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M Bayray:
"Identification of Early Fatigue Crack Growth in a Pressure Vessel Utilising Acoustic Emission (AE) Technique";
Talk: AEGW 45, Evanston IL, USA; 2002-08-19 - 2002-08-21.

Experiments have been conducted at the Institute of Pressure Vessels and Plant Technology on a series of test vessels with partially penetrated longitudinal welds. Acoustic Emission technique has been used to monitor crack growth in the test vessels. In this paper, one of the test vessels (BC34) will be considered. The vessel was made of steel and the main dimensions were outer diameter of 351mm, over all length of 600mm and thickness of 3.5mm. The vessel was manufactured with international lack of weld penetration on the longitudinal weld.
The vessel was loaded under cyclic pressurization 2-39 and AE sensors were mounted to monitor any crack growth on the longitudinal weld. After 310 cycles the AE instrumentation detected the crack growth. AE events were detected almost every cycle with amplitudes 60-65dB after the crack was detected. The AE events occurred at 13 to 15 bars during the increasing pressure part of the cycle. The test was then stopped after 1180 cycles. Samples were cut out around the longitudinal weld for further microscopic investigation. Polished cross section of the weld was prepared for optical microscope while the fracture surface was investigated under scanning electron microscope. The microscopic investigation confirmed the existence of the crack and revealed that the crack was about 0.2mm in length.
The paper will discuss in detail the AE data analysis and present AE waveforms of selected events. The AE waveform analysis is carried out using window Fourier transform and wavelet transform. Also, the microscopic investigation of the crack with the support of pictures will be discussed.