When should wet magnetic particle testing be preferred over dry testing?

Wet magnetic particle testing is preferred over dry testing primarily when fine defects are expected. This method utilizes a liquid suspension of magnetic particles, which allows for better dispersion and coverage on the surface being tested. The wet method provides a higher degree of sensitivity to smaller discontinuities because the particles can easily penetrate and settle into finer cracks or surface flaws, making them more visible during evaluation.

In conditions where small or fine defects are a concern, the ability of the wet method to reveal these issues is significantly enhanced compared to dry methods. The fluid properties of the wet suspension allow for uniform application and adherence to the tested surface, which is crucial when looking for subtle indicators of failure.

In contrast, while testing in a humid environment, on larger surface areas, or when using automated systems may have their own considerations, these factors do not directly influence the choice of wet over dry methods when fine defects are the primary concern. The sensitivity to small imperfections is the defining characteristic that makes wet magnetic particle testing the ideal choice when such defects are anticipated.