Ultrahigh Solids Epoxy Coating Provides Resistance to Corrosion Under Insulation

Sherwin-Williams Protective & Marine provides several ways to mitigate corrosion under insulation (CUI) with its line of Heat-Flex CUI-mitigation coatings. The line includes Heat-Flex ACE, with ACE standing for advanced CUI epoxy. In addition, three coatings featuring a high concentration of micaceous iron oxide (MIO) pigment round out the lineup — the Heat-Flex 750, Heat-Flex 1200 Plus and Heat-Flex 650.

The Heat-Flex Ace is an ultrahigh solids epoxy novolac developed with a functional chemical improvement for CUI mitigation. The two-component, organic, ultrahigh solids epoxy novolac coating is also solvent free. Other CUI-mitigation epoxies can have between 60-80% volume solids. Being an ultra-high volume solids coating, Heat-Flex ACE reduces the release of volatile organic compounds (VOCs) for better environmental stewardship and reduced permitting costs for applicators. In addition, the coating has been developed with a functional chemical improvement and is free from the flake-filled pigmentation that’s common in alternative CUI-mitigation coatings.

In testing, Heat-Flex ACE surpassed the capabilities of solvent-based epoxy phenolic and novolac coatings designed for CUI mitigation, the company says. For example, it displayed best-in-class temperature, corrosion, chemical and mechanical resistance, while providing the most versatile DFT range among CUI-mitigation coatings.

“The battle against CUI is never ending, as coated steel encapsulated in insulation will inevitably corrode over time,” says Mark Rubio, energy business manager, Sherwin-Williams Protective & Marine. “Our goal is to mitigate that corrosion process for as long as possible, and we’ve developed some high-performance coatings that enable just that. For example, Heat-Flex ACE is the best product we’ve tested for long-term CUI mitigation. We anticipate it becoming a preferred specification solution as the industry gains experience with this enhanced CUI-mitigation system. We have also boosted the market’s CUI-mitigation capabilities for existing specifications with the three MIO-enhanced Heat-Flex coatings.”

All four Heat-Flex CUI-mitigation coatings have passed extensive lab testing, according to Sherwin-Williams, showing good to excellent performance in a variety of tests. These tests included various heat cycling, simulated CUI, BS EN 927-6:2016 erosion and dry film thickness (DFT) tolerance testing for thermal resistivity performed on all coatings, as well as cryogenic testing performed on the MIO-enhanced coatings.

To better meet the needs of current CUI-mitigation specifications, Sherwin-Williams also improved three existing formulations by adding MIO reinforcements. Each coating features a minimum concentration of 25% MIO pigment by weight in the dried coating film, which helps extend the life of the coatings and reduces risk by addressing typical CUI failure mechanisms experienced while in service, and during shipping and construction.

“The coatings’ heavy load of MIO reinforcements provides greater durability against impacts, chemicals and corrosion when coated assets are insulated and placed into service,” Rubio says. “In addition, the MIO provides enhanced UV erosion resistance, which protects the epoxy-based coatings from degrading before insulation is installed on assets.”

The Heat-Flex lineup of MIO-enhanced CUI-mitigation coatings includes Heat-Flex 750, Heat-Flex 1200 Plus and Heat-Flex 650.

Heat-Flex 750 is a two-component, high solids alkylated amide epoxy (AAE) coating that offers protection from CUI for long-term asset durability. Sherwin-Williams says Heat-Flex 750 outperforms traditional epoxy phenolics and other AAE technologies in a CX environment with excellent rust creep resistance at high DFTs, and minimal chalking and DFT erosion. In addition, Heat-Flex 750 offers epoxy-type mechanical resistance, minimizing damage potential during transport and assembly of shop-coated steel, and is suitable for temperatures ranging from -196°C to 205°C (-320°F to 401°F).

Sherwin-Williams Heat-Flex 1200 Plus offers CUI-mitigation protection for broad-temperature applications ranging from cryogenic to 649°C (1,200°F). That includes on insulated pipes, valves and process vessels that face very high-temperature service and aggressive cyclic service at high temperatures. As a two-component version of the company’s original Heat-Flex 1200 coating, Heat-Flex 1200 Plus provides added mechanical resistance and corrosion protection even in extreme CX atmospheric environments. Sherwin-Williams says the MIO-enhanced inert multipolymeric matrix (IMM) coating is harder than other silicone-based coatings used in the petrochemical industry, providing protection from impacts and abrasions during transit and installation, as well as from chemical attacks and moisture penetration. The material is also flexible enough to withstand the thermal shock of assets expanding and contracting during extreme temperature fluctuations. The company says the coating additionally passes atmospheric testing without a heat cure, saving application shops the time and expense of heat curing.

For applications requiring high-temperature epoxy novolac phenolic coatings, Sherwin-Williams offers MIO-enhanced Heat-Flex 650. With its higher MIO concentration, the coating represents the next generation of the Sherwin-Williams Epo-Phen FF CUI-mitigation coating. According to the company, testing showed that the combination of MIO with the epoxy phenolic resin in Heat-Flex 650 provides improved crack and UV erosion resistance compared to traditional epoxy phenolics, with the coating showing positive results for use on pipes, valves and vessels operating from cryogenic temperatures to 205°C (401°F). The coating has a higher volume of solids than other traditionally used high-temperature epoxy phenolics, making it a good choice for reducing VOC permitting costs.