One method of reducing nonrelevant indications when eddy current testing ferromagnetic materials is to:

Using a direct current saturation coil to magnetically saturate the test specimen is an effective method for reducing nonrelevant indications when performing eddy current testing on ferromagnetic materials.

Ferromagnetic materials can produce a background magnetic field that can interfere with the eddy current signals being measured. By saturating the material, the magnetic properties are temporarily altered, reducing the magnetic permeability and minimizing the influence of any defects that are not of interest. This process helps to suppress the noise and irrelevant signals, allowing for more accurate detection and characterization of relevant flaws or features.

In this context, the other options do not address the specific challenge of nonrelevant indications due to the properties of ferromagnetic materials. Adjusting the pressure on hold-down rollers, modifying the gain control, or increasing the feed rate through the coil does not inherently reduce the magnetic interference caused by the material itself. Therefore, utilizing a direct current saturation coil is a targeted approach to enhance the clarity and reliability of the eddy current testing results.