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PT Liquid Penetrant Inspection ; It is aimed to make the discontinuities visible on the surface by using a special paint type with very high penetrating properties.
Penetrant (interference) inspection – Relates to the phenomenon of a rising or escalating liquid as it is confined to a small opening due to the characteristics of capillary action or the surface wetting properties of the liquid. Penetrant inspection is used to find surface-open discontinuities on relatively smooth, non-porous surfaces. Types of defects that can be found in penetrant inspection: cracks and porosity.
The basic procedure to perform a liquid penetrant inspection consists of the following:
Rolled Products: Identifies penetrant anomalies (cracks, seams or laminations)
Castings: Cast discontinuities, hot tears, porosity, air holes or shrinkage
Tattoos: Descriptive cracks, thrusts or external crevices
Welds: To identify cracks, porosity, combustion trough, cold thrust, lack of fusion or insufficient penetration
There are two basic types of Penetrants available: Fluorescent or Visible. Within each method, there are many methods including water-washable, post-emulsifiable-lipophilic, solvent-removable, and post-emulsifiable-extreme hydrophilic methods. The type and penetrant method is chosen based on sensitivity level 1 to 4 and depends on site conditions and other variables.
There are six basic steps required by penetrant inspection.
Pre-Cleaning: Parts must be free from dirt, grease, rust, scales, oil or grease.
Application of Penetrant Material: Penetrant material can be applied by brushing, spraying, dipping / dipping or flowing onto the material.
Dwell Time / Penetrant Removal: The solution needs to be allowed to wait on the surface to allow the penetrant to cover any imperfections present. Waiting times vary according to panatrant type, temperature and material types and finishing processes. The removal technique depends on the type of penetrant used, ie whether it is Solvent Cleanable, Water Washable or Post-Emulsifiable.
Developer Implementation
Inspection / Evaluation: In almost all cases, the inspector evaluates penetrant indications against specified acceptance/rejection criteria and attempts to identify the source of the indication.
Final Cleaning: The final step is to clean all penetrant processing materials from the component.
The main advantages of penetrant inspection are:
-Relatively easy to use
-Used on a wide variety of material types
-Large volumes of parts/materials or large areas can be inspected quickly and at low cost
-Parts with complex geometries can be easily inspected
-Indications are produced directly on the part providing a visual display of the anomaly.
-The aerosol spray can makes the equipment highly portable
