Thermal insulation is an integral part of designing any offshore product system, especially in deep, cold waters. This is because effective insulation of subsea structures helps maintain flowrates, optimise productivity and reduce processing costs; flow assurance is a critical element of deepwater developments.
However, subsea thermal insulation is perhaps even more pertinent for subsea architecture and pipelines – insulation materials are used to guard against the build-up of waxes and hydrate crystals in the reservoir fluids which can occur when the hot fluid (oil or gas) is depressurised and exposed to the low seawater temperature at the seabed, or if there is a temporary halt in production.
Furthermore, during shutdown, the insulation gives sufficient time for inspection of the pipe and equipment, so engineers can have time to solve production problems and for methanol or glycol injection, as necessary.
Unchecked, these deposits can quickly build up and cause loss of flow or even a blockage. Downtime means a loss of revenue, and blockages are expensive to rectify, representing a loss on a considerable investment. The greater the depth, the more the value of that investment.
Over the last 10 years subsea oil production has moved to where wellheads are located in water depths in excess of 3500 m and operating temperatures of 150 °C are commonplace (10 000 ft, 350 °F and more). So, as exploration continues to move into ultra deepwaters, the role of insulation in near freezing temperatures becomes ever more critical and investment in high technology HP well heads needs to be protected better than ever.
These extreme temperatures have resulted in an accelerated need for new insulation materials that can keep up with the increasing demands placed on them; many existing insulation materials simply are not up to the job and their use could lead to a rapid degradation of performance.
But it is not just manufacturers that have been spurred on by the challenges faced by the offshore industry, developing new solutions that can keep up with the demands of the offshore engineer; operators have also responded to the trend, adapting their approaches to specification to ensure complete peace of mind throughout the entire project, from production and application, through to subsea installation and use.
More than ever they understand that in addition to having excellent thermal insulation properties, materials need to protect against corrosion, resist seawater and impacts, be incompressible yet flexible, and not degrade during the life of subsea projects, which is often 20 to 25 years or longer. But most of all, they want reassurance that the solution they specify, will continue to perform, now and in the future.
Project specific qualifications
Over the last decade, as lessons have been learnt through project failures, offshore operators have begun looking for more robust solutions to give them the project confidence they need to succeed. These failures, combined with ever increasing subsea production temperatures, have meant the reliability of a complete thermal management strategy has never been more apparent.
With ‘cost’ no longer front of mind when specifying technology, it is evident that generic specifications and product testing just will not cut it anymore. Instead, offshore operators want to dig deeper into the insulation material they are specifying and conduct up front project specific qualifications. Subsea thermal insulation must now be tested against specific project parameters, something that historically was rarely heard of.
Numerous considerations must be made when evaluating the suitability of a material, and a number of testing programs conducted to ensure that the most appropriate material solution is chosen for any given application. While there is a real lack of subsea insulation qualification standards, particularly compared to other subsea technologies, operators are making sure they go far beyond mechanical integrity concerns and now also qualify the application personnel, equipment and processes, just as stringently.
Furthermore, rigorous, project specific qualifications are being set by operators, as well as material screenings in advance of project specific selection.
Taking control of the issue
There has been a significant increase in quality assurance and control measures that must now be taken during application, including an emphasis on operation skill levels, qualification and documentation.
This is because the performance of a thermal insulation system is as dependent upon the quality of its installation as it is upon the quality of the material itself. Given the complexity of many subsea structures, the application of insulation material can present considerable difficulties especially in terms of access, efficiency and completion schedules.
Inconsistent quality control processes have been one of the main failure mechanisms for insulation systems in the past.
As such, for each stage of production and application, checks now need to be made to ensure complete compliance, as well as an onsite verification of applied systems and training programs must now be run to ensure the process is more controlled.
Leading the way
So, in response to this need for better qualification and quality assurance to ensure the reliability of thermal insulation strategies, leading manufacturers have taken steps to make certain that the industry better understands the characteristics of an efficient and effective insulation system.
As standard, leading manufacturers have extremely experienced field service teams comprising highly trained professionals to ensure a total insulation service that assures product performance and quality, at all times. They have also invested heavily in state-of-the-art mixing and dispensing equipment to make sure they have hardware which, when expertly utilised, can provide a functional and robust delivery system capable of applying insulation materials to even the most complex subsea equipment structures.
A holistic approach
However, it is not just about meeting stringent project specific parameters. While this is now tremendously important for operators, and rightly so, more focus is also being given to the solution itself, more specifically the interaction between the anti-corrosion coating and insulation material itself.
Instead of viewing these two elements as separate items, operators have begun to see them as entire systems. This is because these two elements are closely connected and the critical failure of either can cause failure to the entire architecture. Instead, operators are looking for entire systems that have a single point of responsibility, taking more of a holistic approach to the engineered coatings.
Next generation insulation
Manufacturers and applicators are developing innovative solutions, which can keep up with the increasingly demanding offshore industry. In particular, rubber-based materials have come to the forefront as a more popular solution within the offshore industry due to rubber’s extremely flexible and durable nature.
Another popular choice is high temperature castable systems such as silicones or polyether thermosets, and hybrid polyurethanes, which offer ease of application and high degrees of automation to the process. They offer lower labour intensity as they are easy to apply and they are not as susceptible to operator error as with pack-in-place systems.
The latest generation of subsea insulation solutions, an example of this dedicated improvement from Trelleborg, have a k-value of 0.13 W/mK, can be used up to 9842 ft (3000 m) deep and at internal temperatures up to +311 °F (155 °C), as well as external temperatures as low as -31 °F (-35 °C).
These flexible insulation systems consist of a three-layer build-up, which make up the entire, holistic system. First, an inner layer for corrosion and/or hydrogen induced stress cracking (HISC) protection. The middle layer has been designed to provide the thermal insulation protection and various compounds are applicable depending on the specific requirements. The outer layer protects the insulation 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.
As the offshore oil and gas industry continues to push the limits when it comes to demanding subsea applications, the need for reliable and durable solutions that deliver proven performance for critical thermal insulation installations, has never been greater.
Add to this the fact that the lifetime of an oilfield is expected to be a minimum of 25 years and design temperatures of the field can vary throughout (up to +392 °F [+200 °C]), and it becomes clear that it has never been more important for products to prove they can stand the test of time.
Author: Ben Wait, Customer Group Manager, Trelleborg Offshore, North and South America
This an abridged version of the article ‘An evolving landscape’, which was published in the June 2013 issue of World Pipelines. For access to World Pipelines back issues, please click here.
Read the article online at: https://www.oilfieldtechnology.com/drilling-and-production/22072013/extreme_environments_an_evolving_landscape_for_pipelines/