• FerroChem NDT Systems Private Limited

Pie-Field Indicator

In magnetic particle inspection (MPI), the ability of defect detection depends on, amongst other factors, the direction of the magnetic field that is induced in the part. In MPI for powder particles to form indications at the location of the defects, the direction of the induced magnetic field should be at 90º± 45º to the length of the defect. Induction of magnetic field in a favourable direction in the part therefore becomes vital. Since the location and direction of defects in a part are not known, the parts are magnetized in minimum two directions at right angles to each other. ‘Pie Gauge’ is a simple and effective gadget, which helps in identifying direction of the induced magnetic field in a part under test. This is made from eight flat triangular pieces of low carbon steel jointed together to form an octagon. One side of the octagon is plated with copper while the other side is left as it is. A non-magnetic handle is provided for holding. Direction of induced magnetic field in a part is detected with the help of pie gauge as follows: Pie gauge is placed on the part, with copper side up, at the location where the direction of the induced magnetic field is to be affirmed. The part is then processed for crack detection as per standard magnetic particle testing procedure. Direction of the induced magnetic field is established as perpendicular to the indications formed on the copper side of the pie gauge. ASTM Standard Specification E 1444-09 on ‘Standard Practice for Magnetic Particle Testing’ recommends use of pie gauge. FerroChem manufactures and supplies pie gauge as per the requirements of ASTM Standard Specification.