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Introduction to Penetrant Testing

Introduction
History
Improving Detection
—Visual Acuity
—Contrast Sensitivity
—Eye's Response to Light

Principles
Steps for Liquid PI
Common Uses for PI
Pros and Cons of PI

PT Materials
Penetrant Testing Matl's
Penetrants
—Surface Energy
—Specific Gravity
—Viscosity
—Color and Fluorescence
   —Why things Fluoresce
—Dimensional Threshold
—Stability of Penetrants
—Removability
Emulsifiers
Developers

Methods & Techniques
Preparation
—Cleaning Methods
—Metal Smear
Technique Selection
Application Technique
Penetrant Removal
Selecting Developer

Quality & Process Control
Temperature
Penetrant
Dwell
Emulsifier
Wash
Drying
Developer
Lighting
System Performance Check

Other Considerations
Defect Nature
Health & Safety

References

Quizzes
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Advantages and Disadvantages of Penetrant Testing

Like all nondestructive inspection methods, liquid penetrant inspection has both advantages and disadvantages. The primary advantages and disadvantages when compared to other NDE methods are summarized below.

Primary Advantages

  • The method has high sensitivity to small surface discontinuities.
  • The method has few material limitations, i.e. metallic and nonmetallic, magnetic and nonmagnetic, and conductive and nonconductive materials may be inspected.
  • Large areas and large volumes of parts/materials can be inspected rapidly and at low cost.
  • Parts with complex geometric shapes are routinely inspected.
  • Indications are produced directly on the surface of the part and constitute a visual representation of the flaw.
  • Aerosol spray cans make penetrant materials very portable.
  • Penetrant materials and associated equipment are relatively inexpensive.

Primary Disadvantages

  • Only surface breaking defects can be detected.
  • Only materials with a relatively nonporous surface can be inspected.
  • Precleaning is critical since contaminants can mask defects.
  • Metal smearing from machining, grinding, and grit or vapor blasting must be removed prior to LPI.
  • The inspector must have direct access to the surface being inspected.
  • Surface finish and roughness can affect inspection sensitivity.
  • Multiple process operations must be performed and controlled.
  • Post cleaning of acceptable parts or materials is required.
  • Chemical handling and proper disposal is required.