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Purpose This paper aims to establish the downhole CO2 partial pressure profile calculating method and then to make an economical oil country tubular goods (OCTG) anti-corrosion design. CO2 partial pressure is the most important parameter to the oil and gas corrosion research for these wells which contain sweet gas of CO2. However, till now, there has not been a recognized method for calculating this important value. Especially in oil well, CO2 partial pressure calculation seems more complicated. Based on Dolton partial pressure law and oil gas separation process, CO2 partial pressure profile calculating method in oil well is proposed. A case study was presented according to the new method, and two kinds of corrosion environment were determined. An experimental research was conducted on N80, 3Cr-L80 and 13Cr-L80 material. Based on the test results, 3Cr-L80 was recommended for downhole tubing. Combined with the field application practice, 3Cr-L80 was proved as a safety and economy anti-corrosion tubing material in this oil field. A proper corrosion parameter (mainly refers to CO2 partial pressure and temperature) can ensure a safety and economy downhole tubing anti-corrosion design.Design/methodology/approach Based on Dolton partial pressure law and oil gas separation process, CO2 partial pressure profile calculating method in oil well is proposed. An experimental research was conducted on N80, 3Cr-L80 and 13Cr-L80 material. A field application practice was used.Findings It is necessary to calculate the CO2 partial pressure properly to ensure a safety and economy downhole tubing (or casing) anti-corrosion design.Originality/value The gas and oil separation theory and corrosion theory are combined together to give a useful method in downhole tubing anti-corrosion design method. [ABSTRACT FROM AUTHOR]

Purpose CO2 corrosion rate prediction is regarded as the backbone of materials selection in upstream hydrocarbon industry. This study aims to identify common types of errors in CO2 rate calculation and to give guidelines on how to avoid them.Design/methodology/approach For the purpose of this study, 15 different “corrosion study and materials selection reports” carried out previously in upstream hydrocarbon industry were selected, and their predicted CO2 corrosion rates were evaluated using various corrosion models. Errors captured in the original materials selection reports were categorized based on their type and nature.Findings The errors identified in the present study are classified into the following four main types: using inadequate or false data as the input to the model, failing to address factors which may have significant influence on corrosion rate, utilizing corrosion models beyond their validity range and utilizing a corrosion model for a specific set of input, where the model is considered to be inaccurate even though the input lies within the software’s range of validity.Research limitations/implications This study is mainly based on the use of various corrosion models, and except few cases for which some actual field corrosion monitoring data were available, no laboratory tests were performed to verify the predicted data.Practical implications The paper provides a checklist of common types of errors in CO2 corrosion rate prediction and the guidelines on how to avoid them.Originality/value CO2 corrosion rate calculation is regarded as the backbone of materials selection in hydrocarbon industry. In this work, the source of errors in terms of corrosion modeling tool and human factors were identified. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to adopt both the fragments of imidazole and thiosemicarbazide as reaction centers, to synthesize a water-soluble corrosion inhibitor named as thiosemicarbazide-imidazole derivative (TH-IM).Design/methodology/approach This paper presents potentiodynamic polarization tests, electrochemical impedance spectroscopy tests and morphology study of metal surface by scanning electron microscope and thermodynamic study.Findings In the aggressive condition of CO2 saturated Wt. NaCl solution at 333 K for 72 h with 400 ppm inhibitor dosage, the efficiency of inhibition increases approximately 98 per cent through the method of weight loss.Originality/value This paper finds a new corrosion inhibitor about TH-IM which has a good solubility in water. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to solve the tubing corrosion problem of B Block on the Right Bank of Amu Darya river sour gas field.Design/methodology/approach By using four-point-bending method, the tubing's ability to resist sulfide-stress cracking was tested. Simulating the wellbore corrosive environment, the corrosion inhibitor which was suitable for gas filed had been screened. According to the characteristic of Amu Darya river gas field, the corrosion monitor system had been designed.Findings From the feedback of wellbore corrosion monitor result, the corrosion rate was lower than 0.076 mm/a.Originality/value This anti-corrosion technique provides security for the development of gas field. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to present a study of corrosion properties of the highly corrosion-resistant stainless steel Prokron 11Nb, which is suitable for use in high-temperature and high-pressure systems. Design/methodology/approach - Prokron 11Nb was immersed in 0.1?M H2SO4 that had been previously sparged with CO2 and was exposed to high pressures within the range of 1-300 bar at a constant temperature of 25°C. Treated surfaces were scanned with an electronic microscope (scanning electron microscope) equipped with energy spectrum distribution (energy dispersive spectroscopy) to analyze the morphologies and compositions of surface deposits. Corrosion properties were measured using the potentiodynamic method and electrochemical impedance spectroscopy. Findings - The corrosion rate decreased with increasing CO2 pressure, which accelerated surface passivity, but only up to a pressure of 200 bar. Higher pressures (300 bar) increased the corrosion rate. The trends in corrosion rate with CO2 pressure agree with the stability of a protective layer where iron carbonate is present. Originality/value - A high-pressure CO2 treatment at low temperature is found to be a useful method for improving the passivity of stainless steel. Iron carbonate, which is the result of CO2 corrosion, forms a stable protective layer on the steel surface and this lowers the corrosion rate. [ABSTRACT FROM AUTHOR]

Purpose - The use of CO2 as a replacement for conventional air in combustion gas streams of gas turbine power-generation equipment is a novel idea and a potential method of providing an almost pure CO2 stream for subsequent disposal/sequestration. The purpose of this paper is to investigate the effects of this novel gas environment on conventional gas turbine component part materials over the same range of temperatures found in service. Design/methodology/approach - Test samples of candidate materials were tested in simulated environments using controlled gas and steam supplies to sealed horizontal laboratory furnaces. Conventional weight change tests, metal loss tests and electron microscope examination were used to assess the performance of the materials and compare the oxidation morphology. Spectra of the oxidation products were also used to determine the nature of the oxides formed on selected materials. Findings - It is found that changes in the percentage of steam in the novel gas environment made little difference to the performance of the selected alloys. However, when the results of the program are compared with typical data from previous works, where the same alloys are exposed in air, there is a distinct trend. Comparison between the data from air exposed samples and data from those in this paper show the high CO2 environment, envisaged for the GAS-ZEP concept, to be more aggressive to all of the alloys tested. Originality/value - This paper describes the first investigation into the performance of candidate materials for the various components around a GAS-ZEP system in the novel operating environments anticipated. The work has shown that current power plant materials can be considered for use in first generation GAS-ZEP systems, but that care is required in their selection at the higher operating temperatures. [ABSTRACT FROM AUTHOR]

Purpose - This paper aims to further investigate the behavior and mechanism in simulated oilfield solution on CO2 corrosion of P110 steel at various temperatures by potentiodynamic sweep and electrochemical impedance spectroscopy (EIS) measurements, especially discussing the influence of the coverage fraction of corrosion film. Design/methodology/approach - Potentiodynamic sweep and EIS measurements were applied to investigate the behavior and mechanism with the effect of temperature on CO2 corrosion of P110 steel in simulated oilfield solution at 30°C, 60°C and 90°C. Findings - The corrosion parameters of polarization curves, such as corrosion potential (Ecorr), corrosion current density (icorr), anodic and cathodic branches slopes (ßa and ßc), were analyzed and discussed in detail. In addition, the equivalent circuit models and ZsimpWin software were utilized to fit and analyze the Nyquist plots. The plots showed that corrosion potential shifted more negatively as temperature increased. The corrosion current density (icorr) initially increased and then decreased with the increase of temperature. The impedance spectra measured at various temperatures had different time constants. Originality/value - The paper highlights that the coverage fraction of corrosion film is one most important and key variable influencing CO2 corrosion mechanisms. [ABSTRACT FROM AUTHOR]

Purpose – The aim of this investigation was to compare the performance of three typical oil field carbon dioxide corrosion inhibitors in controlling preferential weld corrosion (PWC) of X65 pipeline steel in artificial seawater (3.5 weight per cent) saturated with carbon dioxide at one bar pressure. Design/methodology/approach – A novel rotating cylinder electrode (RCE) apparatus was used to evaluate the effect of flow on the inhibition for the weld metal (WM), heat-affected zone (HAZ) and parent material. To fulfill this objective, the galvanic currents flowing between the weld regions were recorded using parallel zero-resistance ammeters, and the self-corrosion rates of the couples were obtained by linear polarization resistance measurements. Findings – The results showed that when 30 ppm of green oil field inhibitors were present in the service environment, a current reversal took place, resulting in accelerated weld corrosion. At high shear stress, the currents increased and further reversals occurred. The inhibitors were more effective in controlling the self-corrosion rates of the parent material than of the WM and HAZ material. It was concluded that PWC was caused by unstable conditions in which the inhibitor film was selectively disrupted from the WM and HAZ, but remained effective on the parent material. Originality/value – Electrochemical corrosion rate measurements were carried out using an RCE produced from the different regions of the weld. An advantage of using the RCE is that the hydrodynamic conditions are very well defined, and it is feasible to translate the conditions that are known to exist in a production pipeline to those used in laboratory tests. [ABSTRACT FROM AUTHOR]

The article presents a study that demonstrates the importance of high-frequency variations as much as low-frequency variations, which are use to analyze electrochemical signals. The study is undertaken through exposing two identical carbon steel working electrodes to simulated concrete solutions simultaneously sparged with carbon dioxide and silicon dioxide. The results of the study show that high-frequency variations can be considered in analyzing electrochemical activities.

Purpose - The purpose of this paper is to consider the effect of acetic acid and acetate on the anodic and cathodic reactions of carbon steel present in CO2 corrosion. Design/methodology/approach - The corrosion behaviour of carbon steel (N80) in CO2-saturated 1% NaCl solution at 50°C and 0.1?MPa was investigated by using weight-loss tests, electrochemical methods (polarization curves and electrochemical impedance spectroscopy) and surface analysis (scanning electron microscopy). Findings - The results indicated that: both HAc and Ac- significantly increased the corrosion rate of carbon steel, and the surface chemical reactions of cathodic reduction were enhanced in the presence of HAc and Ac-. Because adsorbed HAc could be reduced directly in the presence of Ac-, the corrosion rate increased, even though the pH of the solution increased. Ac- played an important role in the anodic dissolution processes, which mainly affects the formation/adsorption of intermediates, and acts to form more soluble corrosion products. Originality/value - The results of this work clarify the role of acetic acid or acetate in the anodic and cathodic reactions of CO2 corrosion. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this study is to investigate the corrosion behaviour of X70 steel in the presence and absence of various concentrations of inhibitor N-(2-o-Tolyl azophenyl)-acetamide (NTAA) in a CO2 environment.Design/methodology/approach The temperature was set at 80°C, and the flow velocity was 1.5 m/s. The inhibitor concentrations were 10, 20, 30, 60 and 80 ppm, and the CO2 partial pressure was 0.8 MPa. Weight loss method, pitting depth measurement, scanning electron microscopy and electrochemical techniques were used to investigate the inhibitory effects of the inhibitor NTAA.Findings The results showed that a small peak emerged in the curve of the corrosion rate versus inhibitor concentration plot at 20-30 ppm. Polarisation studies revealed that the anodic Tafel slopes changed greatly in the presence of an inhibitor; NTAA behaved as an anode-type inhibitor. At concentrations of 20-30 ppm, the incomplete coverage of the metal surface by inhibitor molecules resulted in macroscopic galvanic corrosion.Originality/value Corrosion behaviour of X70 steel in the presence and absence of various concentrations of an anode-type inhibitor was assessed. Cathodic Tafel slopes are almost unchanged, while the anodic Tafel slopes change significantly with the increase in inhibitor concentration. The corrosion rates of 20 and 30 ppm are almost three times of that of 10 ppm, which is because of the macroscopic galvanic corrosion caused by the inadequate coverage of inhibitor on steel surface. [ABSTRACT FROM AUTHOR]