Downloaded from https://www.everyspec.com AMCP 706-198 0.0014 in. can be distinguished. The method applied which makes the penetrant and the has been used to determine bond quality in flaw visible. large objects such as solid-fuel rocket motor cases (Ref. 5). A practical application of the There are two basic types of penetrants: I R technique is discussed in Ref. 6. The dye penetrants and fluorescent penetrants. big disadvantage is that the emissivity of the Dye penetrants consist of a dye dissolved in surface must be constant. the liquid penetrant. The color of the dye is chosen to give greatest contrast with the , IR photographic equipment can be ob- developer.
One particular dye penetrant pro- tained from many photographic equipment vides a red-on-white record of defects which manufacturers. A sensitive solid-state IR de- can be removed from the material as a tector also has been developed, permanent record. Temperature probes can be used as Fluorescent penetrants coasist of a fluores- temperature profile gages. These probes ute cent phosphor dissolved in the liquid pene- conventional thermometers, thermistors, re- trant. This type of penetrant works in the sistance thermometers, and thermocouples samie manner as other penetrants. However, as the temperature sensing elements.
These flaws must be viewed under near-ultraviolet devices measure temperature accurately, con- light (365 nanometers). veniently, and economically; however, large numbers of them are required to profile a Some precautions must be taken while surface without reducing resolution. Also, using these materials: the devices themselves, and associated lead wires. etc., tend to lower the temperature to 1. The surface of thv specimen must be be measured. Therefore, the temperatures thoroughly cleaned before the penetrant is recorded with these devices arc somewhat applied. lower than these recorded by no-contact tech- niques such as IR scanning. 2, Sufficie-' e must be allowed for the penetrant to *.
,ate the flaw. 8-5 LIQUID PENETRANTS 3, The excess penetrant must be removed Liquid penetrants can be used to detect wi.h care, surface flaws in most materials. Sui.aie flaws are open to the surface but are not readily 4, The developer must be applied in a detectable by visual means. Few flaws are specified temperature range. revealed by penetrant inspection which could not be soen visually, but nenetrants make th2 Two special penretrunt techniques use radio. defects much easier to locate. Penetrants can active penetrants and filtered particles.
The be used with metals, glazed ceramics, plastics, radioactive method uses a radioactive pone- and nonporous materials Specialized peny- trant and detects the amount of this pene- trants arc available for porovs materials. trant trappud in defects by either a photo- graphic metlhod or with a radiation detector. Flaws arc located uy covering the surface of This technique is used primarily to determine the material with a liquid having a low sur- the porosity in metal alloys. The filtered face tension and a low viscosity. The liquid particle methoco is used to detect flaws in is drawn into the surface defects by capil- porous surfaces such as concrcte or carbon. lary action.
After the excess peneti-ant is The pimetrant, in this case, contains sus- removed from the surface, a developer is pended particles. The liquid Is absorbed by ,•,. . . .. ... . . .- .. , ..