Pushing the Limit of Offshore Pipeline Thermal Insulation
Grethe Hartviksen,Innovation & Technology Manager, Trelleborg Offshore

The need for high performance, robust and dependable products, has never been greater in the offshore industry, especially as it continues to move towards even more challenging applications. The thermal insulation of offshore pipelines, has an important role to play to ensure the smooth running of a facility and as such, is a key element of many offshore drilling projects. However, as budgets get leaner, fluids get warmer and water depths get deeper, can the sector keep up? I say "yes" and would argue that innovative synthetic rubber-based solutions not only address these concerns and provide a reliable alternative, but are the only true choice for offshore pipeline thermal insulation.

The offshore oil and gas industry is notorious for continuously pushing the limits. The exploration of offshore gas/oil has been moving to more and more deepwater fields and demanding that wells be drilled deeper and reach further in order to provide more cost-effective and safe well completions. In addition, the requirement to extract more oil and gas than ever before, and exploit ever harsher reservoir environments in new locations around the world, adds a further challenge.

As the water depth becomes greater and the reservoir is located deeper underneath the seafloor, additional pressure is put on the performance of oil and gas products which must now be able to cope with much higher pressures and temperatures than shallow reservoir products.

As such, particularly in this difficult economic climate, customers require solutions which are not only superior when it comes to performance, but more cost-effective, focusing more on price and longer lifetime. Not long ago customers required products that could last 20 years; now its often up to 40 years.

When it comes to material selection to handle these challenges, rubber-based materials are, not surprisingly, becoming a more popular solution within the offshore industry as rubber is an extremely flexible and durable material. Compared to alternative materials, such as steel and fiberglass, rubber has an extensive temperature range and exceptionally high pressure resistance, it is a flexible material that can damp, seal and protect, and most of all, has an extremely long lifetime.

So, as exploration and drilling go deeper, the need for reliable and efficient thermal insulation increases; flow assurance is a critical element of deep and ultra deepwater developments, in particular pipelines. Effective insulation of subsea structures helps maintain flow rates, optimise productivity and reduce processing costs. It also provides optimum defense against wax and hydrate formations.

When reservoir fluids reach the subsea structure they are typically a high temperature mix of condensed hydrocarbon gases, liquid paraffinic materials, waxes and water. As the fluid progresses through the structure to the processing facility or during a system cool-down cycle, heat loss is apparent to the surrounding ocean. As the temperature decreases, waxes and hydrate crystals may deposit, leading to potential flow loss and eventual system blockage. Insulation therefore becomes a necessary part of this process in order to avoid this formation of hydrate plugs and wax build-up (paraffin). The formation of wax and hydrates occurs when the oil or gas composition is depressurised and exposed to the low seawater temperature at the seabed.

A hydrate is formed when crystalline water is stabilised and light hydrocarbon molecules are captured in the crystal lattice. Hydrates can be formed at high pressures and at temperatures around +68 F to 77 F (+20 C to +25 C). Without insulation the cold seawater would rapidly cool the fluid, allowing it to create hydrate and wax formations, and making it impossible for a safe flow.

Thermal insulation materials are often applied in order to prevent formation of hydrate and wax during a shutdown scenario. During shutdown, the extra insulation gives sufficient time for inspection of the subsea pipe and equipment, so engineers can have time to solve production problems and for methanol or glycol injection.

The increasing challenges faced by the offshore industry have spurred manufacturers to consistently push to develop products that can keep up with the demands of the offshore engineer.

However, it's not always about finding completely new solutions. Manufacturers must continuously look at their current product portfolios to find new ways to make existing products work even harder than they already do, if they are to stay ahead of the game.

As such, some leading manufacturers are reassessing subsea thermal insulation materials, which have been successfully installed throughout the subsea oil and gas industry for many years, to see how best to enhance their performance in line with these growing demands.

The latest generation of subsea insulation solutions, an example of this dedicated improvement from one leading manufacturer, have a k-value of 0.13 W/mK, can be used up to 9842ft (3000m) deep and utilised of liquid temperatures up to +311 F (155 C), as well as external temperatures as low as -31 F (-35 C). In order 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, at a water depth of 9842ft (3000m).

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 +203 F (+95 C), or an EPM compound that is qualified up to +311 F (155 C). Both compounds provide excellent corrosion or HISC protection, and have been extensively tested for adhesion, aging 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 0.13 W/m2K up to 0.19 W/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 seventies 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 sea-water resistance, pressure resistance, mechanical properties and temperature. By utilising a solid rubber-based coating, these new products have very good thermal insulation properties while providing maximum corrosion protection.

With the lifetime of an oil field expected to be a minimum of 25 years and design temperatures of the field var ying throughout (up to +392 F/ +200 C), it is impor tant 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 prove their integrity for the lifetime of the field. They are designed to last the life of the subsea project (20 to 40 years), are maintenance free and will normally never be replaced.

But it's not just about subsea pipelines; leading manufacturers are also looking to develop, new and unique solutions to maximise topside offshore pipe insulation.

This is because the insulation of topside pipes usually involves the use of mineral wool to provide insulation, with an outer shell of steel for protection. However, while this insulation system is meant to be water tight , experience shows that this isnt always the case and humidity can often penetrate into the insulation. This will often result in the corrosion of the steel protection layer and a reduction in thermal performance.

Therefore, it is of high importance that its a stratum of air is placed between the insulation and the steel pipe to avoid any damage to the pipe. Historically engineers have made these air gaps between the pipe and thermal insulation using an additional sheet of metal applied in a wave pattern. However, this method can cause undesirable side effects including corrosion of the metal sheet and injury to engineers during work due to its sharp edges.

In a bid to provide a high performance product, which not only provided a reliable solution, helping to guarantee thermal performance, but one that eliminated the undesirable effects that comes with traditional methods of creating an air gap, leading manufacturers developed a new rubber-based alternative.

This unique solution has been specifically developed to effectively create a one to two centimeter air gap between the pipe and insulation, thereby avoiding the corrosion that can occur. By stopping direct contact between the insulation material and the pipe, this new solution prevents any damage to the corrosion protection on the pipe, helping to guarantee thermal performance.

This latest innovation, which is unique to the market, provides a reliable and extremely durable solution to a common problem within the offshore topside insulation market. Furthermore, its rubber construction means that it will last the life of an offshore project, as well as being maintenance free, providing reassurance to the offshore engineer.

It can also be easily installed without using hot work or special tools, and can be connected and split to the desired length using just a pair of scissors, making the installation quick and easy and without any additional safety actions, in turn reducing downtime.

Extensive testing has also been undertaken to ensure that the product is qualified for lifetime performance; it has been qualified for use up to +302 F / +150C continuous service temperature, for more than 30 years.

As the offshore oil and gas industry continues to push the limits when it comes to demanding offshore applications, the need for reliable and durable solutions that deliver proven performance for critical thermal insulation installations, has never been greater.

With the formation of hydrate plugs and wax build up (paraffin), or corrosion of topside steel pipes, a real risk for offshore engineers, rubber -based solutions provide a practically incompressible, seawater and impact -resistant solution that has very good thermal insulation properties and also provides maximum corrosion protection. They are designed to last the life of the subsea project (20 to 40 years), are maintenance free and will normally never be replaced, giving peace of mind to the offshore industry.