Cherdpong Jomdecha

Corrosion-source location by an FPGA-PC based acoustic emission system

This paper presents a novel low-cost acoustic emission (AE) source-location system to locate corrosion sources in AISI304 austenitic stainless steel. The system is implemented using an FPGA-PC configuration. Three AE sensors with 150 kHz resonance frequency were used to detect the AE activities generated from the corrosion. Experiments were set up to show performance of the system in locating uniform and pitting corrosions in stable state using corrosive solutions and electrochemical environment. A commercial AE system was used to assure the AE activities with the location results. Experimental results showed the ability of the AE source location system to locate corrosion sources. In conclusion, the proposed AE source-location system is appropriate and practicable to locate corrosion with flexibility and affordability.

Analysis of Eddy-Current Measurement System for Residual Stress Assessment in Stainless Steel Grade 304

The objective of this paper is an analysis of statistical discreteness and measurement capability of an eddy-current measurement system for residual stress assessment in stainless steel Grade 304 (SS304). Cylindrical specimens with 50 mm in diameter and 12 mm thickness were prepared to generate residual stress by Resistance Spot Welding at which the welding currents were set at 12, 14, and 16 kA. The eddy-current measurement system was including a probe with frequency range of 0.1 to 3 MHz and an eddy current flaw detector. They were performed by contacting the probe on the specimen. The measurements were performed particularly in the vicinity of heat affected zone (HAZ). In order to determine the results of the residual stress measurement, the calibration curves between static tensile stress and eddy current impedance at various frequencies were accomplished. The Measurement System Analysis (MSA) was utilized to evaluate the changed eddy-current probe impedance from residual stress. The results showed that using eddy current technique at 1 MHz for residual stress measurement was the most efficient. It can be achieved the Gauge Repeatability & Reproducibility %GR&R at 16.61479 and Number of Distinct Categories (NDC) at 8. As applied on actual butt welded joint, it could yield the uncertainty of ± 58 MPa at 95 % (UISO).

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

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.

The Comparison of Acoustic Emission Activities between Material Integrity and Leakage during CNG Cylinder Testing

The objective of this paper is to study the different acoustic emission (AE) activities from material integrity and leakage which were obtained from CNG steel cylinder during pressurization. CNG type I cylinders were employed to test by hydrostatic stressing. The pressure was continuously increased to over 1.1 time of operating pressure or leakage occurrences. AE sensors, resonance frequency of 150 kHz, were mounted on the outside cylinder wall to detect the AE activities throughout the testing. AE activities were compared between AE of material expansion and leakage by amount of AE signals detected then analyzed by AE parameters. AE parameters including Amplitude, Count, Energy (MARSE), Duration and Rise time were analyzed to distinguish the AE data. The AE wave form in time and frequency domain were also considered in analysis process. The location of AE sources were located by the calculation the arriving differenced time of 2 or more sensors to indicate the position of cylinder faults. The results showed the AE signals of material expansion were randomly detected throughout the pressurization until the Enegy and Amplitude of detected signals were increased by high incresing rate where was leakage occurrences. AE parameters of Amplitude and Energy can be significantly represented the difference between material expansion and leakage. Addition, the Hit rate monitoring cloud be a notice activity before cylinder leaks. The benefits of this work are the AE characterization of the material expansion, leakage and noise for improvement of Type-1 CNG cylinder tests.

Ultrasonic Testing for Vulcanization Inspection of Natural Rubber

This paper presents a novel method to inspect the levels of vulcanization of natural rubber by ultrasonic testing. In the research, test specimens are natural rubbers of type ‘cis-1,4-polyisoprene’ vulcanized at different durations. Piezoelectric contact transducers were used to transmit and receive ultrasonic to/from each sample. Longitudinal waves at nominal frequency of 2, 2.25 and 5 MHz were used to investigate the samples. Experiments were conducted using two techniques: pulse echo and through transmission. The pulse echo technique was applied to inspect the ultrasonic attenuation and the velocity of longitudinal wave of natural rubber. The through transmission technique was implemented to identify the shape and amplitude of the frequency spectrum. The results from both time and frequency domains can be employed to classify the levels of the vulcanization. From the experiments, this ultrasonic testing provides an effective way to inspect the vulcanization of natural rubber with repeatability and allows faster inspection rate than other methods.© 2003 ASME