The field measurement of carburization and oxidation of ethylene furnace tubes by multi-technique method

A multi-coil electromagnetic induction type detector had been applied for in-field measurement of the depth of the carburized layer in ethylene furnace tubes. Laboratory tests showed that under conditions where the entire tube wall may be carburized, the technique can give erroneous indications. To identify the complex interaction of the inner and the external magnetic layers, a variable frequency metal sorting instrument was included in the field inspection procedures. Furthermore, dimension and thickness measurements, visual inspection and surface replica techniques also support this improvement of the field inspection method.