The header plug seats are subject to abuse by careless plug removal and reaming. The seats become nicked or stretched.
If the plug seats are only slightly damaged, lapping with a repair plug will regain the original taper and finish. If badly damaged or distorted, a special reaming tool is used to correct the seat surface. This procedure results in an oversized hole and an oversized plug which must be fitted. These operations can be done with the header in place. The plugs and seats are marked with matched numbers so each plug is always returned to the same place.
Damaged or oversized tube holes can be built up in the shop with weld deposit and remachined to proper dimensions. The plug seating surfaces are built up with weld deposit and remachined to their original taper and finish. Oversized plugs are made in the same manner. Reject any plugs that have a graphoid tape or other type of packing sealant on it.
Inspection of Headers at Installation. Before the installation of new or reconditioned headers, inspect the interior and exterior surfaces for cracks, and soundness of the lining, if any. Inspect the tube holes for size (with respect to the tube ends), out-of-roundness, and the condition of the serrations. Check the plug holes for fit of the plug, condition of the seating surfaces, and that the plugs are marked. Check that holding members fit and seat securely. Determine that the header is of the proper thickness and material and that a hydrostatic test has been taken.