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Chemetall Non-Destructive Testing (NDT)

What is Non-Destructive Testing?

Non-Destructive Testing (often known by the acronym NDT) is a group of processes used to analyse a material, checking it for defects without causing damage to the item.

Two of the main technologies applicable to NDT are – Penetrant Testing (PT) and Magnetic Particle Testing (MT) – and through our value adding partnership with Chemetall, Silmid are able to supply a wide variety of chemicals and accessories to support both processes.

While the Penetrant Testing Process incorporates 3 product families: Penetrants, Cleaners/Removers and Developers to detect surface defects, the Magnetic Particle Inspection method can detect surface and near subsurface defects through a simpler one or two step process."

Penetrants are categorised into two main types based on the inspection process: red dye penetrants, which are visible against the white developer, and fluorescent penetrants, which reveal imperfections under ultraviolet (UV) light.

Fluorescent penetrants can be further classified according to how excess penetrant on the surface is removed. Method A involves water washable penetrants, which can be removed with water alone, while Method C requires solvent-based cleaners for removal. Method D, (post emulsifiable, hydrophilic) uses an emulsifier to remove the penetrant chemical.

Chemetall has developed newer penetrants based on NPE-free (Nonylphenolethoxylate) technology, characterised by low odour, low toxicity, and minimal environmental impact. The choice of penetrant impacts the type of developer and cleaner/remover needed for the process.

NDT Penetrants

In the NDT process, the cleaner is used to remove excess penetrant from the component, and is sometimes referred to as a remover. There are a number of different cleaning processes available, and this depends on the characteristics of the penetrant used. While Ardrox NDT cleaners are mainly used for the removal of both visible red dye and fluorescent penetrants, they can also be used as a solvent pre-cleaner prior to the penetrant application for the removal of oil and grease. 

NDT Cleaners

The developer is the final chemical used in the process, and this identifies areas where the penetrant has remained, and therefore reveals any defects in the material or component under testing. A brief overview of the process of penetrant testing, including the differences between Method A, Method C and Method D, may be accessed at this link.

NDT Developers

Magnetic Particle Inspection, like penetrant testing, employs two main methods for detecting imperfections: black inks visible against white contrast paints and fluorescent inks revealing defects under UV light. Unlike penetrant testing, magnetic testing doesn't use the penetrant, cleaner/remover, and developer method, but instead employs a one-part or two-part method.

Ardrox black magnetic inks, designed for high sensitivity inspection, ensure reliable detection of defects in ferromagnetic materials when used with Ardrox white contrast paints. These inks contain black iron oxide in a high flash, low aromatic petroleum distillate with a solid content of 1.2 to 2.4 ml/100 ml.

Ardrox fluorescent magnetic inks detect defects in ferromagnetic materials under UV(A) light and are available as powder, ready-for-use fluid, or water-based fluid concentrate.

Magnetic NDT