Study on crack opening area and coolant leak rates on pipe cracks

This study was executed to support the establishment of Leak Before Break (LBB) standards for high energy piping, by examining crack opening shape on the pipe surface and crack opening area which may be used in the leak rate analysis. To decide the crack opening shape, a bending test was conducted by using 8in schedule 80 carbon steel pipe with an artificially produced circumferential through-wall crack. Crack opening displacement (COD) at some points along the crack were measured by clip gages. The results indicated that the crack opening shape was nearly elliptical. When the crack opening area changes from the pipe inner surface to the outer surface, it is also necessary to clarify which part of the crack opening area may be used in the analysis. Therefore expansion and reduction slits leak tests weret done. These results showed that the middle crack opening area between the inner and outer surfaces may be used in the analysis. Using the above results, the analytical leak rate calculated from the Tada-Paris equation and Moody's critical flow model was in good agreement with the measured one obtained from the leak test. (author)