summary of ndt methods
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8/6/2019 Summary of Ndt Methods
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SUMMARY OF NDT METHODS
1. Visual Testing (VT)2. Penetrant Test (PT)3. Magnetic Particle (MT)4. Eddy Current (ET)
5. Ultrasonic (ET)6. Vibration Analysis (VA)7. Acoustic Emission (AE)8. Radiographic Testing (RT)
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VISUAL Testing (VT)
APPLICATIONSSurface discontinuities:
Cracks, porosity, slag misalignment, warpage, incorrect size or number.
COMMENTS
Should always be the first method applied.
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PENETRANT (PT)
APPLICATIONSSurface discontinuities:
Cracks, porosity, seams, laps, leaks.
COMMENTS
Messy; need good ventilation.
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PENETRANT (PT)
ADVANTAGESInexpensive; easy to apply; more sensitive than visual alone; use on
most materials; rapid; portable.
LIMITATIONS
Surface only; not useful on hot, dirty, painted, or very rough surfaces.
Requires some technique.
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MAGNETIC PARTICLE (MT)
APPLICATIONS
Surface and near surface discontinuities:Cracks, voids, porosity, inclusions, seams, laps.
COMMENTS
Messy. Can cause defects.
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MAGNETIC PARTICLE (MT)
ADVANTAGESLow cost; fast; more sensitive to tight cracks than PT; can do near
subsurface; portable.
LIMITATIONS
Material must be ferromagnetic; surface must be clean; part may bedemagnetized; alignment of field is important. Requires operator technique.
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EDDY CURRENT (ET)
APPLICATIONS
Surface and near surface discontinuities:Seams, composition, thickness, eccentricity, surface condition.
COMMENTS
Requires good standards.
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EDDY CURRENT (ET)
ADVANTAGES
Extremely rapid; can be automated; very sensitive; surface contact notnecessary; permanent record.
LIMITATIONS
Shallow penetration; conductive materials only; may require special
equipment; sensitive to geometry; difficult interpretation sometimes.
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ULTRASONIC (UT)
APPLICATIONSSurface and deep subsurface discontinuities:
Cracks, laminations, porosity, lack of fusion, inclusions, thickness.
COMMENTS
Need good standards. Frequently used method.
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ULTRASONIC (UT)
ADVANTAGESRapid if automated but manual is slow; applicable to very thick
specimens; can give location and size of discontinuity; goodsensitivity; inspect from one side; portable.
LIMITATIONS
Couplant required; thin complex shapes are difficult; orientation ofdiscontinuity important; very operator-dependent.
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DYNAMIC TESTING VIBRATION ANALYSIS
APPLICATIONSSystem abnormalities:
Misalignment, lack of bonding, missing or worn components, loose parts.
COMMENTSShould begin with installation of system and test at regular intervals.
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DYNAMIC TESTING VIBRATION ANALYSIS
ADVANTAGESUseful in predictive or preventative maintenance; identify problem
areas or parts; indicate severity in-service; test; portable.
LIMITATIONS
Special equipment; experience required; some systems are too
complex.
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ACOUSTIC EMISSION (AE)
APPLICATIONSSurface and subsurface discontinuities:
Crack initiation and growth, leaks, boiling and cavitations, phase changes.
COMMENTSIndications and usually checked by other methods. Use is growing rapidly.
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ACOUSTIC EMISSION (AE)
ADVANTAGESRemote and continuous surveillance, location, severity, permanent
record. Tests an entire vessel or system.
LIMITATIONS
Contact with system; may need many contact points; complex
interpretation; system must be stressed; usually expensive; somesystems are too complex.
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RADIOGRAPHY (RT)
APPLICATIONS
Subsurface discontinuities:
Cracks, voids, inclusions, thickness variation, lack of fusion, incomplete
penetration, corrosion, missing components, composition>
COMMENTS
One of the most frequently used methods.
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RADIOGRAPHY (RT)
ADVANTAGES
Easily understood permanent record; usually moderate cost; can be portable;applicable to a wide range of materials.
LIMITATIONSCannot detect laminations; radiation hazard and regulations; access to both
sides can be high cost; requires trained operators.