Abstract
Corrosion inhibition and monitoring programs in the 30", 500 mile (805 km) Pipeline in gas service are discussed. The inhibition programs were studied in the laboratory and applied in the pipeline. Twenty-eight pipeline corrosion inhibitors were screen-tested in the laboratory under extreme carbon dioxide and oxygen environments to select the most qualified and effective corrosion inhibitor for the pipeline. In addition to these screen-tests, the inhibitor's "gunk" forming tendency and properties in its condensed form were also studied for minimizing the downstream problems and inhibitor's adverse effects. The amine-based inhibitor, especially when it has an amide combination, was found to be effective and show less side effects at low oxygen concentration. This type of inhibitor is currently used in the pipeline. The inhibitors which are acidic in nature tended to hydrolize in the condensed form and caused stress cracking and pitting problems in the laboratory tests or pipelines. Some of these acidic inhibitors were effective as an oxygen corrosion inhibitor. Neutralization of these inhibitors by amine may minimize the problems.
The inhibitor selected in the laboratory was injected into the pipeline in a diluted form and by an atomizer. The ratio of inhibitor quantity to gas volume depended on the relationship among chemical residuals in the pipeline fluids, coupon corrosion rates, and corrosive environments such as the content of carbon dioxide, oxygen and water. This relationship and ratio determination were monitored by a computer program to achieve the corrosion protection and cost reduction.
Pipeline surveys were conducted by ultrasonic thickness measurements, "smart pig" and x-rays of piping to determine and verify the integrity of the pipeline. A weekly air survey was also carried out to monitor the pipeline. Results of these surveys verify that the integrity of the Seagas Pipeline is well preserved.
