Which Inspection Method Best Maps Porosity Near a Thread or Bearing Seat?

No single inspection method is best for every thread or bearing seat. Visual or borescope inspection maps accessible openings, CT can map detectable three-dimensional distributions, radiography can screen suitable projections, microsections reveal local morphology and functional tests determine whether the finished interface performs. Selection depends on feature size, aluminum thickness, orientation, required resolution and whether the question is surface acceptance, internal extent or function.

Buyers should define the decision first, then qualify the method on representative good and reject conditions.

What Must Be Checked at a Thread?

Map indications on loaded flanks, thread root, entry and engaged length. A pore outside the engagement may be less critical than one removing material across several loaded threads. Inspect burrs and torn metal separately because tapping or thread milling damage can resemble a void.

Go/no-go gauges confirm assembly envelope but cannot prove local flank strength. Torque or pull-out validation can support qualification when specified, yet one destructive result does not screen every production part. Use material continuity rules and traceable process evidence.

What Must Be Checked at a Bearing Seat?

A bearing seat needs size, roundness, cylindricity or other drawing geometry, surface finish and continuous support appropriate to the fit. An indication can create local loss of contact, edge breakout or a path for lubricant. Position relative to peak bearing load matters, but the actual load case must come from product engineering.

Map the complete circumference and depth. A bore view can miss an opening at the back edge or under a press-fit zone. Repeated insertion should not be used to burnish away evidence.

How Radiography and CT Should Be Qualified

Radiography compresses thickness into a projection; geometry can superimpose bosses and walls over the region of interest. Multiple views can help. CT separates volume but its voxel size is not equal to guaranteed defect detectability. Contrast, noise, beam hardening, reconstruction and thresholding affect results, especially near dense geometry and machined edges.

Use reference samples or known indications where practical, record scan parameters and establish what sizes, orientations and locations are reliably found. The industrial CT resource provides context but cannot establish capability for an untested part.

How to Correlate Methods Without Double-Counting Evidence

Assign each part a common coordinate and feature identity. Mark surface openings, retain image slices and section selected locations. Compare method findings rather than assuming a CT indication and visible pore are separate defects. Track false positives, misses and ambiguous results during qualification.

A negative scan does not override a visible out-of-specification opening, and a visual pass does not override a functional failure. The inspection hierarchy should state which evidence controls each decision.

What the Supplier Report Should Contain

Request part, cavity, lot, machining operation, feature zone, instrument or scan setup, calibration/reference, raw images or results, analyst acceptance and disposition. The post-machining process should preserve the indication before local blend or additional cut.

How Reference Defects and Known Samples Establish Detectability

A method should be challenged with representative known conditions near the actual thread or bore. Natural indications confirmed by sectioning can be valuable, while manufactured holes or inserts may not reproduce contrast and orientation perfectly. Use references to establish a practical probability of detection and analyst consistency, not to claim that every smaller void will always be found.

Scan or inspect the same reference in different orientations and positions within the equipment field. Threads and curved bearing walls create artifacts and changing path length. If detectability drops at one side of the bore, add a view, adjust the method or retain another inspection for that zone.

Revalidate after equipment, software, reconstruction, source-to-part geometry or acceptance threshold changes. An old capability claim cannot automatically release a new larger casting or deeper feature.

The best inspection strategy combines accessible surface mapping with a qualified internal or destructive method when extent matters and a functional test when performance matters. Method choice follows the question; no image technology replaces the product requirement.