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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.