Intermittent line. The same defects that appear as straight lines may also appear as linear intermittent
indications This condition is caused by the defect being partially closed at the surface due to metal working such as
machining, forging, extruding, peening, grinding, etc
Rounded areas. Defects of this nature indicate porosity caused by gas holes or pin holes or a
generally porous metal depending on the extent of the indication. Deep crater cracks in welds frequently show up as
rounded indications, since there is a large amount of dye penetrant entrapped. The indications may appear rounded
because of the volume of penetrant entrapped, although the actual defects may be irregular in outline
(d) Small dots Defects of this nature result from a porous condition of the metal. Such indications may
denote small pin holes or excessively coarse grains in casting or may be caused by micro-shrinkage of certain cast
Diffuse or weak indications. Diffuse indications may be caused by a porous surface, insufficient
cleaning, incomplete removal of dye penetrant, or excess developer Weak indications extending over a wide area should
be viewed with suspicion. When this condition is encountered, the operation should be repeated.
Interpretation. Defect interpretation and types of defects are discussed In the following paragraphs.
Defect interpretation. Of the detectable defects, the most visible discontinuities or cracks are more
dangerous in that they readily promote eventual failure by inducing high stress concentrations in the surface of the part.
Wide, shallow defects that are rounded present less of a problem as far as contributing to the failure of a part. Sharp,
shallow defects are serious problems because they may grow in service to deep cracks, and especially so if they are
fatigue cracks The surface defect Is more dangerous than subsurface defects This is because, regardless of depth,
surface defects create a more serious stress condition. In the following paragraphs, developer dwell time and questions
to be answered for accurate interpretations are covered.
Developer dwell time. While many flaws can be detected almost instantaneously after the developer
has been applied or has dried, sufficient time should be allowed for all discontinuities to be revealed A good rule of
thumb is that the developer dwell time should not be less than one-half the minimum dwell time shown for the penetrant
in table 3-1.
Questions to be answered for accurate interpretations. Three basic questions must be answered to
facilitate proper interpretations of the flaw indications. Each question is listed below:
What type of defect would cause the indication?
What is the extent of the defect?
hat effect will this defect have on the anticipated service of the part?
The answers to the first two questions are prime responsibility of the inspector The answer to
the third question, unless specific acceptance criteria are specified, usually requires special
Types of defects. Defects can be divided into five basic types. Each is explained in the following
Fine, tight surface cracks. Such cracks may be shallow or deep, but their most significant
characteristic is their very small and tight surface opening. Deep cracks of this type, once well penetrated, may provide
a reservoir of penetrant, and, therefore, may be easier to show than shallow cracks.
Broad, open surface defects. Defects of this type may be shallow or relatively deep. Their significant
characteristic is their width which tends to permit penetrants to be removed when removal techniques are employed Care
must be taken to ensure this does not occur.
Porosity. Generally speaking, porosity defects are defects having a cavity below the surface which is
connected to the surface by minute channels These defects are typically found in aluminum and magnesium sand
Shrinkage. Micro- or sponge-shrinkage in magnesium castings (wheels) which is opened to the surface
by machining and etching is very hard to differentiate from cracks. Much care must be used in evaluating this type