Liquid Penetrant Testing of Materials

Liquid Penetrant Testing of Materials using Manipulator and Rover Robots

Mechanized liquid or dye penetrant testing (PT) is a non-destructive material testing method in which the capillary forces of find surface cracks or pores are used to make them visible. DEKRA has developed an innovative manipulator able to inspect areas that are not possible to inspect by ultrasonic testing due to high levels of attenuation, geometry or accessibility. The common inspected objects are:
  • T-joint pieces
  • Valve connection welds
  • Piping
Objects like these can be sensitive for IGSCC (Inter Granular Stress Crack Corrosion) and / or thermal fatigue, which makes them highly prioritized for inspection. The materials in T-joints and valve housing are often austenitic castings, which can be impossible to inspect with ultrasonic, due to high attenuation. Therefore, DEKRA developed this new innovative solution for their clients.

About Liquid Penetrant Testing of Materials

Liquid or dye penetrant testing (PT) is based on the infiltration of liquid penetrant into open surface discontinuities. Penetrant testing is not applicable on high porous materials. The dye penetrant method is used to determine surface defects, including surface cracks, pores, lack of fusion and inter-granular corrosion. The common materials for T-joints and valve housings are SS2333 or SA403, these materials can suffer from thermal stress (e.g. a leaking valve). The Octopus system can reach these areas, in pipe diameters from DN 100 – DN 450. In the nuclear power plant the following systems are affected by this kind of wear.
  • Feed Water System / Aux Feed Water
  • Shut down Cooling System
  • Emergency Cooling System
  • Cleaning System
The Octopus system was already successfully used in two Boiling Water Reactors (BWR). The Octopus is equipped with several arms to adjust itself inside the pipe, the system also possesses several cameras beside the PT-nozzle for a better orientation. The system can also be guided by a modular track, which ensures that the crawler arrives even most difficult geometries. After pre-cleaning, the penetrant is applied to the surface area of the test piece. This penetrates into fine cracks or pores through the capillary effect. After carefully removing the rest of the test medium from the surface, a developer is applied to pull the dye penetrant out of the pores and cracks, creating indications, which can then be evaluated.
The dye penetrant test is usually performed with a red dye penetrant, which can be done in daylight. Whereas the fluorescent dye penetrant test uses a fluorescent test agent, which is much easier to evaluate in darkness or under UV light. The Octopus inspection system is qualified for Internally surface breaking defects with sizes from: 3.5mm x 0.5mm x 4µm (Length x Depth x Width).
DEKRA’s penetrant testing specialists are certified according to ISO 9712, ENIQ and we meet the following testing standards: ISO 3452-1:2013, PNAE G-7-018-89, GOST 18442-80.
Our range of mechanized Liquid Penetrant Testing solutions includes:
  • Octopus for mechanized dye penetrant testing using an internal pipe penetrant testing system