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Thorough the last two decades, oil and gas reservoirs discovered and developed in deep and ultra deep waters have continuously posed challenges to petroleum exploration and production activities in offshore basins. Maintaining optimum flow rates of oil and gas from subsea wellheads to surface processing facilities demands new technological solutions for petroleum companies operating in such frontiers. Integrity assurance of structures, equipment, and flow lines plays a major role in maximizing offshore production systems availability while at the same time keeping safety, operational, and environmental risks at minimum levels. In this scenario, implementation of permanent health monitoring solutions must take into account the environment of oil and gas production facilities, where installations in hazardous classified areas require explosion and fire-proof instrumentation. In this context, optical fiber sensors offer an attractive alternative to electrical sensing technologies, which, until now, have been the primary choice by maintenance personnel at offshore production units.

The present paper reports initial results from an investigation program launched with the objective of presenting combinations of analytical, experimental and numerical methods to predict and monitor fatigue initiation and fatigue damage progression in equipment such as pressure vessels, tanks, piping and pipelines with dents or complex shaped anomalies. The monitoring of fatigue initiation and propagation in the actual specimens used nondestructive infrared inspection techniques. Thermoelasticity stress analysis (TSA), three-dimensional digital image correlation (3D-DIC) and fiber optic Bragg strain gages (FBSG) were used to determine strains at fatigue hot spots locations. Strain fields determined from the experimental measurements and from finite element analysis (FEA) were combined with the fatigue Coffin-Manson strain-life equation and the Miner’s fatigue damage rule to predict fatigue life (Nc). Results from one tested 3 m long tubular specimen containing a complex shaped dent are reported and fully analyzed.

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