Penetrant testing (PT) is one of the most popular conventional non-destructive testing methods. Penetrant testing can be used on many types of material but is usually used on non-ferrous materials.
The main reason for this is the method being very simple, effective and highly suitable for detecting very fine surface discontinuities. The defects must, however, have an open connection to the surface. This is a prerequisite for using this technique to diagnose this kind of defect.
THE PROCESS OF PENETRANT TESTING
The penetrant testing process consists of four parts:
- Before a penetrant can be applied, we need to clean the surface so the penetrant fluid works sufficiently into any discontinuities.
- We then cover the dry surface to be tested with penetrant fluid. Capillary action draws the dye into the defect areas on the surface of the material.
- After a predetermined drawing-in time, the surface is cleared of excess penetrant using water or a cleaner.
- Finally, we apply a layer of lime to draw the penetrant out of the discontinuities. This process is called a ‘bleeding’ and is clearly observable. Other combinations start to form depending on the type of penetrant and the dye colouring. Fluorescent penetrant (in ultraviolet light) tends to be more sensitive than visible dye (in visible light). The penetrant test is therefore classified in five sensitivity levels ranging from level 0.5 to level 4.
AT WHICH PHASE DO WE APPLY PENETRANT TESTING?
Penetrant testing (PT) is used in each phase of the life cycle of a product:
- forged parts
- ferrous and non-ferrous materials
ADVANTAGES AND DISADVANTAGES OF PENETRANT TESTING
- quick testing method for large surfaces or a large number of objects
- a highly suitable method for detecting small surface defects
- immediate interpretation of indications
- method can be deployed with relatively cheap working equipment
- this method can only be used on non-porous materials
- slower inspection method due to drawing-in times
- this method only detects surface defects
- thorough cleaning of the surface is required before testing begins
- the finish or roughness of a particular material can affect test results
IN WHICH INDUSTRY DO WE USE PENETRANT TESTING?
Industries in which penetrant testing is used:
- construction steel
- oil, gas and wind industry, onshore and offshore
- shipping industry