It is important yet challenging to monitor and locate corrosion over long-distance natural gas pipelines, especially for internal corrosion. Water vapor condensation can provide an aqueous electrolyte for corrosion to occur inside the pipe. We have previously demonstrated distributed optical fiber-based corrosion and humidity sensors at ambient pressure. In this work, optical fiber sensors were interrogated using an optical backscatter reflectometer and tested under high pressures to simulate pressurized pipeline conditions. When pressurized to 900 psi with dry N2, strains of single-mode optical fiber sections became more negative, indicating compressive strains along the fiber. Humidity was successfully monitored at 900 psi based on water-induced strain changes of the fiber polymer jacket. The corrosion sensor section was electrolessly coated with Fe thin film as the corrosion proxy. The backscattered light intensity didn't show noticeable responses in dry N2, indicating that no corrosion occurred. When wet CO2 gas pressurized the reactor to 850 psi, the backscattered light intensity increased in several locations on the Fe thin film within the first hour, indicating localized corrosion. When a small amount of water was introduced to the CO2 pressurized reactor, the aqueous corrosion was also successfully detected.
Corrosion is a common and critical issue in the oil and natural gas industry and it adversely affects the component functionality and structural integrity of infrastructure for exploration, production, transportation, processing, and CO2 sequestration. The natural gas delivery system includes 528,000 km (328,000 miles) of transmission and gathering pipelines in U.S.1 According to the Pipeline and Hazardous Materials Safety Administration (PHMSA) database, corrosion has caused ∼25% of the natural gas transmission and gathering pipeline incidents over the last 30 years in the U.S., and 61% out of corrosion-caused incidents were due to internal corrosion.2
It is challenging to monitor internal corrosion effectively as the inside of the pipeline is not readily accessible during regular inspections. Moreover, corrosion can occur at some random locations inside the pipelines which extend thousands of miles. Most existing sensor technologies such as corrosion coupons and electrical resistance probes are point sensors and cannot detect corrosion other than at the sensor installed locations. Pipeline inspection gauges (PIG) or in-line inspection tools (ILI) can inspect the whole pipe but they are costly and typically run every 5–7 years per regulatory requirements or company policies.3 Therefore, it is of significant value to have a sensor capable of real-time monitoring and locating internal corrosion inside the long-distance pipelines before the structural integrity is compromised.