Ketos Ring (ASTM E 1444-01)
Ketos ring is made of AISI 01 tool steel, hardness 90 to 95 HRB. It is a magnetic field indicator, but in reality determines the efficiency of the complete MP testing procedure. The sample is a 22 mm thick ring (∅ 127 mm) containing 12 holes (∅ 1.75 mm) drilled at different distance from the ring edge.
The magnetizing current passes through the center of the ring via a central conductor and the leakage fields appear, decreasing as the distance from the hole to the ring edge increases. When the magnetic suspension is applied on the ring, magnetic powder accumulates on the ring edge over the cylindrical holes, forming indication lines. The process corresponding to the recovery of recommended number of holes is accepted as optimal.