Low-Density Polyurethane Foam for Subsea Buoyancy Systems

Addressing Buoyancy Requirements with Hydrostatic, Pressure-Resistant Foam

By Dr. G. Joel Meyer

According to a forecast by the research firm MarketsandMarkets the market for UUVs, specifically ROVs and AUVs, is expected to reach $4 billion by 2020. The increase in the ROV commercial segment is due to the growing demand for survey and seabed mapping, offshore drilling and pipeline inspection, while the increase in the AUV market can be attributed to greater activity on the military and scientific research front.

The design and material considerations for UUVs are heavily dependent on the nature of its applications, with the right buoyancy material counting as one of the critical choices manufacturers have to make. Successful operation of these vehicles requires buoyancy that performs at a specific range of depths, while taking into consideration chemical environment conditions.

The LAST-A-FOAM R-3300 buoyancy foam series provides a range of hydrostatic, pressure-resistant polyurethane foam in various densities that address common buoyancy requirements.

Design
LAST-A-FOAM R-3300 foam is specifically formulated to be a dimensionally stable, closed-cell, water- and impact-resistant foam that can withstand the harsh conditions of shallow to mid-depth subsea operation. The high strength and modulus of the polyurethane foam is a result of the proprietary formulation of highly crosslinked polyurethane foam, along with a manufacturing process that minimizes cell structure variation throughout the material. Polyurethane foam does not support the growth of micro-organisms and will not rot or decay over time. These properties make it optimal for subsea buoyancy systems, marine and underwater robotics applications, and as a core material for resin transfer.

Testing
General Plastics has an in-house testing method based on ASTM-D 570 that was developed to simulate subsea conditions. In this hydrostatic testing, a sample of foam is placed in a reinforced pressure vessel and filled with water to a pressure corresponding to specific oceanic depths, with the assumption that pressure increases by 1 psi per 2.31 vertical feet. For example, material that is qualified to 1,200 ft. is placed in a pressure vessel at 580 psi. Using this method, we can simulate the conditions that the foam will be exposed to at a large number of varying depths. The material is then held at pressure for 24 hours.

After the test is complete, the sample of foam is then measured for dimensional stability and water absorption. As seen below in Table 1, the average volume change for all densities of material is well below 1 percent. With an average weight gain range of only 2.0 to 2.8 percent, the material shows minimal changes when subsea pressures are applied. The data below is based on an average of more than 300 different batches of material produced to full scale.

Table 1

Density	Average of Vol. Change (%)	Average of Weight Gain (%)
12	0.07%	2.0%
15	0.86%	2.8%
18	0.03%	2.0%
25	0.27%	2.2%

LAST-A-FOAM R-3300 has shown to retain strength and stability when put through these harsh underwater conditions. General Plastics Mfg. Co. certifies the naked foam to be stable to up to 1,200 ft. for 25 pcf material, and it gains even more stability when an epoxy or polyurea coating is applied. In all of the foams tested, depths accessible using coated R-3300 foam doubled when compared to the noncoated foam (see Table 2).

Table 2: Depth Chart

Products	Density (lb/ft3)	Tested Depth (ft.) (uncoated)	Tested Depth (ft.) (coated)
R-3312	12	300	600
R-3315	15	700	1400
R-3318	18	800	1600
R-3325	25	1200	2400

Physical and Thermal Property Data: Case Study
Outland Technology, manufacturer of underwater systems, has been using General Plastics’ LAST-A-FOAM R-3300 polyurethane foam series for ROVs in applications such as oil rig and pipeline inspections, collegiate research and military uses. In earlier projects, the company’s ROV flotation material requirements included low-density conditions, buoyancy up to 500 ft., and the ability to customize foam size and thickness to fit individual applications. Their product choice, the R-3315, fit the density requirement at 15 lb. per cubic foot and could go to depths up to 700 ft. uncoated and 1,400 ft. when coated. Additionally, Outland Technology had the ability to machine the foam to desired thickness.

Over the years, Outland Technology designed their ROV with higher voltages and better cables giving it the ability to reach depths of 1,000 ft. or 500 psi. The expanded range of the R-3300 foam series allowed General Plastics to address the customer’s evolving needs. With density ranging from 12 to 25 lb. per cubic foot, the R-3300 foam series provides buoyancy with depths up to 1,200 ft. uncoated or 2,400 ft. coated. It is dimensionally stable, performs in freshwater and saltwater and is easy to machine, coat and paint.

Dr. G. Joel Meyer is the chemistry laboratory manager at General Plastics Manufacturing Co., where he oversees a team of chemists and materials scientists to bring new advanced materials and applications to market. As head of the company’s R&D group, he works with customers to create products that fulfill specific requirements and applications.