Description
The ASME pie gauge is a disk of highly permeable material divided into four, six, or eight sections by nonferromagnetic material. The divisions are artificial defects that radiate out in different directions from the centre.
The diameter of the gage is 3/4 to 1 inch. The divisions between the low-carbon steel pie sections are no greater than 1/32 inch. The sections are furnace-brazed and copper-plated. The gage is placed on the test piece copper side up, and the test piece is magnetized. After particles are applied and the excess removed, the indications provide the inspector with the orientation of the magnetic field.
The principal application is on flat surfaces such as weldments or steel castings where dry powder is used with a yoke or prods. The pie gage is not recommended for precision parts with complex shapes, wet-method applications, or for proving field magnitude. The gauge should be demagnetized between readings.
Several of the main advantages of the pie gage are that it is easy to use and it can be used indefinitely without deterioration. The pie gage has several disadvantages, which include: it retains some residual magnetism so that indications will prevail after removal of the source of magnetisation; it can only be used in relatively flat areas, and it cannot be reliably used for determination of balanced fields in multidirectional magnetisation.
