For decades, cast austenitic stainless steels (CASS) have presented a challenge for inspection. However, recent advanced inspection technologies have shown promise in inspecting CASS materials with wall thicknesses that were once considered impossible.
Before being applied on larger scale, these new inspection methods must be proven to be effective at identifying discontinuities in CASS material. This presents a problem of its own. Several traditional flaw manufacturing methods cannot be applied to CASS due to the disruption of the parent material. Excavation and welding changes the cast material microstructure and thus significantly affects the inspection results. At the same time, due to the significant wall thickness and inspection limitations, the required qualification flaws can be quite large. Until recently, modern flaw manufacturing techniques, that do not require welding, have not been applied to flaws of this size.
In this paper, recent developments will be presented on the manufacturing of thermal fatigue cracks in centrifically CASS material. The presented developments make it possible to use real cracks for demonstrating the effectiveness of CASS inspection techniques.
The results also contain first published UT data on this kind of thermal fatigue cracks in CASS and reveal new insight on the inspectability of this difficult material.