Pipelines and Risers (Elsevier Ocean Engineering Series) (Vol 3)

This book summarizes the author's 18 years research and engineering experience at universities, classification societies and design offices. The intention is to develop this book as a textbook for graduate students, as it includes design guidelines for engineers and references for researchers. It is hoped that this book may also be used to aid the design of offshore structures as it details applied mechanics and design/engineering. The book has been used in a teaching course for M.Sc. students at Stavanger University College and IBC training course for engineers in pipeline and riser industries since August 1998. Its preparation was motivated by recent developments in research and engineering and new design codes. It aims to educate more pipeline engineers and provide materials for on-job training on the use of new design codes and guides.
Chapter One Introduction

1.1 Introduction

Pipelines are used for a number of purposes in the development of offshore hydrocarbon resources (see Figure 1.1). These include e.g.:

• Export (transportation) pipelines;

• Flowlines to transfer product from a platform to export lines;

• Water injection or chemical injection flowlines;

• Flowlines to transfer product between platforms, subsea manifolds and satellite wells;

• Pipeline bundles.

The design process for each type of lines in general terms is the same. It is this general design approach that will be discussed in this book.

Design of metallic risers is similar to pipeline design, although different analysis tools and design criteria are applied. The last part of this book is devoted to riser design.

Finally, in Chapter 26, two pipeline design projects are used as examples demonstrating how technical development described in this book is used to achieve cost saving and safety/quality.

1.2 Design Stages and Process

1.2.1 Design Stages

The design of pipelines is usually performed in three stages, namely;

• Conceptual engineering,

• Preliminary engineering or pre-engineering,

• Detail engineering.

The objective and scope of each of these design stages vary depending on the operator and the size of the project. However, the primary aims are generally as follows (Langford and Kelly (1990)):

1. Conceptual Engineering

The primary objectives are normally:

– To establish technical feasibility and constraints on the system design and construction;

– To eliminate non viable options;

– To identify the required information for the forthcoming design and construction;

– To allow basic cost and scheduling exercises to be performed;

– To identify interfaces with other systems planned or currently in existence.

The value of the early engineering work is that it reveals potential difficulties and areas where more effort may be required in the data collection and design areas.

2. Preliminary engineering or basic engineering

The primary objectives are normally:

– Perform pipeline design so that system concept is fixed. This will include:

• To verify the sizing of the pipeline;

• Determining the pipeline grade and wall thickness;

• Verifying the pipeline against design and code requirements for installation, commissioning and operation;

– Prepare authority applications;

– Perform a material take off sufficient to order the linepipe (should the pipe fabrication be a long lead item, hence requiting early start-up)

The level of engineering is sometimes specified as being sufficient to detail the design for inclusion into an "Engineering, Procurement, Construction and Installation" (EPCI) tender. The EPCI contractor should then be able to perform the detailed design with the minimum number of variations as detailed in their bid.

3. Detail engineering

The detailed engineering phase is, as the description suggests, the development of the design to a point where the technical input for all procurement and construction tendering can be defined in sufficient detail.

The primary objectives can be summarized as:

– Route optimization;

– Selection of wall thickness and coating;

– Confirm code requirements on strength, Vortex-Induced Vibrations (VIV), on-bottom stability, global buckling and installation;

– Confirm the design and/or perform additional design as defined in the preliminary engineering;

– Development of the design and drawings in sufficient detail for the subsea scope. This may include pipelines, tie-ins, crossings, span corrections, risers, shore approaches, subsea structures;

– Prepare detailed alignment sheets based on most recent survey data;

– Preparation of specifications, typically covering materials, cost applications, construction activities (i.e. pipelay, survey, welding, riser installations, spoolpiece installation, subsea tie-ins, subsea structure installation) and commissioning (i.e. flooding, pigging, hydrotest, cleaning, drying);

– Prepare material take off (MTO) and compile necessary requisition information for the procurement of materials;

– Prepare design data and other information required for the certification authorities.

1.2.2 Design Process

The object of the design process for a pipeline is to determine, based on given operating parameters, the optimum pipeline size parameters. These parameters include:

– Pipeline internal diameter;

– Pipeline wall thickness;

– Grade of pipeline material;

– Type of coating-corrosion and weight (if any);

– Coating wall thickness.

The design process required to optimize the pipeline size parameters is an iterative one and is summarize in Figure 1.2. The design analysis is illustrated in Figure 1.3.

Each stage in the design should be addressed whether it be conceptual, preliminary or detailed design. However, the level of analysis will vary depending on the required output. For instance, reviewing the objectives of the detailed design (Section 1.2.1), the design should be developed such that:

• Pipeline wall thickness, grade, coating and length are specified so that pipeline can be fabricated;

• Route is determined such that alignment sheets can be compiled;

• Pipeline stress analysis is performed to verify that the pipeline is within allowable stresses at all stages of installation, testing and operation. The results will also include pipeline allowable spans, tie-in details (including expansion spoolpieces), allowable testing pressures and other input into the design drawings and specifications;

• Pipeline installation analysis is performed to verify that stresses in the pipeline at all stages of installation are within allowable values. This analysis should specifically confirm if the proposed method of pipeline installation would not result in pipeline damage. The analysis will have input into the installation specifications;

• Analysis of global response;

– Expansion, effective force and global buckling

– Hydrodynamic response

– Impact

• Analysis of local strength;

– Bursting, local buckling, ratcheting

– Corrosion defects, dent

1.3 Design Through Analysis (DTA)

A recent technical revolution in the design process has taken place in the Offshore and Marine industries. Advanced methods and analysis tools allow a more sophisticated approach to design that takes advantage of modern materials and revised design codes supporting limit state design concepts and reliability methods. At J P Kenny the new approach is called "Design Through Analysis" where the finite element method is used to simulate global behavior of pipelines as well as local structural strength (see Bai & Damsleth (1998)). The two-step process is used in a complementary way to determine the governing limit states and to optimize a particular design.

The advantage of using advanced engineering is a substantial reduction of project CAPEX (Capital Expenditure) and OPEX (Operating Expenditure) by minimizing unnecessary conservatism in the design through a more accurate determination of the effects of local loading conditions on the structure. Rules and design codes have to cover the general design context where there are often many uncertainties in the input parameters and the application of analysis methods. Where the structure and loading conditions can be accurately modeled, realistic simulations reveal that aspects of the design codes may be overly conservative for a particular design situation. The FEM (Finite Element Methods) model simulates the true structural behavior and allows specific mitigating measures to be applied and documented.

Better quality control in pipeline production allows more accurate modeling of material while FEM analysis tools allow engineers to simulate the through-life behavior of the entire pipeline system and identify the most loaded sections or components. These are integrated into a detailed FEM model to determine the governing failure mode and limit criteria, which is compared to the design codes to determine where there is room for optimization. The uncertainties in the input data and responses can be modeled with the help of statistics to determine the probability distributions for a range of loads and effects. The reliability approach to design decisions can then be applied to optimize and document the fitness for purpose of the final product.

Engineers have long struggled with analytical methods, which only consider parts of the structural systems they are designing. How the different parts affect each other and, above all, how the structural system will respond to loading near its limiting capacity requires a nonlinear model which accurately represents the loads, material and structure. The sophisticated non-linear FEM programs and high-speed computers available today allow the engineers to achieve numerical results, which agree well with observed behavior and laboratory tests.

The simulation of global response together with local strength is often necessary because design parameters and local environment are project-specific. A sub-sea pipeline is subject to loading conditions related to installation, seabed features, intervention works, testing, various operating conditions and shut-downs which prescribe a load path essential to the accurate modeling of non-linear systems involving plastic deformation and hysteresis effects. For example, simulation can verify that a pipeline system undergoing cyclic loading and displacement is self-stabilizing in a satisfactory way (shakedown) or becomes unstable needing further restraint. The simulation of pipeline behavior in a realistic environment obtained by measurement allows the engineers to identify the strength and weakness of their design to obtain safe and cost-effective solutions. Traditionally, pipeline engineers compute loads and load effects in two dimensions and either ignore or combine results to account for three-dimensional effects. This approach could lead to an overly conservative or, not so safe design. DTA has demonstrated the importance of three-dimensional (3D) FE analysis for highly loaded pipelines undergoing large thermal expansion.

Design Through Analysis (DTA) involves the following activities:

1. Perform initial design according to guidelines and codes

2. Determine global behavior by modeling complete system

3. Simulate through-life load conditions

4. Identify potential problem areas

5. Check structural failure modes and capacity by detailed FE modeling

6. Develop strategies for minimizing cost while maintaining uniform safety level

7. Perform design optimization cycles

8. Document the validity and benefits of the design

9. Provide operation and maintenance support.

In order to efficiently conduct DTA, it is necessary to develop a Pipeline Simulator System (see Chapter 1.5).

1.4 Pipeline Design Analysis

1.4.1 General

Pipeline stress analysis is performed to determine if the pipeline stresses are acceptable (in accordance with code requirements and client requirements) during pipeline installation, testing and operation. The analysis performed to verify that stresses experienced are acceptable include:

– Hoop stress;

– Longitudinal stress; code specified

– Equivalent stress;

– Span analysis and vortex shedding;

– Stability analysis;

– Expansion analysis (tie-in design);

– Buckling analysis;

– Crossing analysis.

(Continues...)

Excerpted from PIPELINES AND RISERS by YONG BAI Copyright © 2001 by Yong Bai. Excerpted by permission of ELSEVIER. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site. Content: Series preface Page v Rameswar Bhattacharyya, Michael E. McCormick Foreword Pages vii-viii Preface Page ix Chapter 1 Introduction Original Research Article Pages 1-22 Chapter 2 Wall-thickness and material grade selection Original Research Article Pages 23-37 Chapter 3 Buckling/collapse of deepwater metallic pipes Original Research Article Pages 39-62 Chapter 4 Limit-state based strength design Original Research Article Pages 63-77 Chapter 5 Soil and pipe interaction Original Research Article Pages 79-83 Chapter 6 Hydrodynamics around pipes Original Research Article Pages 85-95 Chapter 7 Finite element analysis of in-situ behavior Original Research Article Pages 97-107 Chapter 8 On-bottom stability Original Research Article Pages 109-116 Chapter 9 Vortex-induced vibrations (VIV) and fatigue Original Research Article Pages 117-135 Chapter 10 Force model and wave fatigue Original Research Article Pages 137-154 Chapter 11 Trawl impact, pullover and hooking loads Original Research Article Pages 155-175 Chapter 12 Installation design Original Research Article Pages 177-217 Chapter 13 Reliability-based strength design of pipelines Original Research Article Pages 219-228 Chapter 14 Remaining strength of corroded pipes Original Research Article Pages 229-255 Chapter 15 Residual strength of dented pipes with cracks Original Research Article Pages 257-275 Chapter 16 Risk analysis applied to subsea engineering Original Research Article Pages 277-303 Chapter 17 Route optimization, tie-in and protection Original Research Article Pages 305-323 Chapter 18 Pipeline inspection, maintenance and repair Original Research Article Pages 325-352 Chapter 19 Use of high strength steel Original Research Article Pages 353-380 Chapter 20 Design of deepwater risers Original Research Article Pages 381-392 Chapter 21 Design codes and criteria for risers Original Research Article Pages 393-411 Chapter 22 Fatigue of risers Original Research Article Pages 413-431 Chapter 23 Piping systems Original Research Article Pages 433-439 Chapter 24 Pipe-in-pipe and bundle systems Original Research Article Pages 441-465 Chapter 25 LCC modeling as a decision making tool in pipeline design Original Research Article Pages 467-488 Chapter 26 Design examples Original Research Article Pages 489-495 Subject index Pages 497-498 Thin-walled structures are designed with advanced numerical analysis techniques and constructed using sophisticated fabrication processes. There are, however, a number of factors that may result in a structure that is not exactly coincident with what was considered during the design calculations. These features may be associated with changes in the properties of the structure, in the geometry, and many others. But even small changes in the structure may sometimes produce significant changes in the response.

The present work is intended to introduce professionals and researchers to the effects of imperfections on the stresses in thin-walled structures. The main idea behind the presentation is that small imperfections may introduce changes in the stresses that are nearly equal to the stresses due to the loads.

The book is organized into two main parts. The first part (Chapters 1 to 6) covers the techniques for analyzing imperfections. In the second part the emphasis is on applications, which at present may be found scattered throughout many scientific and professional journals. More practical aspects of imperfections may be found in Chapter 12.

It is assumed that the reader is familiar with finite element techniques, and with the basics of shell structures.
Thin-walled structures are designed with advanced numerical analysis techniques and constructed using sophisticated fabrication processes. There are, however, a number of factors that may result in a structure that is not exactly coincident with what was considered during the design calculations. These features may be associated with changes in the properties of the structure, in the geometry, and many others. But even small changes in the structure may sometimes produce significant changes in the response. The present work is intended to introduce professionals and researchers to the effects of imperfections on the stresses in thin-walled structures. The main idea behind the presentation is that small imperfections may introduce changes in the stresses that are nearly equal to the stresses due to the loads. The book is organized into two main parts. The first part (Chapters 1 to 6) covers the techniques for analyzing imperfections. In the second part the emphasis is on applications, which at present may be found scattered throughout many scientific and professional journals. More practical aspects of imperfections may be found in Chapter 12. It is assumed that the reader is familiar with finite element techniques, and with the basics of shell structures This book publishes the proceedings from the Third International Workshop on Connections in Steel Structures: Behaviour, Strength and Design held in Trento, Italy, 29-31 May 1995. The workshop brought together the world's foremost experts in steel connections research, development, fabrication and design. The scope of the papers reflects state-of-the-art issues in all areas of endeavour, and manages to bring together the needs of researchers as well as designers and fabricators. Topics of particular importance include connections for composite (steel-concrete) structures, evaluation methods and reliability issues for semi-rigid connections and frames, and the impact of extreme loading events such as those imposed by major earthquakes. The book highlights novel methods and applications in the field and ensures that designers and other members of the construction industry gain access to the new results and procedures. Hardbound. This book summarizes the author's 18 years research and engineering experience at universities, classification societies and design offices. The intention is to develop this book as a textbook for graduate students, as it includes design guidelines for engineers and references for researchers. It is hoped that this book may also be used to aid the design of offshore structures as it details applied mechanics and design/engineering. The book has been used in a teaching course for M.Sc. students at Stavanger University College and IBC training course for engineers in pipeline and riser industries since August 1998. The preparation of the book was motivated by recent developments in research and engineering and new design codes. There is a need for such a book to educate more pipeline engineers and provide materials for on-job training on the use of new design codes and guides. Thin-walled structures are designed with sophisticated numerical analysis techniques and constructed using fabrication processes requiring highly skilled workmanship. However, during construction a number of factors may lead to the final structure varying from the original design. These anomalies may be associated with changes in the properties of the structure or deviations from the structure's design geometry. Even small variations from the proposed design may produce significant changes in response; this book details the influence imperfections may have on the analysis and behavior of thin-walled structures. This work consists of the third International Workshop on Connections in Steel Structures, held in Italy in 1995. It includes assessments of research and developments in steel construction, considering connections as key elements. Topics covered include connection modelling and cyclic response. This volume presents the essence of research undertaken since the 1950s into the difficult problems of the stability of steel and steel-and-concrete composite structures and their components. It focuses not only on theory and computation but also on experimental verification