Dow Chemical discusses the development of non-mercury-catalyzed field joint insulation material for subsea pipelines.
By Amber Stephenson, Dave Parker, Mike Huspek, Kamesh Vyakaranam, and Mark Whelan
For decades, offshore applicators of field joint insulation materials relied on the high performance characteristics of formulations containing mercury (Hg) catalysts. Among the more critical performance characteristics of these Hg-catalyzed field joint materials were outstanding adhesion to different substrates, outstanding hydrothermal aging, robust processability, fast-build of compressive strength, and other mechanical properties.
Pipe sections are connected by field joints in a multi-step process where the slowest step determines productivity—so minimizing cycle time for application of the field joint coatings is critical. Legacy Hg-catalyzed field joint coatings typically exhibited rapid compressive strength buildup, which optimized cycle times to enable high productivity in assembling pipelines.
When the use of mercury catalysts was phased out several years ago, the industry responded with a variety of field joint formulations manufactured using non-Hg catalysts. While these first-generation, non-Hg field joint formulations worked well enough, none of them quite matched the performance of legacy Hg products. The most elusive property was rapid development of compressive strength and other mechanical properties after application, [such as tensile and tear strength]—which can potentially slow the onsite assembly of pipelines significantly.
Critical customer requirements
Dow Oil, Gas & Mining set out to develop a second-generation, non-mercury catalyzed field joint coating, that matched or exceeded the performance of our own legacy formulation—HYPERLAST FJ589 Polyurethane. The first step was to formally survey customers across the offshore value chain, including applicators, lay contractors, and offshore owners/operators. This gave us four primary performance targets for a second generation, non-mercury catalyzed field joint coating:
- Easy processing – applicators asked us to widen the mixing tolerances if possible, up from the standard ±1% by weight, to make the formulation more forgiving than all previous field joint coatings.
- Faster build of compressive strength – all parties wanted a faster build of mechanical properties contributing to more efficient onsite pipeline assembly.
- Strong adhesion to various substrates – primarily the fusion-bonded epoxy (FBE) anti-corrosion coatings and the glass syntactic polyurethane (GSPU) “parent” coatings on the pipe sections.
- Mechanical and aging performance equivalent to legacy Hg-catalyzed systems – subsea flow assurance coatings must withstand thousands of hours of service.
Laboratory screening and testing
Dow’s research and development team initiated an experimental program to deliver against these customer requirements. Starting in April of 2012, a series of different catalysts, chain extenders, polyols, and isocyanates were screened at laboratory scale in Freeport, Texas, using a multi-variable design of experiments to find formulations that matched or exceeded the cure profile, property build and final performance characteristics of the legacy Hg-catalyzed field joint coating.
Formulations were first screened to ensure that the cured elastomer provided the requisite thermal and mechanical properties. Cup calorimetry was then used to optimize catalyst type and loading, to provide the desired cure time and profile. Formulations showing a satisfactory cure profile and final mechanical properties were then screened for property development using reactive rheometry and transient compression testing.
The screening process narrowed our candidates down to five formulations that showed the most promise. These formulations underwent further lab-scale testing measure the rate of development of rheological and mechanical properties. The three most promising formulations were selected for evaluation at the pilot scale, where a plural component polyurethane machine was used to injection mold and bond X760E to a two inch thick coating of Dow HYPERLAST DW512/300E GSPU on a two inch diameter pipe.
Pilot-scale testing was carried out at Dow’s application center in Birch Vale, UK. Full-sized, industry standard equipment was used to produce, mix and apply the test materials, as would happen in the field. These larger samples were then subjected to the same series of tests performed in the laboratory, including adhesion, cure profile, compressive strength, hardness, and thermal conductivity. Based on this testing, XUR-07031977-760 was selected as the best performing of the three development formulations.
NOTE: During customer Interviews, applicators requested minimal values on technical charts rather than typical values. Values shown for HYPERLAST FJ589 are typical or average values. Values shown for XUR-07031977-760 are minimum specifications.
Phase one mission accomplished
Just one year after laboratory testing started, machine-scale testing and lab-scale aging studies confirmed that XUR-07031977-760 is a two-component, non-mercury, catalyzed field joint insulation material that matches or exceeds the important properties of the legacy Hg-catalyzed product. Most importantly, XUR-07031977-760 cures rapidly after the field-joint mold is filled, and it builds compressive strength quickly – comparable to the legacy Hg-catalyzed material (Figure 1).
Final thermal and mechanical properties of XUR-07031977-760 also closely match the Hg-catalyzed legacy material, as shown in Figure 2.
When compared to HYPERLAST FJ589, XUR-07031977-760 shows excellent mechanical integrity during hydrothermal aging, shown in Figures 3 and 4. XUR-07031977-760 and HYPERLAST FJ589 were aged in simulated seawater at 85°C, dried, and tested at 23°C. XUR-07031977-760 demonstrated excellent adhesion to both GSPU parent coatings and FBE substrates. Furthermore, machine-scale testing confirmed that the two-component XUR-760 field joint insulation material is mouldable onto anti-corrosion FBE coatings at temperatures up to 120°C. Finally, processing ratios were doubled from ±1% by weight to ±2% using compact, mobile, standard industry equipment.
Ready for customer evaluation
Based on our machine-scale test results, XUR-07031977-760, now named HYPERLAST FJ 760E, was invited to participate in pre-qualification testing on a major project in the Gulf of Mexico.
Amber Stephenson, is an R&D Manager for polyurethanes R&D application development at The Dow Chemical Company.
Dave Parker is the offshore coatings specialist at Dow Oil, Gas & Mining.
Mike Huspek is a global account manager at Dow Oil, Gas & Mining.
Kamesh Vyakaranam, is a polyurethane associate scientist at The Dow Chemical Company. For the past six years, he has been working in epoxy and polyurethanes product research. His current focus is on oil and gas flow assurance research.
Mark Whelan is a technologist leader at Dow Oil, Gas & Mining.