Active Corrosion Research Articles

Effects of calcium glycerophosphate concentration on micro-arc oxidation coating of Mg alloy

Due to its good biocompatibility and compatible hardness with human bones, magnesium (Mg) alloy is considered as a promising material for bone nails and implants. However, Mg and its alloys are characteristics of active chemical properties and high corrosion rate, which is detrimental to the recovery of patients implanted with Mg alloy bone scaffold. In the present work, to retard the corrosion of the Mg alloy, calcium glycerophosphate (C3H7CaO6P•H2O) was added in the electrolyte to form the micro-arc oxidation (MAO) coatings. Various experimental techniques such as XRD, SEM and EDS have been used to characterize the surface morphology and phase composition of MAO coatings. MAO coatings of different CaP content were studied to explore the synergetic effect between the biocompatibility and corrosive properties by means of electrochemical measurements, hemolysis and pyrogen test. The results showed that higher CaP content can improve the biocompatibility and corrosion resistance while decelerating the hemolysis rate.

Synthesis of hexagonal boron nitride nanocoatings for corrosion prevention of iron substrates

Iron and its alloys have applications in diverse fields such as civil infrastructure, aerospace, and defense. Corrosion of these alloys in saline environments is a significant concern that causes huge environmental losses. The current study explores pulsed laser deposition technique to synthesize hexagonal boron nitride (hBN) films as protective coatings, directly on iron (Fe), to mitigate the corrosion. Microstructural, mechanical, wetting, and corrosion properties of hBN-coated Fe substrates were investigated at different deposition temperatures (25–800 °C) and varying thicknesses (35–115 nm). Raman spectra and transmission electron microscopy confirmed the presence of hBN in as-deposited films. Crystallinity and surface roughness of hBN coatings increased as deposition temperature increased. Electrochemical studies performed in 3.5 wt% NaCl solution showed that the 115 nm thick hBN coatings deposited at 600 °C resulted in lower corrosion rates and has ~6-fold higher corrosion resistance than bare Fe. Also, the corrosion rates decreased with an increase in hBN coating thickness. Overall results suggest that hBN nanocoatings reduced the corrosion activity and can potentially serve as a corrosion-resistant barrier coatings in saline environments.

Lithium salts as active corrosion inhibitors for aluminum substrates

As an effort to replace carcinogenic chromate from protective coatings, researchers are continuously searching and proposing new non-toxic chemicals sharing similar properties: leachable, responsive, and film-forming. Lithium (Li), in the form of either a salt additive in coatings or alloyed with aluminum (Al), is observed to be able to form insoluble protective layers and thus reduce the corrosion rate of the Al substrates. The protective film formed is often composed of Li, Al, carbonate (CO3), hydroxide (OH) etc., sharing similar structure to a layered double hydroxide (LDH) as indicated by several mechanistic studies. The successful formation of the irreversible/insoluble protective film requires oxygen, correct pH, and the right combination of available ion species. In this study, electrochemical impedance spectroscopy (EIS) results show that these leachable inhibitor coatings yield poor barrier properties before and after artificial weathering. Scanning electron microscopy pictures show the growth of an inorganic layer between the coating and aluminum substrate, indicative of the formation of a layered double hydroxide (LDH) structure. Current mapping generated by scanning vibrating electrode technique (SVET) indicates that aerated lithium salt solutions can cause pitting corrosion over bare aluminum, while organic coatings pigmented with lithium were able to keep the surface relatively passive, with and without the presence of a defect. An anodic shift of the surface of the organic coatings pigmented with lithium containing a defect is seen while keeping the surface relatively passive, indicating anodic passivation of the metal surface.

Corrosion and aging risk assessment of an injection system for FCC/Bio-oil co-feed

Fast pyrolysis oil (FPO) is a renewable biocrude with high corrosivity and poor thermal stability. Co-processing FPO with petroleum intermediates in existing fluid catalytic cracking (FCC) units is one of the most applicable methods for transforming low-quality biocrudes into drop-in fuels. Although FPO is immiscible with petroleum intermediates, co-processing can be achieved using two separate feeding lines for FCC injection instead of the premixture. However, the corrosion of structural materials and the thermal stability of FPO pose significant challenges to the co-processing feed injection system, as the feedstocks are usually preheated to 100–300 °C prior to injection. This study focuses on the corrosion of stainless steel (SS) 316L and evaluates the aging risk of FPO at a temperature range of 80–220 °C. SS 316L experienced noticeable degradation with increasing temperature. Corrosion rates of 0.06, 0.62, and 1.77 mm/y were observed at 80, 150 and 220 °C, respectively. The experimental observation also reveals phase separation (liquid and solid phase) of FPO at the experimenting temperatures. However, the change in the physicochemical properties of the phases becomes more significant as temperature increases. Furthermore, a critical temperature of about 80 °C was identified, which signifies both the onset of active corrosion of SS 316 L in FPO and the fast aging of FPO.

Corrosion inhibition properties of spinach extract on Q235 steel in a hydrochloric acid medium

The use of environmentally friendly corrosion inhibitors (CIs) is an effective way to overcome the environmental problems caused by existing CIs that contain nitrogen or phosphorus components. Plant extracts, as a type of environmentally friendly CI, have attracted considerable attention. In this work, the corrosion inhibition properties of spinach extract (AESPE) on Q235 steel were studied in a hydrochloric acid medium. First, AESPE was extracted from spinach by an ethanol-acetone reflux method and its main structural and stability parameters in hydrochloric acid medium were determined by infrared spectroscopy (FTIR) and ultraviolet spectroscopy (UV–vis). Second, the corrosion inhibition properties of AESPE on Q235 steel in a 0.5 M hydrochloric acid solution were studied by weight loss (WTL), dynamic potential polarisation (PDP), linear polarisation (LPR), electrochemical impedance spectroscopy (EIS) and quantum chemical calculation methods. The results showed that AESPE could significantly slow the corrosion rate (Vcorr) of Q235 steel in 0.5 M hydrochloric acid medium, which was via a mixed corrosion inhibition mechanism at the cathode and anode. As the AESPE concentration increased, the cathode and anode currents decreased and the active corrosion sites were blocked; thus, the Vcorr decreased and the corrosion inhibition efficiency (E (%)) increased. Under the conditions of 303 K and 300 mg⋅L–1 AESPE, the E (%) of AESPE for Q235 steel was>90%. As the system temperature increased, the E% of AESPE for Q235 steel decreased but the extent of this decrease was small. This work shows that AESPE is an environmentally friendly CI with a good corrosion inhibition effect.

Durable self-healing coating system based on pH-responsive core-shell nanostructures

A critical access to high-efficiency anti-corrosion coatings is adding pH-responsive nanocontainers encapsulated with corrosion inhibitors into epoxy resin as it endows the composite coating with significant active long-term corrosion protection. Here, two self-healing coating systems (I-PBZ-EP and II-PBZ-EP) were constructed based on epoxy coating (EP) and benzotriazole-loaded zeolitic imidazolate framework (ZIF-8) encapsulated with polydopamine (PDA) by one-pot and two-pot methods, respectively. Electrochemical impedance spectroscopy (EIS) investigation shows that the low-frequency impedance modulus value (|Z|0.01Hz) of I-PBZ-EP still reaches 2.16 × 1010 Ω·cm2 which is the highest among all the coatings after 35 d of immersion. |Z|0.01Hz of the scratched I-PBZ-EP is 1.10 × 105 Ω·cm2 after 13 h of immersion in 3.5 wt% NaCl solution, which far surpasses |Z|0.01Hz of the scratched II-PBZ-EP, exhibiting its excellent self-healing properties. This is because I-PBZ can release more benzotriazole (BTA) (22.5 mg/L and 13.4 mg/L) than II-PBZ (15.8 mg/L and 9.4 mg/L) under acidic and basic conditions to repair the micro-defects. In short, by changing the loading mode of corrosion inhibitors, I-PBZ-EP with a simpler synthesis method manages to provide the long-term anticorrosion protection for the carbon steel substrate.

Research on the Effect of Load and Rotation Speed on Resistance to Combined Wear of Stainless Steels Using ANOVA Analysis.

This research was carried out with the aim of obtaining appropriate principles for describing the influence of working parameters and the aggressive action of an acidic medium on the wear and corrosion resistance of martensitic stainless steels. Tribological tests were performed on induction-hardened surfaces of stainless steels X20Cr13 and X17CrNi16-2 under combined wear conditions at a load of 100 to 300 N and a rotation speed of 382 to 754 min-1. The wear test was carried out on a tribometer with the use of an aggressive medium in the chamber. After each wear cycle on the tribometer, the samples were exposed to corrosion action in a corrosion test bath. Analysis of variance revealed a significant influence of rotation speed and load due to wear on the tribometer. Testing the difference in the mass loss values of the samples due to corrosion using the Mann-Whitney U test did not show a significant effect of corrosion. Steel X20Cr13 showed greater resistance to combined wear, which had a 27% lower wear intensity compared to steel X17CrNi16-2. The increase in wear resistance of X20Cr13 steel can be attributed to the higher surface hardness achieved and the effective depth of hardening. The mentioned resistance is the result of the creation of a martensitic surface layer with dispersed carbides, which increases the resistance to abrasion, dynamic durability, and fatigue of the surface of the protective layer.

Environmentally benign fouling release metallosurfactant coatings; evaluation of surface properties, leaching rate, biocorrosion resistance and durability

Biofouling is the biggest issue that impair the success of marine infrastructure. The biofilm forming aerobic bacteria Pseudomonas aeruginosa present in sea water causes considerable environmental and economic losses by initiating microbially induced corrosion. Concerning the importance of fouling release coatings, we are aimed to fabricate non-toxic metallosurfactants (MS) coating on carbon steel to mitigate growth and adhesion of biofilm and consequent corrosive reactions on its surface. As the toxic ion release from fouling-release metallic coatings have deleterious effect on the aquatic eco-system therefore the MS coatings with slow release of metal ions can be a greener approach in this field. Here, we report the surface modification of CS with self-assembly of a series of MS viz. MC42H76N2Cl4, where M = Co, Ni and Cu. The MS under study is a complex of an anti-corrosive surfactant ligand cetyl pyridinium chloride (CPC) and transition metal salts in a stoichiometry of 2:1 (CPC: M). For surface modification, a cost-effective sol–gel technique was adopted. The coatings were characterized by Fourier Transform Infra-Red Spectroscopy (FT-IR), Atomic force microscopy (AFM), Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The chemical composition of coatings reveals the presence of anti-bacterial metal ions present in mixed oxidation state causing the variable rate of their leaching in sea water media (M1942). The quantification of metal ions leached from metallosurfactant coating after immersing in M1942 media was done using inductively coupled plasma-mass spectrometry (ICP-MS). The ICP-MS data shows 19.86 ng/mL release of Cu ions from coating after 21 days of immersion which advocates its slow-release nature. The corrosion activities of sea water salts and marine bacteria Pseudomonas aeruginosa on bare and modified CS substrates was extensively studied by employing standard electrochemical tests like potentiodynamic and potentiostatic polarisation, Electrochemical Impedance Spectroscopy (EIS). The potentiodynamic polarisation test shows the coatings exhibit corrosion inhibition efficiency up to 93.5%. The coatings remained intact even after polarisation at +0.7 V in sea water media. Atomic force microscopy (AFM) and Scanning Electron Microscopy (SEM) was conducted to check corrosion morphology and biofilm characteristics. The DEAD/LIVE test of biofilm displays a higher ratio of dead bacteria on modified surface as compared to bare which demonstrate the antibacterial character of coatings. The results obtained from various corrosion tests reveal this strategy can be used to develop long term and eco-friendly anti-fouling coatings.

Experimental and theoretical study of polysaccharides extracted from prickly pear nopales Pulp (PPUN) of Opuntia ficus-indica as corrosion inhibitors

Corrosion causes massive damage to our equipment and buildings, wasting billions of dollars every year. Identifying a workable answer to this problem is a priority. Scientists have begun using inhibitors derived from renewable resources and natural ingredients to have a minor possible detrimental impact on the environment. Though many synthetic structures exist to prevent corrosion during the acid pickling process, the persistence of the problem has prompted modern corrosion scientists to investigate this field further by studying natural products with increasingly intriguing moieties for practical applications and their applied capabilities against corrosion. Electrochemical studies have been used to fully explore the inhibitory effects of Pulp (PPUN) from prickly pear nopales of Opuntia ficus-indica (OFI) on mild steel corrosion in 1 M HCl solution. Scanning electron microscopy (SEM) and atomic force microscopy were used to investigate the surface of mild steel (AFM). The XPS method was used to learn about the mechanism of inhibition happening on mild steel. Through its absorption on the metal surface and its inhibition of the active corrosion site, the inhibitor is shown by a potentiodynamic polarization study to slow down both cathodic and anodic processes. The adsorption of PPUN on metal was demonstrated by a shift in impedance characteristics (charge transfer resistance Rt and double layer capacitance Cdl). The PPUN and product film have been analyzed using SEM and AFM. The computed values correspond well with those from the experiments. Based on MDS results, Galacturonic acid and Glucose constituents adsorb tightly on the carbon steel cluster surface.

Effect of the Cu/Mg Ratio on Mechanical Properties and Corrosion Resistance of Wrought Al–Cu–Mg–Ag Alloy

The present study aimed to investigate the influence of magnesium (Mg) on the mechanical properties and corrosion behavior of wrought Al–4Cu–xMg–0.6Ag alloys. The results from Optical Microscope, SEM, XRD analysis, and Thermo-Calc simulation were used to identify the microstructure formed after the aging process. Testing for hardness and tensile strength was conducted, in addition to corrosion testing. It was found that Mg significantly impacts the hardness of the alloys, with a high Mg content (low Cu/Mg ratio) increasing the hardness but reducing the tensile strength and ductility. This study attributed this to the formation of the S phase, which is dependent on both the quantity in the bulk and the size of the phase. The grain size was found to be finer with a higher Mg content, since the particle size inhibits grain growth during the artificial aging process. Counterintuitively, the corrosion activity was reduced in the high-Mg-content alloy due to its large particle size and the reduced galvanic cell effect. This study highlighted the importance of considering the effects of Mg on the mechanical properties and corrosion behavior of Al–Cu–Mg–Ag alloys.

Effect of Si and Nb additions on carbonitride coatings under proton irradiation: A comprehensive analysis of structural, mechanical, corrosion, and neutron activation properties

In the present study, understoichiometric TiZrCN, TiZrNbCN, and TiZrSiCN coatings were produced using the cathodic arc technique with a C/N ratio of approximately 0.5 to investigate their potential use in nuclear technology. The coatings were evaluated for their corrosion resistance in 3.5 % NaCl and neutron activation. The effect of adding Si and Nb to the quaternary TiZrCN system was also investigated. The results showed that the addition of Si (∼4.64 at.%) to the matrix of TiZrCN improved their electrochemical properties in NaCl solution, the protective efficiency was 92%, while the Nb addition (∼5.5 at%) lead to the decrease in corrosion resistance by 1.39 times comparing with TiZrCN. Furthermore, after fast neutron irradiation at a nominal power of 1450 kW, none of the coatings were activated, indicating good radiation resistance. It was determined from the structural analysis that the Ti6Al4V substrate before corrosion consists of hexagonal and cubic space groups with different lattice parameters. By adding Si and Nb, a small amount of ZrO2 and Si3N4 was detected along with the main phases in the TiZrCN structure.

Effect of corrosion inhibitor on service life of cracked and non-cracked concrete

Corrosion of steel in reinforced concrete structures can cause damage and costs involved and attracts researchers to look for solutions that delay the onset of corrosion initiation or slow its development. The effectiveness of four corrosion inhibitors in cracked and non-cracked sections of reinforced concrete was studied: Migrating Corrosion Inhibitor (MCI-2005) based on amine carboxylate; CNCI 1.37 based on calcium nitrite Ca (NO)2 at a concentration of at least 30%; and two lab-made green corrosion inhibitors based on recycled materials – fluorosilicates obtained from fluorosilicic acid (H2SiF6), the by-product of the phosphate industry, and from LABS (Linear Alkyle Benzene Sulphonate), the by-product of the detergent industry. The study followed the guidelines of the ASTM G-109 standard which examines materials intended to inhibit chloride-induced corrosion of steel in concrete, and the ASTM C-876 standard which evaluates the electrical corrosion potential of uncoated reinforcing steel, for the purpose of determining the corrosion activity of the reinforcing steel. Controlled artificial cracks of different depth were created to speed up the corrosion process in the steel. Such cracks allowed a direct penetration of chlorides into the depth of concrete. As was expected, the cracked concrete samples exhibited a significantly higher level of corrosion than the non-cracked samples. In the non-cracked samples, the effectiveness of the CNCI 1.37 commercial corrosion inhibitor was the highest. However, in the cracked samples it appears that its efficiency has decreased, while the recycled corrosion inhibitor based on K2SiF6 has shown the best performance. This result can be explained by the fact that fluorosilicate reacts with calcium hydroxide present in concrete and creates a non-permeable protective layer that inhibits the movement of chlorides to the steel bar.

Inhibition of Localized Corrosion Propagation on Carbon Steel: A Potentiostatic Study

The occurrence of localized corrosion in carbon steel pipelines, even when the uniform corrosion rate remains low, is a major concern in the hydrocarbon production and transmission industry. The propagation of these pits, caused by the galvanic coupling between the inhibited surface and the active pit, can lead to serious consequences such as financial loss, environmental damage, production interruption, and even loss of life. To better understand this phenomenon, this work focuses on using the potentiostatic technique to evaluate the tendency of localized corrosion propagation. The experiments were conducted using a primarily imidazolinium-based corrosion inhibitor in produced water conditions (5 wt% NaCl, pH 4.5, CO2-saturated) at 55°C and 80°C. The baseline results were obtained through linear polarization resistance and potentiodynamic polarization tests. The potentiostatic experiments were then conducted to artificially simulate different levels of galvanic coupling that could exist in case of active localized corrosion. The results showed that, at certain anodic potentials, increased inhibitor dosage was necessary to significantly decrease the current. However, at high current levels, further injections were insufficient, indicating that substrate dissolution may affect the adsorption of the inhibitor. This work provides insights into the role of inhibitors and important factors in stopping the propagation of localized corrosion of carbon steel. Further research, such as designing a proper zero-resistance ammeter setup, will be necessary to fully understand this complex phenomenon. The results show that the potentiostatic methodology can be a rapid and easy alternative to obtain electrochemical information and improve understanding of localized corrosion propagation.

Corrosion of galvanized steel in alkaline solution associated with sulfate and chloride ions

Corrosion mitigation strategies for structural steel bridge elements including post tensioned steel components include the use of galvanized steel. The zinc alloy layers and subsequent precipitation of a dense surface oxide in alkaline environments provide beneficial barrier protection to mitigate corrosion. However, severe corrosion of galvanized steel components in contact with sulfate-rich deficient cementitious grout was documented to occur in less than 8 years of bridge service. Electrochemical testing and material characterization showed that the presence of sulfates in alkaline solutions allow for prolonged zinc activity and hindered passivation by the incomplete surface coverage and the precipitation of large sized calcium hydroxy zincate. OCP, LPR, and electrochemical noise (EN) testing showed greater corrosion activity of galvanized steel in chloride and sulfate solutions. EN identified local corrosion activity of the zinc associated to the porous nature of the surface oxide layer.

Dual self-healing effects of salicylate intercalated MgAlY-LDHs film in-situ grown on the micro-arc oxidation coating on AZ31 alloys

Micro-arc oxidation (MAO) coatings only provide the passive protection of common Mg alloys (AZ31), especially causing severe localized corrosion under accidental damage. Herein, a novel MgAlY-Layered double hydroxides (LDHs) film loaded with salicylate is successfully prepared on flash-MAO coated AZ31 alloys, by the one-step hydrothermal and intercalation methods. The in-situ grown LDHs platelets seal the porous morphology, significantly improving the corrosion performance. Moreover, self-healing measurements (SVET) and characterizations (EDS, XRD, and FT-IR) demonstrate that the endowed active corrosion protection is attributed to the corrosion inhibition of anion-exchange reaction, and dual self-healing effects of yttrium oxide and Y(III) - salicylate complexes.

Facile formation of Zn-incorporated NiFe layered double hydroxide as highly-efficient oxygen evolution catalyst

Electrochemical water splitting is the primary method to produce green hydrogen, which is considered an efficient alternative to fossil fuels for achieving carbon neutrality. For meeting the increasing market demand for green hydrogen, high-efficiency, low-cost, and large-scale electrocatalysts are crucial. In this study, we report a simple spontaneous corrosion and cyclic voltammetry (CV) activation method to fabricate Zn-incorporated NiFe layered double hydroxide (LDH) on commercial NiFe foam, which shows excellent oxygen evolution reaction (OER) performance. The electrocatalyst achieves an overpotential of 565 mV and outstanding stability of up to 112 h at 400 mA cm−2. The active layer for OER is shown to be β-NiFeOOH according to the results of in-situ Raman. Our findings suggest that the NiFe foam treated by simple spontaneous corrosion has promising industrial applications as a highly efficient OER catalyst.

Synthesis of hydroxyapatite from eggshell and its electrochemical characterization as a coating on titanium

This work reports the surface modification of titanium through the deposition of a hydroxyapatite coating synthesized from natural sources. Hydroxyapatite was synthesized from eggshell using a wet precipitation method. It was deposited as a coating on a Ti surface using electrophoretic deposition (EPD) at different electrophoretic deposition times and voltages. The electrochemical evaluation of the obtained coatings was performed through potentiodynamic polarization curves in a simulated physiological solution. The results showed that the eggshell is an excellent alternative for the synthesis of hydroxyapatite, and that its heat treatment at 700 °C shows the best crystallinity conditions. The optimum conditions for deposition of the hydroxyapatite coatings were 30 V and 18 min. Potentiodynamic polarization tests showed that hydroxyapatite coatings improve the chemical stability of the Ti surface when subjected to the corrosive action of simulated physiological solutions at 37 °C.

Hybrid PEO/sol-gel coatings loaded with Ce for corrosion protection of AA2024-T3

Plasma electrolytic oxidation (PEO) has been targeted as an eco-friendly alternative technology to conventional chromic acid anodizing (CAA) for corrosion protection of aluminium alloys in the aircraft industry. However, conventional PEO technology implies high energy consumption. Flash-PEO coatings (≤10 μm) produced in short treatment times (≤ 5 min) constitute a feasible way to overcome this limitation. Nevertheless, the long-term corrosion resistance is compromised, thus requiring novel sealing post-treatments. The present work studies the effect of stand-alone hybrid sol-gel (HSG) and Ce-doped hybrid sol-gel (HSGCe) coatings as a sealing post-treatment to evaluate the long-term corrosion resistance of Flash-PEO coatings on aluminium alloy (AA) 2024-T3. The characterization of the PEO, HSG, and HSG-Ce coatings was performed by scanning electron microscopy, X-ray diffraction, water contact angle, dry adhesion tests (ISO 2409), optical profilometry and Fourier transform infrared spectroscopy. The corrosion behaviour was assessed by electrochemical impedance spectroscopy up to 21 days (3.5 wt% NaCl). Active corrosion protection was assessed by immersion tests of artificially scratched coatings. Present findings reveal that low-energy-cost Flash-PEO coatings were successfully formed on AA2024-T3 alloy. Both HSG and HSG-Ce coatings were homogeneously formed on Flash PEO coating. Regarding the corrosion resistance, HSG-Ce showed significant scratch protection during 21 days of immersion in 3.5 wt% NaCl. The results suggest that, while the release of Si and Ce from the coating provided corrosion protection, NO3−release promoted localized corrosion phenomena in the scribe. This was associated with the preferential pitting corrosion phenomena at the Cu-rich intermetallic compounds instead of forming a thick and stableNO3−-rich passive layer.

TO INDUSTRIAL SAFETY OF HYDROGEN SULFIDE OIL TREATMENT UNITS

The oil of some fields is characterized by a high content of hydrogen sulfide and mercaptans significantly reducing the commercial product quality, besides, due to their high corrosion activity, contribute to emergencies. The oil refining method used at these fields, due to necessity of acid-base effluents neutralizing and the ingress of reaction products into commercial oil, requires adjustment. The article discusses the known physical and chemical methods of hydrogen sulfide and mercaptans removal from oil indicating their advantages and disadvantages. Among the first ones are technologies based on the extraction of undesirable components due to oil separation, rectification or blowing-off. Chemical methods of hydrogen sulfide extraction from well products are based on its extraction with solutions of chemical reagents – hydrogen sulfide absorbers. The most promising among the considered technologies, in our opinion, is the method based on oil blowing-off with hydrocarbon gas. In this technology, the oil extraction from hydrogen sulfide and mercaptans is carried out by passing associated petroleum gas previously purified from hydrogen sulfide through the volume of oil in a column-type apparatus. One of the main advantages of the chosen method is the possibility of associated petroleum gas purification, which also guarantees a reduction in the probability of emergencies, since gas purified from hydrogen sulfide moves through gas pipelines.

Combined effects of freeze–thaw cycles and chemical corrosion on triaxial mechanical properties of sandstone

To study the combined effects of freeze–thaw cycles and chemical corrosion on deterioration mechanism of triaxial mechanical properties of sandstone in cold regions, triaxial compression tests were carried out on homologous sandstone specimens after corrosion action of acidic, alkaline or neutral solution and cyclic freeze–thaw action, by taking the pH value of the hydrochemical solution and the number of freeze–thaw cycles as control parameters. The failure mode of triaxial compression is shear-slip failure, and the deviatoric stress–strain curves can be divided into four stages of compaction, linear elastic, yield, and failure. The stress–strain curves and deterioration law of triaxial mechanical properties were analyzed. With the increase of freeze–thaw cycles, the peak stress, peak strain and modulus all decrease, the deterioration degree of the rock specimens increases, and the yield plateau and plastic characteristics in the yield stage become weaker. The strong acid solution shows the largest degree of damage, and the peak stress, peak strain and modulus decreased significantly. The precipitates produced by the reaction between the strong alkaline solution and the specimens adhere to the specimen surface, pores, and fissures, thereby inhibiting further damage and deterioration. Confining pressure is an essential factor affecting the rock mechanical properties. As confining pressure increases, the strength and deformation-resistant ability of specimens increase, and the yield stage on the stress–strain curve is more obvious. The sensitivity of acidic solution to the deterioration of mechanical properties of sandstone is obviously greater than that of alkaline solution. These results provide a theoretical basis for the construction of geotechnical engineering structures in cold regions.