Metallurgical aspects of induction-bending thick-walled super duplex pipework

Abstract

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.

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

“…As far as possible all of the process variables were kept constant between the linear and bend testing, as well as between the diet of tests, and the previous bend testing, which had previously produced the deterioration in the properties of the pipe [2]. The following points are worth noting.…”

“…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].…”

“…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]. 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].…”

Effects of Induction Heat Bending and Heat Treatment on the Boric Acid Corrosion of Low Alloy Steel Pipe for Nuclear Power Plants

“…In addition, it is well known that the induction heat bending process can produce high quality bent pipes using automatic controls [5]. Analyses and process designs to optimize the bending process have also been studied [6][7][8][9][10][11][12][13][14][15]. As a result, international standards for induction bends have been established [16].…”

An Experimental Evaluation of the Temperature Profiles in Super Duplex Pipe Subjected to Induction Heating and Bending

“…At this temperature, the yield strength of the pipe will be reduced to around 10% of the value exhibited at room temperature ( Ref 2,3). The sizable reduction in yield strength of the material at the heated zone ensures that bending is concentrated at that region ( Ref 1,4). Attempts made to model these geometric changes using elastic-plastic FEA have met with limited success.…”