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

Abstract

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.

Induction bending effects on mechanical properties and corrosion resistance of duplex stainless steel UNS S31803 pipes

“…This is explained by the lower concentrations of austenite, which favors the segregation of nitrogen in the ferrite phase and the precipitation of Cr 2 N when cooling. Similar results were also found by [10][11][12]. The bent tubes (STB) showed a lower amount of chromium nitrides precisely for this reason, as can be seen comparing Figs.…”

Experimental study of cooling during the temper-free induction bending of thick-walled super-duplex pipework to tight bend radii

“…1. The form of chromium nitride which was present following induction bending was previously identified as Cr 2 N [3], which tends to form between 700 and 900 • C [5]. At the temperature at which induction bending is conducted the majority of the The results presented in this paper do not show that any of the surviving thermocouples stayed within any of the critical temperature ranges for prolonged periods of time.…”

“…The authors have previously suggested a thermal history based on the type and quantity of deleterious phases encountered in the bent samples [3]. However, having studied the thermocouple data, it appears that Cr 2 N most likely occurs during the immediate post-bend cooling of the pipe.…”

“…This paper is part of a suite of publications by the same authors [1][2][3][4], which together comprise an industrial study of temper-free (TF) induction bending of pipe. Previous work noted that as well as geometric problems, bending thick-walled superduplex pipe to tight radii can also result in a catastrophic deterioration in mechanical properties and corrosion resistance [2,5].…”

“…Previous work noted that as well as geometric problems, bending thick-walled superduplex pipe to tight radii can also result in a catastrophic deterioration in mechanical properties and corrosion resistance [2,5]. Microscopy and modified double-loop electrochemical potentiokinetic reactivation (DL-EPR) analysis have previously been used to demonstrate that the deterioration in the performance of the material was mainly due to the generation of α , and that the presence of large quantities of chromium nitride (Cr 2 N) may also have played a part [3,6].…”