| 摘要 |
PURPOSE: A steel pipe having an outer circumference of wave form is provided to improve the intensity thereof, and prevent the transformation of a surface by forming a ceramic insulating layer at the outer surface. CONSTITUTION: In a steel pipe(20) having an outer circumference of wave form, a plurality of concave portions(22) and a plurality of convex portions(21) are formed at the outer circumference of the steel pipe, alternately and repeatedly to improve the intensity of the steel pipe. A ceramic insulating layer(30) is formed at the outer surface of the steel pipe. The ceramic layer reinforces the intensity of the steel pipe, and prevents the contact of the steel pipe and oxygen to prevent the steel pipe from rusting.
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