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Master Thesis Analysis and Optimization of Rigid Pipeline

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Master Thesis Analysis and Optimization of Rigid Pipeline Faculty of Science and Technology MASTER’S THESIS Study program/ Specialization: Spring Semester, 2013 Offshore Technology/ Subsea Technology Open / Restricted access Writer: Sankaranarayanan Subramanian ………………………………………… (Writer’s signature) Faculty Supervisor: Prof. Daniel Karunakaran, Ph.D (University of Stavanger, Subsea 7 Norway) External Supervisor(s): Dr. Qiang Chen, Ph.D (Subsea 7 Norway) Title of Thesis: Analysis and Optimization of Rigid Pipeline Installation with Inline Structures Credits (ECTS): 30 Key words: Pages: ………………… Inline Structures, End Structures, Buoyancy, Rigid pipeline, Pipeline Installation, Orcaflex, + enclosure: ………… Riflex. Stavanger, June 10, 2013 Date/year i ABSTRACT Advanced modern technologies and growing demand for oil and gas has led to the discovery and development of smaller and remote fields that were once considered uneconomical. They are made economically more viable by employing a subsea development scheme and directing the output to existing platform for production and processing instead of having their own platform. This has necessitated the introduction of inline structures in the pipelines with the possibility to connect these remote fields when they are developed for production. However the presence of these structures introduces many installation challenges including increased weight and additional environmental loading. In some cases this might drastically reduce the limiting sea state for installation. For the scope of the thesis work, any structure in the middle of the pipeline with stiffness and weight greater than the pipeline is considered as an inline structure. A riser and pipeline installation using J-Tube pull in method is considered as the case study for analysis in the thesis. Analysis and parametric study of the installation is made with emphasis on the initiation phase to determine the limiting sea state for the safe installation of the pipeline. The main focus of the thesis would be to analyze the possibilities to optimize the limiting sea state for the installation of the J-tube seal with the help of buoyancy units by creating a neutrally buoyant catenary during installation. An attempt to develop a generalized optimization procedure to determine the optimal buoyancy unit configuration for all inline structure installation is made although the results indicate that it might be very case specific and a general method might not exist. Analysis to understand the influence of the type of buoyancy unit, the position on the pipeline catenary, net buoyancy, number of buoyancy modules and various other parametric studies are made. In addition, challenges encountered during an inline structure installation and the modifications required to carry out the installation from the vessel is briefly discussed. The analysis reveals that geometry of the buoyancy does not have appreciable impact. A sensitivity study on the added mass of the buoyancy shows that an increased added mass reduces the buckling utilization by its out-of-phase dynamic response with that of the catenary. Sagbend buckling is the most critical concern for installation and it is at its maximum when the structure is at the sagbend. It also reveals that the best results are achieved when the net buoyancy of the module is equal to the excess weight in the catenary due to the structure. A buoyancy unit that is offset from the structure provides better result than a similar module connected over the structure and also better results than the use of multiple buoyancy modules although this might be very case specific. Key Words: Inline structures, Buoyancy, Rigid Pipeline, Pipeline Installation, Orcaflex, Riflex. Sankar Subramanian, University of Stavanger iii ACKNOWLEDGEMENT This thesis is the final work to fulfil the requirement for Master of Science degree in the Offshore Technology at the Department of Mechanical and Structural Engineering and Materials Science, Faculty of Science and Technology, University of Stavanger, Norway. This thesis work is carried out at Subsea7 Norway, starting from February 2013 to June 2013. The Author would like to thank the following people for their support and help in completing this thesis. My professor and faculty supervisor Prof. Daniel Karunakaran, Ph.D. for providing me the opportunity to work on the thesis at Subsea7 under his supervision and for his constant support, guidance and advice with the thesis work. Dr.Qiang Chen, my internal supervisor at Subsea7, for his enthusiastic sharing of knowledge and experience on the thesis work and installation softwares. He was always open to questions and patient while clarifying my queries. Prof. Ove Gudmestad, Ph.D., for his guidance and support during the entire master studies and for his inspirational lectures and for sharing his vast industrial experience. His dedication to the cause of education and science is truly inspiring. Employees at Subsea7 - Dr. Dasharatha Achani, Tommy Andresen, Markus Cederfelt, Heidi Aasen, Tore Jacobsen for their willingness to share their knowledge and experience and numerous assistance rendered to me. Subsea7, Norway for providing me with an opportunity to do the thesis at their office and providing me with an office work space and other facilities. My fellow students and friends, Isaac Ifenna and Indra Permana, who did their thesis along with me at Subsea7, for their inputs and help with the thesis. My friends in Norway, especially Mats Kohlstrom & Tor Edvard Søfteland, for the good times and friendship. Stavanger, 14th June, 2013 Sankar Subramanian Sankar Subramanian, University of Stavanger v Sankar Subramanian, University of Stavanger vi TABLE OF CONTENTS ABSTRACT ........................................................................................................................................ III ACKNOWLEDGEMENT .................................................................................................................... V TABLE OF CONTENTS .................................................................................................................. VII LIST OF FIGURES ............................................................................................................................. XI LIST OF TABLES............................................................................................................................ XIII SYMBOLS ......................................................................................................................................... XV Symbols – Latin Characters ........................................................................................................... xv Symbols – Greek characters .......................................................................................................... xvi ABBREVIATIONS ........................................................................................................................... XVII 1. INTRODUCTION ......................................................................................................................... 1 1.1 Background ................................................................................................................................... 1 1.2 Thesis Purpose and Scope .............................................................................................................. 4 1.3 Thesis Organization ....................................................................................................................... 6 2. OFFSHORE PIPELINES .............................................................................................................. 7 2.1 Historical Background ................................................................................................................... 7 2.2 Pipeline System Components ......................................................................................................... 7 Risers .............................................................................................................................................. 8 Valve Assemblies ............................................................................................................................ 8 Pig Launchers and Receivers ........................................................................................................... 8 Inline and End Structures ................................................................................................................. 9 Internal and External Coating and Anti-corrosion systems ................................................................ 9 2.3 Pipeline Types & Concepts ............................................................................................................ 9 Rigid pipe ........................................................................................................................................ 9 Flexibles .......................................................................................................................................... 9 Composite ..................................................................................................................................... 10 2.4 Steel Pipeline Materials and Grades ............................................................................................. 10 2.5 Major Pipeline Projects ................................................................................................................ 12 3. PIPELINE INSTALLATION METHODS ................................................................................
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