CEMP-E
TI 809-26
1 March 2000
2. PENETRANT TESTING (PT).
a. Method Description. Penetrant testing, also called dye penetrant or liquid penetrant testing, is the
use of a liquid penetrating dye to detect discontinuities at the surface of a weld or base metal. The
penetrant is applied to the surface, allowed to remain on the surface for a specified dwell time to
penetrate cracks, pores, or other surface-breaking discontinuities, and then is carefully removed. A
developer is then applied to the surface, which draws the penetrant out of the discontinuities. This leaves
a visible contrasting indication in the developer, which is then removed for closer visual examination of
the area providing indications. One method of penetrant testing uses a visible dye, usually red, which
contrasts with the developer, usually white. The second method uses a flourescent dye, visible under
ultraviolet light. Flourescent methods are usually more sensitive, but require a darkened area for testing.
b. Advantages and Disadvantages.
(1) Penetrant testing is relatively economical compared to ultrasonic testing, and especially
economical when compared to radiographic testing.
(2) Testing materials are small, portable, and inexpensive, with no specialized equipment required
unless an ultraviolet light is used.
(3) A relatively short period of training is necessary for technicians who will be performing PT.
(4) PT can be performed relatively quickly, depending upon the penetrant used and the required
dwell time.
(4) A disadvantage with some penetrants and developers is the safe handling and disposal of used
liquids and cleaning rags.
(5) Cleaning after inspection to remove residual penetrant and developer prior to weld repairs or
the application of coating systems can sometime be difficult and time-consuming.
(6) Rough surface conditions, and irregular profile conditions such as undercut and overlap, can
sometimes provide false indications of weld toe cracks when cleaning is not thoroughly performed. Weld
spatter can also make surface removal of the penetrant more difficult.
(7) PT cannot be performed when the surface remains hot, unless special high-temperature PT
materials are used, so waiting time is sometimes necessary with PT that would not be required with
magnetic particle testing.
(8) Existing coatings should be removed prior to PT because the coating may bridge narrow
cracks, preventing the entry of the penetrant.
(9) PT is especially effective with small surface-breaking cracks, such as toe cracks, and also
surface-breaking piping porosity, crater cracks, laminations along exposed edges and joint preparations,
and other surface discontinuities.
(10 PT is ineffective for any discontinuity below the surface, such as buried cracks, slag inclusions,
lack of fusion, or incomplete penetration. See Table D-2.
D-3
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