Full-Scale Industrial Instrumented Induction Bending Experiment on Inconel® Alloy 740H®

Full-Scale Industrial Instrumented Induction Bending Experiment on Inconel® Alloy 740H® Authors: Firdosh Kavarana (TTB), John Shingledecker (Electric Power Research Institute), Jack deBarbadillo (Special Metals Corp.), Noah Paulson (Argonne National Laboratory) Induction bending is a preferred manufacturing process for the production of pipe bends in high energy piping systems across the power generation industry. While the induction bending process is well established for ferritic and austenitic stainless steels, there is a desire to utilize nickel-based precipitation hardened alloys in advanced ultra-supercritical steam (A-USC) power plants, supercritical carbon dioxide (sCO2) power cycles, and other advanced energy applications where the industry has less experience. In this work, a highly instrumented induction bending experiment was conducted on a gamma prime strengthened nickel-based alloy, Inconel ® Alloy 740H®, pipe to provide unique data for validation of induction bending models and provide key insights into process limits. The experiment was conducted on a 711 mm (28 inch) diameter by 30 mm (1.5 inch) min WT pipe with over 50 thermocouples installed on the inner and outer diameters (ID and OD) at various circumferential and axial locations to record time temperature histories during induction bending. This instrumented induction bend data was compared to key machine control and monitoring parameters including OD pyrometer temperature control measurements, speed, bend angle, and roller loads. Pre-bend, post-bend, and after solution heat-treatment OD/ID surface visual inspection and volumetric inspection using Phased array ultrasonic testing was conducted in addition to physical thickness measurements for geometry and wall thickness. After bending an ID initiated crack developed outside of the bend arc near the stop location of the induction coil. Analysis of the data showed critical parameters which need to be controlled to obtain successful bends. These results will be discussed in terms of practical application and limits for bending of age hardenable alloys.