The high-temperature performance of nickel-based transition joints: II. Fracture behaviour

Detailed evaluation of the fracture behaviour of nickel-based transition welds has shown that failure develops as a consequence of cavitation at the weld interface with the low alloy steel. This damage process can be accelerated by local oxide formation so that rupture data produced using small-diameter specimens tested in air may be overly conservative compared with the long-term performance of thick-section welds in service. While cavity development was associated with interfacial carbides, tests performed with a pre-existing array of carbides at the weld interface exhibited similar long-term lives to new welds. Thus, it appears that the development of strain at the weld interface is critical in initiating damage. Relationships have been established between life fraction and the number of cavities present and the accumulation of creep strain. These relationships provide the technical information required to support remanent-life decision-making for plant weldments.