Research on ultrasonic phased array system for automatic defect detection of pipeline girth welds

Layer detection method is applied in flaw detection of pipeline girth welds when ultrasonic is used. As every layer must be detected, the detection location is changed continuously. The focal length of traditional ultrasonic transducer is fixed. When tested location is changed, the transducer has to be changed, reducing the detection efficiency. Ultrasonic phased array transducer has the ability of electronic steering and electronic focusing, improving detection efficiency. But detection sensitivity and precision are decided by the characteristics of the transducer. A numerical analysis method is carried out in this article firstly, to investigate the influences of some main parameters of linear phased array transducer on beam focusing. Then, a multi-channel acquisition system connected to the linear ultrasonic phased array transducer is described. The hardware construction of single acoustic channel and the corresponding signal processing procedure are introduced, through which precise delay control of single element in the transducer is realized. Based on requirements of flaw detection and real detection conditions for big inch pipeline girth welds in our country, an ultrasonic phased array is tested on a weld test block. The experiment results illustrate that the optimized phased array transducer and the system has a desired performance, which increases the testing efficiency.