In this article, the authors' present findings indicate that the induction-bending process can have a severe detrimental effect on the mechanical properties and the corrosion resistance of super duplex stainless steel. After outlining the parametric testing of the pipe that produced reduction in properties, the article presents comparative data from mechanical testing, corrosion analysis, and micrographic analysis before and after induction bending and after post-bend heat treatment. An explanation for the deterioration of properties is provided in terms of metallurgical characteristics; the root cause of deterioration is discussed; a method of restoring the mechanical and corrosion resistant properties is provided; and finally, process improvements are suggested which might, if adopted, prevent the re-occurrence of this phenomenon in the future.
This paper briefly describes induction bending and highlights some of the challenges associated with this technique in the production of tight bends in thick-walled pipe. The authors then go on to describe how data obtained from production runs and specifically commissioned trial bends were used to examine the factors believed to influence the generation of adverse geometry during bending, and to determine the relative importance of each factor.The paper concludes by examining previously published empirically derived charts and by comparing the results of the trials. The authors conclude from this that the existing charts are deficient when considering extrados wall thinning, i.e. the charts cannot be reliably extrapolated to cover bends which are beyond their scope and, while addressing the issue of wall thinning at the extrados, they ignore all the other types of deformation.
Deleterious phasesresulting from the induction bending of thick-walledsuper-duplexpipework Temperfree inductionbendingcanh aveasignificantimpacton the mechanicaland corrosion-resistanceproperties of thick-walled superduplexpipe. Sectionsfrom induction bentpipeweresolution annealed at1120 8 Cforv arious periodst osequentiallyeliminated ifferentdeleterious phases.Bycomparing the results of modified DL-EPR analysis,opticalm icroscopy,mechanicaland corrosion testingbeforeand aftert he various heatt reatments,itw as shownthatt he deterioration in propertiesw asduetothe precipitation of a ' .Itwasalsopossible todetermine the orderin which a ' , c 2 and Cr 2 Nhadp recipitated,a nd thus to conclude thatt he unfavourable metallurgyw ast he result of inadequatep ost-bend cooling. Alikelyt hermalh istory fort he pipe isproposed thatleadst othe descriptiono fa modified temperfree process.
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