October 20, 2012 | In: Liquid Penetrant Inspection
LPI Glossary of Terms
Following are some common terms used in LPI method of Non Destructive Testing/Inspections
Background Fluorescence: Fluorescent residues observed over the general surface of he part during Fluorescent Penetrant Inspection (FPI)
Bath: A term used colloquially to designate the liquid penetrant inspection materials into which parts are immersed during inspection process.
Black Light: Ultraviolet light energy between the range of 320-400 nanometers (that is near or just below the visible range). Also known as UV-A, this energy range reacts strongly on certain dyes causing them to emit visible light at about 550 nm, i.e. fluoresce.
Black Light Filter: A filter that transmits black light while suppressing the transmission of visible light.
Black Light Intensity: Intensity is the measure of black light strength in microwatts per centimeter squared (µW/cm²) at any given point on the inspection surface.
Bleed-out: The action by which the penetrant exudes from the discontinuities onto the surface of the material.
Blotting: The action of an absorbing medium soaking up the entrapped penetrant from surface discontinuities. This in-turn, forms penetrant indications with increased contrast and sensitivity.
Capillary Action: The tendency of certain liquids to penetrate, or migrate when exposed to small openings such as cracks or fissures.
Carrier Fluid: A fluid in which liquid penetrant inspection materials are dissolved or suspended. A good example would be the the non-aqueous solution that holds a dye penetrant.
Clean: A part to be inspected that is substantially free of solid or liquid contamination on the surface as well as in the voids of the flaws.
Color-Contrast Dye: When viewed under visible (white) light, this dye is designed to impart sufficient color intensity, enabling a good contrast of indications from the inspection surface.
Color-Contrast Penetrant: A penetrant – usually non-fluorescent – that incorporates the color-contrast dye, which is sufficiently intense to give good visibility of indications under white light.
Comparative Test Block: An intentionally cracked metal block that has two separate but adjacent areas for the application of different penetrants so that a direct comparison can be obtained.
Contrast: The striking difference of the colors used in liquid penetrant when compared under white light.
Dark Adaptation: The adjustment of the eyes when one passes from a bright to a dark area, usually a measure of time.
Defect: a) A discontinuity that interferers with the usefulness of an article. b) A fault in any material or part that is detrimental to its serviceability.
Degreasing Fluid: A cleaning agent employed to dissolve or remove oil and grease from the surface of components before the penetrant is applied.
Developer: A finely divided material – usually white in colour – that is applied to the surface of the component. The developer accentuates the bleed-out process and intensifies the detectability of flaw indications.
Developer Time: The length of time the developer is allowed to remain on the surface of the part under inspection to permit reverse capillary action.
Discontinuity: An interruption in the normal physical structure or configuration of an item such as cracks, forging laps, inclusions, sudden changes in thickness or hardness etc. A discontinuity may or may not affect the usefulness of the material.
Drain Time: The period of time allowed for excess liquid to gradually flow off a part after immersion in a bath.
Dwell Time: The total period of time that the penetrant is in contact with the surface of the part. Drain time is considered to be a portion of the dwell time.