Standard Practice for In Situ Electromagnetic (Eddy Current) Examination of Nonmagnetic Heat Exchanger Tubes

Importancia y uso:

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 nonrelevant 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. Nonrelevant 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 nonrelevant, shall be regarded as unacceptable until it is proven to be nonrelevant. For tubing installed in heat exchangers, predictable sources of nonrelevant 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 nonrelevant 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.

Subcomité:

E07.07

Referida por:

E0243-24, E0543-21, E0543-21

Volúmen:

03.03

Número ICS:

27.060.30 (Boilers and heat exchangers)

Palabras clave:

eddy current; electromagnetic; NDT; nondestructive testing;