Progress in Production and Qualification of Stainless Steel Jacket Material for the Conductor of the ITER Central Solenoid

When energized, the ITER Central Solenoid coils experience large pulsed electromagnetic forces that the conductor jacket itself must withstand. The conductor jacket consists of circle-in-square extruded and drawn austenitic stainless steel pipes. The qualification of the production of stainless steel jacket material was carried out on jackets manufactured in both a very low carbon AISI 316LN grade and a high Mn-bearing austenitic stainless steel, called JK2LB. Two different suppliers provided fully representative batch productions of both grades. Extensive metallurgical and dimensional metrology examinations were carried out at different steps of the processing, starting from the forged billets used as semifinished products to be engaged in the extrusion process, to the solution annealed jackets in their final shape. A specific method of Phased Array Ultrasonic Testing (PAUT) was developed and successfully applied for the non-destructive examination of the different jacket productions. PAUT sectorial scan inspections were carried out with probes traveling on the outer surface of the section, allowing almost 95% of the volume to be examined despite the complex geometry of the jacket.