Penetrant testing, also known as dye penetrant inspection, is a non-destructive testing (NDT) technique used to detect surface-breaking defects such as cracks, porosity, laps, and seams on the surface of solid materials.

Penetrant testing works by applying a liquid dye penetrant to the surface of a material. The penetrant flows into any surface defects and is allowed to soak for a specified time. Excess penetrant is then removed, and a developer is applied, which draws the penetrant out of the defects and makes them visible.

Penetrant testing is a relatively simple and cost-effective method for detecting surface defects on a wide range of materials. It can be used on a variety of surface geometries, including complex shapes, and is capable of detecting very small defects.

Penetrant testing is only capable of detecting surface-breaking defects and is not effective for detecting subsurface defects. It also requires a clean and dry surface to be effective and may not be suitable for use on certain materials, such as porous materials.

There are three types of penetrant testing: Type I (Fluorescent), Type II (Visible), and Type III (Visible & Fluorescent). Each type uses a different type of penetrant and developer and has different application and removal procedures.

Penetrant testing is commonly used in industries such as aerospace, automotive, and manufacturing to detect surface defects in materials such as metal, plastic, and ceramic components. It is also used in the inspection of welds, castings, and forgings.

The typical sensitivity of a visible penetrant is Level 2; as dictated by the EN-ISO 3452-2 standard.

The typical sensitivity classes of a fluorescent penetrant are Level 0.5, Level 1, Level 2, Level 3 & Level 4; as dictated by the EN-ISO 3452-2 standard.

Type testing When seeking approval for a penetrant in accordance with material specifications such as AMS 2644 and EN ISO 3452-2, the penetrant manufacturer is responsible for getting the product Type tested. This involves sending a sample of the penetrant off to an independent laboratory for verification against a comprehensive set of standard tests. Batch testing During the routine manufacture of a penetrant and its associated consumable products, it is a requirement under material specifications such as AMS 2644 and EN ISO 3452-2 to carry out a number of batch-specific tests, including flash point, viscosity and fluorescent brightness (Type 1 systems only). These specifications also specify the sampling rate and dictate that we should publish these results on a certificate of conformance. For MR Chemie penetrants, cleaners, developers and emulsifiers, these certificates of conformance are referred to as Batch Inspection Certificates (or) Test Certificates In-use testing When a penetrant is being used, there are a set of in-use tests that need to be carried out by the customer. ASTM E1417 has established standards for performance checks for in-use materials.

The sensitivity of a penetrant is not just simply its ability to find different sized cracks/defects; it also relates to aspects such as the type of surface finish. For example, on a rough casting you would not want to use a high sensitivity penetrant as it would be too difficult to remove, and you would see a lot of penetrant in the background. Conversely, on a highly polished part you would not want to use a low sensitivity penetrant as the risk of over washing and removing penetrant from the cracks/defects would be high. The sensitivity of a penetrant is ultimately determined by the independent laboratories that assess the penetrant in accordance with material specifications such as AMS 2644 and EN-ISO 3452-2.

MR Chemie offers a range of Eco-Line products like MR67DL, MR313DL in aerosols for use where flammability is an issue. These products are equipped with non-flammable carrier media and propellents. Alternatively, products in bulk can also be opted for.

Minimum penetration time is 2 to 5 minutes, with 10 minutes being adequate for most situations. Lower temperatures will thicken the penetrant and require longer penetration times. Higher temperatures will lower the viscosity of penetrant and requires much lesser penetration time. Please note that this information is for guidance purposes only. With any penetrant – fluorescent or visible – the penetrant dwell time will be dependent on the type of material (metals, plastics, ceramics, castings, forgings, rolled materials, welds, etc) as well as temperature. We recommends that prior testing is carried out when inspecting different material types, or when inspecting at different temperatures, to establish the most appropriate dwell time.

Whilst MR Chemie penetrants can be used on ceramic, plastic and/or composite materials, the dyes within them can cause staining. It is also possible that the penetrant will soften or even dissolve the base material of some plastics. We recommend testing prior to use for compatibility.

Over time, penetrant residue can build up within test panels, which will affect their performance. Also, in a hard water area, it is possible to get salt and limescale deposits within the panels. Our recommendations on cleaning are: Pre-soak the panels in hot water (ca. 50-70ºC) for a few minutes. This will soften any residual penetrant. Use a polar solvent such as acetone, methyl ethyl ketone (MEK) or isopropanol in combination with an ultrasonic bath. This way you get a combination of the solvent action and also a vibrational effect to release any residues. Prior to doing this, we recommend that you carry out a workplace risk assessment to minimise or eliminate any risk to an operator. If you are in a hard water area, you could also use a weak solution of a limescale remover. Avoid using strong acids or prolonged contact with a limescale remover as this will cause damage to the chrome plating. Ensure that all traces of limescale remover are removed by rinsing with deionised water. Ensure that the panels are fully dried before reusing.

The material can be disposed off according to the local regulations. Further details are available in our MSDS.

A dual penetrant is a Type 3 penetrant that is both visible under daylight and fluorescent under UV light.

MR® Chemie offers various Type 3 penetrants which are highly sensitive. This features an advantage where cracks can be made visible under UV light and tends to be much more sensitive than the visible light indications.

MR Chemie has always worked towards making cleaner and greener products and coin it as ECOLINE. Typically, Eco-Line penetrants do not contain any hazardous ingredients and are free from all the GHS labels making it a safer product for both humans and the environment.

While MR Chemie Dual penetrants offer a good sensitivity under UV light, However, we do not recommend switching a fluorescent penetrant with a Dual type penetrant.

MR Chemie offers a wide range of penetrants based on the Carrier Media, Aerosol category, Approvals and others.
Carrier Media

1. Generation 1 - Oil based
2. Generation 2 - Glycol based
3. Generation 3 - Solvent-free medium

Aerosol

1. Flammable
2. Non-Flammable

Approvals

1. Aerospace
2. Nuclear Power
3. General Industry
4. Others

While MR Chemie Dual penetrants offer a good sensitivity under UV light, However, we do not recommend switching a fluorescent penetrant with a Dual type penetrant.