What is the primary advantage of using magnetic particle testing (MT)?

The primary advantage of using magnetic particle testing (MT) lies in its effectiveness in detecting surface and near-surface defects specifically in ferromagnetic materials. This method capitalizes on the magnetic properties of these materials, allowing for the identification of flaws such as cracks, seams, and inclusions that may not be visible to the naked eye. The process involves magnetizing the material and applying ferromagnetic particles, which gather around any discontinuities, making them detectable.

This characteristic of MT makes it particularly valuable in industries where structural integrity is critical, such as aerospace, automotive, and construction. It provides quick results and allows for real-time evaluation of defects, which can be crucial for ensuring safety and compliance with standards.

The other options, while mentioning aspects related to testing in general, do not highlight the specific strengths of magnetic particle testing as accurately as the correct answer does. For instance, subsurface defect detection is more suited to other methods like ultrasonic testing, and permanent records are often associated with methods such as radiographic testing. Non-destructive testing and minimal equipment usage are benefits of various techniques, but they do not pinpoint why MT is primarily favored for detecting flaws in ferromagnetic materials.