Standard Practice for Electromagnetic (Eddy-Current) Examination of Ferromagnetic Cylindrical Bar Product Above the Curie Temperature
The purpose of this practice is to describe a procedure for in-line-eddy-current examination of hot cylindrical bars in the range of diameters listed in 1.2 for large and repetitive discontinuities that may form during processing.
The discontinuities in bar product capable of being detected by the electromagnetic method are listed in 1.3.1. The method is capable of detecting surface and some subsurface discontinuities that are typically in the order of 0.030 in. [0.75 mm] and deeper, but some shallower discontinuities might also be found.
Discontinuities that are narrow and deep, but short in length, are readily detectable by both probe and encircling coils because they cause abrupt flux changes. Surface and subsurface discontinuities (if the electromagnetic frequency provides sufficient effective depth of penetration) can be detected by this method.
5.3.1 Discontinuities such as scratches or seams that are continuous and uniform for the full length of cut length bars or extend for extensive linear distances in coiled product may not always be detected when encircling coils are used. These are more detectable with probe coils by intercepting the discontinuity in their rotation around the circumference.
5.3.2 The orientation and type of coil are important parameters in coil design because they influence the detectability of discontinuities.
The eddy current method is sensitive to metallurgical variations that occur as a result of processing, thus all received signals above the alarm level are not necessarily indicative of defective product.
1.1 This practice covers procedures for eddy-current examination of hot ferromagnetic bars above the Curie temperature where the product is essentially nonmagnetic, but below 2100F [1149C].
1.2 This practice is intended for use on bar products having diameters of 1/2 in. [12.7 mm] to 8 in. [203 mm] at linear throughput speeds up to 1200 ft/min [366 m/min]. Larger or smaller diameters may be examined by agreement between the using parties.
1.3 The purpose of this practice is to provide a procedure for in-line eddy-current examination of bars during processing for the detection of major or gross surface discontinuities.
1.3.1 The types of discontinuities capable of being detected are commonly referred to as: slivers, laps, seams, roll-ins (scale, dross, and so forth), and mechanical damage such as scratches, scores, or indentations.
1.4 This practice does not establish acceptance criteria. They must be specified by agreement between the using parties.
1.5 This practice does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this practice to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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