Electromagnetic testing emt-mft chapter 9b

PART 3. Application
1.0 Flaw Detection by the Flux Leakage Method.
Perhaps the most prevalent use of the flux leakage method is the
inspection of ferromagnetic tubular goods, such as gas pipelines, down hole
casing, and a variety of other forms of steel piping. In applications in the
petroleum industry, the technique is highly developed, but details on
inspection devices and methods of data analysis are, for the most part,
considered proprietary by the companies that provide inspection services.
Still, the techniques currently in use have certain features in common, and
these are exemplified by the typical system described below. The device
shown in Fig. 8 is an inspection tool for large-diameter pipelines.
Magnetization is provided by a large electromagnet fitted with wire brushes to
direct magnetic flux from the electromagnet into the pipe wall. To avoid
spurious signals from hard spots in the material, the magnetization circuit is
designed for maximum flux density in the pipe wall in an attempt to
magnetically saturate the material.
Charlie Chong/ Fion Zhang