A handy guide for using dye penetrant inspection

Dye penetrant

There are many different forms of non destructive testing to choose from. One you will likely encounter is dye penetrant inspection (DPI). It is a useful method of spotting defects on the surface of various materials. However, it requires skill and experience to use the technique effectively. Therefore, it is better to call on a professional like Format NDT Ltd to do the testing.

What can you use it on?

One of the best things about DPI is it is suitable for use on various materials. As long as it is possible for the dye to penetrate the material, it can show up defects. For example, you can use it for metals like steel, copper, cast iron, magnesium and more. In addition though, it works on certain ceramics and plastics.


When you have an item you want to test, you must begin by preparing it. Cleaning is important to remove dirt or film. In some cases you will need to apply a cleaner or remover multiple times. You can test by using a small amount of penetrant. If it pulls back and forms droplets, there is still contaminants on the surface. Once the item is clean, you need to give it time to dry.

Using the penetrant

There are two ways to apply dye penetrant to an item; spraying or brushing. Whichever you choose, make sure there is good coverage but don’t use an excessive amount.

The most important thing here is to give the dye enough time to penetrate the material. In some cases you will only need to wait around ten minutes. However, with some materials you could need to wait as long as half an hour. You also need to wait longer if you are looking for really fine discontinuities.

After waiting a sufficient amount of time, you need to remove the penetrant from the surface. In many cases you will only need to wipe it away. Never flush the surface with cleaner or remover.

Using the developer

The next stage is to use the developer to highlight discontinuities. Here you simply spray the surface with the developer, creating a thin layer. Then you need to let it dry.

The results

Issues in the part will show up as red indications. If you see a line, whether solid or dotted, it indicated that there is a crack, lap, or other issues. The indication will grow if the issue is wide and deep.

You may also see dots or local colouring in different areas. These indicate that there are issues like porosity, leaks, or lack of bond. Again the indication will grow if the defect is extensive.

Call us for dye penetrant inspection

Format NDT Ltd is a company that is very competent at various forms of non-destructive testing. This includes DPI, UT, PMI, and more. So, clients can rely on us if they have concerns about various items, raw materials, and welds. Contact us today to arrange a service.