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

Three-Body Abrasion Corrosion Studies of High-Cr Cast Irons: Benefits and Limitations of Tribo-electrochemical Methods

High-Cr white cast irons (WCIs) are multiphase alloys commonly used in aqueous industrial environments in applications that require both high abrasion and high corrosion resistance. Various electrochemical techniques can be useful in elucidating tribocorrosion characteristics of metallic materials undergoing wear in a corrosive environment. This study is focused on the interpretation of electrochemical measurements applied to three-body abrasion corrosion contacts of high-Cr WCIs. Particular attention has been paid to determine whether tribo-electrochemical data can pick up any effects that the multiphase microstructure of WCIs may have on the tribocorrosion characteristics, especially in environments containing chloride ions. Since both wear and corrosion of multiphase alloys are usually not uniform, their tribocorrosion behaviour is difficult to study and is still poorly understood. The experimental results are discussed in terms of benefits and limitations of tribo-electrochemical techniques such as polarization (potentiostatic, potentiodynamic) and electrochemical noise (galvanic coupling, potentiostatic) in studying abrasion corrosion behaviour of high-Cr WCIs. The application of high-resolution surface analysis techniques (microprobe, NanoSIMS, C-AFM and SKPFM), used in support of the electrochemical data interpretation, is also demonstrated

Three-body tribocorrosion of high-chromium cast irons in neutral and alkaline environments

Two high-chromium cast irons (HCCIs) with different microstructure and Cr:C ratio of 9 and 6 were tested using a new three-body abrasion-corrosion rig incorporating electrochemical techniques. Coarse garnet particles acted as abrasive grits and the effect of mechanical parameters (i.e. load, sliding distance) was investigated. Electrolytes with different pH, neutral and alkaline were used and the effects of chloride ions and elevated temperature were also tested. SEM and optical profilometry were used to analyse the extent of abrasion-corrosion damage and the surface morphology.In the corrosion-only tests it was found that the corrosion rate increased with increasing pH, and both the chloride ions and elevated temperature had a detrimental effect. Increasing alkalinity has shifted the anodic behaviour from the matrix to the carbides. The influence of key alloying elements on the corrosion behaviour is also addressed.Electrochemical measurements revealed that the concurrent three-body abrasion had accelerated corrosion for both HCCIs in most environments tested. The following abrasion-corrosion mechanism for HCCIs in highly alkaline solutions is proposed: (i) removal of a thin oxidized layer from the carbide phase; (ii) plastic deformation and extrusion of the Fe-Cr matrix over the carbide-depleted regions. SEM images revealed repeated plastic deformation with the wear morphology similar to the three-body abrasion of ductile materials, and carbides were not visible. In neutral environments the carbide/matrix interface was the most vulnerable to corrosion initiation, with the matrix dissolving preferentially and the unsupported carbides fracturing. The influence of materials characteristics on the abrasion-corrosion synergistic action is also described in this paper

Tribo-electrochemical behaviour of 316L stainless steel: The effects of contact configuration, tangential speed, and wear mechanism

Tribo-electrochemical behaviour of 316L stainless steel was studied using three contact configurations: two-body ceramic counterface (2B-CC), three-body rubber counterface (3B-RC) and three-body ceramic counterface (3B-CC). Electrochemical methods were employed to investigate the effects of tangential speed and wear mechanism on the tribo-electrochemical characteristics of the 316L samples at each contact configuration. In both 2B-CC and 3B-RC contacts increasing the tangential speed resulted in higher current measured while in the 3B-CC contact the current was an increasing function of time even at a constant rotational speed. After the abrasion-corrosion tests different repassivation kinetics was found for each contact configuration

NanoSIMS investigation of passive oxide films on high-Cr cast iron

The discrete depth characteristics of thin passive oxide films were investigated using high-resolution electron microprobe and nanoscale secondary ion mass spectrometry (NanoSIMS). A novel NanoSIMS method involving a Cs layer deposition before Cs+ sputtering was employed for the first time to determine the elemental distribution at different sub-layers of a passive film. The film was formed in air on the surface of a multi-phase microstructure of high-chromium cast iron (HCCI). It was found that the film composition and thickness varied according to the underlying microstructure phase. Based on the microprobe and NanoSIMS results, the influence of the HCCI passive film thickness and composition on the localized passivity breakdown has been proposed

Influence of phosphate ion dopant on corrosion protection properties of polypyrrole coatings on carbon steel

Polypyrrole (PPy) and polypyrrole-phosphate (PPyP) coatings were electropolymerised onto carbon steel electrodes in aqueous oxalic acid solution using the cyclic voltammetry technique. The electropolymerisation of PPyP was carried out with addition of trisodium phosphate to the supporting electrolyte. Prepared coatings were characterised using scanning electron microscopy. In addition, the ability of the coatings to control the corrosion of carbon steel was studied with the help of a variety of electrochemical methods: open circuit potential monitoring, potentiodynamic polarisation and electrochemical impedance spectroscopy all in 3?5% NaCl solution. All the results have consistently indicated that carbon steel is better protected by the PPyP coating than by the PPy coating. © 2009 Institute of Materials, Minerals and Mining

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

Low-level dissolved oxygen measurement in monoethylene glycol

A test method for low-level dissolved oxygen (DO) measurement in glycol-based conditions is explained. Three independent DO measurement techniques are compared in water-only and monoethylene glycol (MEG) solutions. The objective is to determine limitations and advantages of each technique when the measurement is performed in MEG