| 摘要 |
A production method which can form helical ribs stably by reducing trouble at the time of forming the helical ribs of an internally-ribbed steel pipe by drawing. When an internally-ribbed steel pipe having a plurality of helical ribs in the pipe axis direction is produced by inserting a plug having a plurality of helical grooves in the outer circumferential surface thereof into the inner surface of a pipe to be processed subjected to chemical conversion treatment and then performing cold drawing, drawing is performed by preheating the plug at 50-200°C, thus forming the helical ribs on the inner surface of a bare pipe. The chemical conversion treatment is preferably performed by an acid pickling process for removing oxidation scales and rust from the pipe surface, a process for forming a zinc phosphate film on the neutralized pipe surface, and a process for forming a lubricant layer on the zinc phosphate film. An internally-ribbed steel pipe thus obtained has excellent moldability and quality as a steel pipe for a boiler, and can deal sufficiently with a higher capacity or higher temperature/ higher pressure boiler. |
