Preliminary Study of an Underwater Wireless Sensor Designed for Interrogating the Environmental Condition of Flexible Pipe Annulus

In recent years a number of high-profile cases have shown that flexible pipes are particularly susceptible to the aggressive environments occasionally found in deep-water oil and gas exploration. Ruptures in the outer polymeric layers of the flexible pipes are relatively common in these structures; this often leads to seawater ingress and, under specific conditions involving pressure and CO₂, stress–corrosion cracking of inner metallic layers may occur. In this scenario, a non-destructive technique that is capable of detecting flooding of the annulus region of flexible pipes becomes desirable. Radio frequency identification (RFID) is a well-established technology that allows wireless reading of dedicated low-profile tags. Furthermore, these tags, when designed appropriately, can also detect changes in the surrounding environment, and could in principle be used to detect, for example, seawater ingress in the annular space of flexible pipes. In this paper, a preliminary version of a RFID sensor was designed in order to test this concept through the use of finite-element modelling, and a prototype was used for validation and testing. Results show a marked change in frequency–response between dry and wet conditions. The sensor also allowed differentiation between water or oil-flooding of the surroundings, and also showed to be capable of quantifying proportions in water–ethylene glycol and water–CO₂ mixtures if adequately calibrated.