Nondestructive Evaluation for Duplex Stainless Steel Tube Using Multi-Frequencies Remote Field Testing

Abstract

This paper presents the determination of Remote Field Testing (RFT) frequencies to accomplish the inspection of duplex stainless steel tubes grade ASME/ASTM SA 789. The tube specimen was 25.4 mm of outside diameter, and thickness of 1.65 mm with the different artificial flaws. A dual-pickup coils type of RFT probe was employed to inspect the specimen by inserting a probe within the tube. Optimum of testing frequency Range was determined based on an eddy current through transmission generation to produce different magnetic field density. RFT inspection frequency range for duplex stainless steel was consequently determined from 5 to 25 kHz which was different than those inspection frequencies of general ferromagnetic steel tube. In the experiment, calculated frequencies were then generated to the Eddy current (ET) and RFT probes for detecting the flaws of the tube specimen. The inspection signals were specifically shown in function of impedance plane to identify the flaw characters. The results showed that the RFT can be utilized to quantify the wall loss levels of duplex stainless-steel tube better than the ET. Especially, phase angle of inspection signals can be used to evaluate the different depths of the wall losses. Sensitivity of RFT showed the detection performance at minimum 20% of tube wall loss.