Effect of preload scatter on fatigue life of subsea pipeline connector bolts located at suspended span section

The subsea pipeline connector (SPC) located at suspended span section not only bears the internal pressure from the oil and nature gas of the pipeline, but also needs to withstand the periodic drag force generated by vortex-induced vibration (VIV). This situation may cause fatigue failure of the flange connector fastening bolts. Reasonable preload value can reduce the fatigue stress and improve the fatigue life of the SPC bolts. This paper establishes a calculation model of the SPC drag force under VIV located at suspended span section. Normal distribution function is used to establish random models of preload for corner control pretension method and hydraulic tension pretension method considering the scatter of the preload value. On this basis, the stochastic finite element model (S-FEM) of SPC bolts is established to analyze bolts force under random preload considering VIV. The regression equation of strain-life for smooth fatigue specimens of bolt materials is applied to obtain preload-fatigue life curves of SPC bolts under different pretension methods. Then it is used to analyze the preload scatter on fatigue life of SPC bolts located at suspended span section. The analysis results indicate that the fatigue life dispersion of SPC bolts pre tightened by hydraulic tension pretension method is smaller compared with the corner control pretension method. Compared with the preload value determined by ASME code, increasing the SPC bolts preload appropriately can improve the fatigue life of SPC fastening bolts located at suspended span section.