Ultrasonic Guided Wave-Based Circumferential Scanning of Plates Using a Synthetic Aperture Focusing Technique

Jianjun Wu,Keji Yang,Zhifeng Tang,Shiwei Wu,Fuzai Lv

doi:10.3390/app8081315

Abstract

Tanks are essential facilities for oil and chemical storage and transportation. As indispensable parts, the tank floors have stringent nondestructive testing requirements owing to their severe operating conditions. In this article, a synthetic aperture focusing technology method is proposed for the circumferential scanning of the tank floor from the edge outside the tank using ultrasonic guided waves. The zeroth shear horizontal (SH0) mode is selected as an ideal candidate for plate inspection, and the magnetostrictive sandwich transducer (MST) is designed and manufactured for the generation and receiving of the SH0 mode. Based on the exploding reflector model (ERM), the relationships between guided wave fields at different radii of polar coordinates are derived in the frequency domain. The defect spot is focused when the sound field is calculated at the radius of the defect. Numerical and experimental validations are performed for the defect inspection in an iron plate. The angular bandwidth of the defect spot is used as an index for the angular resolution. The results of the proposed method show significant improvement compared to those obtained by the B-scan method, and it is found to be superior to the conventional method—named delay and sum (DAS)—in both angular resolution and calculation efficiency.

Highlights

Tanks are essential facilities for the storage and transportation of petroleum products.Thousands of tanks may be in service at the same time in one oil depot
The wave velocities are affected by the mechanical properties of the plates, which are changed by the temperature
A synthetic aperture focusing technique method is proposed for circumferential scanning of plates using guided waves

Summary

Introduction

Tanks are essential facilities for the storage and transportation of petroleum products. Thousands of tanks may be in service at the same time in one oil depot. Because of the harsh working conditions and corrosive storage materials, various kinds of defects, which are hidden hazards, may occur in the tanks. It is found that 80% of corrosion, which makes up the majority of the defects in the tanks, occur in the tank floors, making them key areas in the overhauls [2]. The most common non-destructive testing technologies for tank floors based on flux leakage [3,4,5] and ultrasonics [6] are limited for the low working efficiency of testing “step by step.”. The tanks must stop their service and be emptied before the inspection The most common non-destructive testing technologies for tank floors based on flux leakage [3,4,5] and ultrasonics [6] are limited for the low working efficiency of testing “step by step.” The tanks must stop their service and be emptied before the inspection

Methods

Results

Conclusion