Development of Phased-Array Ultrasonic Testing Acceptability Criteria (Phase I)

PDF files can be viewed with the Acrobat® Reader®

This document is a technical summary of the unpublished Federal Highway Administration report Development of Phased Array Ultrasonic Testing (PAUT) Acceptability Criteria (Phase I), available through the National Technical Information Service at www.ntis.gov.

INTRODUCTION

The past decade has seen new, emerging innovations in the field of ultrasonic testing (UT). Specifically, multiple manufacturers have been producing phased-array ultrasonic testing (PAUT) systems. The PAUT system embeds a matrix of multiple (some up to 128) single transducers into one probe used for scanning objects. Exciting multiple transducers simultaneously offers distinct advantages; depending on the sequencing of transducer excitation, the ultrasonic beam could be steered within the material, and multiple beams help develop extra-dimensional data to assist with visualization of discontinuity size, shape, and location. Coupled with a linear encoder, PAUT data could also be digitally stored as a permanent record, something not possible for conventional UT.

Unfortunately, there has not been broad acceptance of PAUT in the bridge fabrication industry because it is currently not a recognized inspection technology in the American Welding Society’s (AWS) D1.5 bridge-welding code. One situation the technology would excel at would be inspection of complete joint penetration (CJP) butt welds. Currently, AWS D1.5 requires CJP welds subjected to tensile or reversal stresses to be inspected by radiographic testing (RT). However, discontinuities normally seen by RT should also be seen with PAUT. Until specification language is adopted into D1.5, there will continue to be hesitancy to use PAUT for the inspection of CJP butt welds, but acceptance criteria and the specification language must first be developed.

Phase I of this research effort involved a review of the current state of the art of weld inspection using PAUT, development of the preliminary technical approach to inspecting CJP butt welds with and without transitions, fabrication of suitable test specimens, and the use of appropriate calibration blocks for inspection of thick weld specimens. Based on a literature review, it was deemed necessary to first explore the phased-array pulse-echo (PE) technique for all inspections in this phase. The preliminary results from the inspections conducted on four butt-weld specimens are presented in this TechBrief. Phase II of the research will include development of scan plans for transition butt-welds. Indepth analysis of PAUT data obtained in phase I and phase II will determine the exact location and sizing information of the defects. Phase II will also compare PAUT results with those obtained using conventional UT and radiography. Phase III of this project will explore the time of flight diffraction and combined time of flight diffraction (TOFD)-PE approach. Phase I developmental efforts are presented in this TechBrief.