How-To Repair the Niche FPP Honeycomb Face in 8 steps!
1). To identify the damaged tube, insert a soft wire or pipe cleaner into the point of tube damage and work it toward the honeycomb face. The wire protruding through the honeycomb face identifies the affected tube within the bundle. Once the damaged tube has been located, repairs may be made.
Warning! Do not attempt to clear undamaged tubes by inserting a welding rod, wire, or other devices.
2). Ensure that the honeycomb face is clean and dry in the area to be repaired.
3). Use a cotton swab or pipe cleaner, and clean the inside of the tube with alcohol or other appropriate solvents.
4). Insert a piece of fluoropolymer plugging material of the proper diameter about 1/2 inch (13 mm) long into the leaking tube end, allowing approximately 1/16 inch (1.6 mm) protrusion from the honeycomb face. If the plugging material is too thick to enter the honeycomb, stretch the plugging material slightly to reduce its diameter.
5). Using a hot air gun at 600O to 700OF (316O to 371OC), apply heat to the plug and surrounding honeycomb. Heat very carefully, allowing the material to slowly come up to temperature. The correct working temperature has been reached when the plug and adjacent tube material become transparent.
6). Apply pressure to the side of the plug by inserting a scribe into the adjacent tubes and pressing the tube wall toward the plug.
7). Using the scribe handle, apply a small amount of pressure to the top of the plug, applying heat as necessary. It is much better to go slowly than to rush this operation. Allow the new plug seal to slowly air cool. Rapid cooling may result in stress to the honeycomb area, which may lead to cracks or failure of the honeycomb.
8). Once plugs on both ends are cool, the heat exchanger may be reassembled and pressure-tested. If further leaks appear, dry the area, reheat the plug, and rework with a scribe.
Keep in mind that in some cases, the 1/4 inch (6.4 mm) plugging material may not be large enough to fill the tube. This may be remedied by inserting several pieces of plugging material to a depth of 1/2 to 3/4 inch (13 to 19 mm) into the tube, leaving 6 to 7 inches (150 to 180 mm) of the exposed plug. Holding the exposed plug end, use a hot air gun to heat the plug and adjacent tubes at the honeycomb face. Apply only enough heat to keep the plug material soft and transparent while working the sides and face until the plug adheres to the tube wall and the tube is full. Once the tube is completely plugged, cut off excess material to make the plug flush with the honeycomb face. Then, use a scribe to work the sides of adjacent tubes toward the end plug, and to work the top of the plug to the wall edges.
Contact Niche FPP for more information about this