| 摘要 |
PURPOSE:To carry out the title control and increase the hardness and compressive residual stress of the inside of the pipe by forming a slit in the pipe, in the longitudinal direction, subjected to shot peening (SP); measuring the outside diameter and thickness of the pipe before and after forming the slit; calculating a specific ratio; and using the value. CONSTITUTION:The thickness of small pipe 1 is measured and the inside of pipe 1 is subjected to peening by SP unit 2. Next the outside diameter D of pipe 1 is measured, slit 3 is formed in pipe 1 in the longitudinal direction, and the outside diameter D' is measured. According to the measured values, the average diameter Dm=D-h and a fluctuation in outside diameter DELTAD/D<2>m are calculated. The residual stress or of the inside of pipe 1 in the circumferential direction is obtd. as a primary approximate value according to formulaI, wherein E is an expansion coefficient and nu is Poisson's ratio. DELTAD/D<2>m is closely related to the residual stress and easily measured. In order to prevent the occurence of stress corrosion cracking or the like on the inside of pipe 1, the SP procedure is controlled according to DELTAD/D<2>m so that the hardness and compressive residual stress of the inside are increased. |
