Aerogel Insulation For Deepwater Reelable Pipe-in-Pipe
Authors: Denniel Sylvain , Blair Chris 
Published: October 2008

Despite very attractive properties, aerogels have been limited to specialist industrial applications due to complex and expensive production procedures.

Aspen Aerogels Inc. have developed a revolutionary process of fabrication that significantly reduces production time and costs. Aspen Aerogels Inc. have also developed a fibre reinforced flexible blanket aerogel. Aerogels can also be produced under several alternate forms to fit a wide range of industry applications at competitive costs.

Aspen Aerogels Inc. and Technip have collaborated on the development of a flexible aerogel blanket for the insulation of a reelable pipe-in-pipe that can meet the lowest overall heat transfer coefficient (OHTC) requirements without a significant increase in overall size and costs.

A qualification programme has been carried out to demonstrate the integrity and thermal performance of the aerogel blanket during the pipe-in-pipe fabrication, reel-lay and service life. The successful results of these qualification tests are presented along with a design example demonstrating the thermal performance of the system.

Introduction

The emerging trend for the development of deepwater and ultra deepwater offshore fields is a requirement for flowline and risers with very high insulating performance in order to minimize the risks of hydrates or wax formation. Technip have already a significant track record of design, construction and reel installation of pipe-in-pipes (PiP), which can meet the insulation requirements. Figures 1 and 2 show the evolution of the OHTC and water depth specifications of PiP installed by Technip of future PiP for contracts awarded to Technip where engineering is in progress. A clear trend towards lower OHTC (below the 1 W/m2K mark) and greater water depths (in excess of 1,000 m) can be seen. The aerogel based system produced by Aspen Aerogels Inc. combines the qualities that allow Technip to design a cost effective, lighter reelable PiP with higher insulating performance. The system is now qualified for reeling and offshore operation.

Aerogel Material

Aerogels were first produced by Klister in 1931. His original aim was to demonstrate that a light solid structure existed within a liquid gel. After several attempts, he managed to extract the liquid phase out of the solid structure, without collapsing it. The new product, called aerogel, gathered a range of attractive physical properties such as very low thermal conductivity, high temperature resistance, good mechanical properties combined with very light weight, sound proofing and high impact energy absorption capabilities.

Aerogels owe their qualities to their structure. It consists of a network of molecular chains, which can be organic or silica based, see Figure 3. Aerogel product is a "micoporous material" having a tridimensional nano-strucutre with pores sizes smaller and more "coherent" than the well known microporous based on fumed or pyrogenated silica used or proposed for years in many industries including offshore pipelines [1].

There are three forms of heat transfer mediums through any porous material, which are conduction, convection and radiation. The long molecular chain generates a very long and tortuous conduction path for heat transfer. The heat exchange due to gas convection is minimized because of the small size of the material pores.