High level nuclear waste tanks were designed and fabricated in 1950’s. A285 carbon steel plates were joined by gas metal arc welding (GMAW) for the construction of these storage tanks with maximum storage capacity of approximately 1 million gallons. The welding process could introduce residual stress in or near the welds, which may lead to stress corrosion cracking (SCC) under certain chemistry conditions of the nuclear waste. Radioactive materials may leak from the stress corrosion cracks if they penetrate the tank wall. Early detection of SCC is crucial in preventing environmental contamination that is hazardous to human health.

This paper aims to establish an ultrasonic inspection system and its fundamental ability to inspect and size the stress corrosion cracks on thick welded steel structures. A 1-foot by 1-foot welded steel plate specimen was fabricated by joining two smaller carbon steel plates with the GMAW procedure used in 1950’s for constructing the nuclear waste storage tanks. The welded plate remained as welded and did not receive heat treatment for stress relief. Starter cracks were produced by electrical discharge machining (EDM) across the weld at various locations and orientations to investigate the stress corrosion induced crack initiation and growth. The plate was submerged in a solution of 5M NaNO~3~ at 90 ºC, which was prepared with reagent grade compound and distilled water. Crack growth was observed in the plate from some starter (machined) cracks after a few weeks. An ultrasonic guided wave inspection system is adopted to detect and quantify the SCC. The inspection system employs a piezoelectric transducer for guided wave actuation and a scanning laser Doppler vibrometer (SLDV) for sensing. The laser doppler vibrometer measures waveforms at predefined points with high spatial resolution and generates time-space wavefield data that can immediately show wave interactions with the crack. Wavefield images are generated based on the acquired time-space wavefield to allow further quantification of the crack length. To demonstrate the crack sizing capability of using the piezoelectric transducer and SLDV, the previous results from the magnetic particle test are compared. Reasonable agreement in crack length measurement is obtained with the ultrasonic test imaging technique.


Ultrasonic Nondestructive Evaluation of Stress Corrosion Crack in Welded Steel Plate

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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