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NDT Definitions
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These specifications are presented in good faith researching information from various sources.   However, no guarantee or warranty is given to the accuracy of the above information.   You are advised to verify the correctness of these specifications prior to using them.  Use of these specifications assumes agreement with the disclaimer below. They are provided as a convenience to fellow enthusiasts and the author makes no expressed warranty to their accuracy, use at your own risk.


  • Adhesive Forces
    Adhesive forces occur between liquid molecules in contact with a solid surface.
     
  • Alternating Current (AC)
    Electric current flows through a conductor in a back and forth direction at specific intervals. Note: It provides the best sensitivity for the detection of surface discontinuities only.
     
  • Capillary Action
    Refers to the tendency of certain liquids to travel or climb into surface openings.
     
  • Cohesive Forces
    Cohesive forces between molecules of a liquid cause surface tension.
     
  • Contact Angle (q)
    Cohesive and adhesive forces jointly determine the contact angle q which in turn controls wetting ability.
     
  • Direct Current (DC)
    Electric current flows through a conductor in only one direction at all times. Note: DC from a battery source has been phased out in favor of rectified forms of AC for surface and subsurface flaw detection.
     
  • Flux Density (B)
    Magnetic field strength per unit volume within a ferromagnetic test part measured in gauss.
     
  • Flux Field Penetration
    The ability to establish and drive high density magnetic lines of force deep into the test part.
     
  • Full-Wave Rectified (FWDC)
    Electric current flows through a conductor in one direction only with an increased rate of pulsating surges and drops at specific intervals. Note: FWDC is recommended for effective surface and subsurface flaw detection when using the wet method of inspection.
     
  • Half-Wave Rectified (HWDC)
    Electric current flows through a conductor in one direction only with pulsating surges and drops at specific intervals-hence the name half wave. Note: It is most effective for surface and subsurface flaw detection when using the dry powder method of inspection.
     
  • Linear Indication
    Any indication having a length dimension at least 3-times greater than its width.
     
  • Liquid Penetrant Inspection
    A nondestructive test method which provides for the detection of surface discontinuities in ferrous and nonferrous test materials.
     
  • Liquid Penetrants
    Generally an oil base chemical solution of dye, either visible or fluorescent, capable of migration into surface openings by capillary action.
     
  • Liquid Viscosity
    Determines the rate of flow into an opening.
     
  • Magnetic Domains
    Ferrous material atoms or molecules normally illustrated as small bar magnets with north and south poles.
     
  • Magnetic Particle Inspection
    A nondestructive test method which provides for the detection of linear, surface and near surface, discontinuities in ferromagnetic test materials.
     
  • Magnetism
    A form of energy directly associated with electrical current, and characterized by fields or lines of force.
     
  • Magnetizing Force (H)
    Magnetic field strength per unit volume in air, measured in oersteds.
     
  • Particle Mobility
    The ability to establish activity or motion to the magnetic particles applied to the test part surface.
     
  • Permeability
    The ease with which a material can be magnetized. The ability of a material to conduct magnetic lines of force.
     
  • Reluctance
    The opposition of resistance by a material to conduct magnetic lines of force.
     
  • Retentivity
    The ability of a material to retain magnetic lines of force following magnetization.
     
  • Right Hand Rule
    Magnetic lines of force will always travel perpendicular or 90 degrees to the direction of electrical current flow.

Last modified: April 26, 2005

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