IMMERSION METHOD (UT): The inspection method in which the search unit and the test part are submerged in a
fluid, usually water, which acts as the coupling medium.
IMMISCIBLE (PT): Pertaining to liquids that will not mix with each other.
IMPACT ENERGY (IMPACT VALUE): The amount of energy required to fracture a material, usually measured by
means of an Izod or Charpy test.
IMPACT STRENGTH: The ability to resist shock, as measured by an impact testing machine.
IMPACT TEST: A test to determine the behavior of materials when subjected to high rates of loading, usually in
bending, tension or torsion. The quantity measured in the energy absorbed in breaking the specimen by a single blow,
as in the Charpy or Izod tests.
IMPEDANCE: This term is used to refer to the total opposition to the flow of current represented by the combined
effect of resistance, inductance and capacitance of a circuit.
IMPEDANCE (ACOUSTIC): Resistance to flow of ultrasonic energy in a medium. Impedance is a product of particle
velocity and material density.
IMPEDANCE PLANE DIAGRAM: A graphical representation of the locus of points indicating the variations in the
impedance of a test coil as a function of basic test parameters such as electrical conductivity, magnetic permeability,
test frequency, thickness and magnetic coupling.
IMPEDANCE TESTING: A term generally applied to eddy current testing which measures the overall change in
impedance caused by variations in electromagnetic properties as differentiated from phase analysis testing which
measures changes in phase.
IMPURITIES: Elements or compounds whose presence in a material is undesired.
INCLUSION: Particles of impurities, usually oxides, sulphides, silicates, and such, which are retained in the metal
during solidification or which are formed by subsequent reaction of the solid metal.
INCOMPLETE FUSION: Fusion that is less than complete. Failure of weld metal to fuse completely with the base
metal or proceeding bead.
INCOMPLETE JOINT PENETRATION (LACK OF FUSION): Appears as elongated darkened lines of varying length
and width that may occur in any part of the welding groove.
INCOMPLETE PENETRATION: Root penetration that is less than complete or failure of a root pass and a backing
pass to fuse with each other.
INDENTATION: In a spot, seam or projection weld, the depression on the exterior surface of the base metal.
INDENTATION HARDNESS: The resistance of a material to indentation. This is the usual type of hardness test, in
which a pointed or rounded indenter is pressed into a surface under a substantially static load.
INDICATION: In nondestructive inspection, a response or evidence of a response, that requires interpretation to
determine its significance.
INDICATION (MT): This term refers to any magnetically held magnetic particle pattern on the surface of a part being