What are the two basic types of penetrant dyes used in inspection?

The two basic types of penetrant dyes used in inspection are visible and fluorescent.

Visible penetrant dyes are used in non-destructive testing (NDT) to detect surface-breaking defects in materials. They work by being applied to the surface of the test object and allowed to penetrate any cracks or voids. After a specified dwell time, excess penetrant is removed from the surface, and a developer is applied to draw out the penetrant from the defects, making them visible to the naked eye. This method is straightforward and easy to use, which is why it is commonly utilized in various industries.

Fluorescent penetrant dyes operate on a similar principle but are specifically designed to fluoresce when exposed to ultraviolet (UV) light. This characteristic enhances the visibility of defects in low-light conditions, allowing for greater sensitivity and detection of smaller flaws that might not be as easily seen with visible dyes. The contrast created by the fluorescent dye against a black or dark background under UV light provides an excellent means of identifying defects in materials.

Understanding the difference between these two types of dyes is crucial for effective inspection procedures and for ensuring the integrity of materials and structures in various applications.