UT on austenitic stainless steel (ASS)

[pandithan]

Is it possible to do UT on ASS base metal and weld metal, if so please give code reference
Pandithan,
Welding Consultant

[Peter Johansson]

The large and coarse austenitic grain and its anisotropic crystal structure makes it difficult to detect and size flaws in the austenitic and ferritic austenitic stainless steel components as well as in the weldings of them by UT technique due to beam skewing, splitting, dispersion and attenuation. So, large size probe which generates high energy ultrasound and using low frequency probe (5 MHz to 2 MHz or 1 MHz, depending on thickness) are proposed as well as shorter ultrasonic wavelengths but slightly larger than the grain size work best. In addition if the inspection with the conventional shear waves does not work you shall try longitudinal waves that penetrate better than shear waves. Moreover, I could say that dual (or twin) probes are the best way to inspect (minimize near-surface reflections).

The code that you shall use depends on the construction code and the project requirements. If, i.e., it is for a pressure vessel under the scope of ASME VIII, then you shall prepare UT procedures both for weldment and base metal based on ASME V, articles 4 and 5 respectively. Because of the above described specific characteristics of austenitic and ferritic austenitic stainless steel, extra qualifications are recommended especially for the weldments and they could be as described in below link (page 62).

DNV - Non Destructive Testing