NEUTRON RADIOGRAPHY (RT): The process whereby a photographic image of an object is produced by neutron
radiation that has penetrated through the object.
NITRIDING: Introducing nitrogen into a solid ferrous alloy by holding at a suitable temperature (below Acl for ferritic
steels) in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition.
Quenching is not required to produce a hard case.
NOBLE METAL: A metal whose potential is highly positive relative to hydrogen electrode. A metal with a marked
resistance to chemical reaction.
NODE: A point in a standing wave where some characteristic of the wave field has essentially zero amplitude.
NODULAR CAST IRON: A cast iron that has been treated while molten with a master alloy containing an element
such as magnesium or cerium to give primary graphite in the spherultic form.
NOISE (UT, ET): Any undesired signal that tends to interfere with normal reception or processing of the desired
signal. Origin may be electrical or from small reflectors in a material.
NONAQUEOUS DEVELOPER: See SOLVENT DEVELOPER.
NONDESTRUCTIVE INSPECTION: A method used to check the soundness of a material or a part without impairing
or destroying the serviceability of the part.
NONFERROMAGNETIC MATERIAL (NONMAGNETIC): A material that is not magnetizable and hence, essentially
not affected by magnetic fields. This would include paramagnetic materials having a magnetic permeability slightly
greater than that of a vacuum and approximately independent of the magnetizing force and diamagnetic materials
having permeability less than a vacuum. Some metals free from iron are zinc, tin, aluminum, brass, copper and pot
NON-METALLIC INCLUSION: Inclusions (or stringers) are impurities in the metal as a mechanical mixture. They
may be stretched out and broken up during rolling or forging and are at various depths from the surface.
NON-RELEVANT INDICATIONS: An indication due to misapplied or improper inspection. Also, an indication
caused by an actual discontinuity in the material that does not affect the usefulness of the part (such as a change of
NONRELEVANT INDICATION (MAGNETIC PARTICLE INSPECTION): A magnetic particle indication due to a
weak leakage field caused by some condition other than a discontinuity but does not affect the usefulness of the part;
such as a keyway, dissimilar parts, etc.
NON-SCREEN FILM (RT): X-ray film designed for use with or without metal screens, but not intended for use with
salt screens. It may be of relatively high speed and coarse grain (ordinary non-screen film) or of lower speed and finer
grain (fine grain non-screen film).
NON-STOCHASTIC EFFECT: Means health effects, the severity of which varies with the dose and for which a
threshold is believed to exist (below which there are no effects). Radiation-induced cataract formation is an example of
a non-stochastic effect.
NORMALIZE: Heating steel to above its critical range, as in annealing, and then cooling it in still air at ordinary room
NOTCH BRITTLENESS: Susceptibility of a material to brittle fracture at points of stress concentration.