Pipe-in-Pipe Swaged Field Joint for Reel Lay
Authors: Jones Richard Lloyd , Geertsen Christian , Booth Paul , Mair John A , Sriskandarajah Thurairajah , Rao Venu 
Published: May 2013

Subsea 7 and ITP InTerPipe (ITP) have developed a highly efficient Pipe in Pipe technology to be installed by the Reel-Lay method. This solution is based upon the ITP technology where insulation material is assembled within the Pipe in Pipe annulus and the annulus pressure drawn down to create the overall enhanced thermal performance.

To adapt this technology to Reel-Lay, the solution has adopted Swaged Field Joints, similar to those of ITP used for J-Lay and S-Lay applications, to provide sealing barriers between each stalk length (typically 1km in length) prior to reeling onto the vessel, but with flush welded half shells to avoid diameter changes.

The outer pipe is typically swaged down close to the inner pipe and welded directly to outer surface of inner pipe between stalks. This full penetration weld (hereafter called swaged weld) works as a structural connection between the inner and outer pipes and seals the annulus between the two pipes for pressure reduction within the annulus. The integrity of this swaged weld and the half shells ensure the structural integrity during reeling and straightening of PiP system as well as its thermal properties.

In order to take advantage of speed and reliability of Reel-Lay of pipe in pipe, the Swaged Field Joint utilising two half shells flush with the outer pipe was studied for reelability using an FE based approach. A qualification plan for testing the design was developed and qualified in compliance with DNV RP A203 [2].

This paper details the test programme which includes test sample fabrication, Non Destructive Examination (NDE), pre test FE based feasibility and post test FE based validation analysis against measured strain gauge results from testing.

The work was performed in compliance with DNV recommended practice for new technology qualification DNV RP-A203. The comprehensive test programme led to the award of DNV " Fit for Service" qualification for a reelable Swaged Field Joint for Pipe in Pipe.

The paper also provides a brief discussion on multiple uses of this Swaged connection as a partial pressure seal, water stop, and integral buckle arrestor for deep water applications.

Introduction

Subsea 7 has been working in conjunction with ITP to qualify the Pipe in Pipe system built on ITP's patented insulation system, making use of Izoflex thermal insulation and reduced annulus pressure. The pipe in pipe system will be provided with a swaged end connection at an angle of 15degrees between stalks at an approximate spacing of 750m equivalent to one stalk length. The as installed thermal conductivity of Izoflex for such condition is 7mW/mK. Since 1994, Subsea 7 has successfully completed various projects using swaged ends pipe in pipe via S lay and J lay methods as shown in Figure 1. The paper details the development and qualification of swaged end pipe in pipe for reel-lay installation where the strain imposed is an order of magnitude larger, thus requiring the operation, reelability and integrity of the swaged connection post reeling to be demonstrated.