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Non-Destructive Testing Methods: UT, MT, PT, RT & ET in Hot Forging
A comprehensive guide to NDT methods for quality assurance in hot forging production, covering procedures, applications, and acceptance criteria.
Ultrasonic Testing (UT)
UT uses high-frequency sound waves to detect internal discontinuities in forgings. It is the primary method for detecting volumetric defects such as inclusions, cracks, pores, and laps. Typical frequency range: 2-5 MHz for steel forgings. UT is capable of detecting defects as small as 0.5 mm equivalent flat-bottom hole (EFBH) under optimal conditions.
Magnetic Particle Testing (MT/MPI)
MT detects surface and near-surface discontinuities in ferromagnetic materials. The part is magnetized and fine iron particles are applied. Surface-breaking defects create leakage fields that attract particles, forming visible indications. Sensitivity: capable of detecting cracks 1 mm or longer with suitable magnetization.
Liquid Penetrant Testing (PT)
PT detects surface-breaking defects in non-porous materials. A colored or fluorescent dye is applied to the cleaned surface, allowed to dwell, then excess is removed. Developer draws dye from defects, making them visible. Sensitivity levels range from 1 (highest) to 4 (lowest) per ISO 3452.
| Method | Detects | Sensitivity | Material |
|---|---|---|---|
| UT | Internal defects | 0.5 mm EFBH | All metals |
| MT | Surface/near-surface cracks | 1 mm | Ferromagnetic only |
| PT | Surface-breaking defects | Level 1-4 | Non-porous |
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