NDT methodology relied on ultrasonic examination during fabrication because of its unfavourable geometry for a complete RT examination. A feasible RT technique was developed any way taking trials in X-ray and gamma with different relative source and film placement.

UT methodology depended on development of mock-up reference blocks with 1: 1 scale model configurations, choice of suitable probes with higher SNRs, establishment of DAC curves for different brands of probes in parent materials and weld metal. Probes from well known manufacturers RTD Netherlands, Krautkramer, Germany, were used. An improvement in noise level was achieved with highly damped probes and use of TR probes with multiple focal depths. One brand of TR probes gave negligible noise levels in weld zones except that it required multiple zone examination with different angles. Probes were characterized with in-house made probe characterization blocks as suggested in the hand book on ultrasonic examination of austenitic stainless steel welds by IIW, 1986.

Ultrasonic examination was conducted in two stages. First, on the stainless steel buttering on the vessel wall to ensure weld volume and fusion face integrity. The K type weld joint on the SS buttering was scanned with multi-directional angle probes from the plate side and with 45 degree and 0 degree probe from the curved vessel wall side. For the later the use of CAD drawings to get the actual angles of beaming in the weld zone and the reflector locations for drawing the DAC was used.

Inservice examination of these critical joints using conventional techniques may require adaptation of probe contact surfaces to suit curvatures and use of non-standard angles. Preparation of the above may give base line data for future examination using conventional techniques. As per the specification requirement continuous recording of ultrasonic signals above recording level was recorded using the P-scan equipment of Danish welding Institute, Denmark. The data created by the above including the weld images in floppies can be used in future inservice examinations. The special advantage of observing lesser levels of defect sizes at a later date than what is recorded is important to observe any growth of discontinuities during service.