H2S and O2 influence on the corrosion of carbon steel immersed in a solution containing 3 M diethanolamine

Aqueous solutions with 3 mol L⁻¹ (M) diethanolamine (DEA) concentration are extensively used in the gas processing industry to remove acid gases. However, the degradation of the DEA and the formation of heat-stable salts (HSS) lead to severe corrosion problems. Even worse, equipment corrosion can be magnified by the unavoidable presence of sulphide acid and dissolved oxygen as a result of hydrocarbon (natural gases and crude oil) processing. The aim of this work is to study the combined corrosion effects of DEA, sulphide acid and oxygen on carbon steel. Electrochemical methods revealed that in the 3 M DEA medium without oxygen, corrosion processes are modulated by adsorbed DEA film formation. Furthermore, it was shown that the addition of oxygen and 15 × 10⁻³ mol L⁻¹ (15 mM) H₂S produced the formation of an adherent film on the carbon steel surface. Chemical analyses by EDAX revealed a homogeneous film of corrosion products composed of iron oxide and sulphide formed in DEA solution containing O₂ and H₂S, respectively. Equivalent circuits were used to estimate the parameters associated with ion diffusion through the formed corrosion films. The results showed that the presence of H₂S induced the formation of thin iron sulphide films that provide protective properties to the metal. It is concluded that the presence of oxygen in a sweetening plant should be avoided as DEA degradation can be produced with the subsequent decrease in chelating process efficiency and the increase in corrosion problems.     

The effect of H2S concentration on the corrosion behavior of carbon steel at 90 °C

The electrochemical behavior of SAE-1020 carbon steel in 0.25 M Na₂SO₄ solution containing different concentrations of H₂S at 90 °C was investigated using the methods of weight loss, electrochemical measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the corrosion rate of carbon steel increased significantly with the increase of H₂S concentration. H₂S accelerated the corrosion rate of SAE-1020 carbon steel by a promoted hydrogen evolution reaction. Severe corrosion cavities were observed on the carbon steel surface in the solutions containing H₂S due to cementites stripped off from the grain boundary. The loose corrosion products formed on the steel surfaces were composed of mackinawite.     

Corrosion and corrosion control of mild steel in concentrated H2SO4 solutions by a newly synthesized glycine derivative

A newly synthesized glycine derivative (GlyD1), 2-(4-(dimethylamino)benzylamino)acetic acid hydrochloride, was used to control mild steel corrosion in 4.0 M H₂SO₄ solutions at different temperatures (278–338 K). Tafel extrapolation, linear polarization resistance (LPR) and impedance methods were used to test corrosion inhibitor efficiency. An independent method of chemical analysis, namely ICP-AES (inductively coupled plasma atomic emission spectrometry) was also used to test validity of corrosion rate measured by Tafel extrapolation method. Results obtained were compared with an available glycine derivative (GlyD2) and glycine (Gly). Tafel polarization measurements revealed that the three tested inhibitors function as mixed-type compounds. The inhibition efficiency increased with increase in inhibitor concentration and decreased with temperature, suggesting the occurrence of physical adsorption. The adsorptive behaviour of the three inhibitors followed Temkin-type isotherm and the standard free energy changes of adsorption () were evaluated for the three tested inhibitors as a function of temperature. The inhibition performance of GlyD1 was much better than those of GlyD2 and Gly itself. Results obtained from the different corrosion evaluation techniques were in good agreement.     

Acoustic emission during the electrochemical corrosion of 304 stainless steel in H2SO4 solutions

Acoustic emission (AE) behaviour during the electrochemical corrosion of 304 stainless steel (304SS) in H₂SO₄ solutions was studied. AE signals which related to transpassive dissolution are detected in solutions with low pH, and are very slightly influenced by current density and pre-strain. During hydrogen bubble evolution, a weak correlation exists between the AE signal amplitude and the hydrogen bubble diameter. The concept of potential – pH – AE diagram is proposed and such a diagram is drawn based on AE activity and b-values. The main mechanisms of AE sources which are transpassive dissolution and hydrogen bubble evolution, are also discussed.     

N-Aminorhodanine as an effective corrosion inhibitor for mild steel in 0.5 M H2SO4

The corrosion inhibition effect of N-aminorhodanine (N-AR) on mild steel (MS) in 0.5 M H₂SO₄ was studied in both short and long immersion duration using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), chronoamperometry and hydrogen gas evolution. The surface morphology of MS was examined with scanning electron microscopy (SEM) in absence and presence inhibitor. The inhibitor adsorption process on MS surfaces obeys the Langmuir adsorption isotherm. The results show that NAR is a good inhibitor for MS in the acidic medium. The inhibition efficiency obtained from potentiodynamic polarization, EIS and LPR up to 98% is determined.     

A comparative H2S corrosion study of 304L and 316L stainless steels in acidic media

H₂S corrosion of 304L and 316L in oxygen-free Na₂SO₄ + Na₂S solution at pH 3 and temperature of 60 °C were investigated by EIS, potentiodynamic polarisation, multi-component Pourbaix diagrams and microstructure characterization. At similar conditions, lower corrosion rate was observed on 316L, attributed to its denser (1.5 times) and smoother (6%) surface layer and confirmed by SEM micrograph. During polarisation, H₂S increases significantly the critical current density on 304L and passivation current density, i_p, on 316L. Higher i_p on 316L was associated to simultaneous FeS₂–MoS₂ preservation, confirmed by XRD examination. H₂S could have an inhibiting effect on 304L in passivity region.     

Copper corrosion inhibition in O2-saturated H2SO4 solutions

Corrosion inhibition of copper in O₂-saturated 0.50 M H₂SO₄ solutions by four selected amino acids, namely glycine (Gly), alanine (Ala), valine (Val), or tyrosine (Tyr), was studied using Tafel polarization, linear polarization, impedance, and electrochemical frequency modulation (EFM) at 30 °C. Protection efficiencies of almost 98% and 91% were obtained with 50 mM Tyr and Gly, respectively. On the other hand, Ala and Val reached only about 75%. Corrosion rates determined by the Tafel extrapolation method were in good agreement with those obtained by EFM and an independent chemical (i.e., non-electrochemical) method. The chemical method of confirmation of the corrosion rates involved determination of the dissolved Cu²⁺, using ICP-AES (inductively coupled plasma atomic emission spectrometry) method of chemical analysis. Nyquist plots exhibited a high frequency depressed semicircle followed by a straight line portion (Warburg diffusion tail) in the low-frequency region. The impedance data were interpreted according to two suitable equivalent circuits. The kinetics of dissolved O₂ reduction and hydrogen evolution reactions on copper surface were also studied in O₂-saturated 0.50 M H₂SO₄ solutions using polarization measurements combined with the rotating disc electrode (RDE). The Koutecky-Levich plot indicated that the dissolved O₂ reduction at the copper electrode was an apparent 4-electron process.     

Experimental and theoretical calculations on corrosion inhibition of steel in 1 M H2SO4 by crown type polyethers

The corrosion inhibitive efficiencies of two crown type polyethers, namely dibenzo-bis-imino crown ether (C-1) and dibenzo-diaza crown ether (C-2), which are macrocyclic Schiff base and its reduced form (macrocyclic amine), respectively, for the steel in 1 M H₂SO₄ have been investigated by Tafel extrapolation and linear polarization methods. Corrosion and adsorption isotherm parameters were determined from current-potential curves. The studies show that C-1 and C-2 inhibit the corrosion of the steel in H₂SO₄ solution. Semiempirical AM1 method was used for theoretical calculations. The obtained results of these calculations for the compounds were found to be consistent with the experimental findings.     

Corrosion behaviour of carbon steel in different concentrations of HCl solutions containing H2S at 90 °C

The corrosion behavior of SAE-1020 carbon steel in H₂S-containing solutions with different concentration of HCl at 90 °C was investigated by weight loss, electrochemical measurements, SEM and XRD analysis. The results showed that the corrosion rate of carbon steel increased with increasing HCl concentration. Uniform corrosion was found on the carbon steel surface in H₂S + HCl solutions, while corrosion cavities were observed in the solution only containing H₂S. The ratio of Faradaic process of total corrosion process increased with the increase of HCl concentration. The corrosion products were solely composed of mackinawite in the H₂S-containing solutions with or without HCl.     

Effect of Mo and Mn additions on the corrosion behaviour of AISI 304 and 316 stainless steels in H2SO4

The work addresses the influence of Mn and Mo additions on corrosion resistance of AISI 304 and 316 stainless steels in 30 wt.% H₂SO₄ at 25 and 50 °C. Corrosion mechanism was determined by gravimetric tests, DC polarization measurements and electrochemical impedance spectroscopy (EIS). The morphology and nature of the reaction products formed on the material surface were analysed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Reduction of temperature from 50 to 25 °C drastically decreased the corrosion rate of AISI 304 and 316 stainless steels in sulphuric acid solution. Mn additions did not affect significantly the general corrosion resistance due to its low ability to form insoluble compounds in acid medium. Meanwhile, the formation of molybdenum insoluble oxides enhanced the corrosion performance.     

Evaluation of corrosion inhibition at sand-deposited carbon steel in CO2-saturated brine

The adsorption of four CO₂ corrosion inhibitors on silica sand and their subsequent inhibition activity at sand-deposited steel has been investigated. The presence of a sand deposit affects the performance of inhibitors at carbon steel due to their competitive adsorption on sand. Sulfur-containing organic compounds show minimal adsorption on sand compared to pyridinium surfactants and provide the highest inhibition efficiency at the sand-deposited steel. The extent of inhibitor adsorption onto sand is discussed in relation to their chemical structures. The significance of determining the adsorption affinity to sand in the selection of inhibitors to mitigate under-deposit corrosion is demonstrated.     

Synergistic effect of halide ions on improving corrosion inhibition behaviour of benzisothiozole-3-piperizine hydrochloride on mild steel in 0.5 M H2SO4 medium

The synergistic effect of iodide ions and benzisothiozole-3-piperizine hydrochloride (BITP) on corrosion inhibition of mild steel in 0.5 M H₂SO₄ solution has been studied by both chemical and electrochemical methods. The corrosion performance of BITP in 1.0 M HCl and 0.5 M H₂SO₄ media was examined and compared. The adsorption of BITP and its combination with iodide ions on mild steel surface followed Langmuir adsorption isotherm via chemisorption mechanism. The calculated values of synergism parameter (S_θ) were found to be greater than unity. This result clearly showed the existence of synergism between iodide ions and BITP molecules.     

Co2 corrosion inhibition of X-120 pipeline steel by a modified imidazoline under flow conditions

A study of the effect of flow conditions on the performance of a carboxyethyl-imidazoline as CO₂-corrosion inhibitor for API X-120 pipeline steel has been evaluated. Testing techniques include polarization curves, linear polarization resistance, electrochemical impedance spectroscopy and electrochemical noise measurements under stirred conditions (0, 250, 500, 1000 and 2500 rpm). All these techniques show that for the uninhibited solution, corrosion rate increases with an increase in the rotation speed, but for the inhibited solution, the lowest corrosion rate is obtained at 500 rpm, and it increases at lower or higher rotation speeds.     

Effect of annealing temperature on the corrosion behavior of duplex stainless steel studied by in situ techniques

The effects of the annealing temperature on the microstructure and the corrosion behavior of duplex stainless steel 2507 were investigated by means of magnetic force microscopy (MFM), scanning Kelvin probe force microscopy (SKPFM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The SEM results indicated that the volume fraction of the austenite phase decreased with the increased annealing temperature. SKPFM/MFM measurements conducted in air at the room temperature and an ambient relative humidity of about 25% showed a higher Volta potential of the paramagnetic austenite than that of the ferromagnetic ferrite. The in situ AFM observation in a hydrochloric acid solution provided solid evidence that corrosion preferentially occurred in the ferrite phase. The sample annealed at 1100 °C exhibited a greater Volta potential difference between the ferrite and austenite and a higher corrosion rate in the ferrite, while that annealed at 1150 °C had a smaller Volta potential difference and a lower corrosion rate. The relative nobility and microstructure change of two phases, as well as their corrosion behavior, can be explained by the effect of the composition of alloying elements.     

Erosion resistance of CO2 corrosion scales formed on API P110 carbon steel

The erosion resistance of CO₂ corrosion scales formed on carbon steel was investigated in water–sand two-phase flow utilizing weight loss test, scanning electron microscopy, and X-ray diffraction. The effects of CO₂ partial pressure, stirring speed, test time, and grain size on the erosion resistance of the scales were analysed. Results show that several characteristics of CO₂ corrosion scales are key factors affecting erosion resistance. Cubic polynomials are used to fit the erosion rate data, and effectively evaluate the ability of CO₂ corrosion scales to resist erosion. An erosion mechanism, based on fluid dynamics and CO₂ corrosion scales characteristics, is discussed.     

Inhibition effect of 2-amino-4-methylpyridine on mild steel corrosion: Experimental and theoretical investigation

The effect of 2-amino-4-methylpyridine (AMP) on the corrosion behavior of mild steel (MS) in 0.5 M HCl is investigated with electrochemical methods and theoretical calculations. The electrochemical tests show that the polarization resistance of MS increasing the presence of AMP in acid solution. Adsorption of AMP on MS surface is a physical and obeys the Langmuir isotherm. The quantum parameters signaled adsorption occurs on amine and methyl substituents of AMP. The inhibition efficiency is related to frontier orbital’s energy band gap of AMP, which are 5.357 and 6.490 eV for neutral and protonated molecules in aqueous solution, respectively.     

Inhibition effect of 6-benzylaminopurine on the corrosion of cold rolled steel in H2SO4 solution

The inhibition effect of 6-benzylaminopurine (BAP) on the corrosion of cold rolled steel (CRS) in 1.0-7.0 M H₂SO₄ at 25-50 °C was studied by weight loss and potentiodynamic polarization methods. Fourier transform infrared spectroscopy (FTIR) and atomic force microscope (AFM) were used to characterize the CRS surface. The results showed that BAP was a good inhibitor in 1.0 M H₂SO₄, and the adsorption of BAP obeyed the Temkin adsorption isotherm. Polarization curves showed that BAP acted as a mixed-type inhibitor in sulfuric acid. Depending on the results, the inhibitive mechanism was proposed.     

Effect of hexamethylpararosaniline chloride (crystal violet) on mild steel corrosion in acidic media

The corrosion inhibition of mild steel in 0.5 M H₂SO₄ and 1 M HCl by hexamethylpararosaniline chloride (HMPC) was investigated using the gravimetric technique in the temperature range 303–333 K. The results indicate that HPMC inhibited the corrosion reaction in both acid media at all temperatures and inhibition efficiency increased with HMPC concentration. The inhibiting action is attributed to general adsorption of protonated and molecular HPMC species on the corroding metal surface. Adsorption followed a modified Langmuir isotherm and the Temkin isotherm, with very high negative values of the free energy of adsorption (). An increase in temperature reduced the inhibition efficiency of HPMC in 0.5 M H₂SO₄ but increased efficiency in 1 M HCl. Activation parameters such as activation energy (E_a), activation enthalpy (ΔH^∗) and activation entropy (ΔS^∗) as well as the adsorption heat (Q_ads) were evaluated from the effect of temperature on corrosion and inhibition processes.