Note
Minimum surface temperature, at hot inspection, must
be > Curie-temp (approx. 765 C° for steel).
Crack detection using eddy current technique is based
on the fact that cracks disturb the eddy current
distribution in the surface of the test object.
It is therefore easy to understand that other
electrical conductive phenomena could also disturb
the eddy current distribution and consequently disturb the measurment.
Scales on the slag surface is in the "hot stage" only
elecrical conductive to a minor extent.
During certain casting conditions, larger volumes
of scales can be produced with local areas of low
temperature scales ( below Curie-temperature).
In this status however, the scales have developed a magnetic
permeability which can disturb the measurement very much.
Therefor, in DELTATEST hot-slab-applications,
a high pressure water descaling unit always must be used.
The descaling unit is not included in the DELTATEST system.