PVC-coated conduit is normally selected over other types for a very corrosive environment such as a food processing plant. For health reasons, corrosion is unacceptable in the food processing industry, so almost all products used in food processing plants must provide corrosion resistance and maintain original surface characteristics under prolonged influence of food, cleaning compounds, and sanitizing solutions. Washdown areas create special corrosion challenges for electrical engineers since a corrosion failure in an electrical raceway can cause a costly shutdown.
Southwest Cheese/Glanbia in Clovis, NM, is one food processor that found PVC-coated conduit to be the best solution to protect its electrical wiring from corrosion. The company selected the KorKap brand to replace its existing conduit, which had corroded.
Joe Burdette of Skanska Electric, Parsippany, NJ, who installed KorKap at Glanbia, knew he needed to follow the correct procedures so that the installed conduit would remain corrosion free.
Guidelines to prevent coating damage during installation of coated conduit:
Clamping: When using a pipe vise, replace the jaw assembly with special vise adapters. When using a chain vise for conduit diameters less than 2 in., wrap the clamp area with emery cloth (coarse surface against the coating). Use half-shell clamps to clamp 2 in. and larger diameter PVC-coated conduit. If you use a power unit that spins the conduit, equip the chuck with inserts designed for use with coated conduit.
Cutting: A roller cutter is recommended for cutting PVC-coated conduit. This will make a square cut end and remove about a quarter-inch of PVC coating, which aids in threading the conduit. A hacksaw can be used to cut conduit, but this method requires a pencil cut so that the die teeth engage the uncoated conduit.
Cutting away ¼ in. of the exterior coating in the same manner as sharpening a pencil allows the pipe guide to ride up and over the PVC coating, facilitates coating removal, and enables cutting the thread in one operation. A reamer is used to remove any rough internal edges caused by cutting, to prevent insulation damage during wire pulling.
Threading: Before threading, make a series of cuts in the PVC along the longitudinal axis of the conduit, using the thread protector attached to the end of each conduit section to gauge the length. These cuts help remove the PVC in small pieces rather than long strips, which can foul the die head and cause the conduit to collapse. Before threading, machine the stationary guide to remove 0.12 in. so the pipe guide can ride up and over the PVC coating. Always use a new die head to thread coated aluminum; using the same die head to thread PVC coated aluminum and coated rigid steel conduit is not recommended.
After threading, clean the threads and conduit interior with a degreasing spray to prepare for the application of the touch-up compound. Cleaning will ensure good adherence of the compound to the unprotected metal substrate.
Hydraulic Bending: For best results, use equipment designed to bend coated conduit. Hydraulic and electric powered benders are available with shoes sized for coated conduit. When bending coated conduit, use rubbing alcohol to clean the inside of the shoe and the area of conduit you wish to bend.
Never use lubricant in the shoe or on the conduit. Lubricant allows the conduit to slip above the center line of the shoe, resulting in flattening of the elbow.
Conventional shoes can be used to bend conduit if 0.06 in. are removed from the inside surface to accommodate the coating thickness.
Hand Bending: When using a conventional hand bender, use the next larger size bending shoe to allow space for the coating. You can make hand bends with a special coated bending hickey that reduces damage potential to the coating when making sharp bends, saddles, or offsets. Installers typically use these tools for diameters ranging from 1/2 to 1 in.
Assembly: You should use special Z wrenches in lieu of standard adjustable pliers to assemble PVC-coated conduit and fittings. Z wrenches spread the clamping force and enable the tool to grip securely, without damaging the conduit coating. Strap wrenches can be used to tighten conduit or couplings without damaging the coating.
For smaller conduit sizes, Spin-It tools are available for use with air impact or standard ratchet wrenches to assemble the conduit and fittings faster than with conventional methods. This method never touches the PVC coating and saves time by eliminating the need to touch up damage marks.
Special sockets are available for use with ratchets to tighten encapsulated screws on conduit fittings, hangers, and clamps.
PVC sleeves on conduit couplings and fittings help isolate corrosives from the threads at joints. Typically the sleeves should not be cut; however, it may become necessary to remove portions of the sleeve when the fitting is close to other sleeves such as with a short nipple. In this instance cut away half of each sleeve and apply touch up compound to the threads and joints.
Certification and Education: Several manufacturers now offer formal installer certification for end users and contractors who install coated conduit systems. Because manufacturers recognize the importance of proper installation, many offer free training for installers. Seminar training is recommended to provide the best possible installation of a coated conduit system.
For more information on Certification and Education visit:www.corrosioncollege.com.
This article was written by Joe Dodds, Robroy Industries, and Rob McIlroy, KorKap.
