In the natural gas sweetening process, amine aqueous solutions are used to absorb CO2 and H2S acid gases. The resultant solution, that is the mixture of acid gases and amines, causes severe corrosion problems in process equipment such as the amine regenerating tower. In the present work the effects of concentration and residence time of diethanolamine were studied in the corrosion of 1010 steel. Electrochemical noise measurements (ENM) was used and correlated with weight loss and surface attack inspection. Tests were performed in a closed loop flow system simulating hydrodynamic conditions, with diethanolamine concentrations in the 30 to 60 % by weight range at 100 °C and a pressure of 15 or 30 lb/in 2 . The results obtained showed accelerated corrosion followed by passive film formation. These effects are related to the increase in amine concentration. That is, the corrosion attack increases but the time of passive film formation decreases as the amine concentration is greater.
At the present time, the use of natural gas as a cheap and environment friendly energy source is becoming important in Mexico and the rest of the world. The Mexican oil industry is planning to double the natural gas offer by the year 2005. This increase in the gas production implies a greater use of gas sweetening installations. Within this process equipment, the CO2 and H20 absorption towers as well as the regenerating amines solution reheater systems present major corrosion problems. Mainly localized corrosion has been reported due to the formation of sulphide deposits, carbamates and amine decomposed products ~. The acid gases amine absorbing solutions widely used industrially are: monoethanolamine (MEA), diethanolamine (DEA) and methyl diethanolamine (MDEA). As for the case of MEA, its use is becoming more limited due to its unstability under the influence of temperature 2,3. Although, at low concentrations the alcaneamines act as film inhibitors, with increasing concentration, as is the case with sweetening systems, they contribute to the corrosion of metallic materials 4,5.
To demonstrate the influence of amines in the corrosion of steel, studies have been performed but under hydrostatic conditions. In the process equipment, the corrosive solutions are not stagnant but under flow conditions. Therefore, the hydrodynamic effect changes the corrosion characteristics, specially when the system is under mass transfer control. In the literature on the subject, only weight loss has been reported for short periods of exposure 6- 9. One of the objectives was to determine the corrosion behavior as a function of time. In this work electrochemical noise combined with weight loss and surface attack inspection. The present work not only studied the influence of amine concentration, but also the effect of residence time and the shear stress conditions. Corrosion was characterized in a flow system with cylindrical geometry same as that found in absorption towers. It was expected that corrosion of steel in the presence of amines, increase its rate as a function of increasing concentration. This was not totally true because for greater residence times, it was found that for greater concentrations corrosion decreases but localized attack may occur.
EXPERIMENTAL
In order to determine the influence of flow conditions in the corrosion of carbon steel under different amine solution concentrations, a closed loop flow system was assembled, which allowed the simulation of the hydrodynamic conditions in cylindrical coordinates. Figure 1 presents the block diagram of such system. A test section was included to apply the electrochemical techniques and register the corrosion of steel in the closed loop
