Effect of Material Properties in Predicting the Fatigue Life of Offshore Pipelines Subjected to VIV

Due to subsurface currents, cold-water pipelines and risers installed for energy conversion processes in ocean environments are frequently subject to Vortex-Induced Vibration (VIV). The VIV response of the member may be “in-line” (IL) in the direction of current flow or “cross flow” perpendicular to the direction of current flow. The focus of the study is the cold-water conduit installed for the desalination process that oscillates in the IL direction, and it is demonstrated that the material properties must be selected in relation to the direction of VIV oscillation of the member. A review of the relevant literature reveals that selecting appropriate material properties for VIV fatigue analysis is assigned negligible weight. This paper discusses and applies the material test results for VIV fatigue analysis, emphasizing the significance of the material property in predicting VIV fatigue damage. Considering the response behavior of the High Density Polyethylene (HDPE) cold water pipeline that experiences inline (IL) or cross flow oscillation in the ocean environment, tests are conducted to estimate the elastic modulus properties. Elastic modulus and flexural fatigue test for HDPE material are carried out, and the VIV numerical analysis tool, Shear7, is used to analyze the additional fatigue results from relevant literature. To acquire reliable results, the numerical analysis is conducted using the test results in the flexural direction rather than the tensile direction, as it is more relevant to the IL oscillation of the pipeline. To enhance the fatigue life, the mitigation analysis of VIV of HDPE pipeline is performed by modeling the helical strakes on a portion of the pipeline using flexural material properties, reducing fatigue damage.