Liquid penetrant testing (PT)

This is a method applied to detect discontinuities unfolding on the surface of any material, of any industrial product made from non-porous materials. This method is commonly used to test non-magnetic materials. In this method, the liquid penetrant is sprayed onto the surface of the product for a certain period of time, after which the excess penetrant is cleaned off the surface. The surface is then dried and it is covered with a coating. The permeable substances located in the discontinuity will be reabsorbed by the present material to form a visible indicator, thereby revealing the location and nature of the discontinuity. This whole process is illustrated in Figure 4.2.

The liquid penetrants used in this method are the visible dye penetrant and the fluorescent penetrant. The visible dye penetrant test is done under normal white light while the fluorescent penetrant test is done under black light (ultraviolet or ultraviolet light) in the area. dark. Liquid penetration testing techniques are classified according to the residual penetrant cleaning method. Penetration agents can: (1) wash off with water, (2) emulsify, that is: emulsifier is added to the excess penetrant on the surface of the test object to make it washable with water. , (3) solvent cleaning, that is: the solvent will dissolve the residual penetrant so that it can be removed from the surface of the test object. To increase sensitivity and reduce cost, the liquid penetrant testing processes are listed as follows:

(1) Emulsifying fluorescent penetrant.

(2) Fluorescent penetrant washes with solvent.

(3) Water-washable fluorescent penetrant

(4) Visible dye penetrant is washed with solvent.

(5) Visible dye penetrant is washed with water.

Figure 4.2 – Steps taken during liquid penetrant testing.


Some advantages of liquid penetrant testing:

(1) Very sensitive to surface defects, if used appropriately.

(2) The equipment and supplies used in this method are relatively inexpensive.

(3) The liquid seepage process is relatively simple and does not cause problems.

(4) The shape of the test piece is not important.

Some limitations of the liquid penetrant test method:

(1) Defects shall open on the surface.

(2) The test material must be non-porous.

(3) The liquid penetrant inspection process is quite dirty, and the test cost is relatively high.

(4) In this method the results do not hold for long.

Video clip for reference: