The inspection area and the hands and clothing of the inspector SHALL be clean and free of extraneous penetrant
material. Non-relevant indications may be formed when parts contact extraneous penetrants. In addition, the
fluorescence from the penetrant will raise the ambient light level, thus reducing sensitivity.
Inspection, Interpretation and Evaluation.
Inspection is the process of detecting an indication. Interpretation is the process of determining whether an indication
is relevant, non-relevant or false. Evaluation involves assessing a relevant indication to determine its cause and type (if
it is a defect or flaw) and reporting its category, location, and approximate size.
A distinction must be made between relevant indications, non-relevant indications, discontinuities, and flaws or defects.
A relevant indication is one resulting from a discontinuity. Non-relevant indications can result from an intentional
change in part shape such as threads or small radii, or may be caused by improper or careless processing procedures.
Non-relevant indications are of concern because they may mask or cover a true discontinuity indication. A
discontinuity is an unintentional change in part surface or physical condition such as tooling marks, scratches or
gouges, cracks, seams, laps, and porosity. A discontinuity may or may not affect the serviceability of the part. If the
discontinuity reduces or interferes with the serviceability, it is classified as a flaw or defect. It is possible for a part to
contain multiple indications that may be any combination of non-relevant discontinuities not affecting serviceability,
and defects requiring corrective action.
The decision to classify the porosity as acceptable is based on the evaluation of the porosity size and density versus the
accept/reject criteria of the specification for the inspection of the part. NDI personnel must be capable of interpreting
indications and evaluating discontinuities in accordance with the specifications and procedures for the inspection
process in use. They are not normally responsible for disposition decisions on flawed parts, but they must report the
type, location and approximate size of any flaws present. Acceptance, rework or repair, and rejection limits are
contained in the repair manuals and are the responsibility of the applicable work center.
Classification of Discontinuities.
There are a number of ways of classifying discontinuities, such as appearance of the indication, its cause, material, and
service conditions. The method of classification used depends upon the test method, the use of the parts, and the
original designer. Many of the NDI application manuals, which are usually prepared by the original manufacturer,
contain several discontinuity classifications in the same manual.
Appearance of Indications.
The appearance of penetrant indications is influenced by the size and shape of the discontinuity, the type of penetrant
system and processing technique, and the type of developer and the length of developer dwell. These factors hold true
for all types and forms of material and apply to both large and small parts.
Continuous Linear Indications.
Linear penetrant indications are caused by discontinuities such as cracks, seams, or laps. The width and brightness of
the indication depend upon the volume of entrapped penetrant. The indication may be fairly straight or may have some
curvature depending on how the discontinuity was formed. Also, the edges may be jagged or smooth, where the
discontinuity meets the part surface. Figure 2-32a shows the surface appearance and a cross-section through a linear
discontinuity with a large reservoir. Figure 2-32b is a narrow or tight linear discontinuity.
Intermittent Linear Indications.
Intermittent linear indications are caused by the same discontinuities that form continuous linear indications. However,
either a subsequent process or service use has partially sealed the surface edges. This occurs in forging laps or where
the part has been subjected to a mechanical smearing action. A sub-surface discontinuity that does intermittently