This paper deals with the investigations carried out to understand the effect of microstructure and weld geometry on the ultrasonic evaluation of single side welded thick (85 mm) austenitic butt weld between ferritic components. The edge faces of the ferritic components are buttered with Inconel and stress relieved prior to Inconel butt welding. This special process permits welding of buttered ferritic steel for which no stress relief is needed. To carry out investigations, test blocks were fabricated simulating the component conditions like material, welding procedure, weld geometry, heat treatment, etc.

Microstructure samples were taken from different regions of the weld joint to study the grain growth pattern. Investigations were carried out with longitudinal wave angle beam as it is established that longitudinal wave angle probe using either single crystal or focused double crystal provides a better and more reliable inspection [2]. Velocity variation and attenuation were estimated on weld samples taken in the envisaged ultrasonic test directions (0, 45 & 60 degrees). Beam skewing and reflection encountered by the sound beam at austenitic - ferritic interfaces as well as buttering -butt weld interfaces were also assessed. The estimated values were analysed with respect to sound beam to fibre angle.

Based on the results of the investigations, special probe (longitudinal wave angle beam transmitter receiver) and the location of the artificial reflectors in the test blocks were finalized for axial and circumferential scanning directions. The pattern of distance amplitude correction curves established were analysed with respect to the probe characteristic and weld structure behaviour. The effect of first layer buttering penetration and bead profile at the ferritic-austenitic interface on the propagation of ultrasonic sound was also analysed.

The results of the investigations were used to establish the testing technique, optimise the choice of transducer and verify inspection capability. The technique established with artificial reflectors was validated with natural flaws like lack of fusion and slag introduced at different locations of a test block.

REFERENCES

1. Handbook on the Ultrasonic Examination of Austenitic Welds (International Institute of Welding, 1986)
2. X. Edelmann, Ultrasonic Testing of Austenitic Stainless Steel Components (Nondestructive Testing, EURO NDT, 1987)