Development and Application of Reelable PiP Bulkhead Technology
Authors: Boi Julie , Lynch Brian , Sloan Craig 
Published: April 2012

The benefits of reelable Pipe-in-Pipe (PiP) technology are well documented, providing exceptional passive insulation, temperature maintenance capabilitiesand efficient offshore installation. This paper documents the significantprogress that has been made through 2010 and 2011 with the firstimplementations of reelable bulkheads on PiP projects. A reelable bulkheadenhances PiP technology by further reducing the duration of pipelay operationsand being used as an enabler in various applications.

Traditionally bulkheads are welded during pipelay on the ramp of theinstallation vessel. Bulkheads may be required at various positions along thepipeline such as at a Tee location or at the end of the PiP pipeline. Conventional insertion of bulkheads is undertaken on critical path duringpipeline installation resulting in extended durations for welding the flowline, carrier and half shells at each end of the bulkhead, NDE and field jointcoating (especially in an application with corrosion resistant alloybulkheads). The innovation of a reelable bulkhead aims to address the inherentissues with a welded bulkhead, decreasing installation durations and allowingNDE to be undertaken in a controlled fabrication environment off criticalpath.

This paper presents the development, design and qualification programme forthree distinct reeled bulkhead applications used in North Sea projects in2011

Introduction

Reel-lay provides a fast, reliable and cost effective method for PiP pipelineinstallation. The individual carrier (outer) and flowline (inner) pipelinejoints are fabricated onshore into long pipeline stalks before being assembledby pushing the flowline within the carrier while inserting spacers and passiveinsulation. The pipe stalks are spooled onto a reel-lay vessel which transitsto field and installs the pipeline. Performing the fabrication onshore, awayfrom the vessel critical path, allows very high quality welding, NDE andinsulation application to be undertaken. Extending these clear benefits withthe introduction of reelable bulkheads is advantageous in terms of fabrication, quality and operational efficiency.

Technip have first developed and qualified reelable bulkhead technology in 2000[OTC 14326]: it has now been implemented in three PiP systems installed in theNorth Sea in 2011.

One application examined in this paper is to allow for a pressure retainingbulkhead in the PiP annular space (annular overpressure isolator). Anotherexample is the specific development of a PiP end bulkhead to facilitatelay-down of a fixed length pipeline (load transfer bulkhead), hence avoiding anoffshore cut and half shells. The final example involves an injection port tobe introduced into a reeled mid-line bulkhead (methanol injection Tee) withoutthe need to cut the PiP offshore.

FEA (Finite Element Analysis) was critical in the optimisation of bulkheadgeometry during the design process, it identified that the geometry andstiffness of nibs (bulkhead connection to the pipe joints) and the pipe eitherside of the bulkhead was key to ensure the system was reelable. Standard designcodes and Technip in house criteria were followed.