Advancements in Response Prediction Methods for Deep Water Pipe-In-Pipe Flowline Installation
Authors: O&apos;Grady Robert , Bakkenes Henk-Jan , Lang Donogh , Connaire Adrian Donald 
Published: October 2008

Abstract
As subsea field developments continue to move into deep and ultra-deep water locations, the operational requirements of flowlines become increasingly significant. As a result innovative and complex technologies such as pipe-in-pipe systems are now being incorporated into the design of flowlines. These technologies, while satisfying the operational requirements of the flowlines, are very sensitive to installation processes. This means there is an increased need for more refined methods of predicting flowline response during installation. This paper describes a new generation engineering tool particularly suited to predicting the response of pipe-in-pipe systems during installation. The tool was developed specifically for the analysis of pipeline/flowline installation and so it incorporates a range of modelling and analytical capabilities of particular relevance to installation analysis.
Current methods of predicting the response of pipe-inpipe flowlines during installation often over simplify the pipe-in-pipe model which makes them unsuitable for determining important installation parameters. The tool discussed in this paper allows for a greater level of detail to be used when defining pipe-in-pipe systems and so it reduces the degree of uncertainty associated with predicting crucial installation response parameters such as the settlement of the inner pipe in the outer pipe and the contact reactions between the inner and outer pipes. The use of this new tool is illustrated by means of a case study describing how the tool was used to carry out a wide-ranging study on the installation of pipe-in-pipe flowlines in the West of Africa. The study presented in this paper consists of an examination of typical J-lay processes where increased certainty in response parameters was needed.
Both the increased use of pipe-in-pipe flowlines as well as the increasing complexity of the pipe-in-pipe systems used, is pushing the requirement for more accurate installation response prediction methods such as the one discussed in this paper.

Introduction
Subsea field developments are constantly pushing the boundaries of current technological capabilities. Developments continue to move into deeper waters and in many cases these developments have to be designed with very stringent insulation and cooldown criteria. This leads to an increasing number of ultra-deep water pipe-in-pipe projects.
Currently two main types (from an installation point of view) of pipe-in-pipe systems are used in the offshore industry. The first type of system is a " sliding?? pipe-inpipe system in which the inner pipe is standing freely in the outer pipe during installation. Connections between the inner and outer pipe are made using bulkheads. The distance between the bulkheads is relatively large (typically approximately equal to the waterdepth). This system requires offshore welds for both the inner pipe and the outer pipe for each pipe stalk. The second type of system is a " single-weld?? pipe-in-pipe system. This system uses pipe stalks that are typically fabricated onshore where the connection between the inner and the outer pipe are made. These systems require only one offshore weld for each pipe stalk. This paper focuses on the installation analysis of " sliding?? pipe-in-pipe systems, although the methods can also be applied to the " singleweld?? pipe-in-pipe systems.