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Quality and evidence

Why '100 per cent inspected' does not tell the whole story

Inspection extent, examined regions and detectability answer different questions. A sound concept addresses each separately.

2 min readUpdated: Editorial team: NPB NDT Consulting

Extent: which components are inspected?

Inspection of every component means that every item enters the defined inspection sequence. It does not automatically establish that every region is examined or every conceivable discontinuity can be detected. For sampling, the selection method and the conclusions that may be drawn require their own definition.

Coverage: which regions are examined?

Access, geometry and scanning motion determine the regions that can be examined. Unexamined or restricted regions should remain visible in the inspection concept. At transitions, edges and complex geometries, a clear illustration is often more useful than a blanket percentage.

Detectability: what can be found under these conditions?

Detectability depends on the method, material, discontinuity type and other conditions. Evaluating reliability may therefore require more than a functional demonstration. Probability of Detection describes a statistical assessment for a defined inspection task; it is not a universal guarantee covering arbitrary components and conditions.

Practical checklist

  • State the inspection extent clearly
  • Show examined and restricted regions
  • Describe target discontinuities and conditions
  • Carry limitations into reporting and release decisions

Planning example

Illustrative planning example, not a customer reference.

Planning example: Every component in a batch passes through an inspection system. A region restricted by geometry is still documented and assessed separately. Inspecting every item does not, on its own, establish the condition of that region.

Key takeaway

A defensible inspection statement combines extent, coverage and detectability. One percentage cannot replace that assessment.

Technical sources

The articles and method descriptions provide general technical orientation. The organisations listed are technical sources, not customers or partners of NPB NDT Consulting. Sources may be in German or English.

These articles provide technical orientation. The specific inspection task and applicable requirements must be assessed for each project.

Would you like to apply this question to your component or process? Start by describing the task in general terms.

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