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Liquid Penetrant Testing (PT)

Assess Non-Porous Materials for Surface Discontinuities

What is liquid penetrant testing?

Liquid penetrant testing (PT) uses visible or fluorescent dyes to identify imperfections and discontinuities in any product fabricated from non-porous materials, particularly non-magnetic materials. In PT, the selected dye is applied to the surface being evaluated. After a pre-determined period, the excess dye is removed from the surface, and the surface is allowed to dry. A separate developing chemical is then applied to the surface, and its interaction with any remaining dye indicates the presence of a surface discontinuity. When fluorescent dyes are used, the inspection of the surface being evaluated is conducted under ultraviolet light. The use of visible dyes requires only normal (i.e., white) lighting for inspection.

What are the advantages of liquid penetrant testing?

Liquid penetrant testing is an inexpensive and highly portable NDT technique for detecting fine, tight discontinuities in pipes and fixtures made from a variety of non-porous materials, including non-ferromagnetic materials. It is also a simple method for identifying surface imperfections, since all discontinuities can be detected in a single operation regardless of the orientation of the surface being evaluated. However, liquid penetrant testing cannot be used on porous surfaces and is especially difficult to use on rough surfaces. In addition, tested surfaces must be free from all contaminants, such as oil, grease, rust and dirt, for liquid penetrant testing to produce useful and accurate results.

Why use TÜV SÜD for your liquid penetrant testing requirements?

TÜV SÜD Chemical, Oil and Gas is a leading provider of liquid penetrant inspection and testing services, and is also experienced in conducting most types of nondestructive testing methods and techniques. Our laboratories and testing facilities can perform quality inspections on almost any form of ferrous material, component or product assembly. In addition, we can provide NDT testing and analysis services at customer site locations and in the field to provide maximum flexibility. Finally, TÜV SÜD’s inspection professionals are certified to the American Society of Nondestructive Testing (ASNT) Level III and Level II requirements.

TÜV SÜD liquid penetrant testing and inspection services include:

  • Fluorescent penetrant inspection and testing - Fluorescent penetrant inspection and testing is especially effective for locating extremely small defects, when testing sensitivity is of paramount importance.
  • Visible dye penetrant inspection and testing - Visible dye penetrant inspection and testing is appropriate for identifying larger defects, as well as in piping and tubing with rough surfaces. It also offers important advantages in field applications where conditions are not optimal for the use of ultraviolet light.


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