# Liquid penetrant testing (PT / DPI)

> Liquid penetrant testing (PT, also dye penetrant inspection) applies a low-viscosity dye to a cleaned surface, lets it seep into surface-breaking flaws, removes the excess and uses a developer to draw the trapped dye back out as a visible indication.

- Source: https://amps.global/glossary/liquid-penetrant-testing/
- Type: Glossary
- Published: 2026-09-05
- Tags: NDT, penetrant testing, surface methods

## Key facts

- Works on any non-porous material: steels, stainless, aluminium, titanium, ceramics, some plastics
- Detects only flaws open to the surface; surface must be clean and free of paint
- Visible red dye (Type II) or fluorescent (Type I, inspected under UV-A); dwell times typically 5 to 30 minutes
- Codes: ASME BPVC Section V Article 6, ISO 3452 series, acceptance in ISO 23277

Also known as: PT, DPI, dye penetrant inspection, penetrant testing, LPI.

## The steps

Pre-clean, apply penetrant, wait the dwell time, remove the excess (water-washable, solvent-removable or post-emulsifiable systems), apply developer, wait, inspect under white or UV light, then post-clean. Temperature, dwell and removal technique are controlled by the procedure, and consumables are batch-tracked.

## Where it is used

Austenitic stainless steel and aluminium welds, machined parts, castings and anything where MPI cannot be used because the material is non-magnetic. It is inexpensive and portable but slower than MPI and sensitive to surface preparation.

## PT in AMPS

Consumable batch certificates and technician qualifications for PT are stored on the AMPS equipment and personnel pages. In AMPS, reports are produced from your own Microsoft Word templates through the template engine: job data such as the client, purchase order number, equipment serial numbers, location and dates is filled in automatically, an AI assistant can tidy the wording, the report can be signed in AMPS, and the finished Word file is saved in the job's report folder in your OneDrive, SharePoint or Google Drive.

## Related pages

- [Magnetic particle inspection (MT/MPI)](https://amps.global/glossary/magnetic-particle-inspection/)
- [Visual testing (VT)](https://amps.global/glossary/visual-testing/)
- [NDT reporting software](https://amps.global/solutions/ndt-reporting-software/)

## Sources

- [Dye penetrant inspection on Wikipedia](https://en.wikipedia.org/wiki/Dye_penetrant_inspection)
- [ASME Boiler and Pressure Vessel Code](https://www.asme.org/codes-standards/bpvc-standards)
- [ISO - International Organization for Standardization](https://www.iso.org/)