An experimental evaluation of induction bending as a method for producing pipe bends with radii ≥2.5D

Abstract

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.

Hot Tube-Forming

“…Tube (pipe) bending using local induction heating is an advanced process that is used to bend thick-walled pipes with small bending radii and large diameters (74)(75)(76)(77). It is cost effective and has been widely used in many fields such as power, transportation, and chemical industries since it was invented by Dai-ichi High Frequency Co. (DHF0 of Japan); Figure 40 shows the bending principle of induction tube bending.…”

“…The thinning and thickening ratio of the pipe wall thickness, the pushing force, the oval shape of the cross section of the pipe, and the springback after unloading were discussed. The literature (76,77) reported the challenges associated with induction bending in the production of tight bends in thick-walled pipe, and concluded that the existing charts are deficient when considering extrados wall thinning. The analytical models predicted the final deformed geometry of induction bends in thick-walled pipe, which was compared with the results of empirically derived charts and computational models.…”

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

“…These problems are most apparent when producing tight bends (i.e. where the bend radius 2.5 × nominal pipe diameter) from thick-walled (>15 mm) pipe [1].…”

“…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].…”

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

“…A previous investigation by the authors considered methods of reducing the manufacturing costs of thickwalled (wall thickness nominal diameter/20) super duplex pipework featuring complex geometry, such as those used in the petrochemical, oil, and gas industries [2]. The form of induction bending of interest to the authors is temper-free (TF), a cost-effective variant where no post-bend heat treatment is used [3].…”