Hot Rolled Steel Bar Testing for Sub-Surface and Internal Defects

Depends on the required depth of detection and the retentivity of the material. Magnetic particle would likely be the cheapest and fastest for surface and subsurface 'discontinuities' no more than 1/16 inch or 1.5mm below the surface.

Ultrasound would be useful in straight beam with radially ground wear shoes up to about 6 inches / 150mm if you are looking just under the surface. The more distance displayed on the screen, the more detail is lost. Shear wave with appropriately ground wear shoes at 60 degrees would be good in diameters over 75mm.

Eddy current can be made to work but is expensive because you have to filter out / eliminate the local changes in permeability and retentivity within the bar.

Use the manufacturers guide to find local suppliers.

We agree on Ultrasonics . I don't see Eddy current nor Mag particle as appropriate methods for "subsurface nor internal discontinuities."

Foerster or Dr Forster is a good name; also Sonatest and Krautkramer.

These methods are not necessarily technologically appropriate if you are trying to use on leaded resulfurized materials due to the high non metallic's volume fraction and frequency.

milo

Agreed. Ultrasound works well only if there is an actual interface for the sound waves to reflect off of. Partial backreflections and / or loss of backwall backreflection techniques do not make for good economics due to the inherent increase in interpretation and verification time.

Magnetic particle only tells you that there is leakage in the magnetic field and is non-specific as to its cause, and is limited in its depth of detection.

Eddy current has a well established reputation in non-ferrous applications, and has been experimented with as a source for ultrasound pulse generation in ferrous pipe and tube, though I'm unsure of the final outcome.