Steps to Reduce Insulation Drying Time

Flooding and strong, wind-driven rain events have historically been a thorn in the side of installers, designers, and engineers who specify insulation systems.  Some specifiers choose to approach these extreme weather events by simply specifying a hydrophobic insulation, under the assumption that the hydrophobicity will prevent water ingress.  However, this approach is sometimes too simplistic to appropriately account for the potential for water ingress, as hydrophobic insulations are not a cure-all.

At temperatures of 600°F and above, insulations with a silicone-based hydrophobic treatment lose their ability to repel water as the silicon oxidizes and burns off.  An insulation that may bead water at 300°F can turn into a sponge after prolonged exposure to temperatures of 600°F or higher.  When this happens, most hydrophobic industrial insulations¹ actually become a hybrid of hydrophilic (absorptive) and hydrophobic. Typically, the insulation will become hydrophilic next to the pipe, where the hydrophobe has been burned away, and hydrophobic at the outer portion of the insulation, where the hydrophobic agent is still intact. 

Rather than relying on hydrophobic insulation as a cure-all, a better approach for high-temperature applications would be to design the insulation system around an assumption that water will eventually enter the system.  With this approach, designers can preemptively address water ingress by creating a means for the water to exit the system quickly once it has been absorbed by the insulation: namely, specifying weep-holes in the jacketing and adding extra insulation to improve the thermal value of the insulation system.

While relying on the heat of the pipe should be a facet of the designed “drying plan,” designers should also consider specifying drainage holes in the jacketing. The reason being that even though most industrial insulations are “vapor open,” meaning they allow water vapor to pass through them, the jacketing is not.  This means that any water vapor that is pushed out of the insulation by the heat of the pipe will become trapped in the system by the jacketing.  This is where the drainage holes, or “weep holes,” come in to play as they allow an easy path for moisture to escape.

System designers can also preempt water intrusion by adding an extra layer of insulation to increase the thermal value of the system, inadditionto specifying weep holes. This sets up the system to optimize the drying process should the insulation become wet or saturated because it increases the thermal value of the system, retains heat, and expedites the drying process.

To explore how much an additional layer of insulation could influence drying times, we ran a test on saturated Thermo-12^® Gold*. In the test, 3’ x 1.5” sections of Thermo-12 Gold* calcium silicate pipe insulation were saturated with water and installed on a room-temperature pipe. This layer of calcium silicate was then covered by a 10 mm layer of InsulThin™ HT, and the insulation system was jacketed with SE aluminum jacketing with 3/4”² weep holes spaced 36” on center. The ends of the insulation and jacketing were sealed to prevent moisture from escaping. The pipe was then heated to 600°F, and the temperatures of the pipe, insulation, and jacketing were recorded. 

For a control, the test was repeated on two different configurations as well (in addition to the dual-insulated configuration): one without the external InsulThin HT layer but with jacketing weep holes, and one without the InsulThin HT or the jacketing weep holes. Results of the testing are shown in the table below.

  **After 100 hours, the test was halted even though the insulation was not dry.

As anticipated, the weep holes reduced the drying time by allowing a path for water to escape. Furthermore, adding InsulThin HT to the system in addition to weep holes,reduced the drying time by more than 75%, dropping it from over 100 hours down to 24 hours.

Clearly, the use of a thin, hydrophobic blanket provides additional protection against water intrusion, but this study has shown that it can also help after water has entered the system. Adding extra thermal value to the insulation system through an additional layer of insulation, retains heat and expedites the drying process. Ultimately, this can make a substantial difference in the drying time – helping to prevent CUI after a water-intrusion event.  

*Thermo-12 Gold, Johns Manville’s legacy calcium silicate, was used for this study because of its existing prevalence in the industry.

1. Insulations that are inherently hydrophobic and not treated with a silicon-based hydrophobic treatment, like cellular glass, will remain water-repellant up to the maximum use temperature.

2. Weep hole size and spacing based on: Shell, DEP Specification. DEP 30.46.00.31 - GEN, February 2015.