Abstract: In an inner pipe assembly step, sheet-metal-made inner-pipe divided bodies and a cast inner-pipe divided body are connected to assemble an inner pipe. In a center flange connecting step, the sheet-metal-made inner-pipe divided bodies are connected to a center flange. In an outer pipe connecting step, an outer pipe covering the inner pipe is connected to the center flange and an exhaust-air-inlet-side flange. In a masking step, at least one of: a connected portion between the sheet-metal-made inner-pipe divided bodies and the cast inner-pipe divided body; or an opening portion between the outer pipe and the inner pipe is sealed. In a cutting machining step, an inner wall surface of the cast inner-pipe divided body facing the turbine wheel is subjected to a cutting machining after the masking step.

Abstract: In an inner pipe assembly step, sheet-metal-made inner-pipe divided bodies and a cast inner-pipe divided body are connected to assemble an inner pipe. In a center flange connecting step, the sheet-metal-made inner-pipe divided bodies are connected to a center flange. In an outer pipe connecting step, an outer pipe covering the inner pipe is connected to the center flange and an exhaust-air-inlet-side flange. In a masking step, at least one of: a connected portion between the sheet-metal-made inner-pipe divided bodies and the cast inner-pipe divided body; or an opening portion between the outer pipe and the inner pipe is sealed. In a cutting machining step, an inner wall surface of the cast inner-pipe divided body facing the turbine wheel is subjected to a cutting machining after the masking step.