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Inspection methods

UT and ET: complementary methods, not blanket alternatives

Ultrasonic and eddy current testing address different tasks. Material, accessibility and the discontinuities of interest determine the choice.

2 min readUpdated: Editorial team: NPB NDT Consulting

Let the required statement guide the method

Ultrasonic testing uses sound propagation within a material and may suit internal examination or thickness measurement. Its capability depends on factors including geometry, material and acoustic coupling. A relevant discontinuity is not equally detectable from every sound direction.

Consider near-surface tasks separately

Eddy current testing requires electrically conductive materials. It can suit defined near-surface tasks and repeated manufacturing inspections. Geometry and probe stand-off affect the signal. Selection should therefore follow a specific task description rather than a general claim such as 'ET is faster'.

Link results through a shared component identity

A combination can help when different regions or discontinuity types need examination. Record the intended statement, evaluation basis and limitations of each method separately. In an automated line, both stations need reliable component identification. A combined status must not conceal an invalid individual inspection.

Practical checklist

  • Distinguish internal and surface-related tasks
  • Consider material and access
  • Demonstrate feasibility for each method
  • Make individual and combined statuses traceable

Planning example

Illustrative planning example, not a customer reference.

Planning example: Define internal examination and a near-surface region of a metallic machine component as two tasks. Then assess whether UT, ET or another method combination is suitable.

Key takeaway

Combining methods does not automatically improve detectability. Value comes from clearly defined tasks and technically assessed results.

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.

Discuss your inspection task

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