The Design of an Ultrasonic Phased Array System on Pipelines’ Weld Inspection

Phased arrays generate ultrasonic waves by using recisely-defined time delays for each element in an ultrasonic array group, this permits constructive and destructive interference of the wavefronts to form the pre-defined beam. So, ultrasonic phased arrays are well suited to weld inspections. First, beams can be multiplexed across the array, in what is called “electronic scanning”. This permits very rapid inspections of components, typically an order of magnitude faster than a single transducer raster scan. Second, the beam can be swept through a range of angles without moving the array; this is called “beam steering”, and the inspections are typically called “azimuthal” scans or “sectorial” scans. Before weld inspecting, the time delays between elements were computed using a specific model and compared to experimental delays obtained using through transmission tests. This paper describes the application of phased array on pipelines’ weld inspection. The detail hardware designs of linear phased arrays system and the summary of system performance are presented. This inspection system includes eight ultrasonic signal transmitting and receiving circuit units, which are used to control time sequence of ultrasonic beam and select channel used for waves construction, and amplify the received ultrasonic signal. Each unit is connected with 16 probe elements (total 128 elements in this system), and can receive 4-way ultrasonic signals (channel selection is done by RF switching). Additional performance is gained by intensively using FPGA (Field Programmable Gate Arrays) technology for memory and delay counters. Since the working frequency or FPGA is 100MHz, the delay time less than 10 ns is realized by analogue delay line. This system not only has the functions of conventional ultrasonic inspector, but also can display the defect shape and its size on the screen.