11.4 PCC-2 Excavation, Flange, Exchanger & Test Articles 304, 305, 312, 501 & 502

PCC-2 Excavation, Flange, Exchanger, and Test Articles

These five articles cover the back half of a repair workflow: remove a flaw, restore specialized components, and demonstrate integrity. Their official titles provide the safest navigation clues.

1. Article 304 - flaw excavation and weld repair

Excavation removes a crack, lack of fusion, contaminated weld metal, local damage, or other rejectable material before restoration. The plan must define the removal method, limits, minimum remaining wall during excavation, surface shape, confirmation examination, weld procedure, final profile, NDE, and testing.

A crucial hold point occurs after excavation and before welding: verify that the flaw is completely removed. Surface examination is selected for the material, and volumetric examination may be needed for depth or remaining ligament. If a crack remains at the bottom, welding over it hides rather than repairs the defect.

Grinding or machining should produce a smooth weldable cavity without sharp notches. Thermal removal must not introduce uncontrolled hardening or contamination. The engineer reassesses the cavity if removal extends deeper or farther than planned. Restoration then uses a qualified WPS and welder, controlled consumables and heat input, interpass examinations when specified, final contour, final NDE, and records.

2. Article 305 - flange repair and conversion

Article 305, not Article 304, governs flange repair and conversion. Flange problems include gasket-face corrosion, erosion, scratches, warpage, loss of serrations, bolt-hole damage, cracking, reduced thickness, and a need to convert facing or joint configuration.

Inspection records facing type, gasket system, material, class/rating, dimensions, remaining thickness, flatness, surface finish, bolting, alignment, and service. Light damage may be removed by controlled machining if minimum dimensions and rating remain adequate. Deeper loss may need qualified weld buildup and re-machining, or replacement. A conversion changes load path or gasket behavior and therefore needs engineering confirmation rather than a maintenance-only decision.

Final checks confirm dimensions, finish, flatness, alignment, material, NDE of welded areas, and compatibility with gasket and bolting. The repair must not silently reduce flange pressure-temperature capability.

3. Article 312 - shell-and-tube heat exchangers

Heat exchangers contain interacting pressure boundaries. Damage may affect tubes, tubesheet ligaments, tube-to-tubesheet joints, pass partitions, channels, bonnets, floating heads, shells, nozzles, baffles, and supports. A leak may be process-to-utility cross-contamination rather than external.

Start by locating the leaking boundary and mechanism. Tube eddy-current or other tube examination, pressure testing by side, tracer methods, visual examination, UT, and surface NDE may be combined. Repair options can include plugging or sleeving tubes, tube-to-tubesheet repair, tubesheet restoration, partition repair, component replacement, or shell/channel pressure-boundary repair within the applicable method scope.

Evaluate lost heat-transfer area, changed flow, vibration, galvanic compatibility, plugging pattern, differential thermal expansion, and ability to identify future leakage. A mechanically sealed tube may stop a leak yet create a different crevice or thermal problem. Document tube maps and repaired locations.

4. Article 501 - pressure and tightness testing

Article 501 addresses pressure and tightness tests of piping and equipment after repair. A pressure test demonstrates pressure-boundary behavior under a defined load; a tightness test looks for leakage at a pressure and sensitivity suited to the service. They are related but not interchangeable.

The test plan defines boundaries, medium, test and examination pressures, stress ratio where applicable, metal temperature, vents and drains, air removal for hydrotest, overpressure protection, isolation, calibrated gauges, hold time, exclusion zone, leak examination, acceptance, depressurization, drainage/drying, and records. Pneumatic energy creates greater hazard than a comparable hydrostatic test, so engineering and safety controls must reflect stored energy.

5. Article 502 - NDE in lieu of pressure testing

Article 502 supplies a route for qualifying repairs or alterations without a pressure test when the method conditions and engineering basis are met. It is not a blanket statement that NDE is equivalent to every test. The engineer and inspector evaluate repair type, materials, weld access, service, failure consequence, flaw types, examination coverage, personnel/procedure qualification, and ability of selected methods to find credible defects.

A robust plan uses complementary surface and volumetric methods where appropriate, examines the required weld volume and surfaces, controls timing for delayed cracking, defines acceptance, and preserves traceable records. If examination access or reliability cannot meet the article, pressure testing or another repair strategy is required.

6. Article map

Exam traps

• Article 304 is flaw excavation; Article 305 is flange repair.
• Tube plugging decisions require exchanger-system evaluation, not just leak stopping.
• A tightness test and a structural pressure test answer different questions.
• Article 502 is conditional and must address credible flaws and examination limitations.