución de cargas uniforme en la junta al final de la secuencia de atornillado.A fin de resolver esta problemática, existen diferentes normas (ASME, NORSOK, API, entre otras) que contienen procedimientos de ensambladopara obtener la carga final uniforme deseada en los tornillos. De este modo, se obtiene una distribución uniforme de presiones en la junta, y así se consiguen reducir al máximo las fugas en la unión. Sin embargo, las secuencias propuestas en las normas son muy costosas debido a que requieren un gran número de pasadas, y cuantas más pasadas, mayor es el tiempo de ensamblado de cada unión. Además, exceptuando las últimas pasadas, la secuencia de atornillado suele seguir un orden de apriete en estrella, lo cual complica aún más el ensamblado. En consecuencia, teniendo en cuenta que el número de uniones suele ser muy elevado, el coste económico del ensamblado acaba adquiriendo una gran importancia. Respecto a las secuencias de atornillado que proponen las normas, también cabe destacar que ellas mismas advierten que solo son orientativas y por lo tanto recomiendan que cada ensamblador desarrolle sus propias secuencias de atornillado para sus productos y condiciones de trabajo en particular. Resumiendo, para ser fiables y competitivos es indispensable crear procedimientos de ensamblado propios que se adapten a los productos propios.A fin de obtener diferentes secuencias para cada unión en particular y así obtener secuencias más eficientes, en los últimos años se han desarrollado métodos que definen las llamadas secuencias optimizadas. Entre ellos, los más populares en la literatura especializada son el ¿Método de los Coeficientes de la Interacción Elástica¿ (MCIE) y el ¿Método de la Secuencia Inversa¿ (MSI). Estos métodos estudian el comportamiento de la unión durante la secuencia de atornillado para así predecir las pérdidas de carga de todos los tornillos. De este modo, se pueden calcular las cargas de apriete de cada tornillo para una carga final deseada, y obtener una carga uniforme en tan solo una o dos pasadas. Sin embargo, estos métodos de optimización tienen la desventaja de que obtener la secuencia optimizada es bastante costoso porque hay que realizar un gran número de aprietes y mediciones previas. Es por ello, que estos procesos de optimización solo resultan rentables cuando el número de uniones a ensamblar es muy elevado o cuando se trata de una aplicación bastante crítica.Esta Tesis Doctoral tiene como objetivo global estudiar el proceso de optimización de secuencias de atornillado en las uniones Ring Type Joint (RTJ) de ASME con junta metálica. Estas uniones son ampliamente utilizadas en el sector del Oil&Gas por su capacidad de proporcionar un buen sellado a temperaturas y presiones internas muy elevadas, gracias a la junta metálica que va introducida en el surco que tiene mecanizado cada una de las superficies de sellado. Para definir su proceso de optimización, el primer objetivo es estudiar los dos métodos anteriormente mencionados en este tipo de uniones y así obtener sus ventajas y sus desventajas. El segundo objetivo, y también el objetivo principal de esta Tesis Doctoral, es desarrollar una nueva metodología para la optimización de secuencias de atornillado en uniones RTJ. Para finalizar con la Tesis Doctoral, el último objetivo es programar la nueva metodología desarrollada en ¿Visual Basic for Applications¿ de Microsoft Excel, para dar lugar a una aplicación de gran aplicabilidad y muy sencilla de utilizar.Para ello, la tesis Doctoral se ha dividido en varios capítulos y se ha estructurado como se expone a continuación.En primer lugar, en el Capítulo 1 se describen los antecedentes y se presentan los objetivos. Se comienza explicando la necesidad de utilizar uniones atornilladas en las líneas de tuberías destinadas al Oil&Gas, yla dificultad que supone ensamblar correctamente estas uniones debido a fenómenos muy diversos que complican obtener una distribución de cargas uniforme en los tornillos. Además, se explican las diferentes alternativas que existen hoy en día para tratar de ensamblar correctamente una unión. En este Capítulo también se presenta el tipo de unión atornillada a estudiar a lo largo de esta Tesis Doctoral.En el Capítulo 2 se presentan las herramientas de análisis utilizadas a lo largo de la Tesis Doctoral. Por un lado, se presenta un modelo multiparamétrico de Elementos Finitos desarrollado en ANSYS® Workbench, el cual tiene automatizada toda la extracción de resultados. Por otro lado, se presenta un banco experimental de la unión atornillada que ha sido fabricado y ensamblado con la ayuda de las empresas ULMA y MATZ-ERREKA. Además, se le ha implementado tecnología muy avanzada con el fin de obtener resultados muy precisos. Por último, en este Capítulo también se valida el modelo de Elementos Finitos comparando bajo diferentes situaciones de carga sus resultados con los resultados que proporciona el banco experimental.El Capítulo 3 explica en profundidad los dos métodos mencionados anteriormente para definir secuencias de atornillado óptimas: el MCIE y el MSI. Seguidamente, ambos métodos son detenidamente estudiados y validados mediante Elementos Finitos para el tipo de unión estudiado a lo largo de esta Tesis Doctoral, ya que en la literatura especializada no se encuentran estudios acerca de la optimización de secuencias de atornillado en uniones RTJ.En el Capítulo 4 se desarrolla la nueva metodología para la optimización de secuencias de atornillado en uniones RTJ, la cual se ha llamado el ¿Método Tetreparamétrico de Ensamblado¿ (TAM). En este Capítulo la metodología se desarrolla únicamente para secuencias de atornillado de una sola pasada y se valida únicamente para la geometría de unión del banco experimental. Con dicha metodología se consigue definir el comportamiento de una unión mediante tan solo cuatro coeficientes que se obtienen de un sencillo análisis; además, se demuestra que es más eficiente que los métodos anteriormente expuestos. Las validaciones se realizan tanto por Elementos Finitos como por el banco experimental.Con el fin de generar una metodología completamente aplicable en diferentes situaciones, en el Capítulo 5 se generaliza la metodología para secuencias de atornillado de múltiples pasadas. Esta generalización es de gran utilidad ya que en ocasiones, con el fin de no dañar la unión, es imprescindible reducir las cargas de apriete, lo que conlleva secuencias de atornillado de múltiples pasadas. La validación se hace nuevamente mediante Elementos Finitos y mediante el banco experimental. Por otro lado, en este mismo Capítulo también se estudia y se define el rango de aplicación de la metodología dentro de las uniones RTJ. Además, a continuación se genera una librería con los cuatro coeficientes de todas las uniones que se encuentran dentro del rango de aplicación.En el Capítulo 6 se desarrolla una aplicación programada en ¿Visual Basic for Applications¿ de Microsoft Excel, en la que se implementa el MTE generalizado y la librería con todos los coeficientes. Da lugar a una aplicación de gran interés y muy sencilla de utilizar para los usuarios, y por lo tanto fácil de implementar en una compañía del área del Oil&Gas. Para su mejor entendimiento, también se presenta un ejemplo ilustrativo paso a paso en el que se puede apreciar en detalle todo su potencial.En el Capítulo 7 se desarrolla otra metodología de optimización, pero en este caso para el estudio de secuencias optimizadas en otro tipo de uniones, que por lo tanto están fuera del rango de aplicación establecido en el Capítulo 5. Esta metodología, la cual también es mucho más eficiente que los métodos explicados en el capítulo 3, está basada en la técnica de los superelementos. En comparación con un modelo de Elementos Finitos convencional, se consigue un modelo mucho más eficiente ya que reduce el coste computacional sin tener ninguna pérdida de precisión. Para ello, mediante la técnica de los superelementos se construye una matriz de rigidez condensada a partir de una selección apropiada de los nodos principales del modelo. Así se reducen significativamente las dimensiones y el coste del problema.En el Capítulo 8, se presenta por un lado todas las conclusiones principales obtenidas a lo largo de toda la Tesis Doctoral. Por el otro lado, también se presentan las líneas de investigación que han quedado abiertas como consecuencia del trabajo de investigación realizado. Además, para concluir con el Capítulo, se listan todas las publicaciones derivadas de esta Tesis Doctoral.Por último, el apartado bibliográfico recoge las referencias citadas a lo largo de toda la Tesis Doctoral