Condensation corrosion of carbon steel at low to moderate surface temperature and iron carbonate precipitation kinetics

© 2016 Elsevier Ltd. This study investigates the influence of surface temperature and droplet retention time (DRT) on the corrosion rate, FeCO3 supersaturation, and scaling tendency of carbon steel exposed to water condensation. This corrosion phenomenon is also known as top of the line corrosion (TLC). TLC is found to be governed by surface temperature irrespective of water condensation rates (WCR) at low surface temperature (15°C). The results also demonstrate that the DRT directly influences FeCO3 supersaturation and scale formation. A new kinetic constant for the calculation of FeCO3 precipitation rate under condensing condition at the top of the line is proposed

The influence of mono ethylene glycol (MEG) on CO2 corrosion of carbon steel at elevated temperature (80 to 120°c)

Monoethylene glycol (MEG) is injected in the pipelines to prevent hydrate formation, and subsequent pipeline blockage. Recent investigations indicated that presence of MEG could impede CO2 corrosion of carbon steel, although many aspects remain unknown. In the current study, experiments were conducted at 80 oC (176 oF), atmospheric pressure, and 100 oC (212 oF), and 120 oC (248 oF) at pCO2 of 10 bar. Test solutions had different ratios of MEG/Ultra-pure water with 3 wt. % NaCl concentration. Electrochemical techniques such as linear polarization resistance (LPR), Electrochemical Impedance Spectroscopy (EIS) and Tafel polarization were employed to investigate the corrosion rate and phenomenon. Corroded surface of the samples were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) techniques. This research aims to provide an improved insight on contribution of MEG on CO2 corrosion of carbon steel, at elevated temperatures

Top-of-the-Line Corrosion in The Presence of Hydrocarbon Co-Condensation in Flowing Condition

During the transportation of wet gas, temperature gradient between the internals of the pipeline and the outside environment leads to the condensation of water vapor. Freshly condensed water is very corrosive and can lead to the so-called Top-of-the-Line Corrosion (TLC). However, a certain fraction of hydrocarbons will co-condense along with the water vapor resulting in two immiscible liquids at the pipe wall with a different wettability and different corrosivity. To elucidate the role of co-condensation, corrosion tests in the absence and presence of hydrocarbon were conducted. In the experiments, hot vapors of water and n-heptane saturated with CO2 were generated and transported through a one-inch internal diameter condenser tube, with 2 carbon steel samples located at the inlet and outlet of the tube. Condensation took place on the inner surface of the tube and was related to the TLC. Corrosion rate was evaluated by the weight loss method. In the absence of co-condensation, corrosion rates increased with water condensation rates. In the presence of n-heptane co-condensation, water condensation rates had less influence on the corrosion rates. Iron carbonate (FeCO3) was observed only in the co-condensation scenario, suggesting the change of the chemistry of condensed wate

Corrosion of carbon steel under condensing water and monoethylene glycol

© 2018 Elsevier Ltd The influence of monoethylene glycol (MEG) on the condensation process and corrosion behaviour of carbon steel is investigated. The results show that increasing MEG concentrations at the bottom of the line increases MEG co-condensation, reduces condensation rates and, consequently, uniform corrosion rates. However, localised corrosion occurs and pits aggregate within the droplet boundary when MEG co-condenses with water. The corrosion product comprises of FeCO3embedded in a Fe3C matrix. Its thickness in the areas outside the condensed droplet boundary is greater compared to that of the inside. Localised corrosion mechanism of carbon steel under condensing MEG and water is proposed

Development of an Electrochemical Method to Study Top-of-the-line Corrosion

Top-of-the-line corrosion (TLC) is a concern for subsea wet-gas transportation pipelines operating in a stratified flow regime. The insufficient volume of electrolyte at the top-of-the-line (condensation) combined with the low electrical conductivity of the condensed liquid has confined, to-date, TLC studies to the weight loss method which only provides an average over a long period of time information. The onset of localized corrosion cannot be exactly determined, which makes it difficult to determine localized corrosion rates and mechanistic data. The instantaneous monitoring of TLC rates using electrochemical methods is still a challenge for researchers and in the field. To overcome this limitation, a novel TLC monitoring cell has been developed, which is capable of measuring in-situ corrosion rates by electrochemical methods such as Linear Polarization Resistance (LPR), Electrochemical Impedance Spectroscopy (EIS) and Electrochemical Frequency Modulation (EFM). The data presented in this paper have been conducted over 5 days at variable condensation rates to evaluate the feasibility and accuracy of the methods applied. In addition, TLC rates have also been measured by weight loss and monitored in-situ by measuring the iron concentration in the condensed liquids in order to compare these results with electrochemical methods. Thus, this paper presents the comparability and limitations of different techniques applied to TLC studies

Effect of mercury on corrosion in production wells in Gulf of Thailand

The effect of mercury on the corrosion of materials used for tubing in oil and gas production wells was studied. Carbon steel (L80) and 13% chromium stainless steel (13Cr) were selected for study by potentiodynamic polarisation. Simulated produced water, with the composition obtained from the Gulf of Thailand field, was used as a corrosive solution. Temperature kinetically increased the corrosion reaction. Chloride ions and carbon dioxide also enhanced the corrosion. Acidity increased the pitting corrosion of 13Cr and increased the corrosion rate of both 13Cr and L80. A concentration of 3-12 ppm of mercury lowered the current density in the passive region and increased the pitting potential of 13Cr. The corrosion rate of L80 was decreased with small amount of mercury addition. The 13Cr showed lower uniform corrosion rate than the L80 in all conditions of the simulated produced water. © 2011 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute

Efficacy of bisulfite ions as an oxygen scavenger in monoethylene glycol (at least 20 wt%)/water mixtures

Copyright © 2017 Society of Petroleum Engineers. This study investigates the oxygen-scavenging behavior of bisulfite ions in monoethylene glycol (MEG)/water mixtures at concentrations commonly found in gas-transportation pipelines. Temperatures and pH values were varied. The influence of transition-metal (TM) ions to catalyze the bisulfite oxygen scavenging was studied. Experimental results indicate that MEG significantly inhibits bisulfite oxygen removal, which is hindered at low pH values and, to some extent, temperature. TMs can accelerate the oxygen-scavenging reaction in pH-unadjusted solutions, although the rate was still lower than that of the pH-adjusted solutions. The possible mechanism for such behavior and industrial implications are discussed

Investigation of the Effect Chloride Ions on Carbon Steel in Closed Environments at Different Temperatures

This paper investigated carbon steel corrosion in an enclosed environment, where one set of steel was immersed in 3.5 wt.% NaCl solution and another exposed to humid (condensation) conditions. The study employed electrochemical noise and electrochemical impedance spectroscopy techniques to monitor real time corrosion behaviour. The samples were evaluated with surface characterisation techniques including optical light microscope, scanning electron microscope with energy dispersive X-ray spectroscopy, and Raman spectroscopy. The results showed that carbon steel immersed in the liquid phase at a constant temperature exhibited the highest weight loss. However, the carbon steel exposed to water condensation (gas phase) at 80 °C manifested extensive localised corrosion. EN results agreed with the microscopy findings

Comparison of insulation materials and their roles on corrosion under insulation

Thermal insulation is used in petrochemical and refinery plants where pressure vessels and piping system are insulated to conserve energy. Over time, water enters into the insulation through various pathways and is entrapped at the steel surface leading to corrosion under insulation (CUI). Mineral wool is one of the most used thermal insulation even though it is prone to absorbs water and causes CUI. A water repellent insulation can be an alternative thermal insulation to prevent CUI. However, limited research has been done in the public domain. Therefore, the present study investigates and compares the roles and influences of mineral wool and a water repellent insulations on CUI. In addition, the presence of drain holes and its ability to reduce CUI was evaluated. The susceptibility to CUI of carbon steel was investigated at 80 °C using a newly developed test rig in a controlled environment (25 °C and 50 %RH). An electrochemical impedance spectroscopy technique was used to monitor the rate of insulation dry-out. Due to localized nature of CUI, a 3D light microscope was used to analyze the surface profile of the samples after exposure to CUI. The results has emphasized the correlation between the wet time and severity of CUI