• Well-understood course

A Course to Better Understand Penetrant Testing

• Non-destructive testing

So called PT (Penetrant Testing) or LPT (Liquid Penetrant Testing), this method can be applied to the surface flaw inspection of almost every materials and products irrespective of their stuff. When the “penetrant”, vivid colored or fluorescent, is applied to the surface to be inspected, it penetrates into the surface breaking flaw and the flaw is filled with the penetrant. Then filled penetrant will be taken up from the flaw by the “developer” applied and will spread around the flaw on the surface.
Inspector easily finds the flaw observing the taken up penetrant on the surface.

Penetrant testing products

Procedure of PT

Procedure of PT is usually

 “Pre-cleaning” – “Penetrating” – “Penetrant Removal (Washing)” – “Developing” – “Observation” – “Post-cleaning”.

Penetrant flaw detection materials

Penetrant (P), Developer (D) and Remover (R) are usually used for PT.
There are two types of PT method, those are Dye penetrant PT using visible dye penetrant flaw detection material and Fluorescent PT using fluorescent penetrant flaw detection material.

（1）Water washable penetrant

Since almost penetrant is oil based, it is difficult to wash it off by water. The water washable penetrant is emulsifier (surface-active agent) added penetrant in order to be water washable.

（2）Solvent removable penetrant

This is oil based penetrant and the organic solvent is used for removing excess penetrant.

（3）Post emulsifiable penetrant

This penetrant does not contain emulsifier. After penetrating, the emulsifier is applied to remove excess penetrant for water washing.

（4）Developing agent

The main component of the developer is an inorganic fine powder. There are dry developers used as is, wet developers suspended in water, and quick-drying developers where the powder is suspended in a solvent and filled into aerosol cans.

Various types of penetrant fluids and their applications

The table below shows the very general application range of penetrant testing using various penetrant agents.

Various types of penetrant fluids and their applications

Items covered	Details of items	Water washable fluorescent penetrant	Post-emulsifiable fluorescent penetrant	Solvent-removable fluorescent penetrant	Water washable dye penetrant	Post-emulsifiable dye penetrant	Solvent-removable dye penetrant
Type and size of defect	Fine cracks, wide and shallow cracks		✓			✓
	Very narrow cracks such as fatigue cracks and grinding cracks	✓	✓
Test specimen	Small mass-produced parts, sharp corners such as screws and keyways	✓
	Test items with rough surfaces	✓		✓
	When detecting flaws in parts of large parts or structures		✓				✓
Environmental conditions	When it is not feasible to make the test area dark				✓	✓	✓
	When there is no water supply or electrical equipment						✓

Source: “Non-destructive Inspection Technology Series” compiled by the Japan Society for Non-Destructive Inspection
Penetrant Testing (1989), P-9, Table 1-1