Measurement of electromagnetic properties of heat exchanger tubes

Electromagnetic properties of heat exchanger tubes made of SAF 2205, Type 439 and Sea-Cure stainless steels were determined with magnetic and electrical techniques. The standard magnetic measurements were conducted at direct (DC) and alternate (AC – 200 Hz) current excitation. The magnetic permeability, coercivity, retentivity, and other magnetic parameters were measured in tube axial and circumferential direction, in open and closed magnetic circuits and in wide range of magnetic field strengths from 10 A/m to 82 kA/m. The electrical conductivity was determined with custom-designed fixture in axial direction only at DC and AC (50 – 200 Hz). The unique set of results revealed that a certain anisotropy of properties existed between the two geometric directions. The agreement between the measurements from the different techniques was good where comparison was possible.