TOFD, the emerging ultrasonic technique, for heavy wall pressure vessel welds examination

• Published in: E-journal of Nondestructive Testing Vol. 4; no. 9
• Main Authors: Nardoni, G, Betti, F, Guidi, A, Raffarta, B, Nardoni, P, Nardoni, D, Nottingham, L
• Format: Journal Article
• Language: English
• Published: 01.09.1999
• ISSN: 1435-4934; 1435-4934

The paper presents TOFD, the Time of Flight Diffraction Technique, currently the most promising ultrasonic technique for examination of heavy wall thickness welds on pressure vessels. TOFD is a computerized ultrasonic system, able to scan, store, and evaluate indications in terms of height (through thickness weld), length, position, with a degree of accuracy never achieved with other ultrasonic techniques. A record of examined sections is available in unprocessed form on floppy disk or CD and readable in Word for Windows 95. The ASME Code, with Code Case no. 2235 has accepted this method in lieu of radiography examination for thicknesses over 4" (1). Experiences on 75 mm up to 300 mm thick welds of 2.5 /3% Q 1 Mo, 0.25 V and Carbon steel are discussed. The technique has been applied on longitudinal, circumferential and nozzle-shell /bead welds. Scanning Plan Data and its validation are reported with used test blocks. Cladded layers in TOFD images are presented. Based on experience to date, prospects for this new technique are of great interest.