W-PG Pie Gauge

The Pie Gauge is used to measure Magnetic Field Direction, and unfortunately it is often

used to ensure the presents of an adequate magnetic field. Outside North America, the

Pie Gauge is often referred to as an ASME Magnetic Field Indicator. The design dates to

the earliest versions of industry specifications, and is still outlined in ASME, ASTM, and EN

versions. The Pie Gauge is very robust, but due to the size (thickness), it is not that effective

as a representative of artificial defects. A QQI (CX type) is far superior to a Pie Gauge and

even a Castrol Strip can be used to measure field direction.

The overall thickness of the octagon disk is approximately 3mm (0.125”), with it’s copper

backing plate being almost a third of its thickness. While the magnetic side (low carbon

steel) is placed on the workpiece, it means the separation of the 8 pie segments are well

off the workpiece. Where a QQI or Castrol Strip is flexible and virtually conforms to the

workpiece, the field on a Pie Gauge must extend though its  copper backing. With all

Flux Sharing Devices, intimate contact with the surface is absolutely necessary. It is recognized

that Pie Gauges are most suited to Dry Method Inspection, and to be used on fairly flat surfaces.

Western Instruments Pie Gauges (W-PG) are supplied with a vinyl storage sheath and a

Certificate of Conformance. The W-PG can be re-certified, when necessary, by an authorized

agency, however this is only required when there are signs of physical damage.