Influence of pH on corrosion behavior of carbon steel in simulated cooling water containing scale and corrosion inhibitors

In this paper, the influence of pH on the corrosion behavior of AISI 1020 carbon steel in simulated cooling water was investigated by using electrochemical and surface analysis methods. The results of polarization showed that the corrosion resistance of carbon steel increased with an increase in pH of the simulated water, and the corrosion control process changed from cathodic polarization to anode polarization control. The scale and corrosion inhibitor 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) had a certain anodic corrosion inhibition effect on carbon steel, whereas Zn²⁺ acted as a cathodic inhibitor for carbon steel in simulated water with pH 7–9. In simulated water containing both PBTCA and Zn²⁺, a good synergistic corrosion inhibition was found between PBTCA and Zn²⁺, and their corrosion inhibition effect on carbon steel was the best at pH 8. This was attributed to the formation of Zn(OH)₂ precipitate film in the cathode region and the formation of Zn–PBTCA complex film in the anode region at this pH.     

Sodium monocarboxylates as inhibitors of AZ31 alloy corrosion in a synthetic cooling water

This research investigated the inhibiting effects that sodium salts of linear monocarboxylic acids displayed towards the corrosion process of AZ31 Mg alloy in ASTM D 1387 saline solution (a synthetic industrial cooling water). The length of the aliphatic chain of the acids ranged between 7 and 15 carbon atoms. The inhibiting action of these salts can be related to the precipitation of an insoluble magnesium salt, which mainly affected the anodic reaction. The aliphatic chain length controlled the anion solubility and the reaction rate of magnesium carboxylate formation. For all the salts, an optimum concentration was experienced: 10⁻² M for sodium decanoate (caprate), 10⁻³ M for sodium dodecanoate (laurate), 10⁻⁴ M for sodium tetradecanoate (myristate); when this concentration was exceeded, a diminution (even a disappearance) in the inhibiting action was found.     

Properties and effects of water-soluble inhibitors on the corrosion rates of structural metals

The effects of six commercial water-soluble inhibitor formulations on the corrosion rates of aluminum and steel in seawater were determined. Corrosion rates were measured by the weight loss of specimens following long-term immersion in artificial seawater containing inhibitors at the developer’s recommended dosages. The effects of environmental changes on inhibitor behavior were also investigated by varying the seawater concentration in certain tests. Surface plasmon resonance (SPR) spectroscopy was investigated as a method to observe the inherent adherence and persistence of the inhibitors at a metal surface. Results show that the level of effectiveness of the test inhibitors varies significantly and is dependent on the nature of the metal being protected. While some inhibitors reduce the corrosion of steel by up to 80%, others actually increase the corrosion rate. Four of the six inhibitors were observed to increase aluminum pitting; the other two offered protection. Two of the inhibitors reduced the corrosion rates for the aluminum and steel. Surface plasmon resonance spectroscopy was able to detect and discriminate between inhibitors. These measurements show good correlation between the adherence of an inhibitor to a metal surface and its ability to reduce corrosion rates. Results of this study provide a firm measure of the levels of corrosion control that can be achieved by commercially available inhibitor formulations. They also provide a quantitative basis for comparison and selection of corrosion inhibitors for use in a variety of applications (i.e., metal holding tanks and cans, recirculation loops, and modified wash downs of outdoor equipment typically experiencing deterioration due to exposure to salt-containing environments).     

F2000水基淬火液浓度对其冷却特性曲线及42CrMo钢性能的影响

采用热处理虚拟模拟仪,测定了N32机械油及F2000淬火液冷却特性曲线,研究了浓度变化对F2000淬火液冷却特性曲线及42CrMo钢硬度的影响。结果表明,随着浓度升高,F2000淬火液特性温度和最大冷却速度降低。采用浓度15%的F2000淬火液和N32机械油分别对42CrMo钢进行淬火处理,试样性能接近,可见15%的F2000淬火液在一定条件下可以替代N32机械油用于淬火。     

Composite corrosion inhibitors for secondary alkaline zinc anodes

The corrosion inhibition property of PEG600 and In(OH)3 as composite corrosion inhibitors for secondary alkaline zinc electrodes was studied, and the inhibition efficiency was determined as 81.9%. The research focused on the mechanism by the methods of electrochemical impedance spectroscopy, polarization curves and IR spectroscopy. The results indicate that the corrosion inhibition effectiveness is attributed to the joint inhibition of anodic zinc dissolution and cathodic hydrogen evolution. And the anodic process is depressed to a greater extent than the cathodic process. The synergistic mechanism of the composite inhinbitors proves to be the enhancement of adsorption of PEG600 by In(OH)3. Potentiostatic experiment results and SEM images verify the inhibition of dendritic growth by the composite inhibitors.     

Effects of cooling rate on the precipitation behavior of grain boundary carbide and corrosion resistance of 5Cr15MoV stainless steel

High-carbon and high-chromium alloy steels are prone to pitting and intergranular corrosion, which reduces corrosion resistance. The precipitation behavior of the carbides of high-carbon and high-chromium alloy steels is one of the main factors affecting pitting and intergranular corrosion of stainless steel. In this study, 5Cr15MoV stainless steel was heated to 1,200℃ and then cooled by cooling rates varying from 25 to 150°C/min. The precipitation behavior of grain boundary carbides of 5Cr15MoV steel at different cooling rates, and its effect on the corrosion resistance of materials was studied. The results show that the carbides of 5Cr15MoV steel mainly precipitate along the grain boundaries, which leads to the formation of chromium-depleted zones near the grain boundaries and reduces resistance to intergranular corrosion. It has been found that a higher cooling rate shortens the width of the Cr-depleted zone near the boundary from 0.871 to 0.569 μm, reduces the Cr-concentration gradient near the grain boundary from 36.422% to 12.667%, and suppresses the nucleus growth rate of grain boundary carbides. As the cooling rate increases, the corrosion current density decreases from 13.29 to 2.42 μA/cm². The corrosion rate is the lowest, while the cooling rate is 150°C/min. The corrosion rate decreases from 218.339 to 158.488 mm/a. The phenomenon of intergranular corrosion and pitting corrosion was found to be weakened; and thereby, it is shown that an intensive cooling rate can improve the corrosion resistance of 5Cr15MoV steel.     

DFT theoretical studies of antipyrine Schiff bases as corrosion inhibitors

The anti‐corrosive properties of some antipyrine Schiff bases (benzylidine amino)antipyrine (a), 4‐hydroxy 3‐(benzylidine amino)antipyrine (b), 2‐hydroxy 3‐(benzylidine amino)antipyrine (c), and 2‐hydroxy 3‐(naphthylidine amino)antipyrine (d) are studied using density functional theory at the B3LYP/6‐31G level. The computational calculations are performed to find a relation between their electronic and structural properties and the inhibition efficiency. The calculated quantum chemical parameters correlated to the inhibition efficiency are, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), the separation energy (ΔE), the dipole moment (µ), the softness (σ), the total negative charge on the whole molecule (TNC), the total charge on the azomethine moiety, the molecular volume (V_i), and the total energy (TE). A good correlation between the quantum chemical parameters and the experimental inhibition efficiency is found.     

冷却速度对Zn-Al-Mg合金组织及腐蚀性能的影响

研究了不同冷速下Zn+6%Al+3%Mg合金原始镀液凝固组织和形貌的变化,并对不同冷速下合金的耐腐蚀性能进行了分析。结果表明,不同冷速条件下,合金中出现先析出相Al、Al和Zn、Al/Mg Zn2共晶组织、Zn/Al/Mg Zn2三元共晶组织,但炉冷,水冷下还生成了Zn/Al/Mg Zn11三元共晶。随冷却速度增加,晶粒尺寸愈加细小。空冷下合金耐腐蚀性能相对较好,炉冷相对较差,这与其晶粒度和Mg2Zn11相有关。     

Electrochemical injection of organic corrosion inhibitors into concrete

Two organic bases (ethanolamine and guanidine) that are known to act as corrosion inhibitors for steel in aqueous media were introduced into saturated specimens of carbonated and non-carbonated concrete from external electrolytes under the influence of an electrical field applied between embedded steel cathodes and external anodes. The cathodic current density was galvanostatically controlled at values in the range 1-5 A/m² for periods of 3-14 days. Control experiments, in which the corrosion inhibitors were applied to similar saturated concrete surfaces from external electrolyte without current, were also conducted. After treatment, the specimens were sectioned and analysed to determine the concentration profiles of the corrosion inhibitors within the concrete. It was found that the efficiency of injection of both ethanolamine and guanidine under the applied field was far higher in carbonated concrete than in non-carbonated concrete and that, in the carbonated specimens, the inhibitors became concentrated near the embedded steel. In non-carbonated concrete, guanidine penetration was accelerated to a modest extent by the applied field but ethanolamine penetration was not significantly enhanced by the field. These findings were explicable in terms of the influence of the pH values of the pore solutions in the various specimens on the degrees of ionisation of the organic bases concerned and hence on their tendencies to migrate and neutralise cathodically-generated hydroxyl ions.     

Effect of cooling conditions on corrosion resistance of friction stir welded 2219-T62 aluminum alloy thick plate joint

Friction stir welding (FSW) with water cooling and air cooling was used to weld 2219-T62 aluminum alloy joints with a thickness of 20 mm. The effect of cooling conditions on the corrosion resistance of joints in 3.5% NaCl solution was investigated using the open circuit potential (OCP), the potentiodynamic polarization, and the corrosion morphology after immersing for different time. And the precipitates distribution was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the weld nugget zone (WNZ) owning positive potential, lower corrosion current density and fine and uniform precipitates, is much more difficult to corrode than the heat affected zone (HAZ) and the base metal (BM). Compared with air-cooled joint, the water-cooled joint has better corrosion resistance. In addition, the results of microstructure observation show that the potential, distribution and size of second phase particles determine the corrosion resistance of FSW AA2219 alloy joints in chlorine-contained solution.     

冷却条件对镁合金耐蚀性能的影响

通过浸泡腐蚀质量损失试验,研究了不同凝固冷却速度(空冷、水冷和盐水冷)对AZ31和AZ81镁合金在3.5%Na Cl溶液中耐腐蚀性能的影响。研究结果表明,镁合金中Mg17Al12相的尺寸、形貌、分布、析出量及合金凝固组织的均匀性对抗Na Cl溶液腐蚀产生重要影响;Mg17Al12相对镁合金耐蚀性能具有双重作用(起阻障及电偶阴极的作用);同时凝固组织均匀化程度的改善能提高耐蚀性能。在3种因素的叠加作用下,AZ31合金的耐蚀性能随着冷却速度的提高而得以改善,而AZ81合金的耐蚀性能则表现为:空冷盐水淬水冷。     

Electrochemical impedance spectroscopy for the detection of stress corrosion cracks in aqueous corrosion systems at ambient and high temperature

Electrochemical impedance spectroscopy (EIS) has been used as a tool to detect stress corrosion cracking in a stainless steel sample exposed to an aqueous environment at ambient and high temperature. A model has been developed to describe the impedance of a cracked surface. This model could distinguish between a flat electrode surface and an electrode surface with cracks. To test this technique, three case studies were considered: (1) Slow Strain Rate Tests (SSRT) on sensitised Type 304 SS specimen in a 5 N H₂SO₄ + 0.1 M NaCl solution at room temperature, (2) constant load tests on Type 304 SS in a boiling (±110 °C) acidified sodium chloride solution, and (3) Slow Strain Rate Tests (SSRT) on Type 304 SS in an oxygen containing solution of 0.01 M Na₂SO₄ at 300 °C.EIS measurements were always performed simultaneously on two identical samples: one stressed with a SSRT or a constant load test and one free of stress. Kramers Kronig Transformations have been used to validate the experimental data obtained with the EIS measurements. It was shown that the phase shift between the two samples could be related to the stress corrosion cracking process. Analysis of the fracture surfaces confirmed that stress corrosion cracks were formed in all three cases.     

高温钢板连续喷水冷却换热系数的研究

采用有限差分法建立了高温钢板连续喷水冷却过程中一维非稳态传热条件下冷却水换热系数的计算模型,将试验测量到的数据应用该模型计算出了试验过程中冷却水与高温钢板间的换热系数[h。]分析结果表明：在流量一定的情况下,压力对换热系数的影响较明显,而在压力一定的情况下,流量对换热系数的影响较小,冷却水的换热系数随喷水密度的增加而增大,随钢板表面的温降呈先增加后减小的趋势。总结出了钢板表面温度为400～1 000 ℃,喷水密度为90～180 L/(m2·min)的条件下,喷水冷却换热系数[h]的经验计算公式。     

Sodium gluconate as corrosion and scale inhibitor of ordinary steel in simulated cooling water

The effect of sodium gluconate anion (SG) on the corrosion and scale inhibition of ordinary steel in simulated cooling water has been studied using weight loss, polarisation curves, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) techniques. SG was studied in concentration from 10⁻⁴ M to 10⁻¹ M. Results obtained reveal that SG perform excellently as corrosion and scaling inhibitor for ordinary steel in simulated cooling water. An increase of SG concentration leads to the increase of the corrosion potential towards the positive direction. The inhibition efficiency was a low temperature dependence. The inhibitor mechanism was treated as an adsorption process according to Langmuir adsorption isotherm. The SEM/EDAX data show that was a corrosion and scale inhibitor.     

Improving the corrosion resistance of a cooling water system at an ammonium sulfate crystallization plant by corrosion inhibitors

This paper deals with some analyzed corrosion problems occurred in a cooling water system at an ammonium sulfate crystallization plant. A visual inspection to the cooling system was realized to evaluate the corrosion situation of the cooling system and determine the factors, which promoted corrosion damage. Chemical and physical properties of the water at the cooling system were determined, and corrosion rate measurements by different procedures were carried out. To improve efficiency, sodium monophosphate and thiourea, were added to one commercial inhibitor used at present. To evaluate the effectiveness of the modified inhibitor, a series of potentiodynamic polarization curves were accomplished. It was found that the best result was obtained by using sodium monophosphate at 500 ppm in the commercial corrosion inhibitor.     

Pitting corrosion transformation of SUS304 stainless steel in lithium bromide solution at high temperature

The foundational data and rules of SUS304 corrosion in aqueous lithium bromide solution at 150–200 °C have been investigated by means of weight loss in this paper. The Taguchi method was chosen to investigate the effects of variables on corrosion at higher temperature. Concentration of dissolved oxygen was controlled by keeping the vessel pressure at 1.3 kPa (absolute) before the experiment. The results showed that there was a transformation tendency from pitting corrosion to general corrosion and transition concentration of pitting and film corrosion decreased with increase in solution temperature. The adsorption, activity, and diffusivity of bromine ion led to different corrosion modalities.