Importance

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Abstract

After an inner wall tube, made of steel or alloy containing not less than 2% of Cr, whose outer surface thereof is machined and/or ground to a thickness of 0.1 mm or more including the scale layer, is inserted into an outer wall tube, made of ferritic steel containing not less than 2% of Cr, in which an oxide scale layer containing Cr and having a thickness of 10 to 30 μm is formed in the inner surface thereof, cold working at an outside diameter reduction rate of 5 to 30% is performed. Similarly cold worked after an inner wall tube having an oxide scale layer on the outer surface thereof, is inserted into an outer wall tube whose inner surface is machined and ground. A double-walled tube made has a uniform gap and an excellent thermal conductivity, and is suitable as materials for SG tubes of future FBR.

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First Claim