The main methods and what each finds
| Method | Finds | Limits |
|---|---|---|
| Visual testing (VT) | Surface cracks, undercut, porosity open to the surface, poor weld profile | Surface only |
| Penetrant testing (PT) | Fine cracks open to the surface, on any non-porous metal | Surface only; needs a clean surface |
| Magnetic particle testing (MT) | Surface and near-surface cracks | Ferromagnetic steel and iron only, not austenitic stainless or brass |
| Ultrasonic testing (UT) | Internal flaws, laminations, lack of fusion; also wall thickness | Needs a skilled operator and reference blocks |
| Radiographic testing (RT) | Internal porosity, shrinkage and inclusions in castings and welds | Radiation safety controls; a permanent film or digital record |
| Eddy current testing (ET) | Surface flaws in tube and bar, often on an automatic line | Conductive materials; shallow depth |
NDT finds flaws. It does not confirm the grade of the metal, which is what positive material identification and the mill certificate are for.
Who may perform and sign NDT
NDT is only as reliable as the person doing it. ISO 9712 sets out how NDT personnel are qualified and certified by method, at Levels 1, 2 and 3; in the US many buyers refer instead to the ASNT SNT-TC-1A practice. A Level 2 technician can set up the test, carry it out and judge the results against the acceptance standard. Ask for the technician's certificate for the method used, and for the written procedure, the equipment calibration and the acceptance level on each report.
Note that a hydrostatic pressure test is not counted as NDT under ISO 9712: its leak-testing method excludes hydraulic pressure tests.
How Clear To Load uses it
We do not have NDT-certified staff or our own NDT equipment. In a witness inspection, the inspector watches the factory's certified technicians, or an outside NDT agency, test parts the inspector picks, checks the technician's certificate and the procedure, and records the results with photos. We do not arrange independent NDT: where your order requires an independent certified technician, appoint an NDT agency and name it in the order, and our inspector can witness its work. See iron castings, steel forgings and structural steel fabrication.