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Dye penetration test (PT)

The penetration test is one of the oldest non-destructive surface testing methods and is used in almost all industrial sectors. Like in magnetic particle testing, it immediately provides imaging and offers visual evidence of material separations such as cracks and pores, e.g. on welding joints and castings. In contrast to magnetic particle testing, the penetration test does not require the magnetization of the material and can, therefore, be basically used on all materials. The prerequisite, however, is that the test specimen does not have a porous or spongy surface or consist of a material that could be affected by the test medium. In addition, the area of the defects must be exposed to the surface and free of impurities.

Therefore, testing begins with a thorough cleaning of the test piece to ensure that the testing agent can sufficiently moisten the surface and penetrate the cracks for an optimum capillary effect. After a period that is dependent on the contact time and the material, the test piece is cleaned again, so that the intrusion agent remains only in the faulty areas. This is followed by the application of a developer, serving as a contrast agent to enhance the visibility of the defect. Usually, it is a white, fine-grained, limestone-based powder which in turn, uses the capillary effect, the pull the intrusion agent out of the cracks. Since the intrusion agent in the developer layer also increases its width a bit, the area of the defect will always be slightly larger than its actual dimensions.

Depending on the desired sensitivity, process reliability, surface texture, and existing infrastructure, one can choose between two different methods.
During the dye penetration test, a red colored solution serves as an intrusion agent, forming a clear contrast to the white developer.
The other method uses a fluorescent test agent. Due to the better luminosity of this intrusion agent, the fluorescent method shows clear advantages over the red-and-white test, as it allows to detect errors with higher sensitivity and reliability. However, the fluorescent process is only possible in dark environments under UV light.
Both methods are independent of the size of the part to be tested and can be applied to many component geometries and contours, if necessary even on a large scale. However, these applications require a certain amount of time. In addition, repeat tests are only possible to a limited extent, as dried-up test material residues are difficult to remove and hinder a re-penetration of the testing compound.

Scope:

  • Irrespective of the material and component geometry
  • Welded joints
  • Castings
  • Forgings
  • At NDT Westfalen or at the customer's site
  • Plain bearings, and bearing shells

Normative Verweisungen:

AD 2000-Merkblatt HP 5/3 2002-01
Anlage 1
Zerstörungsfreie Prüfung der Schweißverbindungen – Verfahrenstechnische Mindestanforderungen für die zerstörungsfreien Prüfverfahren – Kapitel 5: Eindringprüfung

DIN ISO 4386-3 1992-11 Gleitlager – Metallische Verbundgleitlager – Zerstörungsfreie Prüfung nach dem Eindringverfahren
DIN EN 571-1 1997-03 Zerstörungsfreie Prüfung – Eindringprüfung – Teil 1: Allgemeine Grundlagen (zurückgezogene Norm)
DIN EN ISO 3452-1 2013-09 Zerstörungsfreie Prüfung – Eindringprüfung – Teil 1: Allgemeine Grundlagen
DIN EN 1371-1 2012-02 Gießereiwesen – Eindringprüfung – Teil 1: Sand-, Schwerkraft-kokillen- und Niederdruckkokillengussstücke
DIN EN 1371-2 2013-06 Gießereiwesen – Eindringprüfung – Teil 2: Feingussstücke
DIN EN 10228-2 2012-12 Zerstörungsfreie Prüfung von Schmiedestücken aus Stahl – Teil 2: Eindringprüfung
DIN EN ISO 10893-4 2011-07 Zerstörungsfreie Prüfung von Stahlrohren – Teil 4: Eindringprüfung nahtloser und geschweißter Stahlrohre zum Nachweis von Oberflächenunvollkommenheiten
ASME-Code 2010 + 2011a Addenda / Section V / Article 6 Liquid Penetrant Examination

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