PPP 2021 - Development of friction stir welding for joining cladded pipes

Pipes in deepwater application have to cope with a high pressure in combination with aggressive corrosive environmental conditions. To protect the pipes against corrosion impact and avoid potential failure during usage, the use of a Corrosive Resistant Alloy layer (CRA) on the inner diameter surface is a potential solution. However, the bi-metallic nature of these pipes poses a substantial challenge to potential welding processes. Solid-state welding processes, such as friction stir welding (FSW) offer an ideal solution to join bi-metallic pipes. In FSW no bulk melting of the base materials take place, reducing the formation and growth of intermetallic phases to a minimum. Moreover, the thermo-mechanical characteristics of the process lead to fine equiaxial recrystallized microstructures, which ensure superior mechanical properties of the weld. However, the possibility of joining bi-metallic pipes with the FSW process has not been explored in depth so far. Therefore, the present project aims at closing this knowledge gap by addressing the complete development chain, from process development over the analysis of the microstructure evolution as a result of the welding operation and the determination of the mechanical and corrosion performance of the joints. The work will be performed in close collaboration with the Universidade federal do Rio Grande do Sul in Brazil and the Helmholtz-Zentrum Geesthacht.