Abstract
Volatile corrosion inhibitor (VCI) was developed to inhibit Top of Line Corrosion (TLC) in wet gas pipelines and its injection methods can significantly affect the required dosage and consequently, its efficiency. In this study, a VCI’s efficiency was compared using batch and continuous injection methods. A series of TLC tests, including a 5-day control test, a 7-day continuous injection test (200 ppm of VCI every 3 days), and a 5-day batch injection test (1000 ppm of VCI) were conducted using API 5l X65 carbon steel grade samples. The uniform corrosion rates (UCR) were determined using the Weight Loss method (ASTM G1-03). The pitting rates (ASTM G1 46-21) were assessed with an Infinite Focus Microscope (IFM), and surface morphology characterisation was analysed using Scanning Electron Microscopy (SEM). Overall, both tests were unable to efficiently inhibit corrosion, due to under dosage of VCI concentration. However, the batch injection test performed better than the continuous injection test (UCR: 0.40 mm/y vs. 0.69 mm/y; pitting rate: 0.70 mm/y vs. 3.28 mm/y) as it only caused uniform corrosion. The severity of the corroded sample from continuous injection test was due to partial coverage of VCI film on top coupon surfaces, that led to the local breakdown of VCI and consequently, resulted in a high pitting rate. In conclusion, in this testing environment, both methods require a higher concentration of VCI to reduce the corrosion rate efficiently.
