Design and Experimental Validation of an Integrated Four-Stage D.D.I. Process for STS316L Seamless High-Pressure Cylinders

STS316L seamless high-pressure cylinders are used for high-purity specialty gases, motivating efficient manufacture by deep drawing and ironing (D.D.I.). This study presents a six-to-four stage integration that combines baseline Stages 2–3 and 4–5 while retaining the first-drawing and final-ironing functions. A Tractrix die supports initial drawing, and a multi-step die distributes deformation through successive contact regions. Process planning is supported by design rules and development finite-element analysis. Die-angle screening gave normalized Cockcroft–Latham values of 0.82 at 35° and 0.99 at 36°. Preliminary final-stage annealing tests gave yield strengths of 256 MPa at 1000 °C and 237 MPa at 1050 °C, informing stage-specific temperature selection. Grain growth is discussed as a possible explanation for this response. Finished-cylinder tests from the development program provide a performance basis with reference to ISO 9809-4 and KGS AC212. Eliminating two of six preparation cycles gives a conditional energy reduction of 33.3% for those operations under equal energy per cycle and equal batch size.