The ultrasonic signal severity was equal to reference echo minus 6 dB to reference echo. The UT unit calibration was equal to 3 mm CRR with 250 mm range. The side wall lack of fusion also can give similar indications. Hence, the UT which has to be cleared by customer hold point, necessitated to examine the reliability of indications to ensure the quality of the product. They doubted these indications as may be from micro crack or lack of fusion. We were asked to investigate the cause of these ultrasonic echoes and to find the nature of defect and the orientation of defect if any.

The root indications were analysed and investigations were done utilising other NDT methods like magnetic particle testing, penetrant testing and radiographic testing. One area was selected and MT and PT was repeated after opening the fusion zone by grinding. Radiographic testing, magnetic particle testing and penetrant testing investigations proved that there is no presence of weld defects like lack of fusion or crack. Hence, the reason for these ultrasonic signals were doubted that it may be due to coarse grain structure of weld metal at fusion zone at surface of root side, due to lack of tempering bead.

Ultimately, another area was selected and tempering bead was welded over that area alone. After flush grinding the tempering bead, ultrasonic testing was repeated and spurious indications were found removed while scanning. This proved that the original indication was due to coarse grains of weld metal in fusion zone. Replica was taken to analyse the same at fusion zone, both before tempering bead welding and after tempering bead welding. The grain structure after tempering bead welding was found more fine grained. Hence, the tempering bead was welded over the entire circumferential seam and problem was solved. While repeating ultrasonic scanning, the spurious echo was not received. The ultrasonic testing recording, both before tempering bead welding and after tempering welding is furnished.