If it is necessary to repair ATS FXP™ duct that has been damaged during shipment or by other means, in almost every instance, the duct can be repaired at the job site. Below are the recommended procedures for performing both liner and exterior structural repairs at the site.
1. Spider Cracks: Generally these can occur on the back heel of elbows. If someone drops the elbow, a “Spider Crack” (small cracks in the interior liner emanating from the impact point on the exterior surface) develops in the corrosion resistant liner as shown below. (See Figure 1.)
Repair of Spider Cracks: Sand the surface 2 to 3 inches around the perimeter of the crack. (See Figure 2.) Using ChemBond resin mix, wet out the sanded area with a liberal amount of resin. Next, apply one layer of Nexus veil onto the resin and finish the repair by wetting out the veil. For a mirror finish, place a waxed mylar film over the repair layup and roll out any air pockets that become trapped between the mylar and the resin. After the resin has cured, remove the mylar. The repair process is complete.
Repair of Split Liner if split is close to the end of the duct –
A split liner (see Figure 3) is usually near the end of the duct or fitting. It may be a result of two pieces coming into contact during shipment. In most cases, the outer structural duct wall is slightly scarred, but the inner corrosion resistant liner has split away from the structural wall.
Sand the area to make a uniform flat surface and to remove glass laminate splinters. Apply a liberal amount of ChemBond™ putty mixture into the repair area and a thin film of putty around the interior perimeter of the duct end. Next, apply a liberal amount of putty to one end of a slip collar, as described on page 147. Insert the putty end of the collar into the duct or fitting end and smooth the excess putty into the collar and liner seam. Remove the excess putty from the exterior surface of the collar, around the bead, if the joint will be completed at a later time.
Repair of Split if the split is not close to the end of the duct –
Sand the inner surface until uniformly flat, if the split is raised. Fill the liner void with ChemBond™ putty mix. Next, wet out the putty and a few inches of the good liner surface with a mixture of ChemBond™ resin. Then, apply a layer of Nexus veil to the resin-coated area, followed by a final application of ChemBond™ resin. For a mirror finish, place a mylar film over the repair layup and roll out any air pockets that become trapped between the mylar and the resin. After the resin has cured, remove the mylar and the repair process is complete.
A break through is where there has been a complete breach through the duct wall and liner. On small diameter ducts (those that are not accessible for a person to repair the damage from inside the duct), we advise cutting the duct circumferentially, removing the damage by creating two smaller lengths of duct. On larger diameter ducts (i.e. 24” diameter and larger) where access inside the duct is possible, repairs can be made to the interior to restore the duct integrity.
Repair of Break Through
Inside Repair: Sand away any glass laminate splinters and the immediate area around the damaged area on the inner liner surface. Tape a piece of flexible plastic, such as polypropylene to the outer duct surface, covering the hole in the duct. Apply a mixture of ChemBond™ putty into the void in the duct wall from inside the duct, pressing the mixture into the material covering the hole. Next, wet out the putty and a few inches of the good liner surface with a mixture of ChemBond™ resin. Then, apply a layer of Nexus veil to the resin coated area and saturate the veil with ChemBond™ resin. Add a second layer of Nexus veil and a final application of resin. For a mirror finish, place a waxed mylar film over the repair layup and roll out any air pockets that become trapped between the mylar and the resin. After the resin has cured, remove the mylar and the liner repair process is complete.
Outside Repair: After the resin patch on the inside has cured, remove the backing material from the outside duct wall. Apply liberal amount of ChemBond™ resin to the repair area and 3 to 4 inches of the undamaged exterior duct surface around the perimeter of the patch. Apply two layers of 9-oz. boat cloth (ATS Part Types 535-539) saturated with ChemBond™ resin over the entire wet out area to complete the repair.
If you have any questions or you need further assistance regarding duct field repair, please contact our Engineering Department at +1-510-234-3173.