Reaching new highs and lows

Increasing oil demand and depletion of existing hydrocarbon reserves are driving investment in harsher subsea installation and operating environments, including arctic conditions, deeper waters, higher well temperatures, and higher water pressures. These conditions stretch or exceed the thermal and mechanical capabilities of current wet insulation offerings for subsea flow assurance.

To bridge the performance gap, a multiyear research project was initiated to develop a wet insulation solution that would reliably perform at higher service temperatures, lower installation temperatures, and greater water depths. The result of this multiyear effort is the patent-pending Neptune Advanced Subsea Flow Assurance Insulation System.

The system may be installed or used in temperatures as low as -40°C (-40°F) and has been tested at operating temperatures of up to 160°C (320°F). Complete end-to-end protection is achieved through the use of the three grades: Neptune C coating for subsea equipment, Neptune P coating for line pipe, and Neptune F coating for field joints. Comprehensive field testing conducted in partnership with industry-leading coaters and validated by a third-party witness demonstrates that the system offers a new level of installation and operating performance for subsea flow assurance.

The test results of the tensile properties of Neptune C Insulation Coating at 0 hours and 3,000 hours of wet aging at 160°C (320°F) demonstrate the hydrolytic and thermal stability of the coating in these conditions. (Images courtesy of Dow Oil & Gas)

Taking the heat

High-temperature stability is a key limiting factor to successful exploitation of higher temperature wells commonly encountered in deep and ultra-deep water. Future subsea equipment, line pipe, and field joints may be subject to interior temperatures that exceed the capabilities of traditional wet insulation materials. The Neptune system is based on a proprietary hybrid polyether thermoset technology developed by Dow to boost performance relative to operating temperature. In lab testing, hydrolytic performance was determined in a worst-case hot and wet interface scenario in which Neptune C coating dog-bone samples were aged in simulated seawater at 160°C and 4,300 psi for 3,000 hours. Table 1 presents the test results. Initial and post-aging tensile properties were determined according to ATSM Standard D412.

To further quantify hydrolytic stability, thermal stability, and hydrostatic crush performance, a 28-day simulated service test was performed on a composite 4.2-m (13.7-ft) section of 4-in.-diameter Schedule 120 pipe with 2 in. of proprietary coating. The pipe was tested at an internal pipe temperature of 160°C and an external temperature of 4°C (39°F) in simulated seawater.

A hydrostatic pressure of 4,351 psi (300 bar) was applied to the sample for the duration of the test.

The test results of a thermal conductivity evaluation of Neptune C Insulation Coating are compared by date.

Temperature, pressure, and heat flux were measured over the pipe length throughout the duration of the test to calculate thermal conductivity. Results are presented in Figure 1. Spikes in the graph indicate the planned shut-down periods employed to measure cool-down time. The uniform pattern of the line graph demonstrates the stability and consistency of the thermal conductivity measured throughout the course of the test, confirming that the coating exhibits very stable thermal conductivity performance, even at the 160°C operating temperature. At 0.152 Watts per meter Kelvin (W/mK), the measured K-factor compares very favorably with reported data of other wet insulation products available on the market today.

Taking the cold

As reported in 2008 by the US Geological Survey, areas north of the Arctic Circle are estimated to have 90 Bbbl of technically recoverable oil, with the vast majority located offshore. In these environments, extreme cold temperatures are a limiting factor for subsea flow assurance.

The test results of Neptune P and F Insulation Coating elongation at break are shown at -40°C, 0°C, and 50°C (-40°F, 32°F, and 122°F) temperatures.

The Neptune system was designed to provide flexibility and durability at very low temperatures. These properties are important for offshore use in any climate but especially in cold weather. Low-temperature flexibility helps maintain productivity during cold weather reeling versus incumbent materials, some of which can show embrittlement in colder climates. When tested according to ASTM D412 at -40°C, 0°C, and 50°C (-40°F, 32°F, and 122°F), Neptune Insulation Coating demonstrated flexibility in temperatures as low as -40°C as presented in Table 2.

Taking the pressure

The results of hydrostatic compression of Neptune C Insulation Coating are shown at 23°C (73°F) and 0 psi to 5,800 psi (400 bar).

Neptune Insulation Coating is a solid elastomer and is therefore virtually incompressible. Figure 2 and Table 3 show hydrostatic crush performance at 23°C (73°F) and 160°C respectively when subject to pressure up to 5,800 psi (400 bar), representing a water depth of at least 4,000 m (13,123 ft). There is virtually no change in the insulation coating under these conditions.

Additionally, the insulation coating does not incorporate glass beads, driving simplification, eliminating the potential of glass breakage during processing, and contributing to reduced risk. All of these advantages are achieved without the loss in thermal insulation performance typically associated with solid elastomers.

End-to-end simplicity

The results of hydrostatic compression of Neptune C Insulation Coating are shown at 160°C (320°F) and 5,800 psi.

The anti-corrosion performance for line pipe and field joints is achieved by using a fusion-bonded epoxy that is specially designed for high-temperature applications. The anti-corrosion coating for subsea equipment is provided by industry standard liquid epoxy materials. Combined together in the Neptune Advanced Subsea Flow Assurance System, the insulation coating and these epoxy anti-corrosion coatings provide a strong bond that eliminates the need for an adhesive tie layer, further driving simplification and contributing to risk reduction.

Some flow assurance systems can require multiple coating and tie layers to achieve insulation performance and may also require different insulation materials to provide end-to-end thermal protection. This introduces a level of complexity that increases the risks associated with bonding of dissimilar and potentially incompatible materials. The Neptune system, by contrast, employs a simple dual-layer technology with a single homogenous layer of anti-corrosion coating and a layer of proprietary insulation coating that provides end-to-end thermal and mechanical protection from the wellhead to the delivery point.