Non-destructive testing (NDT) finds defects in welds, plates, pipes and components without damaging them. Each method suits different materials and defect types, so the right choice depends on what you are inspecting and what you are looking for.
| Method | Finds | Best for | Limitations |
|---|---|---|---|
| Visual testing (VT) | Surface defects, corrosion, misalignment | All materials; first step in any inspection | Surface only; depends on access and lighting |
| Penetrant testing (PT) | Surface-breaking cracks and porosity | Non-porous metals, including stainless steel and aluminium | Surface-breaking defects only; needs clean surfaces |
| Magnetic particle testing (MT) | Surface and near-surface cracks | Ferromagnetic steels, welds | Not for austenitic stainless steel or non-ferrous metals |
| Ultrasonic testing (UT) | Internal flaws, wall thickness, lamination | Welds, plates, pipes, thickness surveys | Needs skilled operators; coarse-grained materials are harder |
| Radiographic testing (RT) | Internal volumetric defects (porosity, inclusions) | Weld quality records, castings | Radiation safety controls; access to both sides |
| Eddy current testing (ET) | Surface cracks, coating thickness, tube wall loss | Conductive materials, heat-exchanger tubes | Limited depth; conductive materials only |
Choosing a method
Methods are often combined: VT first, then a surface method (PT or MT) for cracks and a volumetric method (UT or RT) for internal defects. The applicable design code, your client’s inspection and test plan and the material decide which is required.
NDT personnel qualification
NDT technicians are normally qualified by method and level – Level 1, 2 or 3 – under schemes such as ISO 9712 or ASNT SNT-TC-1A. Ask for the technician’s method and level when you book.
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