Non Destructive Testing
From transcript: 20ME723 Non Destructive Testing (C)
Cheat sheet
Formulas
PT: clean → penetrant → dwell → remove excess → developer → inspect
MT: magnetize → particles → interpret leakage field at surface cracks (ferro only)
UT: v = f λ ; longitudinal & shear waves; TROD / DAC curves
RT: optical density; IQI sensitivity; safety distance & badges
ET: impedance change from conductivity/permeability/geometry (conductive)
Acceptance per code (ASME V, ISO) — indication ≠ automatic reject
UT: v = f λ ; distance from time-of-flight
RT: exposure ≈ f(kV, mA, time, distance) — inverse square
PT/MT: indication ≠ automatic reject — interpret per code
Definitions
- Indication vs defect
- NDT signal vs rejectable discontinuity per criteria
- Couplant
- Transmit UT energy into part
- Near field / dead zone
- UT limitation near probe
- IQI
- Image quality indicator for RT sensitivity
- Permeability
- MT requires ferromagnetic materials
- Skin depth
- ET penetration decreases with √f
- False call
- Indication without relevant discontinuity
- Written practice
- SNT-TC-1A / ISO 9712 qualification framework
- NDT vs DT
- Inspect without impairing serviceability vs destroy sample
- Discontinuity vs defect
- Indication vs rejectable per acceptance criteria
- Calibration
- Reference standards / DAC curves for UT
Topic-wise short notes
PT, MT, UT, RT, ET
- PT cheapest surface-breaking (non-porous).
- MT fast for ferromagnetic surface/near-surface.
- UT thickness, laminations, welds — needs skilled interpretation.
- RT permanent record — access both sides often.
- ET tubing, coatings, conductivity sorting — rapid.
Standards & reporting
- ASME Section V techniques; VIII/XI acceptance contexts.
- Technique sheets: frequency, angle, medium, magnetization.
- Traceability of calibrations and operator certs.
Method selection matrix
- Surface crack steel → MT/PT; aluminum surface → PT.
- Internal weld steel → UT or RT; thin wall often RT.
- Tube ID inspection → ET often; composites → UT/special.
Exam traps & quick notes
- Method selection: material, defect type (surface vs volumetric), access, cost.
- Codes: ASME Sec V / ISO — interview awareness beats memorizing every procedure.
- Weld quality stories: visual + PT/MT first line.
- Surface methods (PT/MT) miss deep subsurface; UT/RT for volume.
- Geometry, coating, grain noise affect UT.
- Radiation safety is non-negotiable for RT.
- Always report procedure, calibration, acceptance standard.
- Combine methods for critical parts (aero/pressure).
Comprehensive notes
PT, MT, UT, RT, ET
Principles, capabilities/limits, typical indications for welds/castings/forgings.
External: ASNT NDT overview ↗ NDT Resource Center ↗
Standards & reporting
Written procedures, personnel qualification levels, acceptance criteria documentation.
External: ISO 9712 NDT personnel ↗
Indication vs defect
Codes (ASME/ISO) define acceptance. Procedure + qualified personnel. Weld visual+PT as first line.
External: NPTEL ↗ Engineering Toolbox ↗
Interview Q&A for this subject
Q: Can NDT guarantee no defects?
A: No — sensitivity/coverage limits; probabilistic detection; still essential for risk reduction.
External: ASQ / quality ↗ MIT OCW ↗