Feasibility Study Using Time of Flight Diffraction Technique in Lieu of Radiography on Heat Exchanger Shell Weld Joint

Welded constructions play a vital role in power plant components. Power industry utilization of radiography for integrity of welds is a common practice in the vessel manufacturing industry. Recent developments in the field of ultrasonic utilize Time of Flight Diffraction Technique (ToFD) for evaluation of welds with respect to Engineering Critical Assessment approach for evaluation of welds. Recent ASME Code case 2235, revision 9 recommends the use of alternate techniques such as Computerized imaging techniques i.e. ToFD, Phased array as an alternative methods that can be used in lieu of radiography. In order to validate the ASME Code Case-2235(9) a feasibility study was attempted on a 40mm thick heat exchanger shell circumferential weld. The results of Radiography and ToFD are discussed in detail in the paper. The results of analysis reveals ToFD combined with Pulse Echo using encoded scans are comparable to radiography and more stringent than radiography for defect detection and repairs.