Thermal insulation: pushing the limits

July 1, 2012

Subsea thermal insulation has an important role to play in ensuring the smooth running of offshore facilities as the industry moves into deeper waters and fluids get warmer. Trelleborg Offshore's Grethe Hartviksen argues that innovative synthetic rubber-based solutions not only address these concerns and provide a reliable alternative, but are the only true choice for challenging subsea applications.

The offshore oil & gas industry is notorious for continuously pushing the limits. Exploring and developing deepwater fields with higher pressures and temperatures places greater demands on product performance. Not long ago the offshore industry required products that could last 20 years; now it's often up to 40 years.

thermal insulationThermal insulation being extruded onto pipe by Trelleborg.

When it comes to material selection to handle these challenges, rubber-based materials are, not surprisingly, becoming a more popular solution. Rubber has an extremely long lifetime, is flexible and durable, has an extensive temperature range and exceptionally high pressure resistance, and can damp, seal and protect.

Application of Trelleborg's Vikotherm II system and (right) a thermally insulated valve.

As the industry goes deeper, the need for reliable and efficient thermal insulation increases. Effective insulation of subsea structures helps maintain flow rates, optimize productivity and reduce processing costs. It also provides optimum defence against the formation of hydrate plugs and wax build-up during shutdowns, the extra insulation giving sufficient time for inspection of the pipe and equipment and for methanol or glycol injection.

In developing products that can meet the challenges of the offshore industry's not always about finding completely new solutions. To stay ahead of the game, manufacturers must continuously review their portfolios to find new ways to make existing products work even harder. Some leading manufacturers are reassessing subsea thermal insulation materials, which have been successfully installed throughout the subsea oil & gas industry for many years, to see how best to enhance their performance in line with today's changing demands.

The latest generation of subsea insulation solutions from one leading manufacturer have a k-value of 0.13W/m2K, and are rated for water depths up to 3000m, liquid temperatures up to 155°C and external temperatures as low as 35°C. To provide even more flexibility when it comes to design and logistics, it now also allows for mobile production and can be installed on-site in 3000m of water.

A layered solution

These flexible insulation systems consist of a three-layer buildup. First, an inner layer for corrosion and/or hydrogen-induced stress cracking (HISC) protection; this could be a Neoprene compound that is qualified up to 95°C, or an EPM compound that is qualified up to 311°F (55°C). Both compounds provide excellent corrosion or HISC protection, and have been extensively tested for adhesion, ageing and cathodic disbondment.

The middle layer has been designed to provide the thermal insulation protection and various compounds are applicable depending on the specific requirements. The compounds provide a k-value of 0.13W/m2K up to 0.19W/m2K. The flexibility and stability of the rubber makes this an excellent choice with respect to thermal expansion.

The insulation layer is protected by the outer layer. This is a strong and robust layer that provides excellent seawater and mechanical protection and has a successful track record as far back as the early 1970s in the North Sea.

The insulative elastomer coating system used is a development based on ordinary rubber technology and consists of a rubber elastomer chemically modified to give a very high insulating property, while maintaining its inherent rubber properties in respect to seawater resistance, pressure resistance, mechanical properties and temperature. By utilizing a solid rubber-based coating, these new products have very good thermal insulation properties while providing maximum corrosion protection.

Grethe Hartviksen is innovation & technology manager of Trelleborg Offshore. She has an MSc in chemistry from the Norwegian Science & Technology University (NTNU ) and has worked in the industry for over 17 years. She joined Trelleborg Offshore eight years ago, having previously worked for Draka Norsk Kabel and Bredero Shaw.

Lifetime performance

With the lifetime of an oil field expected to be a minimum of 25 years and design temperatures of the field varying throughout (up to 200°C), it is important that products can prove they stand the test of time. Continuous and extensive testing is the only way to remain at the forefront of material development and lies at the heart of material advances and product solutions.

Extensive test programming has been carried out on these next-generation insulation solutions to demonstrate their integrity for the lifetime of the field. Maintenance free, they are designed to last the 20-40 year life of a subsea project and will normally never be replaced. OE



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