Pipeline integrity management: Internal corrosion detection of oil and gas pipelines using fiber optics

Oil pipelines are monitored for corrosion on regular intervals using conventional tools. A real-time monitoring solution was developed to avoid spontaneous failures that may occur between inspection intervals using distributed fiber optic sensors which are intrinsically safe. The fiber consists of a silica core and a polymer cladding coated with a metal layer from the pipeline's construction which upon corrosion exposes it to hydrocarbons altering its refractive index. Intensity of a traveling pulse drops and is captured by reflectometry techniques. The system was simulated and a laboratory scale setup is being developed to validate the model and test the solution.;Alternatively, a strain based corrosion sensor for the detection of external and internal corrosion of pre-stressed and pressurized structures was developed and tested on mild steel samples readily available. Theoretically, a beam shaped sample under a displacement load exhibits a linear relationship between the strain observed at any point and the thickness of the beam cross-section. This property was exploited to detect thickness changes in pre-stressed mild steel samples in double bending under an electrochemically excited corrosion reaction. The corrosion reaction was excited by supplying a DC current to the cell in which the samples act as the anode of the system while graphite rods serve as the cathodes. A salt water electrolyte was used to complete the electrochemical cell while the strain was logged using Fiber optic Bragg Grating technology and conventional electrical strain gages simultaneously. The results showed a strong relationship between the corrosion rate observed by back calculation from supplied current and the time derivative of the measured strain values. This sensor can therefore be extended to a variety of structures under mechanical loading proving both valuable for its ability to measure corrosion rate in real time while maintaining an intrinsically safe nature appropriate by oilfield standards.