Liquid penetrant testing (LPT Test) is one of the most widely used non-destructive testing methods. LPT test is based on capillarity or capillary attraction, where a liquid is able to flow into narrow spaces without the assistance of – or even in opposition to – external forces such as gravity. The materials processes and procedures used in liquid penetrant testing are designed to make the results of this capillary action visible and capable of interpretation. Liquid penetrant testing is an effective means of locating and determining the severity of surface discontinuities in materials, including those that are not visible to the naked eye.

Applus+ uses only quality products from the industry’s top suppliers, such as Sherwin and Magnaflux. We also have laboratories available that can provide testing on products shipped to these locations. Our procedures comply with ASNT and ASTM requirements. We have certified Level III technicians on staff to provide support and guidance as well as developing new procedures when required.
LPT can be used to locate and evaluate defects throughout an items life-cycle, such as:
  • Manufacturing defects open to the surface (such as cracks)
  • Lack of fusion
  • Porosity (gas pockets)
  • Cold shuts, inclusions
  • Hot tears
  • Gas holes
LPT can also detect in-service discontinuities such as:
  • Fatigue cracks
  • HIC
  • SCC
Early identification of in-service discontinuities means that outages can be planned and executed properly rather than as an emergency. This testing method is used in a variety of industries such as aerospace, food processing, power generation, oil/mining production and refining, maritime and more.
The complexity of modern industry and the demand for safer and more reliable products and equipment dictate the use of fabrication and testing procedures that will ensure maximum reliability. Liquid penetrant testing, when applied properly, can provide:
  • Increased product reliability
  • Improved production processes by identifying problems in a timely fashion so that they can be corrected
  • Reduced costs in terms of fewer returned items and less rework
  • Overall improved quality

NDT penetrant testing includes fluorescent dye penetrant, which is typically green and uses a white developer to draw the dye back to the surface from inside the discontinuities by 'wicking' or capillary action. The fluorescent penetrant is characterised by its ability to emit visible radiation when excited by UV-A light and may be used on a variety of materials. Fluorescent penetrant is typically more sensitive than visible dye and is ranked into 4 levels of sensitivity. It does, however, require special lighting conditions: NDT penetrant technicians must have UV-A lamps, blackout shades and power generators in the field. Fluorescent-dye testing is easily performed under laboratory conditions.

Visible dye penetrant is a method of NDT penetrant testing, which is typically red and uses a white developer to draw the dye back to the surface from inside the discontinuities by 'wicking' or capillary action. This is often referred to as the 'colour contrast' method. The colour contrast created in the dye penetration test is highly visible under natural light and may be used on a variety of materials. It is generally not as sensitive to very small discontinuities as the fluorescent penetrant testing method. However, it does not require special lighting conditions, therefore NDT technicians do not have to carry UV-A Lamps, blackout shades or power generators.

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