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Dye Penetrant Inspection (DPI)

Dye Penetrant Inspection (DPI), also known as liquid penetrant inspection, is used to locate surface cracks and defects and the porosity of the material. It is easy to perform and easy to clean up, causing minimal disruption to productivity, but also only detects flaws on the surface of the material.

How Dye Penetrant Inspection Works


The test surface needs to be properly cleaned (free from debris, oil, water etc.) and dried in preparation for this method. We need to pre clean any contaminants to ensure nothing compromises the results and to ensure the dye can reach the defects for proper analysis.

Application of penetrant

The test surface then gets covered in a film of the penetrant liquid (either colour contrast dye, or fluorescent dye is used) to create a capillary action to penetrate any flaws. This process can take up to 30 minutes depending on the material being used. ‘Dwell time’ is allowed to ensure the liquid is soaked into any flaws. Once done, any excess penetrant is removed from the surface.

Application of developer

A developer is then added to the test surface to draw out the invisible flaws and now make them visible to the technician, sometimes under either normal white light, but also using ultra-violet black light depending on which dye was used.


The inspector will assess the results and record the observations.

DPI is a portable and efficient method so we can conduct testing on site at customer premises or offsite at our laboratories. It can be used across a variety of materials to quickly observe large and difficult surface areas. We offer a quick turnaround service with some locations available at a 24-hour response time. Contact us today to talk to our consultants.

Contact us today to discuss your welding requirements, call 0800 999 3834

Client Testimonials

Tech Inspections have shown professionalism and experience in assisting us to obtain welder approvals and weld procedures to both 15614 & ASME standards we would highly recommend them to other engineering companies who require assistance in these areas

Chris Ryder

We are proud to use Tech Inspections Ltd & welding services, for their professionalism and expertize in the training of our engineers to the standard of coded welding, and obtaining the necessary certificates.

Ray Duncan
Rating : 5

Tech Inspections have always shown professionalism and vast experience in the role as our Responsible Welding Co-ordinator. They have assisted with audits and given us appropriate guidance where required, whilst offering practical  hands-on training and advice whenever needed.