Chapter 4
Chapter 4
Miscellaneous Applications
Although piping penetrations are the most common in a processing environment, several other types of penetrations are equally critical.
Wire/Cable/Pneumatic
All wire, cable and pneumatic tubing that runs in and out of electrical cabinets, control panels and enclosures must be securely sealed to meet NEMA or IP ratings. Rigid plastic connectors or standard elastomer grommets are commonly used to seal these penetrations.
When applications require more flexibility and sealing area than a rigid connector or standard grommet can provide, a silicone grommet offers a tight, reliable seal that stands up to high temperatures and harsh processing environments. The lip seal is easy to install and the long sealing area allows significant movement without losing its airtight and watertight seal. They are NEMA rated for Type 4, 4X and 6 enclosures and are available in a variety of sizes for sealing cable or tubing up to 1/2” diameter. In their untrimmed form, they provide an excellent solution for covering unused knockout holes in panels and cabinets.
Electrical Conduit
Electrical conduit penetrations in sizes up to 4” are common in process environments. A number of standard conduit connectors are available in a variety of materials and designs for conduit penetrations through knockout holes in thin sheet metal and plastic.
A flexible silicone grommet for large diameters can also provide an airtight, washable seal with the additional advantage of allowing the conduit to move or flex without losing its seal. The lip seal is secure and installs easily into the knockout hole, and the tapered cone end can be trimmed to size on site. With no exposed threads or crevices, silicone grommets are not only a cleaner option in most cases, but they also give conduit penetrations a neatly trimmed appearance.
Air Hoses/Air Lines
For many years the standard fix for air hose or rigid air-line penetrations through walls has been to fill the gap with a liquid sealant and hope for the best. But hoses flex and rigid air lines lurch with pressure fluctuations, so the sealant inevitably tears, dislodges or falls out completely. Until it fails, the sealant does an adequate job of filling the void and offering some vibration and sound-dampening qualities, but the sealant alone can’t withstand the movement and vibration. The addition of a base-mounted flexible silicone boot on both sides of the wall significantly extends the life of the liquid sealant barrier by supporting the hose or air line and allowing movement without losing the seal.
Jacketed Tanks and Vessels
External piping penetrations in jacketed processing tanks and vessels need a secure, sanitary seal that allows movement and vibration without compromising the seal. But often the piping that emerges from the tank jacket is immediately connected to an elbow, tee, instrument or other piece of equipment that severely reduces the space available to seal the penetration.
These applications require a low-profile solution to seal the penetration in the jacket. Metal escutcheon plates are sufficiently low profile and are used in some cases but have limitations that also preclude them from other sanitary penetration applications (non-hygienic, require caulks or sealants, mounting failures, etc.). A flat, low-profile version of the cone-style flexible silicone boot is available for these tight-fit applications. They can be trimmed in the field for piping over 5” in diameter.
Outdoor Applications
Penetrations located outdoors and constantly exposed to the elements are rarely required to be sanitary, but they must still be properly sealed. The concern becomes less about hygienic sealing and more about durability. Sealing devices for outdoor penetrations must withstand constant exposure to ultraviolet rays and extreme temperature changes. Stainless steel escutcheon plates can withstand the UV and temperature challenges of outdoor use, but the caulk or sealants they require to provide the actual seal are prone to shrinkage and brittleness over time. Once the seal is broken, water and airborne particles can enter the penetration. Flexible silicone boots have proven to be a good solution for outdoor penetrations because of their ability to remain pliant and hold their seal indefinitely, even after years of outdoor use. They are constructed of a silicone compound that is UV stable and has a temperature range of -40° to 500° F, which makes them less susceptible to degradation.
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This technical guide is a general education tool for mechanical and electrical contractors, process designers and engineers, production managers and anyone else who has a stake in ensuring that their processing environment is clean and safe. Properly sealing all of the various penetrations in a processing plant is a shared responsibility that requires contributions from many different groups and departments.