Subsea custom coatings

Suresh Choudhary, Adam Jackson, Paul Kleinen

December 4, 2013

Bredero Shaw discusses the various factors and challenges behind high-temperature subsea custom coating.

Due to the increased technical requirements within new well development, the proportion of subsea products requiring insulation suited to high-temperature operating conditions is increasing. It is required to thermally insulate not only the field joint area of offshore pipelines, but also various custom fabricated parts of subsea production systems, such as bends and spools, pipelines and terminations (PLETs), jumpers, goosenecks, etc. Any new product for high-temperature insulation must not only perform at the desired temperature ranges, but also easily assimilate into the contractors’ technology and process. This includes application processes, installation procedures, and cycle times to properly fit the work flow, which adds a high level of difficulty to the product development process.

Challenges of existing solutions for custom coating and field joints

The existing solutions for custom coating and field joints include polyurethane (PU), injection-molded polypropylene (IMPP), and syntactic epoxy-based, silicone-based, among others. PU and IMPP are widely used for insulating subsea production structures and field joints. PU-based systems are best suited to low-temperature applications (<80°C) and generally have problems with hydrolysis at higher temperatures. IMPP-based systems have been used in harsh environments with operating temperatures up to 150°C, but prove to be expensive for mid-range temperature (80-120°C) applications.

Although a very popular insulation material for subsea structures, PU is not suitable at higher temperatures due to hydrolysis, poor adhesion to polypropylene and other thermoplastics, and high dependence on mix ratio. Existing systems face other challenges such as long demold times, high exothermic energy release, and cracking under casting. There have been attempts to formulate high-heat, hot-wet polyurethane systems, but this led to relatively stiff and lowductility products.

Advanced epoxy chemistry solution Proper selection of insulation material can offer significant advantages in terms of reduced risk and reliable continuous operation of the subsea production structures. In order to achieve this goal, the new chemistry uses a two-pronged approach that combines superior material chemistry and ease of application. The advanced epoxy chemistry lowers the heat released during the curing reaction and the material remains ductile during installation. This low-curing exotherm also provides better cast-to-cast bond strength.

The formulation also allows for a subsequent in-service cure to a product with further enhanced hydrothermal stability, under the effect of the process heat experienced during operation. The high hydrothermal stability at elevated temperature ensures reliable mechanical performance over the field life, while the low water absorption of the material provides stable and predictable thermal performance. The solid material is also incompressible and performs well under high pressure, guaranteeing stable thermal performance of the applied coating.

Finally, the residual reactivity of the material provides high bond strength to flame/corona modified polystyrene/polypropylene and unmodified polyurethane, and enables its use in a wide range of applications.

The flexibility of the application process allows it to be used in various configurations – on spoolbases, fabrication yards or offshore on pipelaying vessels. The application process utilizes standard equipment as used in PU systems and personnel can be easily trained.

NEMO coatings for specific needs

Network epoxy modified olefin (NEMO) is an elevated-temperature insulation product that can be easily applied for subsea custom coating and field joint application. The NEMO product family currently comprises NEMO 1.1 and NEMO 2.1 and can be used on applications up to 120°C (tests are ongoing for 130°C and 140°C).

NEMO 1.1 is an epoxy-urethane hybrid system, developed for subsea pipeline and structure installation. It is a plural component suitable for low-pressure casting applications. It can be used up to a maximum continuous operating temperature of 95°C. NEMO 1.1 material overcomes the challenges associated with traditional PU systems and at the same time allows for cycle times similar to PU systems (Fig. 1).

NEMO 2.1 is an epoxy-olefin hybrid system, allowing processing speed and demold times comparable to PU. A novel latent additional cross-link system provides high ductility for deployment. In-service curing allows the formation of a highly cross-linked system, capable of handling continuous operation of at least 120°C. The molecular architecture provides improved hydrolytic resistance in the subsea environment, while ensuring a good bonding to adjacent olefinic, styrenic and urethane-based wet insulation systems (Fig. 2).

The system can be applied to fusion bonded epoxy (FBE) or to a suitable primer. The surface preparation steps are same as for PU or IMPP systems. A mold is placed over the field joint or the subsea structure and NEMO material is injected into the annulus. The exact demold time is specific to the dimensions of the field joint but can be as low as six minutes (Fig. 6). The excess material is trimmed and the surface is inspected for quality (Fig. 3).

Technical performance

Mechanical and thermal properties of the cured system are given in Table 1.

The mechanical performance of the system has been verified through interface adhesion testing, system to substrate testing and cast-to-cast interface testing. Values at ambient temperature are given in Table 2. Mechanical performance of the field joints was verified through simulated reeling testing, where a 60 mm FJ on a 10.75in.-diameter pipe was successfully reeled (4 cycles) with no incident at 0°C on a 7.6m radius former.

NEMO 1.1 and 2.1 were exposed to 18 months and 12 months, respectively, of aging under hot-wet conditions (95°C for NEMO 1.1, 120°C for NEMO 2.1). The properties of the system were measured at various intervals during the testing.

For NEMO 1.1, Fig. 4 shows the same trend as can be seen in polyurethane materials: a period of plasticization due to water absorption leads to a reduction in tensile strength and a reduction in ductility. After a period of 10 months, NEMO 1.1 entered a plateau state with no further loss in ductility or tensile strength (Fig. 9). For NEMO 2.1, Fig. 4 also shows an initial increase in tensile strength due to continued bond formation. This is followed by the effects of plasticization in the material, and reduction in tensile strength close to the initial value and approaching a plateau phase. The ductility of the material to this point is sustained or even slightly increased during the exposure period.

In conventional PU systems, high water uptake results in loss of thermal and mechanical properties. The uptake of water in the NEMO system has also been measured over time. The results are shown in Fig. 5. Limited water uptake at higher temperature is one of the key advantages that NEMO has over the PU systems.

Additional tests were conducted on the NEMO system, including the hot water soak test (Fig. 7) and the cathodic disbondment test (Fig. 8).

Conclusion

NEMO is tailored to meet the increasing technical demands of new well developments that require subsea products to operate continuously and reliably at higher temperature operating conditions. Based on technical performance, NEMO helps meet the performance void created by problems associated with the PU systems and offers a reliable solution for 80-120°C temperature range. OE

Suresh Choudhary, Regional Technical Lead for flow assurance technologies, is responsible for the development of new products and provides technical expertise on Bredero Shaw’s product spectrum within flow assurance products and services. Suresh graduated from Texas A&M University in Business Administration (MBA), and the University of Twente, Netherlands, in Chemical Engineering (MS). Suresh has more than seven years of experience in management, and business development.
Dr. Adam Jackson, Vice President of Technology for global flow assurance, is the technical authority for the development of new products in the flow assurance group. Adam has a Ph.D. in chemistry from the University of Hull, UK. He is based in Orkanger, Norway and has more than 25 years of experience in materials technology for the offshore oil and gas industry.
Paul Kleinen, P.E., Vice President of Engineering and Technology, is responsible for capital projects and process technology at Bredero Shaw. Paul earned a BS in civil engineering from the University of California, Berkeley and is a registered professional engineer in California.