Learning Objective: Recognize the mainte-nance practices and procedures used in the repair and fabrication of tubing and tube assemblies.

Maintenance of tube assemblies at the organizational level is limited to inspection, removal, installation, repair and replacement. Inspections are performed during fabrication, installation, and on in-service equipment. During fabrication, inspect bulk tubing and fittings before and during fabrication of a tube assembly. Before replacing a defective tube assembly, find the cause of failure, and inspect the tube assembly before and after its installation. Inspect in-service tube assemblies at regular intervals in accordance with applicable maintenance directives.

When you inspect the tube and tube assemblies for damage, look for chafing, galling, or fretting, which may reduce the ability of tubing to withstand internal pressure and vibration. Replace tubing that shows visible penetration of the tube wall surface caused by chafing, galling, or fretting. Tubes that have damage (nicks, scratches, or dents) caused by careless handling of tools are acceptable if they meet the following requirements: Any dent that has a depth less than 20 percent of the tubing diameter is acceptable unless the dent is on the heel of a short bend radius. A nick or scratch that has a depth of less than 15 percent of the wall thickness of aluminum, aluminum alloy, or steel tubing should be reworked by burnishing with hand tools before it is acceptable. Any aluminum, aluminum alloy, or steel tubing carrying pressures greater than 100 psi with nicks or scratches greater than 15 percent of wall thickness should be replaced.

Inspect each fitting (fig. 6-20) before it is installed. Visually or flow check to make sure that fitting passage or passages are free from obstructions.

Figure 6-20.Damaged fittings.