PIE GAUGE

PIE GAUGE – FULL DESCRIPTION

A Pie Gauge (also called Pie-Shaped Gauge or Star Gauge) is a reference block used mainly in Magnetic Particle Inspection (MPI) and other NDT processes to check the direction, sensitivity, and effectiveness of magnetic fields on a part during inspection.

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✔ What is a Pie Gauge?

A Pie Gauge is a circular metal disk divided into six or more segments by radial copper or non-ferromagnetic inserts. These inserts create artificial defects that simulate cracks.

Its purpose is to show whether:

• The magnetic field is strong enough

• The direction of the field is correct

• The magnetic particles can reveal fine defects

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✔ Construction

• Shape: Circular disk

• Material: Ferromagnetic steel body

• Segments: Generally 6 wedges, separated by copper shims

• Diameter: Typically 1 – 1.5 inches

• Thickness: Approx. 0.1 to 0.2 inches

• Surface: Ground smooth

Each wedge creates a different crack orientation.

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✔ How It Works

1. Place the Pie Gauge on the test surface.

2. Apply magnetic field (circular, longitudinal, or yoke field).

3. Apply magnetic particles (dry or wet).

4. The segments perpendicular to the magnetic field show indications.

5. If indications appear clearly → field strength & direction are correct.

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✔ Why Use a Pie Gauge?

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✔ Advantages

• Quick and easy to use

• Works on uneven or slightly curved surfaces

• Shows multiple flaw orientations in one step

• Ideal for bench-type MPI machines, yokes, and coil systems

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✔ Limitations

• Not suitable for highly contoured surfaces

• Indications may vary slightly with different magnetizing techniques

• Not a substitute for actual calibration blocks (ASME, ASTM standards)

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✔ Applications

Widely used in:

• Magnetic particle inspection (wet bench, yoke, coil)

• Automotive parts testing

• Weld inspection

• Aerospace components

• Manufacturing quality checks