Deleterious phases resulting from the induction bending of thick-walled super-duplex pipework

Temper free induction bending can have a significant impact on the mechanical and corrosion-resistance properties of thick-walled super duplex pipe. Sections from induction bent pipe were solution annealed at 1 120°C for various periods to sequentially eliminate different deleterious phases. By comparing the results of modified DL-EPR analysis, optical microscopy, mechanical and corrosion testing before and after the various heat treatments, it was shown that the deterioration in properties was due to the precipitation of a'. It was also possible to determine the order in which a', ?₂ and Cr₂N had precipitated, and thus to conclude that the unfavourable metallurgy was the result of inadequate post-bend cooling. A likely thermal history for the pipe is proposed that leads to the description of a modified temper free process. © 2010 Carl Hanser Verlag, Munich, Germany.