Investigation on AC-Induced Corrosion Behavior and Product Film of X70 Steel in Aqueous Environment with Various Ions
张慧, 杜艳霞, 李伟, 路民旭
北京科技大学新材料技术研究院腐蚀与防护中心 北京 100083
ZHANGHui, DUYanxia, LIWei, LUMinxu
Corrosion and Protection Center, Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083, China
Cite this article: ZHANGHui, DUYanxia, LIWei, LUMinxu. Investigation on AC-Induced Corrosion Behavior and Product Film of X70 Steel in Aqueous Environment with Various Ions. Acta Metallurgica Sinica[J], 2017, 53(8): 975-982 doi:10.11900/0412.1961.2016.00566
During the past decades, more buried oil or gas pipeline failures have been attributed to alternating current (AC) interference, and finally, those corrosion failures were investigated and the AC current density was identified as the critical influence parameter. There is general agreement on AC current density as a chief factor in determining metal wastage condition or assessing the AC corrosion risk for any type of soil in the presence of AC corrosion. Different degrees of AC corrosion may occurr if long distance pipelines pass through different kinds of soil environments, however, the effect of soil ions on pipeline steel without cathodic protection is still not well understood. Therefore, it is imperative to study the AC corrosion behaviors of pipeline steel in different soil environments. In the AC corrosion simulation experiment, by investigating the AC corrosion behaviors of X70 steel in 4 kinds of environmental media, the corrosion rates (Kd) were obtained, whose order was >>>. SEM, EDS and XRD were used to characterize and analyse the microscope morphologies, elements and phase compositions of the corrosion product films surfaces/cross-sections. Under the same AC current density, the reasons of differences of X70 steel's corrosion rate in different media were discussed. The presence of corrosive ions SO42- and Cl- would accelerate the corrosion rate, Na+ would not affect the formation of corrosion product film in NaCl and Na2SO4 solution media, however, the presence of Ca2+ and Mg2+ were helpful to form protective corrosion product films in MgCl2 and CaCl2 solution media.
corrosion product film
图20412-1961-53-8-975/img_2.png图2 300 A/m2交流干扰下X70钢在4种介质中腐蚀168 h后的腐蚀速率 Fig.2 Corrosion rates of X70 steel under alternating current (AC) interference density of 300 A/m2 in 4 kinds of simulated media exposed for 168 h
Fig.20412-1961-53-8-975/img_2.png图2 300 A/m2交流干扰下X70钢在4种介质中腐蚀168 h后的腐蚀速率 Fig.2 Corrosion rates of X70 steel under alternating current (AC) interference density of 300 A/m2 in 4 kinds of simulated media exposed for 168 h
图30412-1961-53-8-975/img_3.png图3 300 A/m2交流干扰下X70钢在4种介质中腐蚀产物的XRD谱 Fig.3 XRD spectra of the corrosion product films on X70 under AC interference density of 300 A/m2 in simulated media of Na2SO4 (a), MgCl2 (b), CaCl2 (c) and NaCl (d)
Fig.30412-1961-53-8-975/img_3.png图3 300 A/m2交流干扰下X70钢在4种介质中腐蚀产物的XRD谱 Fig.3 XRD spectra of the corrosion product films on X70 under AC interference density of 300 A/m2 in simulated media of Na2SO4 (a), MgCl2 (b), CaCl2 (c) and NaCl (d)
图40412-1961-53-8-975/img_4.png图4 X70钢腐蚀产物膜表面微观形貌的SEM像 Fig.4 Low (a, c, e, g) and high (b, d, f, h) magnified surface SEM images of corrosion product films on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)
Fig.40412-1961-53-8-975/img_4.png图4 X70钢腐蚀产物膜表面微观形貌的SEM像 Fig.4 Low (a, c, e, g) and high (b, d, f, h) magnified surface SEM images of corrosion product films on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)
Low (a, c, e, g) and high (b, d, f, h) magnified surface SEM images of corrosion product films on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)
图50412-1961-53-8-975/img_5.png图5 X70钢腐蚀产物膜截面微观形貌的SEM像 Fig.5 Low (a, c, e, g) and high (b, d, f, h) magnified cross-sectional SEM images of corrosion product films on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)
Fig.50412-1961-53-8-975/img_5.png图5 X70钢腐蚀产物膜截面微观形貌的SEM像 Fig.5 Low (a, c, e, g) and high (b, d, f, h) magnified cross-sectional SEM images of corrosion product films on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)
图60412-1961-53-8-975/img_6.png图6 X70钢在4种介质中腐蚀产物膜截面成分的EDS分析 Fig.6 EDS analyses of inner corrosion product films (a, c, e, g) and outer corrosion produt films (b, d, f, h) on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)
Fig.60412-1961-53-8-975/img_6.png图6 X70钢在4种介质中腐蚀产物膜截面成分的EDS分析 Fig.6 EDS analyses of inner corrosion product films (a, c, e, g) and outer corrosion produt films (b, d, f, h) on X70 steel in simulated media of Na2SO4 (a, b), MgCl2 (c, d), CaCl2 (e, f) and NaCl (g, h)
Abstract The corrosion rates of low alloy steel and carbon steel in 0.1 N NaCI were accelerated by factors of 4 to 6 when an alternating current density of 30 mA/cm2 (60 cps) was applied in dilute salt solutions purged with nitrogen. Tests with low frequency alternating anodic and cathodic current showed that both steels polarized more rapidly in the cathodic direction than in the anodic. Thus, the anodic half-cycle of AC did not have time to restore the potential to its original value after the preceding cathodic half-cycle. The result is a net cathodic polarization which accelerates or “depolarizes” the anodic metal-dissolution reaction by lowering the anodic Tafel slope. Depolarization of the anodic reaction was confirmed by polarization measurements in the presence of AC. Depolarization of the anodic reaction by AC was also observed in aerated solutions, but the corrosion rate was controlled by diffusion of dissolved oxygen, and no increase in corrosion rate was measured. Possible mechanisms of anodic...
Pookote SR, Chin DT.Effect of alternating current on the underground corrosion of steels[J]. , 1978, 17(3): 9
Results of tests involving imposition of 60 Hz AC at various densities in an oxygen concentration corrosion cell on DC between 2 electrodes are reported. AC imposed on DC increases the corrosion rate of steel in soil with high initial and then steady state attack following after a time interval. High densities increased attack rate and if sufficiently high, pitting. Corrosion products from AC-DC were friable. Temperature increases in the soil had negligible effect on corrosion rate. It is postulated that AC acts as a depolarizer and that reversible potential characteristics may be significant.
ColletE, DeloresB, GabillardM, et al.Corrosion due to AC influence of very high voltage power lines on polyethylene-coated steel pipelines: Evaluation of risks-preventive measures[J]. , 2001, 48(4): 221
Shows how observations (1993-1999) and on-site and laboratory measurements (1993-1996) have made it possible to define certain prevalent parameters concerning AC corrosion risks. These are from the evaluation and prevention of AC corrosion risks as practised by Gaz de France.
PourbaixA, CarpentiersP, GregoorR.Detection and assessment of alternating current corrosion[J]. , 2000, 39(3): 34
A measuring system to determine the rue peak potential, without ohmic drop error, is described. There is no alternating current (AC)-induced corrosion when the true max. peak potential is below the potential for cathodic protection (CP). Methods are studied to determine the importance of AC corrosion when the potential is higher than the critical potential for CP during a part of the AC period.
Pipelines and AC power transmission lines frequently share corridors leading to AC interference corrosion problems, as documented by pipeline failures that have occurred in the USA, Canada and Europe, even when cathodic protection is applied. In order to investigate these phenomena, weight loss tests on carbon steel samples were performed in soil-simulating conditions (aerated and de-aerated sulphate solutions) at various AC current densities from 10 to about 900聽A/m. Tests on freely corroding samples showed that the corrosion rate increased as AC current density increased; the effect of AC on corrosion rate was also detected at current densities lower than 30聽A/m. The results obtained are analyzed and discussed together with polarization test results, which were presented in a previous paper by Goidanich et al. (submitted for publication) .
(曹楚南. [M]. 北京: 化学工业出版社, 2005: 373)
Cao CN. [M]. Beijing: Chemical Industrial Press, 2005: 373
TorstensenA.AC corrosion on cathodically protected steel [D]. , 2012
LillebyL.Effect of AC current on calcareous deposits [D]. , 2009
ABSTRACT Overhead power lines are often placed in the same right of way as buried pipelines. Long term AC interference on a buried pipeline may cause corrosion due to an exchange of AC-induced current between the exposed bare metal at unavoidable coating defects in the structure and the surrounding soil. The exchange of current depends on the AC voltage whose amplitude is related to various parameters. The mechanism of the AC corrosion is not very well understood, particularly as it applies to corrosion in soils. The objective of this paper is to present the application of the model based on the conventional (DC) treatment of the corrosion processes to the case of cathodically protected pipeline. The adopted model suggests that the AC currents cause positive polarization shifts during the positive half period of the imposed AC sinwave along with negative polarization shifts in the negative half period. It is shown on an example, that during the cathodic (negative) semi-cycle, the current exhibits shifts to considerable magnitudes, much greater then the protective current. During the anodic semi-cycle the reduction current decreases, but not to the same degree as the increase during the cathodic semi-cycle. Therefore, the complete AC cycle results in a net increase in the reduction current.
HelmG, HeimT, HeinzenH, et al.Investigation of corrosion of cathodically protected steel subjected to alternating currents[J]. , 1993, 32: 246
Fu AQ, Cheng YF.Effects of alternating current on corrosion of a coated pipeline steel in a chloride-containing carbonate/bicarbonate solution[J]. , 2010, 52: 612
In this work, the alternating current (AC)-induced corrosion of a coated pipeline steel was studied in a chloride-containing, concentrated carbonate/bicarbonate solution, which simulated the trapped high pH electrolyte under coating, by potentiodynamic polarization measurements, immersion tests and surface characterization technique. It was found that an application of AC resulted in a negative shift of corrosion potential of the steel, caused an oscillation of anodic current density, and degraded the steel passivity developed in the solution. With the increase of AC current density, the corrosion rate of the steel increased. At a low AC current density, a uniform corrosion occurred, while at a high AC current density, pitting corrosion occurred extensively on the steel electrode surface. At individual applied AC, there was a higher electrochemical dissolution activity of the coated steel electrode containing a 1聽mm defect than that of the electrode containing a 10聽mm defect.
A method for detecting rotational speeds (n) of an internal combustion engine having a signal wheel having marks (M 1 through M 7 ) for signaling on a crankshaft of the internal combustion engine is described. The marks (M 1 through M 7 ) on the signal wheel are detected with the aid of a sensor and evaluated by a detection and evaluation device. To implement high-precision detection of a rotational speed, the rotational speeds (n) are evaluated using a sector section of approximately 6° to 35° to increase the accuracy on the basis of a reduced sector section of the signal wheel.
Smith DC, McEnaney B. The influence of dissolved oxygen concentration on the corrosion of grey cast iron in water at 50 ℃[J]. , 1979, 19: 391
The formation of corrosion scales has been studied on grey cast iron in flowing water at 50°C as a function of O 2 concentrations from 0.1 to 3.95 ppm O 2. Below 1.0 ppm O 2, nodular scales form containing Fe 3O 4 and a green rust, GR. At higher O 2 concentrations, a continuous scale eventually forms, consisting of a porous subscale of Fe 2O 4 + GR overlaid with a compact crust of Fe 3O 4 + GR and a thin surface layer of γ-FeOOH. ‘Chimneys’ oriented in the water flow direction grow out of the crust. γ-FeOOH is reduced to Fe 3O 4 which becomes the principal constituent of the scale. Scales on cast iron components from central heating systems closely resemble those found in the present work.
RamanA, NasrazadaniS, SharmaL.Morphology of rust phases formed on weathering steels in various laboratory corrosion tests[J]. , 1989, 22: 79
The morphology and growth characteristics of rust phases formed on ASTM A-588 weathering steel in three different types of laboratory tests—accelerated atmospheric exposure simulation tests (AAEST), salt fog test, and continuous immersion test in plain as well as salt water—are analyzed using microstructural information obtained from representative exposed specimens studied in a scanning electron microscope (SEM). The ultimate and most dominant phase in the AAEST was α-FeOOH whereas an amorphous phase designated as amorphous bulk (AB) appeared as “cotton bolls” in the adherent, sedimentary layer formed on the steel surface during continuous immersion. Crystalline phases α-, δ-, and γ-FeOOH as well as γ-Fe 2O 3.H 2O were found developed on top of the first-formed sedimentary amorphous layer, containing another amorphous phase designated as amorphous mix (AM). Magnetite was the dominant phase obtained in the salt fog test. It forms in layers and seems to transform to α-FeOOH through formation of whiskers and rods on its surface. Sandy grains of γ-Fe 2O 3.H 2O were also seen in the rusts obtained in this test.
MajzlanJ, MazeinaL, NavrotskyA.Enthalpy of water adsorption and surface enthalpy of lepidocrocite (γ-FeOOH)[J]. , 2007, 71: 615
Lepidocrocite (γ-FeOOH) appears to be thermodynamically metastable with respect to goethite (α-FeOOH) and yet the former phase forms and persists both in nature and laboratory. Here we show that the thermodynamic factors relevant to these observations cannot be dismissed, although kinetics undoubtedly plays a significant role in the formation and preservation of metastable phases. To understand the relationships of the FeOOH polymorphs in the bulk and nanoscale, we investigated the energetics of lepidocrocite nanoparticles. We measured enthalpy of water adsorption and enthalpy of formation of lepidocrocite samples with surface area of 42–103 m 2/g. Having both quantities measured allowed us to calculate the surface enthalpy for a water-free surface of this phase as 0.62 ± 0.14 J/m 2 and the energy of a relaxed (hydrated) surface as 0.40 ± 0.16 J/m 2. Our measurements show that a portion of the adsorbed water (6540% under laboratory conditions) is chemisorbed (strongly bound) with enthalpy of adsorption of 6165.8 ± 2.6 kJ/mol of H 2O relative to vapor (or 6121.8 ± 2.6 kJ/mol relative to liquid water). The standard enthalpy of formation from elements for a hypothetical lepidocrocite with nominal composition FeOOH and zero surface area is 61552.0 ± 1.6 kJ/mol. Our results demonstrate that when considering the thermodynamic properties of iron oxides in the environment, a conclusive statement about their stability cannot be made without specifying the particle size of individual phases.
MisawaT, AsamiK, HashimotoK, et al.The mechanism of atmospheric rusting and the protective amorphous rust on low alloy steel[J]. , 1974, 14: 279
Atmospheric rusting of mild and low alloy steels was studied by means of infra-red and far infra-red spectrophotometries, X-ray and electron diffraction methods and scanning electron microscopy. The rusting process can be interpreted on the basis of a previously reported diagram for rust formation in aqueous solution. A large amount of amorphous matter in rust formed in semi-rural atmosphere was identified by infra-red and far infra-red spectra as amorphous ferric oxyhydroxide, FeO x (OH) 8鈥2x. The amorphous ferric oxyhydroxide rust on low alloy steel was dense and uniform, and contained a considerable amount of bound water. From these results it can be concluded that the amorphous ferric oxyhydroxide rust acts as a protective barrier against atmospheric rusting of the steels. Cu, P and Cr in low-alloy steels are inferred to favour the formation of crack-free, uniform rust layer and help to produce uniform amorphous ferric oxyhydroxide.
The purpose of this study is to identify the chemical composition of corrosion material accumulated on the inner wall of a mild steel “water pipe”, and the iron species present. It will be shown that the material accumulated is predominantly derived from in situ iron corrosion processes rather than from the sedimentation of particles introduced into the water distribution system. The dominant iron species found was Fe(III) – >90%, with concentrations of Fe(II) and Fe free+amorphous (free and amorphous Fe) being <10%. The results also showed that the accumulated material was composed predominantly of goethite (α-FeOOH – 75.6%), with magnetite (Fe 3O 4 – 21.5%) and lepidocrocite (γ-FeOOH – 2.9%) also being present. It is assumed that FeOOH is derived from amorphous Fe(OH) 3 when it dehydrates.