5.1 Eddy current testing is a nondestructive method that can be used to locate discontinuities in tubing made of materials that conduct electricity. Signals can be produced by discontinuities located either on the inner or outer surfaces of the tube, or by discontinuities totally contained within the tube wall. When using an internal probe, the density of eddy currents in the tube wall decreases very rapidly as the distance from the internal surface increases; thus the amplitude of the response to outer surface discontinuities decreases correspondingly.5.2 Some indications obtained by this method may not be relevant to product quality. For example, an irrelevant signal may be caused by metallurgical or mechanical variations that are generated during manufacture but that are not detrimental to the end use of the product. Irrelevant indications can mask unacceptable discontinuities occurring in the same area. Relevant indications are those that result from nonacceptable discontinuities. Any indication above the reject level, which is believed to be irrelevant, shall be regarded as unacceptable until it is proven to be irrelevant. For tubing installed in heat exchangers, predictable sources of irrelevant indications are lands (short unfinned sections in finned tubing), dents, scratches, tool chatter marks, or variations in cold work. Rolling tubes into the supports may also cause irrelevant indications, as may the tube supports themselves. Eddy current examination systems are generally not able to separate the indication generated by the end of the tube from indications of discontinuities adjacent to the ends of the tube (end effect). Therefore, this examination may not be valid at the boundaries of the tube sheets.1.1 This practice describes procedures to be followed during eddy current examination (using an internal, probe-type, coil assembly) of nonmagnetic tubing that has been installed in a heat exchanger. The procedure recognizes both the unique problems of implementing an eddy current examination of installed tubing, and the indigenous forms of tube-wall deterioration which may occur during this type of service. The document primarily addresses scheduled maintenance inspection of heat exchangers, but can also be used by manufacturers of heat exchangers, either to examine the condition of the tubes after installation, or to establish baseline data for evaluating subsequent performance of the product after exposure to various environmental conditions. The ultimate purpose is the detection and evaluation of particular types of tube integrity degradation which could result in in-service tube failures.1.2 This practice does not establish acceptance criteria; they must be specified by the using parties.1.3 This standard 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 standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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5.1 The purpose of this practice is to outline a procedure for the detection and location of discontinuities such as pits, voids, inclusions, cracks, or abrupt dimensional variations in ferromagnetic tubing using the electromagnetic (eddy current) method. Furthermore, the relative severity of a discontinuity may be indicated, and a rejection level may be set with respect to the magnitude of the indication.5.2 The response from natural discontinuities can be significantly different than that from artificial discontinuities such as drilled holes or notches. For this reason, sufficient work should be done to establish the sensitivity level and set-up required to detect natural discontinuities of consequence to the end use of the product.5.3 Eddy current testing systems are generally not sensitive to discontinuities adjacent to the ends of the tube. The extent of the end effect region can be determined in accordance with 8.6.5.4 Since the density of eddy currents decreases nearly exponentially as the distance from the external surface increases, the response to deep-seated discontinuities decreases and some deep-seated discontinuities may give no detectable repsonse.5.5 Discontinuity orientation also affects the system response and should be taken into consideration when establishing the examination sensitivity.5.6 In preparing a reference standard for welded tubing, artificial discontinuities should be placed in both the weld metal and the parent metal when the responses are expected to be different and if both are to be examined. The apparatus is then adjusted to obtain an optimum signal-to-noise ratio.5.6.1 When examining only the weld area, the discontinuities shall be placed only in the weld area.5.7 The examination frequency and the type of apparatus being used should be considered when choosing the examining speed. Certain types of equipment are effective only over a given speed range; therefore, the examining speed should fall within this range.5.8 Discontinuities such as scratches or seams that are continuous and uniform over the full length of the tube may not always be detected with differential encircling coils or probes scanned along the tube length.1.1 This practice2 covers a procedure for applying the eddy current method to detect discontinuities in ferromagnetic pipe and tubing (Note 1) where the article being examined is rendered substantially non-magnetic by the application of a concentrated, strong magnetic field in the region adjacent to the examining coil.NOTE 1: For convenience, the term tube or tubular product will hereafter be used to refer to both pipe and tubing.1.2 The procedure is specifically applicable to eddy current testing methods using an encircling-coil assembly. However, eddy current techniques that employ either fixed or rotating probe-coil assemblies may be used to either enhance discontinuity sensitivity on the large diameter tubular products or to maximize the response received from a particular type of discontinuity.1.3 This practice is intended for use on tubular products having outside diameters from approximately 1/4 to 10 in. (6.35 to 254.0 mm). These techniques have been used for smaller and larger sizes however, and may be specified upon contractual agreement between the purchaser and the supplier.1.4 This practice does not establish acceptance criteria; they must be specified by the using party or parties.1.5 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.1.6 This standard 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 standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

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5.1 The thickness of a coating is often critical to its performance. This eddy-current method is nondestructive and is suitable for measuring the thickness of anodic coatings on aluminum, as well as the thickness of most nonconductive coatings on nonmagnetic basis metals.5.2 This test method requires that the conductivity of the substrate be the same in the reference standard used for calibration adjustment and in the coated article to be measured.1.1 This test method covers the use of eddy-current instruments for the nondestructive measurement of the thickness of a nonconductive coating on a nonmagnetic basis metal. It is intended to supplement manufacturers’ instructions for the operation of the instruments and is not intended to replace them.1.2 This test method is particularly useful for measuring the thickness of an anodic coating on aluminum alloys. Chemical conversion coatings are too thin to be measured by this test method.1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.1.4 This standard 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 standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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