DELAYED SWEEP (UT): An A-scan or B-scan presentation in which an initial part of the time scale is not displayed.
DELTA EFFECT: Acoustic energy re-radiated by a discontinuity.
DEMAGNETIZATION (MT): The reduction in the degree of residual magnetism in ferromagnetic materials to an
DENDRITE: A crystal that has a tree-like branching pattern being most evident in cast metals slowly cooled through
the solidification range.
DENSITOMETER: Instrument utilizing the photoelectric principle to determine the degree of darkening of developed
photographic film. Measures optical density of films.
DENSITOMETRY (RT): The measurement of the degree of darkening of a developed photographic/radiographic film,
providing one measure of the quality of the film. Measuring the optical density of films.
DENSITY COMPARISON STRIP (RT): Alternative term for step-wedge comparison film.
DENSITY, FILM (RT): The degree of blackening of a film is density. Film blackening or density is usually expressed
in terms of the H & D curve (Hurter & Driffield) which is defined a the logarithm of the reciprocal of the transparency
of the film. D Log2Io where D density, Io = Light incident on the film, and I = Light intensity transmitted.
DENSITY GRADIENT: The change in density of a radiographic film at a particular film density per unit change in the
logarithm of the exposure received by the film. The maximum density gradient of a film is usually called gamma.
DEOXIDIZER: A substance that can be added to molten metal to remove either free or combined oxygen.
The removal of oxygen from molten metals by use of suitable deoxidizers.
Sometimes refers to the removal of undesirable elements other than oxygen by the introduction of elements
or compounds that readily react with them.
In metal finishing, the removal of oxide films from metal surfaces by chemical or electrochemical reaction.
DEPTH OF FUSION: The depth to which the base metal melted during welding.
DEPTH OF PENETRATION (MT, EC): The depth at which the magnetic field or induced eddy currents has decreased
to a specified percentage of its surface value or has reached the limit of its effectiveness. The depth of penetration is an
exponential function of the frequency of the signal and the conductivity and permeability of the material.
DESCALING: Removing the thick layer of oxides formed on some metals at elevated temperatures.
DESENSITIZATION (RT): An effect on the emulsion of a radiographic film caused by pressure of any type exerted on
the emulsion prior to exposure. A desensitized area on a film is characterized by low density in the affected area.
DETAIL: See DEFINITION, RADIOGRAPHIC
DETAIL SENSITIVITY (RT): The radiographic definition or sharpness of detail as indicated by the drilled holes in a
penetrameter. It is expressed by a number x-yT, where x is the thickness of the penetrameter expressed as a percentage
of the nominal subject thickness, and y is the diameter of the hole expressed as a multiple of the penetrameter thickness