Contact corrosion of metals in aqueous and aqueous organic environments: III. Corrosion of metals aqueous glycol solutions with high water contents

The corrosion behavior of aluminum, steel, and cast iron as either individual metal specimens or as parts of contact aluminum-steel, aluminum-cast iron, steel-cast iron, and aluminum-steel-cast iron systems in aqueous glycol solutions containing 5–50 vol % water is studied. In all systems, aluminum is found to act as a cathode with respect to steel and cast iron and, in contrast to them, is not corroded under the effect of electrolytes. With an increase in the water content in the ethylene glycol solution from 70 to 95%, the corrosion behavior of the metals becomes similar to that in water.     

灰口铸铁空泡腐蚀过程的SEM跟踪观察

采用空泡腐蚀与定位跟踪观察交替进行的方式,研究了灰口铸铁在自来水中空泡腐蚀过程的表面形貌演变。结果表明:灰铸铁空泡腐蚀系由两个相继发生而又彼此联系的过程组成:(1)片状石墨由表及里脱落形成表面缝隙;(2)表面缝隙的扩展与交汇导致珠光体团块状剥落。还讨论了石墨片的空间取向对珠光体团剥落的影响。     

Inhibierung von wässerigen und alkoholisch wässerigen Wärmeträgern

Inhibition of aqueous and alcoholic-aqueous heat-carriers To examine the effect of corrosion inhibitors mainly ®Preventol CI-2 in aqueous and aqueous alcoholic heat transfer media gravimetric and electrochemical corrosion tests were carried out with the materials grey cast iron, unalloyed steel, copper, brass, lead-tin-solder, aluminium and aluminium alloys up to a temperature of 90°C. In the presence of the inhibitor Preventol CI-2 uniform layers from 10 to ? 50 nm thickness are found on the metal surfaces and the measured massloss (ASTM, EMPA) decreased decidedly. Local corrosion as occurs e.g. by insufficient concentration of inhibitors forming surface layers, was found in none of the cases. The electrochemical examinations confirm the results of the chemical tests and provide indications with regard to the effective mechanisms. The influence of temperature and flow rate on the protective efficiency of the inhibitor can be showed. It is possible to eliminate the risk of galvanic corrosion by contacting copper and aluminium. The cavitation corrosion of grey cast iron is also appreciably reduced. Preventol CI-2 is a broad spectrum inhibitor for aqueous and aqueous alcoholic heat transfer media.     

Corrosion and self‐healing behaviour of AZ91D magnesium alloy in ethylene glycol/water solutions

Corrosion behaviour of magnesium alloy‐based engine parts in cooling system is an urgent fundamental issue in automotive field where magnesium alloys are increasingly used. In the present work, the corrosion behaviour of AZ91D magnesium alloys in various ethylene glycol/water solutions was studied by electrochemical measurements and immersion tests at room temperature. The surfaces of the samples after immersion tests were examined using scanning electron microscope (SEM) and X‐ray diffraction (XRD). The results showed that the corrosion rates of AZ91D magnesium alloys decreased with the increase of ethylene glycol concentration in ethylene glycol/water solutions and the corrosion process was dominated by pitting corrosion. A continuous protective film transferred from corrosion products was formed on the corroded surface after sufficient immersion duration in ethylene glycol/water solutions, which is able to heal the corrosion pits. The self‐healing behaviour inhibited the further corrosion of AZ91D magnesium alloy.     

Untersuchung der Korrosionsschutzwirkung von Wärmeträgern Teil 1: Chemische Prüfungen,Screening- und Spezial-Tests

Testing the corrosion protection of heattransfer fluids Part 1: Chemical, screening and special tests As supplement to AGK Arbeitsblatt W l “Corrosion testing in heat-transfer fluids of solar heating installations” the different methods applied for testing the corrosion protection in heattransfer fluids provided with anti-freeze mixtures on glycol basis have been checked. The coupon tests corresponding to ASTM D 1384, the EMPA-Test, special tests according to ASTM D 4340 as well as the FVV-Heat-Test were part of these investigations. The investigations were carried out with steel, cast iron, two wrought aluminium alloys, one cast aluminium alloy, with copper and brass as well as with tin solder in non inhibited as well as inhibited heat carriers. The non inhibited heat-transfer fluids were composed of water with ethylene and propylene glycol, the others were made up with antifreeze concentrates prefabricated by well known producers. All investigated products provide excellent protective qualities against corrosion. The coupon test according to ASTM D 1384 has been the most effective of all methods tested up to now. This article will be continued.     

Einfluß mechanischer Spannungen auf die Zerstörung durch Strömungskavitation

Influence of mechanical stresses on the destruction by flow cavitation The destruction produced by the formation of cavitation bubbles are enhanced in the presence of mechanical stresses. One may conclude therefrom that such effects will be encountered in the presence of residual stresses, too, e.g. in the case of cast steel pieces or in the vicinity of weld seams. Consequently the cavitation resistance may be improved by a thermal treatment (provided of course the treatment does not give rise to the formation of a corrosion sensitive structure). The destructions produced by cavitation are losses characterized by a specific crystallographic orientation. Erosion effects which are connected with cavitation on the other hand are not effected by mechanical stresses.     

Corrosion in solar heating systems. II. Corrosion behaviour of AA 6351 in water/glycol solutions

A research was carried out in order to investigate the corrosion behaviour of the metals most commonly used as construction materials for solar absorber plates. With this view, an attempt was made to test the corrosion resistance of the aluminium alloy AA 6351 (nominal composition: 1% Si, 0.6% Mg, 0.3% Mn, the balance Al) towards common uninhibited heat transfer fluids, such as ethylene and propylene glycol/water mixtures. Long time gravimetric tests consisted in up to 60 day exposures of the aluminium specimens to pure, chloride-polluted, or degraded glycol/water solutions, at the temperature of 80°C. The degradation into acidic products, experienced by heat transfer liquids in service, was simulated by keeping the ethylene and propylene glycol/water solutions at their boiling temperature for 30 days, in contact with copper. In glycol/water solutions the presence of chlorides at low concentration (200 ppm) caused the aluminium corrosion rates to increase by more than one order of magnitude, while in degraded solutions, containing 143 or 86 ppm cupric ions, corrosion rates higher than two order of magnitude with respect to pure solutions were obtained. During the gravimetric tests, pitting corrosion was observed in some cases and its extent was rated by evaluating the deepest and the average metal penetration, the pit density and the average pit size. The influence of heat transfer on the alloy AA 6351 corrosion and on the couple copper/AA 6351 efficiency was evaluated by gravimetric and electrochemical tests. Heat transfer through aluminium was found to significantly increase the aluminium alloy pitting potential. On the contrary, it stimulated the aluminium galvanic corrosion, when applied on either aluminium or copper. Under galvanic coupling conditions, the aluminium corrosion rates calculated from the average galvanic currents were a very little contribution to the gravimetric corrosion rates. This demonstrates that in low conductive solutions the risk of matching such dissimilar metals as copper and aluminium does not reside in the galvanic contact itself, but mainly in the mere presence of the noblest metal in the same solution where aluminium is immersed.     

Korrosionsverhalten einiger hochlegierter Stahl und Hartgußsorten in Waschwässern von Rauchgas-Entschwefelungs-Anlagen

Corrosion behaviour of some cast stainless steels and high alloy white irons in scrubber solutions of flue gas desulfurization plants Weight loss and electrochemical measurements have been used to determine the ranges of applicability of cast austenitic stainless steel Werkstoff No. 1.4408, of two special cast ferritic-austenitic stainless steels NORIDUR® 9.4460 and NORICLOR® NC 24 6 and of two high alloy Cr and CrMo white irons in scrubber solutions of Flue Gas Desulfurization (FGD) plants. Whereas the Werkstoff No. 1.440 8 cannot be used due to its insufficient resistance to general and localized corrosion, NORIDUR® 9.4460 can be used in scrubber solutions with pH > 2.5 and chloride concentrations up to 80 g/l, NORICLOR® NC 24 6 with 5% Mo even in liquids with pH > 1.5 and chlorides up to 100 g/l. At lower pH-values both duplex stainless steels show active corrosion of either the austenite or the ferrite depending on the contents of hydrochloric acid in the solution. At higher chloride concentrations pitting occurs on the passive materials. The CrMo white iron NORILOY NL 25 2 with 25% Cr and 2% Mo can be used in scrubber liquids with pH > 3.5. As the ferritic matrix is cathodically protected by the precipitated carbides, there is no sensitivity of this alloy to chlorides. In liquids with pH < 3.5 there is selective corrosion of the ferritic matrix. For practical application of all these cast alloys the limits for purely corrosive attack have to be modified to assure. resistance to a superposition of corrosion, erosion/abrasion and cavitation on parts exposed to real flow conditions in FGD scrubbers.     

Contact corrosion of metals in aqueous and organic-aqueous environments. II. Concentrated glycol-water solutions

Corrosion behavior of individual aluminum, steel, and cast iron, as well as aluminum-steel, aluminum-cast iron, steel-cast iron, and aluminum-steel-cast iron contact systems, in ethylene glycol solutions containing 5 or 30 vol % fresh water is studied. By contrast to water, these solutions are shown to be inert with respect to steel, while aluminum anodically dissolves in them. Cast iron is least stable, though its dissolution rate in the solutions is still substantially lower than in water.     

Corrosion in solar heating systems. I. Copper behaviour in water/glycol solutions

A research programme has been developed in order to investigate the corrosion behaviour of metallic materials commonly used in solar heating systems. This paper presents the results of an experimental study on copper corrosion resistance in ethylene and propylene glycol/water solutions (1:1 by volume) constituting the most common bases of heat transfer fluids. Long time gravimetric tests were carried out on electrolytic copper at 80°C, even in glycol/water solutions previously degraded at their boiling temperature or polluted with 200 ppm chlorides. Chemical compositions, semiconducting properties and morphological characteristics of all surface products were investigated by X-ray diffraction analysis, pulse photopotential technique and SEM observations, respectively. Heat transfer effects on copper corrosion and copper/6351 aluminium alloy couple efficiency were evaluated by electrochemical tests. The following results were obtained:

• – Ethylene and propylene glycol/water solutions are low corrosive media. Nevertheless, chloride pollution and/or high temperature degradation of glycols markedly increase their aggressivity. Under all the experimental conditions, copper corrosion rates are higher in ethylene than propylene glycol solutions.
• – In chloride-free solutions, heat transfer stimulates the cathodic reaction of the copper corrosion process.
• – Galvanic contact between copper and aluminium alloy always causes pitting corrosion on aluminium electrodes. The severity of the pitting attack is enhanced by the presence of heat transfer conditions on copper and/or chloride ions in the solutions, particularly in ethylene glycol.

     

Zum Mechanismus der Erosionskorrosion in schnell strömenden Flüssigkeiten

Mechanism of erosion corrosion in fast flowing liquids The corrosion behaviour of copper, brass and gray cast iron has been studied in 3 % air-saturated NaCl solution and seawater respectively. The tests have been carried out in an experimental setup enabling a circular Couette type flow to be formed. At low and very high rates the corrosion rate clearly depends from the flow. Above certain critical flow rates the attack is localized and erosion corrosion is found at high turbulence spots. By electrochemical methods the particular corrosion rates are determined and it is shown, that the cathodic partial corrosion reaction is rate-controlling. The origin of mechanical interaction between the medium and the metal surface, but also to processes occurring within the covering layer. Erosion corrosion consequently depends from flow conditions and surface properties and also from type and stability of the surface layers.     

Nachweis der Korrosionsbeständigkeit von Lagerbehälterwerkstoffen gegenüber wassergefährdenden brennbaren und nichtbrennbaren Lagermedien durch die Bewertung von Korrosionsdaten

Proof of the corrosion resistance of tank materials with regard to water-polluting inflammable and non-inflammable storage liquids by evaluating corrosion data The general protection requirements and arrangements determine in regards to the anxiety principles of the water conservation law a respective construction and observation of the storage tanks with the storage of water pollution liquids. The proof of the corrosion resistance of the tank materials in relation to the long-term influence of the storage liquids belongs to the general protective arrangements. Suppositions for the proof of the corrosion resistance are the definition of the used materials, welding seams and liquids. Liquid-materials-combinations are evaluated as qualified when the decrease of the wall-thickness caused by uniform-corrosion does not exceed 0,1 mm per year and local corrosion in form of pitting corrosion or stress corrosion is not expected. In the DIN 6601 which includes the socalled positive-liquid list are evaluated water-polluting liquids in regards to their material resistance with carbon steels and austenitic stainless steels at a temperature of max. 30°C on the base of relevant literature, user experience of producers or users over a time of min. five years and laboratory tests. The positive testify is only valid for a lot of liquids if special conditions related to liquids or related to the working conditions are fulfilled. For liquid-materials-combinations not mentioned in the positive-liquid list is the proof of the corrosion resistance through separate expert opinion necessary.     

Untersuchung der Korrosionsschutzwirkung von Wärmeträgern Teil 2: Chemische Korrosionsuntersuchungen mit dem Rotations-Zylinder und zum Schutz gegen Spaltkorrosion

Testing the corrosion protection of heat-transfer fluids Part 2: Chemical corrosion tests using the rotating cylinder and for the protection against crevice corrosion The second part of the report refers to chemical corrosion tests of the protective effect of inhibited heat-transfer fluids provided with anti-freeze mixtures of water and glycol on metals by means of the rotary cylinder testing method. The metals to be tested were plain steel, cast iron, wrought and cast aluminium alloys, copper materials as well as a solder alloy. Moreover the influence of time, dilution ratio and flow on the corrosion protection of some metals was investigated. Based on the test results of part one and two, standard testing methods and limiting maximum values were defined for the evaluation of the protective effects proved by these testing methods. Finally investigations for the protection against crevice corrosion are described. This publication will end with a third part reporting on electrochemical investigations according to the RZ-testing method.     

Corrosion behaviour of brazed multilayer material AA4343/AA3003/AA4343: Influence of coolant parameters

This paper is the second part of a work devoted to corrosion in brazed AA4343/AA3003/AA4343 materials on the water side of automotive heater cores. In the first part of the study [S. Tierce, N. Pébère, C. Blanc, C. Casenave, G. Mankowski, H. Robidou, Electrochim. Acta 52 (2006) 1092], corrosion initiation in the surface layer (i.e. the residual cladding) has been investigated. It has been associated to defective sites in the passive film covering the alloy. The defective sites are linked to α-Al(Mn,Fe)Si particles built up during brazing process. Interactions between α-Al(Mn,Fe)Si particles and the matrix are responsible for the observed behaviour. The present study focuses on the propagation of corrosion through the material in neutral water–ethylene glycol mixtures with and without chlorides. Comparison of the electrochemical behaviour of the three layers of the brazed material (i.e. the residual cladding, the “band of dense precipitates (BDP)” and the core material) revealed that the residual cladding was nobler than the BDP and the core material and thus that the corrosion should propagate through the inner layers due to galvanic coupling: the inner layers constitute the anode and the residual cladding the cathode. Increasing the ethylene glycol content in the water–ethylene glycol mixture decreased the rate of consumption of the materials whereas addition of chloride ions increased it. Mass variation measurements of brazed material in different solutions containing the degradation products of ethylene glycol showed that only glycolate ions had a slight detrimental effect. Corrosion tests performed in heater core tubes allowed the propagation mechanisms to be confirmed.     

Corrosion behaviour of magnesium in ethylene glycol

Corrosion of magnesium engine components by coolant is an important issue in the automotive industry where magnesium alloys may be used. It is of significance to understand the corrosion behaviour of pure magnesium in ethylene glycol solutions, as this can provide a basis for developing new coolants for magnesium alloy engine blocks. In this paper, through corrosion and electrochemical tests, it was found that the corrosion rate of magnesium decreased with increasing concentration of ethylene glycol. Individual contaminants, such as NaCl, NaHCO₃, Na₂SO₄ and NaCl can make aqueous ethylene glycol solution more corrosive to magnesium. However, in NaCl contaminated ethylene glycol, NaHCO₃ and Na₂SO₄ showed some inhibition effect. The solution resistivity played an important role in the corrosion of magnesium in ethylene glycol solutions, and the competitive adsorption of ethylene glycol and the contaminants on the magnesium surface was also responsible for the observed corrosion behaviours. The corrosion of magnesium in ethylene glycol can be effectively inhibited by addition of fluorides that react with magnesium and form a protective film on the surface.     

Simulation atmosphärischer Korrosion durch dünne Elektrolytfilme

Simulation of atmospheric corrosion by thin films of electrolyte A method for investigation on atmospherical corrosion with the aid of thin electrolyte films is described, the special feature of this being the exact adjustability of the corrosion determining parameters. The investigations on the influence of pollutants showed that small additions of sodium chloride and sulphur dioxide into the water film cause two different types of corrosion of electrolytic copper: uniform growth of layer thickness and/or lateral surface growth of the corrosion products. In the initial phase the uniform growth of layer thickness on electrolytic copper depends on t² (t = time), later on proportional on t. The investigation of the corrosion in dependence on the thickness of electrolyte film showed new results regarding the transition of the bulk-electrolytical to thin film electrolyte corrosion (atmospheric corrosion). At electrolytic copper transition from uniform growth of layer thickness to lateral surface growth comes off, when reaching a film thickness of approx. 100 μm. The electrolyte was distilled water with an addition of 0,01%SO₂. The corrosion intensity of grey cast iron GG 25 under a film of pure water passes through a wide maximum of film thickness between 300 and 20 μm, with a weakly marked minimum on 100 μm, the corrosion intensity is decreasing at thinner films. It is herewith demonstrated that also under conditions excluding largely the convective oxygen transfer other corrosion types and -intensities show up when the films are only thin enough. The comparison of the effect of two vapour inhibitors, having been dissolved directly in the electrolyte films (dicyclohexyl-ammoniumnitrite and one usual in the trade of unknown composition) in different concentrations showed on grey cast iron GG 25 the superiority of the latter one.     

Corrosion of iron in highly acidic hydro-organic solutions

In acidic water-organic solvents of ethylene glycol (EGOH), propylene glycol (PGOH), methanol (MeOH) and ethanol (EtOH), iron corrosion was studied by monitoring the corrosion potential, the potentiodynamic polarization curves and electrochemical impedance diagrams. In these aqueous glycols and alcoholic solutions containing HCl having concentrations of 0.5 up to 9 M, it has been shown by electrochemical analysis (I-E curves) that dissolution mechanism of iron is similar to that one in pure acidic aqueous solutions if only we take into account the relative amount of water in the medium. Based in our experimental data, water has an important role in the transfer kinetics of protons to the metallic electrode and limits electro dissolution rate of iron. When water quantity is sufficient at the metal surface, the acidity is a governing factor in the evolution of corrosion process.     

熔铝灰铁坩埚的腐蚀与防护

详细论述了熔铝灰铁坩埚的氧化腐蚀、铝液腐蚀及其腐蚀机制,介绍了能够提高灰铁坩埚抗高温氧化能力的铸态表面合金化法和能够提高灰铁坩埚抗铝液腐蚀能力的调整成分法与浸渗保护法,这些方法通过减少腐蚀贞坩埚表面向基体内部发展的各种“通道”,有效地改善了灰坩埚抗腐蚀性能,提高了坩埚使用寿命。     

Korrosionsverhalten von austenitischen und ferritisch-austenitischen Gußwerkstoffen in Gaswaschwässern

Corrosion behaviour of austenitic and ferritic-austenitic cast alloys in gas liquids The corrosion resistance of some cast stainless steels used for pumps and valves was investigated in gas liquids containing NH₃/CO₂/H₂S and HCN. Primary tests showed that hydrogen cyanide is not stable in those liquids even in absence of corroding metal surfaces and that its decomposition is caused by several independent reactions. Two similar types of solutions were used for the investigations: first, solutions with defined concentrations made in the laboratory, second original solutions taken from a pilot plant for gas liquid preparation. The corrosion rates are a function of the CN^?-content of the solution, however, they are higher in the field tests because of the constant high cyanide concentration. In solutions without CN^? all materials are resistant. With increasing CN^?-concentration only alloy NORIDUR® 9.4460 having a high Cr-content is resistant, while at high CN^?-concentrations none of these materials can be used.     

Untersuchungen über die Oxidation and die mechanischen Eigenschaften von Aluminiumgußeisen bei Temperaturen von 923 bis 1373 K

Investigations into oxidation and mechanical properties of aluminium cast iron at temperatures of 923 to 1373 K An analysis of the oxidation process of aluminium cast iron containing up to 30% Al has been made and tests of the mechanical properties of cast iron have been carried out at different temperatures (923–1373 K). The oxidation process was carried out in air of 1 bar pressure. Measurements of kinetics were made using the gravimetric method in the above temperature range. The oxidation products were identified by x-ray microanalysis, x-ray diffraction and metallographic analysis. The mass change during the oxidation process was evaluated in cycling temperature conditions. Mechanical properties were determined and involved hardness, impact resistance and abrasion behaviour. The corrosion resistance was defined as well as the change of mechanical properties of the cast iron at higher temperatures.