During recent pipeline construction seasons, there have been reported difficulties in cold field bending different joints of line pipe produced by the same manufacturer during a particular production run. These difficulties were typically manifested as an inability to achieve bends of one to one-and-a-half degrees per diameter in the pipe without forming ripples. Some of these problems could be traced to poor bending practices, i.e., inappropriate bending machine set-up and operator inexperience. However, it was observed that even with proper machine set-up and experienced operators, some "bad...
During recent pipeline construction seasons, there have been reported difficulties in cold field bending different joints of line pipe produced by the same manufacturer during a particular production run. These difficulties were typically manifested as an inability to achieve bends of one to one-and-a-half degrees per diameter in the pipe without forming ripples. Some of these problems could be traced to poor bending practices, i.e., inappropriate bending machine set-up and operator inexperience. However, it was observed that even with proper machine set-up and experienced operators, some "bad pipe" exists that could not be bent as far as desired without introducing ripples. The objective of this program was to develop an acceptance criterion for an allowable ripple in a gas-transmission pipeline as a result of a cold field bend. Previous acceptance or rejection criteria for ripples in cold field bent pipe were quite subjective. The purpose of this study was to define quantitative limits for acceptable ripple heights that will not compromise the integrity of the pipe during its expected life. In a program discussed at the 9th PRCI/EPRG meeting, the work performed during a joint Australian Pipeline Industry Association/Line Pipe Research Supervisory Committee effort on the mechanics of cold field bending was presented. Based on theoretical and experimental studies, it was found that modern, high-strength, high D/t pipe forms ripples at very low bend angles during cold field bending. Although there was some circumstantial evidence that some amount of rippling can be tolerated in a pipe, there had been no systematic effort to quantify the influence that the ripples have on the long-term integrity of pipe.