It may be tempting to assume that utilizing a hydrophobic blanket insulation, like InsulThin® HT or silica aerogel blankets, will be sufficient to address CUI, but it’s important to remember that hydrophobicity is not a panacea solution for CUI. While hydrophobic treatments do help prevent water from penetrating into the system, most hydrophobic treatments are silicone-based additives that are organic in nature. As such, these types of silicone-based hydrophobic treatments begin to burn off around 450°F and have an upper temperature limit of 600°F. When exposed to these temperatures, silicone-based hydrophobic treatments will burn off and become ineffective.
For systems that operate at temperatures above 450°F, any outer layers of insulation will likely remain hydrophobic as insulation systems are usually designed to prevent surface temperatures from reaching such extremes; however the inner layer that is next to the pipe will experience much higher temperatures that will likely burn away the silicone-based hydrophobicity. While it may seem that having a single, outer layer of hydrophobic insulation is sufficient to protect the pipe, designers should reconsider this perspective. If any damage is done to the system that compromises the outer layer, the inner layer may be susceptible to water infiltration/absorption. As such hydrophobic insulations should not be considered the be-all-end-all solution for CUI prevention, but rather one component of a robust CUI-prevention strategy.
To account for the loss of hydrophobicity at such high temperatures, designers could consider utilizing a hybrid system. Hybrid systems layer two different types of insulation to capitalize on the benefits of both. An example of a hybrid system would be specifying a thin, hydrophobic blanket, like InsulThin HT, over an insulation with exceptional compressive strength and corrosion inhibitors, like Thermo-1200™ calcium silicate or Sproule WR-1200® expanded perlite.
While the base layer of Thermo-1200™ or Sproule WR-1200 would be expected to lose its hydrophobic or water-resistant treatment (at 450°F+ temperatures), they each have a proprietary corrosion inhibiting formula, the XOX Corrosion Inhibitor®, that is not affected by the operating temperature of the system. Thus, even if the hydrophobicity/water-resistance of the base-layer burns away, it will still have a hydrophobic outer layer and a corrosion-inhibiting inner layer to help protect the pipe. Additionally, a hybrid system, like the one described above, would capitalize on the thin, space-saving benefits of InsulThin HT and the compressive-strength and the XOX Corrosion Inhibitor of Thermo-1200™ or Sproule WR-1200.
Hybrid systems are one solution that can help system designers adapt to unique circumstances or needs for their application. As always, systems should be designed with multiple methods to help protect against CUI, whether that is a pipe coating, hydrophobic insulation, corrosion inhibitors, or more.