Dye Penetrant Testing (PT)
Dye Penetrant Testing (known as DPI, PT or Dye Pen) is sometimes specified in addition to visual examination on welds.
How Does PT Weld Inspection Work?
Firstly, the surface to be inspected is cleaned thoroughly to remove all traces of dirt and grease.
A brightly coloured or fluorescent liquid is then applied liberally to the component surface and allowed to penetrate any surface-breaking cracks or cavities.
The time specified for the liquid to soak into the material’s surface is normally about 20 minutes. After soaking, the excess liquid penetrant is wiped from the surface and a developer applied.
The developer is usually a dry white powder, which draws penetrant out of any cracks by reverse capillary action to produce indications on the surface. These (coloured) indications are broader than the actual flaw and are therefore more easily visible. Dye penetration testing can be performed in all positions and does not need to be the gravity position.
There are several different liquid penetrant systems used in industry. Fluorescent penetrants are normally used when the maximum flaw sensitivity is required. However, these penetrants must be viewed under darkened conditions with a UV lamp, As one of the top DPI testing companies in the UK, Surecheck can offer this method of non destructive testing using dye penetrant at our premises in Cannock.
The more commonly used systems are solvent removable, or water washable, red dye systems, which typically comprise three aerosol cans – cleaning fluid, penetrant and developer. These systems are often used to check weld quality during fabrication. These methods can be offered on or off site.
Important Considerations While Using a DPI Test
Despite DPI testing being one of the popular methods, liquid penetrant testing is often misused and spurious results can be obtained which are mainly down to operator error during PT weld inspection.
Some of the most common mistakes are: Test surfaces are not cleaned adequately, the contact time between the penetrant and the test surface is too short, or the excess penetrant is removed carelessly (i.e. from flaws as well as from the test surface). For these reasons, it is important that anyone carrying out liquid penetrant inspections are properly trained and qualified (for example, in accordance with the British Institute of Non-Destructive Testing’s PCN certification scheme or equivalent schemes such as those operated by CSWIP and ASNT) and work for reputable NDT companies in the UK.
At SureCheck, you can be confident in our diligent staff, high-quality equipment, and years of experience to conduct DPI testing efficiently. Get in touch for a quote or to find out more.