<p>Ultrasonic testing is one of the most commonly used NDT methods for periodic inspection of crude oil storage tanks. Ultrasonic phased array system can effectively and efficiently image different types of defects in the structures&nbsp;through direct contact&nbsp;method. However, the sludge remained on the tank floor gives rise to difficulties on detecting the defects in the floor plate using existing techniques. Therefore, this paper focuses on the development of novel phased array testing methods&nbsp;without requiring complete&nbsp;removal of the sludge.&nbsp;The acoustic characteristics of the oil sludge is first investigated and then&nbsp;the methods for estimating acoustic parameters of the oil sludge layer are proposed. The delay law of the phased array for focusing through sludge is optimised. Furthermore, a novel phased array beamforming method is explored based on multi-aperture full matrix capture. The imaging algorithm using total focusing method (TFM) is studied by considering the existence of sludge. The experimental results from the sludge thickness study demonstrate that the TFM imaging technique can more accurately measure one millimetre change in thickness of the metal sample. Additionally, high resolution imaging of side drilled holes in size of 1 millimetre can be realised on the samples covered with sludge. Last, the effect of aperture size, centre frequency and other parameters of the array elements on the sludge penetration depth is investigated. Consequently, the results obtained from different sludge experiments show good reliability and measurement consistency with our proposed methods. It delivers great potential to accurately locate and quantitatively evaluate the corrosion defects frequently found in the tank floor.</p>

Study on Ultrasonic Phased Array Detection and Imaging Techniques for Oil Storage Tank Floor Covered With Sludge

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

ASME 2021 Pressure Vessels & Piping Conference (PVP2021)

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