Liquid Penetrant Testing, also known as Dye Penetrant Inspection (DPI) or Liquid Penetrant Inspection (LPI), is one of the most popular and affordable NDT inspection methods. It is heavily used in identifying defects, flaws and surface-breakages in all kinds of non-porous materials like plastics, metals and ceramics. Indications of discontinuities can be identified regardless of the size, internal structure and configuration.

Liquid Penetrant Testing was first adopted in the railroad industry. After dipping in used oil, the cast railroad wheels were then dried off and coated with suspension of chalk in alcohol or powder chalk. When the wheels got dried, any oil stored in the cracks would bleed out into the chalk and be detected. Over the years Liquid Penetrant Inspection (LPI) has become the prime choice in the sector of NDT technology in Malaysia.

The entire process of Liquid Penetrant Testing consists of six different stages. These are as follows:

Stage 1 – Surface Preparation

Preparing the surface is one of the most important steps of Liquid Penetrant Testing. The surface must be cleaned properly and there should be no trace of grease, dirt, paint, rust, scale, and grease.

Stage 2 – Application of Penetrant

After the proper preparation of the surface, the penetrant material is applied. There are several ways penetrant can be applied such as brushing or spraying. A fixed amount of time should be given to allow the penetrant to permeate into cracks, fractures and laps.

Stage 3 – Removal of Excess Penetrant

Excess penetrant removal is considered to be the most crucial part. The access penetrant should be wiped off in different ways:

Clean the surface with dry lint-free rags Direct rinsing with water Cleaning with a solvent

Stage 4 – Developer Application

On the examined part, a light thin layer of developer is then applied to the sample to draw penetrant trapped in flaws back to the surface where it will be visible. The dwell time for developer is typically ten to sixteen minutes.

Stage 5 – Evaluate Indications

As the penetrant bleeds out from the defects and flaws, it offers a clear indication of a rejectable defect. Liquid Penetrant Testing gives results so fast and accurately that it is used in all the advanced NDT inspections in Malaysia.

Stage 6 – Post-inspection Cleaning

After the inspection and evaluation are completed, a thorough clean of the part surface is conducted to remove the developer from the parts that were found to be acceptable.

Liquid Penetrant Testing is versatile, cost-effective, and requires minimal training when compared to other advanced NDE inspection methods.