The dehydration of natural gas consists of water removal that is associated with the natural gas in form of vapor. The removal of water prevents the formation of gas hydrates and reduces corrosion in pipelines and components. The present study addresses the aggressiveness of the environment and the possible prevention methods in a corrosive environment containing MEG (Monoethylene Glycol) in presence of a neutralizer (Monoethanolamine MEA). The materials used were ASTM A106 gr. B and A285 gr. C, steels that are extensively used by the oil industry in the construction of pipelines and pressure vessels. Corrosion rate measurements were carried out through weight loss (in situ) measurements, under normal operating conditions at different steps of the process: rich glycol-chiller (- 6°C), rich glycol filter (60°C) and lean glycol-reboiler (95°C). The laboratory tests were performed by means of linear polarization resistance (Rp) under the presence of MEG, MEG/H20 and MEG/MEA ratios at 25, 60 and 93°C using a nitrogen atmosphere. For rich glycol at high temperatures, both steels showed a relatively high corrosion rate (0.45 ram/y) and internal pitting. This investigation suggested that the presence of rich MEG at low pH increases the corrosion rate and may affect the susceptibility of pitting of the steel. An optimal neutralizer dosage is an important factor to prevent the corrosion of the components. The morphology of the corrosion products and the characteristics of pitting were studied employing SEM-EDS techniques and optical microscopy.
Natural gas usually, contains between 20 to 100 pounds of water by MMSCF of gas, depending on the saturated point at the operation conditions. This water could be removed by passing the gas through separators. Nevertheless, it is impossible to remove 100% of liquid, in addition to the partial condensation of vapor that takes place by effect of changes in gas pressure and temperature. The presence of this liquid can induce different problems in dehydration plants, such as: pipeline corrosion, reduced gas transmission capacity and hydrate formation I~
I In order to avoid corrosion problems, it is necessary either to remove water or carbon dioxide, or both from the natural gas streams to desirable levels. For this reason, glycol solutions are used in natural gas dehydration processes. After the absorption, the solution has a low pH (-5) and a high water content (30-35%) in a relatively high temperature environment, this conditions are favorable to induce corrosion of carbon steel [21
PDVSA Exploration and Production has established a program of internal corrosion control methods to suppress or reduce it to a desirable level. As part of this effort, weight loss coupons have been installed in situ to measure the extent of damage from a morphological point of view and the effectiveness of chemical treatment (neutralizer of rich glycol) injected up stream of the measuring locations. The product used for this purpose in this system has been Monoethanolamine (MEA) and a neutralizing/film amine based complex (commercial product) injected in the glycol regeneration step in Lamarliquido dehydration plant (Figure 1). Due to the failures reported above, an effort was made to determine the effectiveness of the current treatment (MEA) and to evaluate alternative ones in the dosage and neutralization capacity 13.41
Lamarliquido dehydration plant, a unit for treatment of natural gas at Lake Maracaibo in northwest Venezuela, extract liquids from natural gas by a cooling process with propane, through an heat exchanger. Natural gas is cooled, from 52 to -37°C (125 to -35°F), and some liquids condensed including water steam with the forma
