Investigation of Alternating Current Density and its effect on Corrosion of Underground Hydrocarbon Pipelines

ABSTRACT

This study investigated AC density and its effect on corrosion of underground hydrocarbon pipelines within the Niger Delta area of Nigeria. It entailed the measurement of AC interference level on selected pipelines, soil test to ascertain the cation exchange capacity (CEC) of the soil along the pipeline ROW among other soil properties, the measurement of soil resistivity, location and the sizing of coating defects on the pipelines, determining AC density and the rate of AC corrosion on the pipelines. Four hydrocarbon underground pipelines were chosen for the study due to their proximity to HVTL. The pipelines were 457 mm diameter and 1.2 km long gas pipeline at Owaza in Abia State, 457 mm diameter and 4 km long gas pipeline at Alaoji in Abia State, 508 mm diameter and 36 km long Kolo Creek Trunkline (KCTL) in Bayelsa State and Oma 609.6 mm diameter and 30 km gas pipeline in Akwa Ibom State. Digital Earth Resistance Tester DY4300, Cath-Tech CTL-3000 DCVG, AC/DC Digital Clamp Multimeter Tester DT3266L and Cosasco Model 620HD Underground ER Probe instruments were used to measure the resistivity of the soil, locate coating defects, measure AC voltage interference level, and rate of AC corrosion respectively. The induced AC voltage from HVTL was measured daily for 92 days in wet season and 31 days in dry seasons. Direct current voltage gradient survey technique was adopted to locate and size the coating defects. Soil samples were taken along the pipelines ROWs to determine the physical and chemical components. Electrical resistance (ER) probe was used to monitor the rate of corrosion of the pipelines.