After testing to failure, several of the wrinkles were fractured to determine the location of crack initiation.One wrinkle on each of the samples was reinforced using composite materials (i.e., four repaired and four unrepaired).The strain gage results also provided information regarding the level of strain reduction provided by the addition of composite materials.

Strain gages were placed on all of the wrinkles to make measurements during pressure cycling.

A total of four test samples were pressure cycled, resulting in a total of eight wrinkles.

Each pipe sample integrated two wrinkle bends.

This program involved the following aspects. The wrinkle bends used in the program were those cut out from a pipeline that was installed in late 1940s. Using some of the insights extracted from prior wrinkle bend studies, a program was developed to specifically assess the performance of wrinkle bends as a result of vintage construction on a vintage pipeline. Whereas the wrinkle bends found typically on pre-1955 built pipelines are sharper than these ripples with length to height ratios on the order of 4. Additionally, “mild ripples” are those developed using modern-day field bending techniques where such ripples bear a length to height ratio on the order of 12. Vintage wrinkle bends are often of the wave shape with outward deformations. Bending practices used during pipeline construction, up until 1955, typically resulted in circumferential pipe deformation or wrinkles on the inside bend radius of the pipe. Wrinkle bending is a process where wrinkles are introduced in a steel pipe during construction to obtain pipeline alignment. The experimental results demonstrated that composite materials can extend the fatigue life of wrinkle bends when designed and installed properly. The effects of metal loss due to corrosion were also considered. Strain gages were installed on select samples to determine alternating stresses. Included in this study was an evaluation in using composite materials to determine the potential for life extension considering the presence of reinforcement. For this reason, a study was conducted to assess the relative severity of wrinkle bends present in a pipeline system. Concerns exist among the pipeline industry about the effects of wrinkle bends on the long-term integrity of pipelines.

Tube bending wrinkle chart