NDT Definitions

NDT History | Definitions | Liquid Penetrant FAQ's | Magnetic Particle FAQ's

• 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.