Imidazoline, which is known as one of the active ingredients of corrosion inhibitors, is used in a lot of oil and gas facilities in order to mitigate corrosion problems. However, it is easily hydrolyzed to amide, which leads to the change of inhibitor efficiency. Therefore, the inhibitor efficiency of imidazoline-type and amide-type inhibitors was evaluated by several tests such as electrochemical measurements, weight loss test and quartz crystal microbalance measurement. Furthermore, the effect of one intensifier for corrosion inhibitor was also evaluated by the same tests.
As a result, the large difference of inhibitor efficiency between the imidazoline-type and amide-type inhibitor was not observed by the electrochemical measurements. On the other hand, the weight loss test under turbulent flow indicated that imidazoline-type inhibitor performed higher inhibitor efficiency than that of the amide-type. This intensifier improved the inhibitor efficiency of both types.
A lot of oil and gas facilities face corrosion problems because the production fluid contains some corrosive components represented by CO2. Generally, corrosion inhibitors are used in order to mitigate corrosion problems of tubing and pipeline. Imidazoline is known as one of the active ingredients of corrosion inhibitors and widely used in the oil and gas industries. However, imidazoline-type inhibitor is easily hydrolyzed to amide if water mixes into it. This hydrolysis reaction could progress in the stock tanks exposed to the weather. Once imidazoline changes into amide, not only its physical characters such as solubility to solvent but also its inhibitor efficiency changes1, 2. Consequently, the inhibitor efficiency as expected might not be obtained, and corrosion problems would occur. Therefore, it is necessary to evaluate the inhibitor efficiency of amide-type inhibitor that imidazoline-type inhibitor transforms to under operating condition.
For improving the inhibitor efficiency, an intensifier is added to corrosion inhibitor. The intensifier may assist the adsorption of inhibitors and/or have corrosion inhibition itself. Hence, it is important to select the effective intensifier for corrosion inhibitor, which can lead to preventing corrosion problems. In this study, one intensifier that contains sulfur was chosen and added into both imidazoline-type and amide-type inhibitors. The efficiency of four inhibitor formulations (imidazoline, amide, imidazoline with intensifier and amide with intensifier) and the intensifier itself was evaluated by electrochemical measurements, weight loss test, quartz crystal microbalance (QCM) measurement and time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement. Through these evaluation tests, each inhibitor efficiency was ranked, and the inhibitor mechanism was considered.