Abstract
This study involved evaluating the corrosion resistance of American Petroleum Institute (API) (1) 5L grade B, X52 and X70 carbon steel coupons in localized areas of Trinidad’s soil environments, to determine the most suitable pipeline to be used in different soils. The investigation was inspired by the fact that pipeline life in soils varied throughout the country. A comparison was made between the results of the laboratory electrochemical techniques and the field gravimetric weight loss method. It revealed that corrosion rate trends between coupons in similar types of soil were comparable and corroborative. However, the corrosion rate values did not compare well with the two methods, but they both revealed that the API X70 steel had the greatest corrosion resistance in all soils, at the same time no appreciable statistical difference in corrosion rates. This was followed by the X52 and finally the 5L grade B steel. The analysis showed that microstructures having finer grain sizes with less pearlite gave better corrosion performance. The analysis also indicated that the most corrosive soil was peaty clay soil followed by the Silty clay soil, and finally the sandy soil. After one-year retrieval of coupons, all displayed general and pitting corrosion. Additionally, coupons from the silty clay and the peaty clay soils showed irregular shaped pit morphology typical of Sulfate-reducing bacteria (SRB).
