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Advantages and Disadvantages of Selected Non-Destructive Inspection Methods (NDI)

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Quality and Inspection Services

The following table contrasts the Disadvantages and advantages of Selected Non-Destructive Inspection Methods (NDI)"

METHOD ADVANTAGES DISADVANTAGES

VISUAL

Inexpensive Highly portable Immediate results Minimum training Minimum part preparation Surface discontinuities only Generally only large discontinuities Misinterpretation of scratches
DYE PENETRANT Portable Inexpensive Sensitive to very small discontinuities 30 min. or less to accomplish Minimum skill required Locate surface defects only Rough or porous surfaces interfere with test Part preparation required (removal of finishes and sealant, etc.) High degree of cleanliness required Direct visual detection of results required
MAGNETIC PARTICLE Can be portable Inexpensive Sensitive to small discontinuities Immediate results Moderate skill required Detects surface and subsurface discontinuities Relatively fast Surface must be accessible Rough surfaces interfere with test Part preparation required (removal of finishes and sealant, etc.) Semi-directional requiring general orientation of field to discontinuity Ferro-magnetic materials only Part must be demagnetized after test.
EDDY CURRENT Portable Detects surface and subsurface discontinuities Moderate speed Immediate results Sensitive to small discontinuities Thickness sensitive Surface must be accessible to probe Rough surfaces interfere with test Electrically conductive materials Skill and training required Time consuming for large areas
Can detect many variables

ULTRASONIC

Portable Inexpensive Sensitive to very small discontinuities Immediate results Little part preparation Wide range of materials and thickness can be inspected Surface must be accessible to probe Rough surfaces interfere with test Highly sensitive to sound beam discontinuity orientation High degree of skill required to set up and interpret Couplant usually required
X-RAY RADIOGRAPHY Detects surface and internal flaws Can inspect hidden areas Permanent test record obtained Minimum part preparation Safety hazard Very expensive (slow process) Highly directional, sensitive to flaw orientation High degree of skill and experience required for exposure and interpretation Depth of discontinuity not indicated
ISOTOPE RADIOGRAPHY Portable Less expensive than X-ray Detects surface and internal flaws Can inspect hidden areas Permanent test record obtained Minimum part preparation Safety hazard Must conform to Federal and State regulations for handling and use Highly directional, sensitive to flaw orientation High degree of skill and experience required for exposure and interpretation Depth of discontinuity not indicated

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