Значение и использование

The penetrant is one of the major components of the fluorescent penetrant process, and very influential in the degree of performance attained by a given system or group of materials. The penetrant must enter the discontinuity, be removed from the part surface but not from the discontinuity, be brought out of the discontinuity by the developer, and finally viewed and detected by the inspector. If all processing parameters are optimized for the parts being examined and the examination materials in use, the intrinsic brightness of the penetrant becomes the factor which governs the sensitivity of the system.

Because the eye responds logarithmically rather than linearly to changes of brightness, differences in brightness must be fairly large to be significant. Differences of 25 % are obvious, 12 % noticeable, and 6 % detectable by the eye. Experts may sometimes detect 3 % differences, but these are not usually significant to the average observer.

The significance of the results also depends on the deviation between readings on the same material sample. Different samples, even when prepared out of the same initial quantity of penetrant will not exactly reproduce readings. These differences occur because of paper differences and penetrant migration on the paper samples.

To determine the confidence limits for the test results, it is necessary to perform certain statistical calculations. The confidence limits are determined by the equation:

where: CL= the limits within which we can be confident the value lies, ¯X= the average of all readings, t= “student's t” (values of which are given by statistical manuals), n= the number of readings used, s= the standard deviation determined by the equation:

where: X= the individual readings.
In this use, the 95 % confidence level (the value will lie within the limits 95 % of the time) is sufficient. At this level, t for 4 samples is 3.182.

If the confidence limits of two material samples overlap, the materials must be considered equal even though the measured average values are different.

Область применения

1.1 This test method describes the techniques for comparing the brightness of the penetrants used in the fluorescent dye penetrant process. This comparison is performed under controlled conditions which eliminate most of the variables present in actual penetrant examination. Thus, the brightness factor is isolated and is measured independently of the other factors which affect the performance of a penetrant system.

1.2 The brightness of a penetrant indication is dependent on the developer with which it is used. This test method however, measures the brightness of a penetrant on a convenient filter paper substrate which serves as a substitute for the developer.

1.3 The brightness measurement obtained is color-corrected to approximate the color response of the average human eye. Since most examination is done by human eyes, this number has more practical value than a measurement in units of energy emitted. Also, the comparisons are expressed as a percentage of some chosen standard penetrant because no absolute system of measurement exists at this time.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.