Phased array ultrasonic testing (PAUT) performed on electroslag weld specimen subject to cyclical tension load testing

Abstract

Following the discovery of discontinuities in a weld specimen, which was made with a process called narrow gap electroslag welding (ESW-NG), the specimen was subject to mechanical cyclical tension loading until failure. The loading involved one block of 100 tension-only cycles at 42 ksi peak stress followed by a second block of 20 tension-only cycles at 55 ksi stress. Phased Array Ultrasonic Testing (PAUT) was performed to understand whether or not the loading protocol has caused the internal discontinuities to increase in length. The PAUT was performed before cycling began and after the end of first block of cycles. Conventional Ultrasonic Testing was also performed in order to develop comparative baseline results. PAUT utilizes an aperture, which is composed of multiple individual small transducer elements which can be pulsed individually at a computer-calculated timing (“phased or delay laws”) producing a sound beam which is swept through a volume of material. Utilizing PAUT, the operator has the ability to “steer” and “focus” the beam electronically through the material being examined at multiple angles in one scan (for example 45° through 75°) in lieu of being fixed at a certain angle as in conventional Ultrasonic testing (UT). The PAUT equipment utilized has the capabilities of 16 active pulsars capable of multiplexing over 64 channels (16:64) displayed in A, B, C, S, Linear scans, or a combination thereof. Scanning with a digital encoder was utilized in order to collect the data for post processing, analysis and data documentation. This presentation will discuss the findings of the PAUT on this weld specimen. The PAUT aperture utilized was a 5L-60 with 1 mm pitch and Sectorial and Linear scans were utilized. The sectorial scan results of the PAUT before and after cycling showed an increase in dimensions of the recorded indications by an average of 6–8 mm or approximately 50% of the original dimensions. The presentation will also include a discussion of the advantages and limitations of PAUT for various bridge applications. The advantages of PAUT include speed, flexibility, and the ability to perform complex inspections.