How flange bore misalignment creates wear in lined piping

Two flange faces can meet without producing a continuous bore. Differences in liner thickness, centring, flange drilling, spool rotation or field fit-up can leave one side projecting into the stream. That projection may receive direct particle contact, expose ceramic or joint edges and generate a wake downstream. In abrasive slurry or pneumatic service, the damage can then appear at the interface and again farther along the wall. Record the actual flow direction before dismantling and mark which side is upstream. Without that reference, the same flange can be reassembled in a different orientation and erase the most useful clue.

A useful inspection follows the stream across the joint. Look for an upstream polished lip, chipped edge, opened joint, fan-shaped clean area or elongated downstream scar. Compare the pattern around the full circumference because a single accessible view can miss the controlling offset. Deposits may shield part of the step and redirect the flow, so preserve photographs before cleaning. The absence of severe damage at the flange does not clear the interface: the disturbance may transfer energy to a downstream wall or concentrate particles at the next bend. The complete pattern should be compared with neighbouring aligned joints.

Misalignment may originate in the lined spool, flange concentricity, gasket selection, bolt-hole clearance, forced fit-up or movement after the line is loaded. A support that settles or a flange pulled into position by bolts can recreate an offset even when each loose component met its own dimensions. Review as-built bore measurements, match marks, spool drawings, gasket condition and support loads together. Check whether the joint can be assembled without force and whether thermal or mechanical movement changes the position in service. This avoids assigning every internal step to the lining supplier when the installed system is what controls the final geometry.

Use a method suited to the diameter, access and safety conditions to record bore continuity around the circumference. The record should identify equipment, joint number, spool orientation, measurement datum, instrument and uncertainty. A profile gauge, internal survey, controlled template or other approved method may be appropriate; the choice belongs in the project inspection plan. Do not infer the internal transition solely from external flange alignment. Store photographs and measurements with the line isometric so the next shutdown can determine whether the geometry was corrected, moved in service or continued to generate the same damage.

Correction may require reorientation, support adjustment, replacement of a mismatched spool, an engineered transition or approved rework of the component. Do not grind, machine, weld or alter a pressure-containing assembly without the responsible engineering review and procedure. The repaired lining should finish with protected edges and the required bore, and the joint should retain clear match marks for future assembly. After commissioning, inspect the former downstream scar and the interface at an interval appropriate to its risk. A successful repair is shown by the new evidence, not by the fact that the flanges can be bolted together.