Diverless Flowline Connection System - Description Of System And Results Of Land Based Test
Authors: Ames Tom , Harper Roland , Cuiper Glen 
Published: October 2008

This paper presents a system for making diverless subsea flowline connections and discusses the results of a land based pull-in test of a typical flowline bundle.

A brief description of the major system components including the flowline connector, alignment structure and hydraulic running tool is given. Operation procedures for placement and connection of a flowline using this system is outlined ... including method description of both first and second end flowline connections.

A geometric non-linear computer analysis of a 2" × 2" × 2" flowline bundle during pull-in, was completed prior to a land test of the same bundle configuration. The analysis was used to establish the starting point of the flowline bundle and to determine the accuracy of predicting pull-in cable tension loads with a computer. Stress levels were also predicted in the analysis.

An actual land based flowline pull-in was conducted using a bundle configuration identical to that used for the computer analysis. Strain gages on the flowline bundle and cable tension were monitored throughout the pull-in. It was determined that the theoretical and empirical data correlated closely and that the use of the analysis is an important tool in establishing the initial placement of the flowline bundle prior to pull-in.

INTRODUCTION

The placement and connection of subsea flowlines ranks high on the list of difficult tasks for completing a subsea production system. The operator has several critical decisions to make prior to selection of a system including:Diver assist or diverlessFirst end or second end connectionMethod of flowline placementIn the case of a satellite tree...flowline placement before or after tree is installed.

The flowline connection system discussed in this paper is a diverless system that can be used in either first or second end connections. First end connections are accomplished by means of a pivoting funnel assembly that allows vertical lowering of the flowline bundle to the seafloor receiver structure, and then laying away to the second station using a semi-submersible or reel barge. Once the bundle is locked into the receiver structure, a hydraulic running tool is lowered to complete the connection operation.

This connection system will also accommodate several second end connection methods including the flowline "warping" technique as used for the Canadian Arctic Islands and described by A. C. Palmer1.

This paper will deal primarily with the on bottom pull-in or "sweep" method and, in particular, in predicting the starting point of an on bottom pull-in using computer aided techniques. Initial placement of the flowline prior to pull-in is important since it is the starting geometry that dictates 1) cable tension 2) pipe stress, and 3) final approach angle. The on bottom sweep is one of the more difficult placement methods since the bundle is laying directly on the seafloor and is directly affected by soil friction and seafloor terrain. This makes it more difficult to predict placement without knowing some specifics about the area in which the flowline will be laid.