Syntactic Foam Thermal Insulation for Ultra-Deepwater Oil and Gas Pipelines

Abstract

Syntactic foam has been used successfully for over thirty years in the offshore industry, primarily as a buoyancy material for supporting marine riser pipe, and in floats and buoys of various kinds. Now its use is growing as a thermal insulating material for subsea equipment and pipelines, ensuring continued flow of hydrocarbons under adverse conditions. Experience to date shows that syntactic foam can in many cases offer significant engineering and economic advantages compared to more conventional insulation. However, realizing the full benefit of these new materials requires careful selection of ingredients and optimization of all relevant properties using a systems approach to the manufacture, assembly, and installation of the equipment. Introduction Syntactic foam is a composite material made from tiny hollow glass microspheres embedded in a polymeric binder, as shown in Figure 1. In some cases other fillers are added as required to modify the composite properties. High compressive strength and low density are the properties that make syntactic foam an efficient buoyancy material, and low thermal conductivity is a byproduct of its construction. Given its thermal efficiency and water resistance, syntactic foam is a natural choice for insulating subsea equipment. However, syntactics for thermal insulation are designed differently than are materials intended solely for buoyancy purposes. Density of the material is of less interest, while long-term thermal stability becomes critical. As long as service is limited to cold water, a wide range of polymer binders is available, and the spherical fillers are strongly reinforced by the surrounding matrix. At elevated temperature, on the other hand, materials choices are limited and the strength of the composite may be affected in ways that are difficult to predict. Such are the challenges that are continuing to shape the development of syntactic foam insulation. History and Applications It has long been known that subsea production of hydrocarbons is prone to blockage by paraffins or hydrates that can form when the fluid temperature falls below some critical level. One aim of flow assurance technology, therefore, is to conserve the heat of the fluid and prevent excessive cooling, even during shutdown periods. This has become an increasingly important concern as production has moved into deeper water and longer flowlines have been required, and a variety of different insulation methods have evolved. The following components have received attention to date: Wet trees and valves are routinely insulated. Key issues include high temperature, differential thermal expansion and contraction, and the necessity of some parts to move or to be serviced or replaced while in service. Jumpers are also frequently insulated. These pipes are often of complex curvature and usually require insulation materials with a great deal of flexibility. Speed and ease of installation is an important objective. Sleds and PLEM's often require not only thermal insulation, but also buoyancy to aid in installing the subsea system. Syntactic foam can be designed to combine the buoyancy and insulation functions. See Figure 2 for a typical PLEM application.

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Ageing of composites in underwater applications

“…26 Initially this material was used for buoyancy for ultra-deep underwater exploration in the marine science domain in the 1970s. In this context, syntactic foams, which can be used alone or as the core of composite sandwich structures, are particularly attractive owing to their excellent specifi c properties, i.e.…”