Alignment rules for multiple flaws vary between fitness-for-service procedures in different countries. In order to understand the behavior of alignment rules, quasi static failure bending tests have been performed on 2- and 4-inch diameter full-scale pipes with two similar flaws at ambient temperature. The pipe materials employed in the experiments were both ferritic and stainless steels. The two flaws are circumferential surface flaws situated inside the pipes. The non-aligned flaws are located in the circumferential distance S and axial distance H. The experiments showed that when the flaw shapes were short and deep, maximum loads occurred after the flaws had penetrated to the outer wall of the pipes. When the flaws were long and shallow, maximum loads occurred at the point when the flaws penetrated the outer wall of the pipe. With respect to the maximum loads under the condition of the same circumferential distance S, the maximum loads were found to increase with increasing axial distance H for short and deep flaws. However, the maximum loads were found to be unaffected by H for long and shallow flaws.
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