Study on steel corrosion in different seabed sediments

A series of simulation experiments on carbon steel (A(3) steel) and low alloy steel (16 Mn steel) in marine atmosphere (MA), seawater (SW) and seabed sediment (SBS) including rough sea sand, fine sea sand and seabed mud were carried out indoors for a year or so by means of individually hanging plates (IHP) and electrically connected hanging plates (ECHP). The corrosion of steels in SBS was mainly due to the macrogalvanic cell effect. The steel plates at the bottom of SBS, as the anode of a macrogalvanic cell, showed the heaviest corrosion with a corrosion rate of up to 0.12 mm/a, approximately equal to that of steel plates in marine atmosphere. The test results showed that the corrosion rates of A(3) and 16 Mn steel in marine environment were in the order: MA > SW > SBS by the IHP method; and MA > SBS > SW by the ECHP method. The corrosion rates of steels in the water/sediment interface were directly proportional to the grain size of the SBS by the ECHP method, but those of steels in the water/sediment interface did not vary with the grain size of SBS by the IHP method. The corrosion rate of low-alloy steel was a little higher than that of carbon steel. The results of this study have important applications for design of offshore steel structures such as oil platform, pier, and port.

The inhibition of mild steel corrosion in 1 M hydrochloric acid solutions by triazole derivative

The title compound 1-(4,5-dihydro-3-phenylpyridine-1-yl)-2-(1H-1,2,4-triazole-1-yl)ethyl ketone (DTE) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M hydrochloric acid solutions was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electronic microscope (SEM). Results obtained revealed that DIE performed excellently as a corrosion inhibitor for mild steel in 1 M hydrochloric acid media and its efficiency attains more than 90.9% at 1.0 x 10(-3) M at 298 K. Polarization curves indicated that the inhibitor behave mainly as mixed-type inhibitor. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions. Adsorption of the inhibitor on the mild steel surface followed Langmuir adsorption isotherm. And the values of the free energy of adsorption Delta G(ads) indicated that the adsorption of DTE molecule was a spontaneous process and was typical of chemisorption. (c) 2008 Elsevier B.V. All rights reserved.

Experimental and theoretical investigation of the adsorption behaviour of new triazole derivatives as inhibitors for mild steel corrosion in acid media

Three triazole derivatives (4-chloro-acetophenone-O-1'-(1',3',4'-triazolyl)-metheneoxime (CATM), 4-methoxyl-acetophenone-O-1'-(1',3',4'-triazolyl)-metheneoxime (MATM) and 4-fluoro-acetophenone-O-1'-(1',3',4'-triazolyl)-metheneoxime (FATM)) have been synthesized as new inhibitors for the corrosion of mild steel in acid media. The inhibition efficiencies of these inhibitors were evaluated by means of weight loss and electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and polarization curves. Then the surface morphology was studied by scanning electron microscopy (SEM). The adsorption of triazole derivatives is found to obey Langmuir adsorption isotherm, and the thermodynamic parameters were determined and discussed. The relationship between molecular structure of these compounds and their inhibition efficiency has been investigated by ab initio quantum chemical calculations. The electronic properties such as the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels, energy gap (LUMO-HOMO), dipole moment and molecular orbital densities were computed. (c) 2007 Elsevier Ltd. All rights reserved.

Some new triazole derivatives as inhibitors for mild steel corrosion in acidic medium

Two triazole derivatives, 3,4-dichloro-acetophenone-O-1'-(1',3',4'-triazolyl)-methaneoxime (4-DTM) and 2,5-dichloro-acetophenone-O-1'-(1',3',4'-triazolyl)-methaneoxime (5-DTM) were synthesized, and the inhibition effects for mild steel in 1 M HCl solutions were investigated by weight loss measurements, electrochemical tests and scanning electronic microscopy (SEM). The weight loss measurements showed that these compounds have excellent inhibiting effect at a concentration of 1.0 x 10(-3) M. The potentiodynamic polarization experiment revealed that the triazole derivatives are inhibitors of mixed-type and electrochemical impedance spectroscopy (EIS) confirmed that changes in the impedance parameters (R-ct and C-dl) are due to surface adsorption. The inhibition efficiencies obtained from weight loss measurements and electrochemical tests were in good agreement. Adsorption followed the Langmuir isotherm with negative values of the free energy of adsorption Delta G(ads)(o). The thermodynamic parameters of adsorption were determined and are discussed. Results show that both 4-DTM and 5-DTM are good inhibitors for mild steel in acid media.

Corrosion behaviour of steel in beach soil along Bohai Bay

Research on corrosion of steel structures in various marine environments is essential to assure the safety of structures and can effectively prolong their service life. In order to provide data for anticorrosion design of oil exploitation structures in the Bohai Bay, the corrosion behaviour and properties of steel in beach soil, using typical steel samples (Q235A carbon steel and API 5Lx52 pipeline steel) buried 0.5, 1.0 and 1.5 m deep under typical beach soils in Tanggu, Yangjiaogou, Xingcheng, Yingkou and Chengdao for 1-2 years were studied. The carbon steel and pipeline steel were both corroded severely in the beach soil, with the form of corrosion being mainly uniform with some localised attack (pitting corrosion). The corrosion rate of the carbon steel was up to 0.16 mm/year with a maximum penetration depth of 0.76 mm and that of the pipeline steel was up to 0.14 mm/year, with a maximum penetration depth of 0.53 mm. Compared with carbon steel, the pipeline steel generally had better corrosion resistance in most test beach soils. The corrosion rates and the maximum corrosion depths of carbon steel and pipeline steel were in the order: Tanggu>Xingcheng>Chengdao>Yingkou>Yangjiaogou with corrosion altering with depth of burial. The corrosion of steel in the beach soil involves a mixed mechanism with different degrees of soil aeration and microbial activity present. It is concluded that long term in situ plate laying experiments must be carried out to obtain data on steel corrosion in this beach soil environment so that the effective protection measures can be implemented.

Inhibition Effect of 2,3,5-Triphenyl-2H-tetrazolium Chloride and 2,4,6-Tri(2-pyridyl)-s-triazine on the Corrosion of Mild Steel in 1 mol/L HCl and Mechanism Study (II)

The inhibitory effect of 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and 2,4,6-tri(2-pyridyl)-s-triazine (TPT) molecules on the corrosion of mild steel in 1 mol/L HCl and microcosmic inhibitory mechanism were investigated by X-ray photoelectron spectroscopy and ellipsometry. XPS results showed that C Is and N Is peaks of TTC, C Is and N Is peaks of TPT and their integral areas were obtained, which suggested the layer of the inhibitors (TTC or TPT) should have effectively protected the mild steel surface from the corrosion; and the depression from the inhibitors for the corrosion of mild steel surface was studied using ellipsometry combined with potentiodynamic polarization and the phasic difference was gained, which displayed the inhibitory coverage of the inhibitors formed.

Electrochemical, SEM/EDS and quantum chemical study of phthalocyanines as corrosion inhibitors for mild steel in 1 mol/l HCl

The inhibition effect of metal-free phthalocyanine (H2Pc), copper phthalocyanine (CuPc) and copper phthalocyanine tetrasulfuric tetrasodium salt (CuPc center dot S(4)center dot Na-4) on mild steel in I mol/l HCl in the concentration range of 1.0 X 10(-5) to 1.0 X 10(-3) mol/l was investigated by electrochemical test, scanning electron microscope with energy dispersive spectrometer (SEM/EDS) and quantum chemical method. The potentiodynamic polarization curves of mild steel in hydrochloric acid containing these compounds showed both cathodic and anodic processes of steel corrosion were suppressed, and the Nyquist plots of impedance expressed mainly as a capacitive loop with different compounds and concentrations. For all these phthalocyanines, the inhibition efficiency increased with the increase in inhibitor concentration, while the inhibition efficiencies for these three phthalocyanines with the same concentration decreased in the order Of CuPc center dot S(4)center dot Na-4 > CuPc > H2Pc according to the electrochemical measurement results. The SEM/EDS analysis indicated that there are more lightly corroded and oxidative steel surface for the specimens after immersion in acid solution containing 1.0 x 10(-3) mol/l phthalocyanines than that in blank. The quantum chemical calculation results showed that the inhibition efficiency of these phthalocyanines increased with decrease in molecule's LUMO energy, which was different from the micro-cyclic compounds. (c) 2005 Elsevier B.V. All rights reserved.

Effects of anaerobe in sea bottom sediment on the corrosion of carbon steel

The in-situ study of steel corrosion in sea bottom sediment (SBS) was carried out by Transplanting Burying Plate method (TBP method). It was found that the corrosion rate of steel in the sea bottom sediment with sulfate reducing bacteria (SRB) could be as high as ten times of that in sea bottom sediment without SRB. The experiments in simulated sea bottom sediments with different SRB contents by artificial culturing showed that the electrochemical behavior of steel in the sea bottom sediment with SRB was different from that without SRB. SRB altered the polarization behavior of steel significantly. The environment was acidified due to the activity of SRB and the corrosion of steel was accelerated. The corrosion of carbon steel in sea bottom sediment is anaerobic corrosion, and the main factor is anaerobe. There are SRB commonly in SBS, and the amount of SRB decreases along with the depth of sediment. Because of the asymmetry and variation of sea bottom sediment, the most dangerous corrosion breakage of steel in SBS is local corrosion caused by SRB. So the main countermeasure of corrosion protection of sea bottom steel facilities should be controlling of the corrosion caused by anaerobe.

2,3,5-triphenyl-2H-tetrazolium chloride and 2,4,6-tri(2-pyridyl)-s-triazine on the corrosion of mild steel in HCl

Electrochemical measurement, quantum chemical method, and scanning electron microscopy (SEM) were performed to investigate the inhibitive effect of 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and 2,4,6-tri(2-pyridyl)-s-triazine(TPT) on the corrosion of mild steel in 1mol.L-1 HCl at room temperature. Impedance spectroscopy measurement showed that the polarization resistance increased and that double layer capacitance decreased with the increase in the inhibitive concentration, and the results of potentiodynamic polarization showed that the inhibitors suppressed both cathodic and anodic processes of steel corrosion without change in the mechanism. Higher the orbital density distribution strength of the lowest unoccupied molecular orbital, higher is the molecule dipole, and lower energy gap between the energy of the highest occupied molecular orbital and the energy of the lowest unoccupied molecular orbital resulted in higher inhibitory efficiency. The results of SEM analysis showed that the metal was protected from aggressive corrosion by the addition of TTC and TPT.

Electrochemical, quantum chemical and SEM investigation of the inhibiting effect and mechanism of ciprofloxacin, norfloxacin and ofloxacin on the corrosion for mild steel in hydrochloric acid

The inhibiting effect and mechanism of 1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylicacid(ciprofloxacin), 1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid (norfloxacin) and (-)-(S)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7 H-pyrido(1,2,3-de)-1,4-benzoxazine-6 carboxylic acid (ofloxacin) on the corrosion of mild steel in 1 mol/L HCl have been studied using electrochemical method, quantum chemical method and SEM at 303 K. The potentiodynamic results showed that these compounds suppressed both cathodic and anodic processes of mild steel corrosion in 1 mol/L HCl. The impedance spectroscopy showed that R-p values increased, and C-dl values decreased with the rising of the working concentration. Quantum chemical calculation showed that there was a positive correlation between some inhibitors structure properties and the inhibitory efficiency. The inhibitors function through adsorption followed Langmuir isotherm, and chemisorption made more contribution to the adsorption of the inhibitors on the steel surface compared with physical adsorption. SEM analysis suggested that the metal had been protected from aggressive corrosion because of the addition of the inhibitors.

Effects of sulfate-reducing bacteria on the corrosion behavior of carbon steel

The influences of the growing process of sulfate-reducing bacteria (SRB) in seawater system on the medium state and corrosion behavior of carbon steel were studied by detecting solution state parameters and using corrosion electrochemical methods. The growing process of SRB in the seawater shows the three stages of growing, death and residual phases. The solution state parameters of the concentration of sulfide, the pH value and the redox potential changed during the three stages of the SRB growing process. And the corrosion rate of D36 carbon steel was accelerated during the growing phase and stable during the death and residual phases. The results indicate that the medium state and the corrosion rate of the steel do not depend on the number of active SRB, but depend on the accumulation of the metabolism products of SRB. (c) 2007 Elsevier Ltd. All rights reserved.

Electrochemical and quantum chemical study of purines as corrosion inhibitors for mild steel in 1 M HCl solution

The purines and its derivatives, such as, guanine, adenine, 2,6-diaminopurine, 6-thioguanine and 2,6-dithiopurine, were investigated as corrosion inhibitors for mild steel in 1 M HCl solution by weight loss measurements, electrochemical tests and quantum chemical calculations. The polarization curves of mild steel in the hydrochloric acid solutions of the purines showed that both cathodic and anodic processes of steel corrosion were suppressed. The Nyquist plots of impedance expressed mainly as a depressed capacitive loop with different compounds and concentrations. For all these purines, the inhibition efficiency increased by increasing the inhibitor concentration, and the inhibition efficiency orders are 2,6-dithiopurine > 6-thioguanine > 2,6-diaminopurine > adenine > guanine with the highest inhibiting efficiency of 88.0% for 10(-3) M 2,6-dithiopurine. The optimized structures of purines, the Mulliken charges, molecular orbital densities and relevant parameters were calculated by quantum chemical calculations. The quantum chemical calculation results inferred that the adsorption belong to physical adsorption, which might arise from the pi stacking between the pi electron of the purines and the metal surface. (C) 2008 Elsevier Ltd. All rights reserved.

Long-term anticorrosion behaviour of polyaniline on mild steel

Anticorrosion performances of polyaniline emeraldine base/epoxy resin (EB/ER) coating on mild steel in 3.5% NaCl solutions of various pH values were investigated by electrochemical impedance spectroscopy (EIS) for 150 days. In neutral solution (pH 6.1), EB/ER coating offered very efficient corrosion protection with respect to pure ER coating, especially when EB content was 5-10%. The impedance at 0.1 Hz of the coating increased in the first 1-40 immersion days and then remained constant above 10(9) Omega cm(2) until 150 days, which in combination with the observation of a Fe2O3/Fe3O4 passive film formed on steel confirmed that the protection of EB was mainly anodic. In acidic or basic solution (pH 1 or 13), EB/ER coating also performed much better than pure ER coating. However, these media weakened the corrosion resistance due to breakdown of the passive film or deterioration of the ER binder.

Investigation on the corrosion inhibitive effect of 2H-pyrazole-triazole derivatives in acidic solution

Four research methods, such as weight loss test, electrochemical techniques, adsorption isotherm, and quantum chemical calculation, were employed in this paper to study the inhibition efficiency (IE) and inhibition mechanism of three 2H-pyrazole-triazole derivatives, BHOT, FHOT, and CHOT in 1 M HCl solution for mild steel. Using the electrochemical technique, three inhibitors were proved to show a mixed-type character for mild steel by suppressing both anodic and cathodic reactions on the steel surface. The adsorption models of three compounds were established at different temperatures according to their adsorption isotherms. The results of the quantum chemical calculation method indicated that the adsorption sites of 2H-pyrazole-triazole derivatives were strongly centralized on benzene ring, triazole ring, or other substituents. All the results showed that the three derivatives were excellent inhibitors in I M HCl solution for mild steel.

Alloy elements' effect on anti-corrosion performance of low alloy steels in different sea zones

The corrosion rate of low alloy steel in different sea zones has close correlation with the content of the alloy element. From the field data of steel corrosion rates in atmospheric zone, splash zone and immersion zone, regression analysis was used to study the correlation between the corrosion rate of steels and the amount of added alloy elements. Three regression equations were obtained in different sea zones. Based on the equations, the anti-corrosion performance of the alloy elements can be deduced which can be used to screen out low alloy steel with good anti-corrosion performance. (C) 2007 Elsevier B.V. All rights reserved.