Sour natural gas compositions can vary over a wide concentration of H2S and CO2 and a wide concentration of hydrocarbon components. If the H2S content exceeds the sales gas specification limit, the excess H2S must be separated from the sour gas. The removal of H2S from sour gas is called "sweetening." The selected process must be cost effective in meeting the various specifications and requirements. Throughout the world, regulations generally limit the flaring of H2S. Sweetening of gas streams containing very low concentrations of H2S can be done in many ways, depending on the general conditions. If the sour gas stream contains more than 70 to 100 pounds of sulfur/day in the form of H2S in the inlet gas to a sour plant, a regenerative chemical solvent is usually selected for the sweetening of the sour gas stream. For very low H2S content sour gas, a scavenger chemical is usually used.
Specifications for sales gas describe the required physical properties of the gas such that it can be transported under high pressure through long distance pipelines at ground temperature without forming liquids, which could cause corrosion, hydrates, or liquid slugs into downstream equipment. Limits on the content of certain nonhydrocarbon compounds are also specified. Sour gas is natural gas that contains hydrogen sulfide (H2S). A natural gas is "sour" when the H2S content of the gas mixture exceeds the limit imposed by the purchaser of the gas, usually a transmission company or the end user. Generally, the limit for H2S content is one grain of H2S per 100 scf of sales gas. The limit for H2S content in sales gas in some areas is 1/4 grain of H2S per 100 scf of gas. The mass specification of one grain per 100 scf converts a volumetric limit of 16 ppm. Sour natural gases can contain H2S in concentrations from several ppm to over 90%. While the foregoing defines sour gas from a sales gas perspective, the standards and regulations applying to sour gas service and operations may use a different definition. In this respect, the National Association of Corrosion Engineers (NACE), which developed the standards for materials for use in sour service, defines sour gas service, to which their standards apply, on the basis of partial pressure of H2S and total pressure. NACE Standard MR0175 applies to natural gas systems having a partial pressure of H2S of 0.05 psia or greater, at an absolute pressure above 65 psia. If the partial pressure of H2S is at or above these limits, the steel and other equipment exposed to the sour gas must meet the conditions specified in NACE Standard MR0175 for sour service. While H2S is the compound responsible for designating a natural gas as sour, there are other sulfur compounds, also present in sour gas, in much smaller concentrations. The sales gas specifications normally set a limit of 5 grains per 100 scf of gas for total sulfur content. Thus, sweetening solvents must be able to remove other sulfur compounds, as well as H2S, from the sour gas to meet the total sulfur limitation. Some of the other common sulfur compounds found in sour natural gas are mentioned next.
Wang, Yefei (Key Laboratory of Unconventional Oil & Gas Development, China University of Petroleum East China, Ministry of Education, P. R. China, School of Petroleum Engineering, China University of Petroleum East China) | Yang, Zhen (Key Laboratory of Unconventional Oil & Gas Development, China University of Petroleum East China, Ministry of Education, P. R. China, School of Petroleum Engineering, China University of Petroleum East China) | Wang, Renzhuo (Key Laboratory of Unconventional Oil & Gas Development, China University of Petroleum East China, Ministry of Education, P. R. China, School of Petroleum Engineering, China University of Petroleum East China) | Chen, Wuhua (Key Laboratory of Unconventional Oil & Gas Development, China University of Petroleum East China, Ministry of Education, P. R. China, School of Petroleum Engineering, China University of Petroleum East China) | Ding, Mingchen (Key Laboratory of Unconventional Oil & Gas Development, China University of Petroleum East China, Ministry of Education, P. R. China, School of Petroleum Engineering, China University of Petroleum East China) | Zhan, Fengtao (College of Science, China University of Petroleum East China) | Hou, Baofeng (School of Petroleum Engineering, Yangtze University)
A novel indolizine derivative inhibitor for acidization was introduced. It could exhibit effective corrosion inhibition at a much lower concentration without propargyl alcohol and shows economic and environmental advantages. From quinoline, benzyl chloride, and chloroacetic acid, two indolizine derivatives were prepared under certain conditions. These inhibitive indolizine derivatives were both synthesised from benzyl quinoline chloride (BQC), which one of the conventional quaternary ammonium corrosion inhibitors used for acidising. The target compound was purified and instrumental analysis methods including elemental analysis, high-resolution mass spectrometry (HRMS), and NMR were used to characterise the chemical structure. The inhibition performance of the indolizine derivatives in 15 wt.% HCl, 20 wt.% HCl, and mud acid (12%HCl + 3%HF) for N80 steel was investigated by weight loss measurement, electrochemical method (potentiodynamic polarization and EIS), and SEM surface morphology assessment.
When 0.1 wt.% indolizine derivative was added, the inhibition efficiency of N80 steel in 15 wt.% HCl at 90 °C increased to 98.8 % and 99.1 % respectively without the synergistic effect of propargyl alcohol: however, in terms of BQC, even at a dosage of 1.0 wt.%, the inhibition efficiency of N80 steel only reached 83.3 % under the same conditions. The novel derivative could impart an improved corrosion resistance effect. Compared with BQC, there are more active adsorption sites in the derivative and therefore the inhibitor could be better fastened to the steel surface. The firmly adsorbed inhibitors would thereby prevent the metal surface from making contact with H+ ions and finally increase the inhibitory effect. As a high-efficiency corrosion inhibitor, the novel indolizine derivatives may offer a new strategy for corrosion protection in acidising.
Typically, the concentration of corrosion inhibitor levels in field fluids is routinely monitored. Understanding the level of corrosion inhibitor can provide information on the correct functioning of chemical injection pumps as well as determine the effects of changing system conditions, such as water cut or solids production, on chemical availability. Yet, despite the value of monitoring, the residual methods available to operators are often not sufficiently reliable or are too complex to apply in the field. A corrosion inhibitor micelle-detecting technique offers an alternative approach. A significant body of work can be found in the literature regarding the formation of micelles in model fluids and for single chemical species. The relevance of the approach for the significantly more complex field fluids and commercial corrosion inhibitor formulations is shown and discussed.
Radwan, A. Bahgat (Qatar University) | Ahmed, Said Elmi (Qatar University) | Kahraman, Ramazan (Qatar University) | Montemor, F. M. (Universidade de Lisboa) | Ali, Kamran (DHA Suffa University) | Mahmoud, Abdelrahman Adel (Qatar University) | Shakoor, R. A. (Qatar University)
Corrosion is a major cause of materials and equipment failure in the oil and gas industry, and its prevention is crucial to ensure reliability of the assets. Towards, this goal, Ni-B/AlN nanocomposite coatings were synthesized through electrodeposition technique and their properties were investigated. It is noticed that the incorporation of AlN nanoparticles into Ni-B matrix has a pronounced effect on its surface, structural, mechanical and anticorrosion properties. The improved properties of Ni-B/AlN nanocomposite coatings make them attractive for many industrial applications.
Over the years, nanostructured coatings have gained great attentions in many engineering applications because of superior structural, mechanical, electrical, thermal and anticorrosion properties. The small grain size (<100 nm) of nanostructured coating results in superior attributes that may be sometimes entirely novel when compared to the conventional coatings with coarse grained structure. The appealing properties of nanostructured materials make them attractive for hydrogen storage and purification, electrodes fuel cells, batteries, wear resistance hard coatings (automobiles, aerospace), synthesis of soft magnets and catalysts etc.1,2
Ni-B coatings possess highly desirable attributes such as high hardness, high wear resistance, uniform thickness, high density, low porosity and good ductility. Such properties make them strong candidates towards applications in automobile, aerospace, petrochemical and many other related industries. Instead of such core competencies, the Ni-B coatings have certain limitations and weaknesses such as inferior anticorrosion properties as compared to Ni-P coatings. It limits their application in more demanding industries such as oil and gas, etc. Therefore, it is necessary to improve the characteristics of Ni-B coatings so that it can be used in more aggressive and harsh conditions. In this regard, a well competent research work has already been in progress and different research groups have made attempts to improve the properties of binary Ni-B coatings. Some of the strategies include the incorporation of either alloying elements such as Zn3 or insoluble, hard second phase particles like Y2O34, CeO25, Al2O36, and ZrO27 etc.
In this work, urea-formaldehyde resin was applied to enhance the corrosion protection properties of an epoxy coating. The urea-formaldehyde (UF) resin was synthesized through in situ polycondensation and the coatings were prepared by ball-milling grinding. The UF powder and coatings were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transforms infrared spectroscopy (FTIR), sedimentation test, and electrochemical impedance spectroscopy (EIS). One major finding was that superior compatibility of UF resin with epoxy resin retained the high dispersion of UF in polymer matrix, leading to barely reunion during grinding. UF presented nano-scale size after grinding as shown by TEM measurements. In addition, there was not any flaw revealed from cross-sectional microstructural features of coatings. The UF resin has effectively prevented the corrosive medium from further permeating through diffusion channels to the interface between coating and steel substrate. Results further revealed that the UF resin could significantly reinforce the corrosion protection property of epoxy coatings on carbon steel substrate.
The corrosion of metallic materials poses a great threat to humans. Unfortunately, corrosion cannot be fully prevented, but only retarded and minimized. Many corrosion control strategies are currently available, such as the use of corrosion inhibitors, electrochemical cathodic protection, surface treatments, and coatings.1, 2, 3, 4 Among them, the use of protective coatings is attracting global attention because of their convenient construction and outstanding protection.5, 6, 7 Epoxy resin coatings are widely used because of their versatility, superior adhesion onto various substrates, high resistance to chemical solutions, intrinsic toughness, excellent electrical resistance, and durability at high and low temperatures.8, 9
However, the corrosion protection capability of neat epoxy resin coating is limited by the hydrolytic degradation after exposure to corrosive electrolyte. Corrosive media, such as oxygen, water, and chloride ions, reach the substrate/coating interface through diffusion channels.10 Adhesion is then lost, and the coating deteriorates.
Nickel-based alloy have an excellent corrosion resistance and good mechanical properties. The nickel-copper alloys (UNS(1) N04400) are used for broad of applications in an equally broad range of industries including chemical and petrochemical processing and oil and gas extraction. This paper present a comprehensive corrosion investigation of benzene condenser pipeline made of UNS N04400 at one of Saudi Basic Industries Corporation affiliates. Samples of the failed pipeline were obtained for analytical investigation. Metallographic examination was performed to evaluate microstructure of the failed pipe. The chemistry of a deposit collected from the pipe was analyzed by X-ray fluorescence (XRF) and carbon/ sulfur (C/S) analyzer. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy was used to study the corrosion damage morphology and the chemical composition of the deposit at the leak points. The study concludes that the pipe failure attributed to acidic corrosion that form inside the pipeline.
Nickel-copper alloys are widely used as corrosion resistant materials in a wide range of industrial applications. On account of its high strength and excellent corrosion resistance, UNS N04400 is extensively utilized to a range of media including seawater, dilute hydrofluoric and sulfuric acids, and alkalies1. The alloy has been used extensively in many applications such as chemical processing equipment, gasoline and fresh water tanks, crude petroleum stills, valves and pumps, propeller shafts, marine fixtures and fasteners, electrical and electronic components, deaerating heaters, process vessels and piping, boiler feed water heaters and other heat exchangers1,2.
This paper describes tube failure investigation that took a place in benzene condenser pipeline. The material of construction of the tube is UNS N04400. Table 1 shows the chemical composition and mechanical properties of the tube material according to ASTM(2) B163 specification3. The operating temperature and pressure are around 45°C and 45 kg/cm2g respectively. The tube diameter is 4 inches SCH40. The as-received failed tube sample is presented in Figure 1.
Oluwabunmi, Kayode (University of North Texas) | Rizvi, Hussain (University of North Texas) | D’Souza, Nandika (University of North Texas) | Nazrazadani, Seifollah (University of North Texas) | Sanders, Steve (University of North Texas) | Hemmati, Vahid (University of North Texas) | Argade, Gaurav (University of North Texas)
The corrosion properties of PBAT/LDH coating on mild steel substrate was investigated. Tafel tests and electrochemical impedance spectroscopy tests (EIS) was used to analyze the corrosion resistance of the coating on the mild steel substrates. The morphological characteristics of the coatings was done using the scanning vibrating electrode technique (SVET) and environmental scanning electron microscopy (ESEM). Buffered saline solution containing NaCl-0.138 M, KCl-0.0027 M at room temperature and pH of 7.4 was used as electrolyte in the 3 corrosion tests. The tafel results showed that least corrosion current density value of 0.315 (μΑ/cm2) was recorded for 50 % LDH concentration in PBAT. This suggests that 50 % LDH in PBAT was about 98.5 % more corrosion efficient than 1018 bare mild steel and 0.7 % more that the 65 % concentration. The EIS results showed a similar trend. The 65 % LDH concentration showed about 25 % greater impedance to current flow over the 50 % LDH concentration in both the nyquist and bode plots. The SVET results revealed that the greatest corrosion protection of the mild steel substrates was observed with 50 % and 65 % LDH coating. This proved that an increased concentration of LDH in PBAT could potentially improve the corrosion resistance of mild steel when in service in a phosphate buffered saline environment.
Metallic materials used in the biomedical field are susceptible to localized corrosion especially pitting when they come in contact with body fluids and other solutions.1 The phenomenon of corrosion, a natural process that all metallic materials irrespective of the service environment suffer from have been examined using different techniques.2,3 Various forms of protective coatings have been used in the past to mitigate this effect.4 The use of organic coatings has recently gained more attention in the medical field as an environmentally friendly and economical technique for the corrosion protection for metals that come in contact regularly with body fluids. Surface coating of many products have to be carried out not only for aesthetic reasons, but specifically to maintain the integrity of the metallic substrate during their service life.5 Poly (butylene adipate-co-terephthalate) (PBAT) an aliphatic-aromatic biodegradable polyester primarily utilized in packaging industry;6,7 was investigated for its potential medical application.8 The non-cytotoxic behavior of the polymer using different cation exchange montmorillonites as filler at less than 10% by weight showed that through cytotoxicity tests, protein absorption analysis and total blood counts, PBAT composites are valuable in biomedical applications.9,10 Though, low hardness values and inherent non-conducting properties makes it suffers rapid delamination when used as a corrosion resistant coating, it was observed that it possessed the ability to enable platelet mobility which improved its mechanical properties with (less than 6%) of layered clay11,12. Based on this, we hypothesized that, reinforcing PBAT with LDH fillers a type of anion exchanged clays also known as hydrotalcite, with a brucite like structure; having a general formula [MII1-xMIIIx(OH)2x]x+(An”)x/n.mH2O, where Mn represents a divalent metal, Mra a trivalent metal, and An- an anion will help to increase the corrosion resistance of PBAT and give birth to a new set of bioinspired coatings suitable for use in medical implants.
A novel experimental methodology for investigating the relationship between corrosion inhibitor adsorption and micellization processes was developed and implemented using typical components of commercially available corrosion inhibitors for oil and gas applications (e.g., quaternary amines, imidazolines).
This paper presents the methodology and approach used to characterize micellization and adsorption related parameters for an individual corrosion inhibitor components; specifically, data for a homologous quaternary amine series is presented in this manuscript.
The micellization phenomenon associated with an inhibitor molecule in aqueous solutions was studied using surface tension measurements and fluorescence spectroscopy. For the same molecule, the adsorption phenomenon onto a platinum surface was studied, using quartz crystal microbalance and electrochemical methods, which included Capacitance vs potential measurements and Cyclic Voltammetry. Micellization and adsorption were found to be closely related. Free energy change associated with adsorption onto the Pt/solution interface was more negative than that associated with the micellization process. The effect of temperature on the adsorption and micellization process was also studied to provide insights into the thermodynamic constants - enthalpy and entropy changes, associated with micellization and adsorption processes. Thermodynamic data could potentially be used to help tailor corrosion inhibitor for specific and / or challenging conditions encountered in oil and gas industry.
The experimental methodology was implemented to investigate different pure components of typical corrosion inhibitors at different environmental conditions (salinity and temperature). Important thermodynamic parameters such as free energy, entropy and enthalpy associated with the adsorption and micellization process were also derived from these studies. This paper will show results obtained with quaternary amine based inhibitor family.
Corrosion inhibitors, which for oil and gas applications are often formulated based on surfactant molecules, are widely used to protect infrastructure and pipelines from internal corrosion. The corrosion inhibitors protect metallic surfaces by forming a protective film on metallic surfaces, which disrupts and slows corrosion reactions on the surface.
The most common type of corrosion inhibitors used in the oil and gas industry are organic molecules with amphiphilic characteristics. These molecules are composed of at least two parts - a highly polar or ionized functional group which is hydrophilic in nature (head group), another part being hydrophobic (tail), which is usually a a C10-C20 aliphatic chain. These types of molecules are surfactants (short for surface active agents), which when in solution reduce the total energy of the system by attaching to a surface or interface so that the solubility of both parts of their structure is satisfied. A schematic showing the adsorption of surfactants from aqueous solution is shown in Figure 1.1 The surfactant molecules orient themselves as to have their hydrophobic tails away from water by adsorbing onto the air/water or the solid/water interface as shown in Figure 1a. Above a certain surfactant concentration, the thermodynamically favorable configuration for the surfactant monomers is to form aggregates in solution which are termed ”micelles”. In this circumstance, the surfactant molecules orient themselves such that their hydrophobic tail is shielded from the aqueous medium as shown in Figure 1b. The figure also shows the existing equilibrium between the monomers, adsorbed layer and the micelles.
For the last decades, continuous global trend towards more stringent safety, commercial and environmental specifications kept processing sour natural gas containing acid gas such as H2S and/or CO2 a growing challenge. If mercaptans are present in the sour natural gas, the limited mercaptans absorption capacity of the well known alkanolamine solvents can be a major problem. The operating companies have to upgrade their production units to comply with these specification and environmental constraints evolutions. Additional treatment steps are often required to achieve the total sulfur specification in the sales gas, adding process complexity and further increasing cost.
An efficient solution to solve the problem would be to replace the usual alkanolamine aqueous solvent by a hybrid formulation allowing simultaneous removal on mercaptans and acid gases. This approach has been rarely considered because of the side effects of traditional hybrid solvents: hydrocarbon co-absorption, negative impact on the downstream sulfur recovery units. It may be necessary also to replace the internals of the absorber column in the Acid gas Removal Units.
To address this issue, TOTAL is now using a new dedicated hybrid formulation since 2007. This new solvent has been developed by TOTAL by taking advantage of its intensive know-how and experience in gas processing. The hybrid solvent is obtained by addition of a physical component into a generic alkanolamine-water solvent. The final solvent composition is determined to optimize mercaptans removal and minimize hydrocarbon coabsorption, without affecting acid gas removal capabilities.
Without any plant modification, this hybrid solvent can be implemented in existing unit to remove mercaptans with the acid gases, with no detrimental impact on downstream SRU. It allows operating cost reduction of the existing downstream units. Last but not least, the energy consumption of the acid gas removal units can be lowered by 10- 15%.
This paper presents several applications cases where the benefit of using the hybrid solvent is demonstrated.