Magnetic Yokes – FAQs
Magnetic yokes are a versatile, portable way to perform magnetic particle inspection in the field and on hard-to-reach areas. These FAQs cover when to use a yoke, how to verify performance, and how AC versus DC magnetization affects the types of indications you can see.
Q1: What is a yoke and when would you use one?
A yoke is a portable magnetizing device used for spot inspections or hard-to-access areas during magnetic particle inspection. It is especially useful on large components, welds, and locations where using a bench unit or coil is not practical.
Q2: How can I check the performance of my yoke?
You can check yoke performance with a simple lift test using a certified weight, or by measuring the magnetizing field strength with an appropriate instrument. Regular performance checks help confirm that the yoke continues to meet applicable code and procedure requirements.
Q3: What is the difference between using AC and DC when using a yoke?
AC magnetization is generally used to reveal surface-breaking indications because the magnetic field is concentrated near the surface. DC or half-wave rectified DC penetrates deeper into the part, making it more suitable for detecting some subsurface flaws, but it can also result in higher levels of residual magnetism.
Q4: What is the correct orientation for a yoke when looking for defects?
For best sensitivity, the yoke poles should be positioned approximately perpendicular to the expected direction of any cracks or discontinuities. This orientation forces the magnetic flux lines to cross potential defects, helping magnetic particles gather and form clear indications.