Abstract
For long-distance natural gas pipelines, it is important to monitor and locate corrosion events, especially for internal corrosion. Water vapor condensation can provide aqueous electrolytes necessary for corrosion to occur inside the pipe. Based on previous work, a multi-parameter optical fiber sensor was developed and demonstrated for simultaneous monitoring of corrosion and water/humidity with location information along the fiber. Corrosion was detected through light intensity changes associated with the corrosion proxy coating and the presence of water was monitored based on water-induced strain changes on the optical fiber. The multi-parameter sensor was tested in both aqueous (acidic solution) and humid gas (N2 or CO2) conditions. As the humidity varied between 0% relative humidity (RH) and 100%RH, the single-mode fiber section showed water sensing capability with good reversibility and sensitivity. The corrosion sensor didn't show cross-sensitivity to humidity. In corrosive conditions, the corrosion sensor showed an increase in the backscattered light intensity at corroded locations because light absorption of the metallic thin film decreased as the film was corroded. Importantly, the corrosion sensor was able to monitor localized corrosion in wet CO2 gas, which is representative of internal corrosion in natural gas pipelines. The XPS (X-ray photoelectron spectroscopy) results indicate formation of iron carbonate after wet CO2 corrosion.
