Análise de fadiga nas armaduras de tração de dutos flexíveis considerando efeitos da corrosão marinha

Abstract

Statistics show that the most frequent damage type in flexible pipe is the outer sheath damage. Typical consequences are sheath rupture, annulus flooding and tensile armours corrosion by seawater. Integrity assessment in this type of occurrence is usually limited to a reassessment of the fatigue life considering the new annulus conditions, possibly conservatively estimating some armour damage. The objective of this work is to develop a methodology capable of assessing the sheath damage impact in the riser fatigue life considering armour corrosion, the associated stress concentration factors and S-N fatigue curves. It was devised i) a stress concentration model based on uniform corrosion, ii) a fatigue curve selection criteria with annular conditions and armour surface deterioration inferred from corrosion data and iii) a loading case pre-processing model to optimize local analysis computational cost in each fatigue assessment iteration. From those models, a methodology was devised to discretize the analysis interval, calculate the stress concentration factors and select the fatigue curves, run the cases local pre-analysis and, finally, calculate the fatigue damage through time. From the accumulated fatigue damage history, fatigue life or the remaining life are determined.