Research - (2021) Volume 10, Issue 5
Corrosion control in sour environments is a serious challenge for oil and gas industry in dour media. One of the approaches to mitigate such problem is to use corrosion inhibitors (CI). The selection of a single or a mixture of CIs for a particular oil or gas production, transportation or storage facility depends on different parameters e.g. the ratio between carbon dioxide and hydrogen sulfide, pH, pressure, temperature, and brine chemistry where different kinds of iron sulfide and/ or iron carbonate layers can be formed. To select the right corrosion inhibitor/s, it is highly crucial to understand the mechanism of corrosion of C-steel and its inhibition in H2S systems in absence and presence of CIs [1,2].
In this work, the electrochemical behavior of C-steel in (i) deionized water (DIW) and (ii) different NaCl solutions were examined in an H2S system. A series of experiments were conducted at different temperatures and two concentrations of inhibitors (A and B). The corrosion behavior of C-steel was investigated by measuring the open circuit potential (OCP), linear polarization resistance (LPR), and potentiodynamic polarization (PDP) in addition to scanning electron microscopy (SEM) coupled with an energy dispersive X ray (EDX) besides Raman spectroscopy (RS). The results have shown that the corrosion rate of C-steel gradually decreased then stabilized with time in the inhibited solutions. The inhibition efficiency was found to increase in the presence of both types of inhibitors with temperatures. Surface analysis shows that no film of corrosion products existed. In fact, CIs controlled the corrosion process and prevented passive film formation (iron sulfide), even in the presence of H2S in all tests.
Scale formation, Mechanism, Sour environment, Environmental factors
Iron and its alloys are generally utilized in several tenders; most of it is as pipeline material because it has suitable properties which can be broadly utilised in natural gas, and crude oil pipelines in the oil and gas manufacturing. Nevertheless, it is vulnerable to critical degradation by H2S contained in the transported fluid that always exists in both natural gas and crude oil [3]. In fuel manufacture, a sour brine is mainly used (NACE ID 182) and usually utilized to execute corrosion research and the assessment of Corrosion Inhibitors (Cls) [4]. Significant attention has been given to the usage of inhibitors due to it being one of the best approaches controlling corrosion, specifically in acidic media. It prevents the iron dissolution ‘reducing metals loss in areas and acid consumption and therefore reduces the corrosion rate to a noticeable extent. Corrosion inhibitors for metal are chemicals once added in slight quantities to corrosive media, suppress the metal dissolution rate [5].
Investigation of CIs has been primarily concentrated on the inhibitor framework link with its mechanism and adsorption features. It has been detected that adsorption is hugely influenced by particular physicochemical properties of the CI molecules, such as groups of atoms (i.e. functional sets), aromacity, steric impact, electron density of atoms (donor), and the π-orbital type of donating electrons. Besides, it is contingent on the electronic framework of the molecules and the ability to interface between the inhibitor and the iron. Hence, the effectiveness of any compound is primarily reliant on its strength to be adsorbed on the iron surface an enriching the surface with electrons [6]. CI can be a single (organic) or a compound/solvents mixture of compound surfactant or compound co solvents [7].
CI can be classified into three groups: (I) Inorganic Substances such as Rare Earth Metal (REM) salts, borates, silicates, and molybdates. (II) Organic Compounds such as thioglycollates, phosphonates, sulfonates, carboxylic acids/salts (amino acids, fatty acids, gluconates), vitamins, pigments, antibiotic/antifungal drugs (e.g., imidazole compounds), alkaloids (nicotine, caffeine). (III) True ‘Green’ Inhibitors, for example, several herbal extracts (water, alcohol or acid extracts) [7]. Over the last decade, commercial inhibitors have been manufactured and working effectively to impede corrosion of iron in sour system. Those products contain at least one of the subsequent surfactants: fatty (acids, amines, diamines, amido amines or imidazolines), (quaternary oxyalkylated) amines, other amine derivates, and oxygen, sulfur or phosphorus containing compounds which act as film forming inhibitors [8]. The most efficient inhibitors used in the industry contain heteroatoms. For example, nitrogen, sulfur, and/or oxygen and also the hydrophobic hydrocarbon series in the structures create a decrease in corrosion rate of metals, although this has not been fully investigated yet over the past few decades. While many synthetic composites revealed good anticorrosive achievements, many of them were extremely toxic to both humans and the environment. Therefore, strict ecological laws and increasing environmental consciousness have led experts to concentrate on the improvement of ‘green’ alternatives to moderate corrosion [5,9–11].
Many types of research have been carried out on the impact of CIs on the C-steel corrosion in several situations. Recently, several investigations have been carried out on the CI of metals. Huilong et al. [9] examined corrosion inhibitor of steel in HCI acid media using bis quaternary ammonium salt as a corrosion inhibitor. The investigation was in 1M HCl with the adding many CI concentrations at several immersion times from 2 to 10 hours and at a constant temperature of 25 ± 0.5°C further characterised by a weight loss scheme, electrochemical systems (current potential curves) and surface analyses. The outcomes were compared to a commercial corrosion inhibitor used in industry for sour media. The consequences displayed good prevention action by the inhibitor. Also, the impact of Fe³+ ions on IE% in sour system was studied signifying that ferric ions can catalyse the corrosion of metal. The IE rise with the CI amounts is, nevertheless, temperature–independent because of the development of a stable deposit firmly connected to the iron surface.
Moreover, Shahabi et al. [12] studied the theoretical and electrochemical investigation of the inhibition outcome of two synthesised CIs on CS in sour solutions. They did many measurements using mass loss, Tafel polarisation technique, electrochemical impedance spectroscopic and fast fourier transform continuous cyclic voltammetry. The results demonstrate that the studied organic compounds of CI drop the corrosion rate and the inhibition effectiveness grows with rising the concentration inhibitors. The inhibitors were found to be of the mixed category or adsorptive inhibitors with a mainly anodic effect.
Also, the experimental and theoretical investigation was studied by Hemapriya et al. [13] using two synthesised inhibitors that were derived from benzothiazines for corrosion inhibition of CS in an acidic medium (1M H2S O4). They used weight loss measurements for corrosion inhibition efficiency (IE%), polarisation technique (potentiodynamic), impedance spectroscopy, SEM and FT-IR spectroscopy. The data obtained showed that the IE% improved with inhibitor concentration and dropped at higher temperatures. The inhibitors were found to be influencing both cathodic hydrogen progression and anodic metal dissolution.
The temperature effect on the inhibition in acidic media for CS was examined by Yahya et al. [14] using one type of inhibitor; lignin. He performed weight loss corrosion assessments at a different range of temperatures (30°C-70°C). The finding was that the efficiency (IE%) of lignin was reduced while the temperature was raising from 60°C-70°C. Subsequently, in the range from 30°C-50°C (lower temperatures) the IE% was high that casue by the adsorption of lignin on the surface.
Conversely, the very minimal effect on quaternary ammonium mixtures as inhibitors for metal corrosion in sour system has been addressed. Although slight progress has been accomplished in sympathetic H2S corrosion mechanisms, the kinetics of the inhibition progression required to measure formulations for essential protection remains incomplete. Therefore, a systematic approach to the inhibition and adsorption behaviour of imidazole based inhibitors is essential. In addition to our work on the improvement of CIs in acidic system, we have examined the preventing impact on the C-steel corrosion in HCl media using three altered investigational performances (for instance open circuit (OPC) linear polarization resistance (LPR) and polarization measurements) and surface analytical techniques for characterization of the corrosion inhibitor film. These techniques assess corrosion routes and inhibitor enactment in many concentrations and at several temperatures.
Corrosion inhibitor overview and qualification
Qualification and selection of corrosion inhibitor for oil and gas field applications include the requirement of corrosion inhibitors in the laboratory is explained in ASTM standards [15]. Based on our communication with an industry expert from Shell, several different inhibitor formulations are offered in the market, and the choice for a particular application is classically based on a programme of selection and qualification testing in the laboratory. Such programmes are proposed to guarantee that the selected inhibitor will offer acceptable protection to the process in all probable environmental situations that are possible to be developed throughout the project lifetime. Since it is not typically applied to trial all possible combinations, a selection is regularly made based on the presumed ‘worst case’ conditions [16]. Some features might influence the performance of inhibition in pipelines. Factors, for instance, are the nature of inhibitor, operating conditions of a system as temperature and pressure, oil/water partitioning, water chemistry and flow situations and the technique by which it is added have been generally studied. In the past, less awareness was given to some aspects, for example, the microstructure and element of the CS, the kind of corrosion results shaped on the CS surfaces, inhibitor adsorption on postponed components in the generated water and inhibitor increase on boils and water/oil drops [17]. The usual main acceptance criterion for such an inhibitor is evaluated the corrosion rate (general and pitting) and stability. The essential principles are that the general corrosion percentage must be under 0.1 mm/y under numerous operating conditions. Likewise, for pitted corrosion, to get a ‘pass’, it needs to be less than 0.18 mm/y, which corresponds to a 10 μm pit formed in 500 hours of required testing. Minor properties are, for instance, emulsification and foaming tendency and long term storage stability, condensate stabiliser stability and compatibility with other chemicals [16]. All corrosion inhibitors used are scale inhibitors that manufactured by Baker Hughes and are typically injected into oil and gas pipelines. CIs named as A and B correspond to applicants, and two commercial inhibition supplied by Qatar Shell via various vendors for qualification for a specific field as is seen in Table 1 [16,18,19].
| Inhibitor | A | B |
|---|---|---|
| Trade Name | CRONOXâ?¢CRW9258/SSWL0228 | CGW80742P |
| Company | Baker Hughes | |
| Information | It is a water-soluble/oil insoluble organic corrosion inhibitor. It is effective against corrosion caused by hydrogen sulfide, carbon dioxide, organic and mineral acids, salts, etc. This product exhibits excellent solubility in a variety of high dissolved solids content brines. | It is a water-soluble organic corrosion inhibitor. It is effective against corrosion caused by hydrogen sulfide, carbon dioxide, organic and mineral acids, and salts commonly found to cause extensive corrosion in oil-field production. |
| Features and benefits | A general-purpose corrosion inhibitor where high temperature and water solubility are desired. | A general-purpose corrosion inhibitor where pitting in sour systems is a potential problem. |
| Rate | Typical continuous injection rates are 100 to 500 ppm based on total water being treated and the severity of corrosion experienced | Typical continuous injection rates are 200 to 1000 ppm based on the total water being treated and the severity of corrosion experienced. |
| Specific gravity at 60 °F (16°C) | 1.02 | Approx. 1.0 |
| Typical density at 60 °F (16°C) | 8.51 lbm/US gal (1019.72 kg/m3) | - |
| Flash point | SFCC 87.8 °F (31°C) | Approx. 16°C [PMCC] |
| Pour point | -20 °F (-29°C) | - |
The influence of inhibitors on the corrosion was performed using CS coupons with a combination (wt.%) of 0.02% S, 0.05% P, 0.12% Mn, 0.17% Si, 0.20% C and equilibrium Fe were slashed into 1.00 cm3 features for the electrochemical investigates. Prior to measurements being taken, the specimens were degreased with ethanol and cleaned with demineralised water. The area of bare surface of the electrochemical sample was 1 cm2; however, the rest was implanted in an epoxy resin. Later the coupons, the working electrodes, were submerged in an electrochemical cell including 20 ml of studied solution. All investigations were completed at ambient temperatures (RT), 50, and 80°C, and atmospheric pressure. Operations were performed on 4 different media: DIW with and without salts such as NaCl (0.01 M, 0.1 M, and 1 M). Two kinds of corrosion inhibitors (A and B) were used with different concentrations and added to the media. Table 2 displays the test circumstances and demonstrates the experimental procedures. The electrochemical cell was made up of a three electrode structure and consisted of CS (WE), a Pt counter electrode (CE) and an MSE reference electrode (RE). As the iron specimen was obscured in the electrolyte, the OCP was measured until the specimen accomplished a steady potential Ecorr (usually after one hour). Afterwards, linear polarisation measurements were started (±20 mV, polarization scan rate 0.15 mV·s−1) with the aim of determining the corrosion rate (CR) and the assessment of polarization resistance (Rp). Lastly, the routine of the polarization curve was executed recording the curves in the series – 250 mVvs. OCP to 100 mVvs. RE with a polarization rate of 0.5 mV·s−1. In the situation of polarization technique, the relative establishes the inhibition efficiency (I E%) [22]:
| Material | Carbon steel |
|---|---|
| Solution | Deionized water, 0.01 M NaCl, 0.1 M NaCl, and 1 M NaCl |
| Inhibitor type and concentration | A and B @50 ppm and 500 ppm |
| Temperature | Ambient temperature, 50°C, and 80°C |
| Pressure | Atmospheric |
Where Icorr and Icorr (inh) are the corrosion current density amounts without and within the inhibitor, individually specified by extrapolation of cathodic and anodic Tafel lines to the corrosion potential [22], this examination technique was aimed to inspect the influence of inhibitors on the H2S corrosion of CS. After the test, the samples were utilised for further ex situ studies. The morphology and compositions of corrosion specimens from each period were explored with Raman spectroscopy (RS), scanning electron microscopy (SEM), and energy dispersive X ray spectroscopy (EDS).
In the current investigation, by carrying out comprehensive experiments with assured concentrations and types of corrosion inhibitors, at a selection of temperatures, results showed that the inhibiting effect of two inhibitors, in particular, was obvious in all solutions. In tests with just one effective inhibitor, all samples expressly showed scale formation, and the various properties of the inhibitors became obvious. The subsequent conclusions were drawn from this study. The timing of the addition of the Cl to the solution played a significant role in the corrosion within a hydrogen sulfide environment, prevent formed of FeS. All investigational specimens in a sour medium in the absence and presence of inhibitors with two distinct concentrations. The potential of the experiment was monitored as a function of time to survey the progression of the film chemistry as it fell to equilibrium with the solution. When Cls were added at the initiation of the reactions, the EOCP values reduced at all temperatures to negative values with different concentrations of CIs. The characteristic behaviour of inhibitors acted in conjunction with the solution as a mixed kind of inhibitor and was adsorbed on the bare metal surface. Both types of inhibitors, A and B, worked by decreasing both the anodic and cathodic responses. Most surface images displayed a protected bare metal surface, which results from the adsorption of inhibitors onto it, and the decline of the CR. The value of CR of CS decreases as the concentration of CI (A and B) increases with regard to temperature. The presence of CI reduces the CR and Icorr conspicuously with a rise in the quantity of inhibitor linked with changing of corrosion potential (Ecorr). The protection delivered by the inhibitor was limited, and the amount of protection declined with the low concentration of Cl ions and in the rise up of the temperature. The inhibition efficiency of the inhibitor rose with the inhibitor amount, but it fell slightly with a rise in temperature. In the existence of CIs at a temperature of RT -50°C, ideal corrosion inhibition with good IE% resulted. At high temperatures, i.e. 80°C, the IE% decreased. Adding the Cls during the reaction, after the iron film was formed on the surface had different results. A free solution, the CR of CS, increases with time, which in turn indicates that more and more CS is lost by dissolution. However, when CIs are introduced in the solution, the absolute values of corrosion rate are low than those in the absence of CIs, indicating inhibition of CS corrosion. Exposure to the CI solution altered the film morphology. SEM images showed significant inhibition effect in the presence of A and B with higher CI concentrations compared to the corroded iron surface in the acids alone.
Outcomes showed that the most significant active CI commercial products; however, they were less efficient at higher temperatures. The value of IE% reduces with the rise in temperature. Thus, both CI (A and B) performs as a temperature dependent inhibitor and the correlation among temperature and inhibition efficiency is as well a characteristic of the physical adsorption.
The authors wish to thank Qatar Shell (QS), Shell Global Solutions, Advanced Interfacial Materials Science (AIMS), and Qatar University (QU) for continuous financial support and technical guidance led to this publication.
Journal of Material Sciences & Engineering received 3677 citations as per Google Scholar report
