Effects of Hydrostatic Pressure on the Corrosion of Copper in Sea Water

Abstract

A study has been made of the effect of hydrostatic pressure, ranging from 1 to 300 atm. (0·102 to 30·6 N.mm^?2) on the corrosion of copper in sea water at pH 7·8 and at a temperature of 10°c. The experimental technique ensured that the content of dissolved oxygen in the sea water was virtually constant over the pressure range, at a value of 7·0 ppm. The same test series was also carried out in a 3·5% NaCl solution.

The weight loss of the copper was found to increase with increase in pressure, both in sea water and in NaCl, and reached a maximum at a pressure of 150 atm. (～15 N.mm^?2) in both solutions. The increased pressure has no influence on the anodic dissolution process for copper, but accelerates the cathodic process. Protective films adhering to the corroded surfaces are identical for the two solutions at ambient pressure. However, at higher pressures adherent corrosion products form only in NaCl solutions. These products were found to be the same as those formed at ambient pressure.     

Vergleichende Untersuchungen des SwRK-Verhaltens verschiedener Dampfturbinenschaufelstähle

Comparative investigations into the corrosion fatigue behaviour of different steam-turbine-blade steels Corrosion fatigue tests in NaCl-solution in the temperature range from ambient temperature to 150°C revealed a decrease of the corrosion fatigue strength of the steels X20Cr13 with 1% resp. 2.5% Mo, X4CrNiMo 16 5 1 and X2CrNiMoN 22 5 with increasing temperature; a minimum of the corrosion fatigue strength is reached at 150°C. At temperatures of about 80°C it was found an optimum corrosion fatigue behaviour of the Mo-alloyed steel X20CrMo13 2.5 in comparison with the other investigated steels. It was observed that crack initiation of the ferritic, Mo-alloyed steel is caused by Cl-induced pitting, of the soft martensitic steel by oxide inclusions and of the duplex steel by non metallic, brittle inclusions and/or by grain boundarys of the ferritic/austenitic microstructure. Crack initiation caused by pre-deformation at slip bands was observed on the duplex steel. All materials investigated failed at elevated temperatures. At temperatures higher than 80°C an optimum corrosion fatigue behaviour was not found.     

Effect of heat treatments on Cu-Ni 70/30 alloy pitting susceptibility in sea water at different temperatures

A series of experiments was carried out on Cu-Ni 70/30 commercial alloy specimens presenting different microstructures. The microstructure of homogeneized specimens was modified with annealing treatments by which grain size significantly increased and intermetallic compounds precipitated, thus creating some dishomogeneity in the alloy. Free corrosion and electrochemical tests were carried out at 20, 40, 60, 80°C in quiescent sea water at pH 8.2 with dissolved oxygen (D.O) content ranging from 6.5 ppm (at 20°C) to 3.0 ppm (at 80°C). The corrosion products adherent to the metallic surface were analyzed with chemical and XPS methods. The following could be observed:

• with increasing temperature, a decrease in corrosion rate and selective copper dissolution was observed in homogeneized and annealed specimens
• the annealed specimens have the highest corrosion rate in the whole temperature range and undergo pitting corrosion at low temperature.

     

Electrochemical Corrosion Study of Tin-based Solders in Potassium Formate Brines for Heat Transfer Applications

Electrochemical corrosion tests were performed on various tin-based solder alloys in stirred potassium formate solutions, pH = 8 and 10.5, with or without additives of corrosion inhibitor, between 20 °C and 75 °C. Open circuit and corrosion potentials and corrosion rates were measured, and galvanic corrosion of the tin-silver solder/copper couples was evaluated. The effects of pH and inhibitor on corrosion of tin-based solder alloys were also assessed.     

Die Beeinflussung des Schwingungsrißkorrosionsverhaltens des Stahles X 20 Cr 13 durch einen Molybdänzusatz in chloridhaltigen Medien

Influence on the fatigue corrosion behaviour of the steel X20Cr13 in chloride containing media by molybdenum additions The fatigue corrosion behaviour of a 13% Cr steel (used for turbine blades) has been studied in terms of its dependence on carbide shape and molybdenum additions in aqueous NaCl solutions of various concentrations at temperatures between room temperature and 200°C. Further tests in autoclaves were carried out in order to study the surface layers formed above 150°C without mechanical loads. Addition of 1% molybdenum yields a considerable increase of corrosion fatigue strength at room temperature, while there is no influence attributable to different shapes of graphite precipitations. At 150°C the corrosion fatigue strength is largely independent from sodium chloride concentration (0,1 to 27%); this means that very small quantities of sodium chloride are sufficient to produce heavy corrosion in wet steam at > 106 cycles. A range particularly suitable for such tests is the load range between ± 150 and ± 200 N/mm² at 150°C, because these conditions approach those encountered in practice. The passivating layers are very thin (interference phenomena). Considering the increase of corrosion resistance produced by 1% Mo it is expected that 2.5% Mo will produce a further improvement, in particular with regard to pitting corrosion since rupture generally starts at the pits.     

Influence of hydrostatic pressure on pitting of aluminium in sea water

Abstract

The effect of hydrostatic pressure on the corrosion of aluminium in sea water oj pH 8·2 containing 7ppm dissolved oxygen has been investigated at 20°C. On increasing the pressure from 1 to 300 atm, the corrosion rate increased, an effect attributable to an increase in the rate of the anodic reaction while the cathodic rate remained unchanged. The observed increased susceptibility to pitting corrosion with increasing pressure was found to correlate with the presence of increasing quantities of SO^2?₄ and Cl^? ions in the oxidation layer. The introduction of electron acceptors such as SO^2?₄ and Cl^? into n type compounds such as aluminium oxides increases the density of lattice dejects and promotes breakdown oj the barrier provided by the oxidation layer.     

Inhibitive action of some schiff bases and amines towards the corrosion of copper in an aqueous alcoholic medium

Some Schiff bases and relative amines were tested as copper corrosion inhibitors in aqueous 25 vol.% ethanolic 0.1 M NaCl solution at 30 °C. Polarization curves and weight loss measurements allowed the inhibitor efficiencies of the additives to be screened. The data showed a remarkable decrease in the corrosion rate only in the presence of N-2-mercaptophenyl-salicylideneimine (BSS) or 2-mercaptoaniline (AS). Nevertheless, better results were always obtained with the Schiff bases than with the amines.In order to study the nature of the solid products formed in free corrosion conditions or, in the case of BSS, in anodic galvanostatic conditions, their IR spectra were compared with those of synthetic complexes obtained with these organic substances and copper(I) or copper(II). The surface analysis of the specimens at the end of the immersion tests was carried out using scanning electron microscopy and photopotential measurements.Further investigation showed that the inhibition of copper corrosion by BSS and AS followed the Langmuir and the Frumkin adsorption isotherms, respectively, over a wide range of concentrations. The computed adsorption energies together with some tests on the pre-filming action of the two substances indicated chemisorption as the inhibition mechanism.     

The kinetics of the corrosion of copper containing different amounts of oxygen in 1.7 M H2SO4

The rate of corrosion of rotating copper discs was measured as a function of the concentration of oxygen in metal. It was found that the catastrophic acceleration of the corrosion of the sample occurs at 3 × 10³ ppm of oxygen in metal. In the temperature range 5–75°C, the corrosion resulting from the presence of the oxygen in the metal occurs in the regime of activational control, and it is not influenced by the oxygen dissolved in the acid. The corrosion resulting from the oxygen depolarization occurs in the activational control regime in the temperature range 5–35°C, in the mixed kinetics regime in the range 45–55°C, and in the range 65–75°C in the diffusional regime with respect to the oxygen dissolved in the acid. The overall rate of corrosion of copper containing 8 × 10³ ppm of oxygen is about 20 times greater than the rate of corrosion of copper with oxygen depolarization.     

In-Situ Electrochemical Corrosion Behavior of Nickel-Base 718 Alloy Under Various CO<Subscript>2</Subscript> Partial Pressures at 150 and 205 °C in NaCl Solution

The electrochemical corrosion behavior of nickel-base alloy 718 was investigated using electrochemical impedance spectroscopy and potentiodynamic polarization techniques at various partial pressures of CO₂ (\(P_{{{\text{CO}}_{2} }}\)s) in a 25 wt% NaCl solution at 150 and 205 °C. The passive films composed of FeCO₃ exhibit good corrosion resistance with a feature of Warburg impedance, Tafel plots show a complete passivation and the anodic reactions was dominated by a diffusion process at low \(P_{{{\text{CO}}_{2} }}\)s (1.8–9.8 MPa) at 150 °C. While numerous dented corrosion areas appeared on the sample surface for the \(P_{{{\text{CO}}_{2} }}\) of 11.6 MPa at 205 °C, the Tafel plot with three anodic peaks and the Nyquist diagram with an atrophied impedance arc were present. This dented corrosion attribute to the synergistic effects of stress, temperature, \(P_{{{\text{CO}}_{2} }}\) and Cl^?, the temperature and stress could play crucial roles on the corrosion of the alloy 718.     

Ergänzungsversuche zum Einfluß des Werkstoffs CuNi20Fe auf das Korrosionsverhalten verzinkter Rohre in warmen Wässern

Supplementary experiments concerning the influence of CuNi20Fe on the corrosion behaviour of galvanized tubing in warm waters The influecne of CuNi20Fe, a material used for constructing boilers, on the corrosion resistance of galvanized tubes in mixed installations was investigated in hot- water-pilot-plants. The investigations were made with Berlin tap-water, pH=7,0 t-65°C. The results demonstrate that under these conditions the dissolution of copper ions due to the corrosion of “Nickelbronze” is sufficient to induce pitting in the galvanized tubes. Further investigations show, that the corrosion rate of CuNi20 Fe without heat transfer in water of pH = 7,4 is largely independent form temperature in the region of 65–90°C.     

Sulphide stress cracking behaviour of weldments produced by indirect electric arc welding

Abstract

The aim of the present study was to evaluate the corrosion resistance of weldments produced by the Indirect Electric Arc technique. The material studied was API grade X-65 steel, which was corroded in NACE solution saturated with H₂S. Three different temperatures were employed, room temperature (25°C), 37°C and 50°C. The test methods used included potentiodynamic polarisation curves, hydrogen permeation measurements and slow strain rate tests. The anodic corrosion current density and sulphide stress cracking susceptibility of the weldments were found to be unaffected by temperature over the range 25–50°C. However, values of the steady-state hydrogen permeation current, hydrogen permeation rate, effective diffusion coefficient, and the concentration of hydrogen atoms at the entrance side all increased with temperature. The cracking of the X-65 weldments is explained in terms of a hydrogen embrittlement mechanism.     

Einfluß von Beschichtungen auf das Schwingungsrißkorrosionsverhalten des Chromstahls X20Cr13

Influence of coatings on the corrosion fatigue behaviour of 13% chromium steel The influence of coatings on the corrosion fatigue behaviour of 13% chromium steel has been studied. There have been selected different coating systems: Barrier coating (enamel), diffusion coatings, (aluminizing, chromizing) and anodic coating, (aluminium, zinc, tin, cadmium). The corrosion fatigue limits of coated with uncoated specimens in neutral NaCl-solution are compared. Salt-concentrations were 0,01 and 22% (? 0,38 M) NaCl at 80°C and 150°C. The tests were carried out with alternating tensions and a constant frequency of 50 Hz. Only the use of andic coatings improved the corrosion fatigue behaviour of the chromium steel.     

Joining of alumina via copper/niobium/copper interlayers

Alumina has been joined at 1150°C and 1400°C using multilayer copper/niobium/copper interlayers. Four-point bend strengths are sensitive to processing temperature, bonding pressure, and furnace environment (ambient oxygen partial pressure). Under optimum conditions, joints with reproducibly high room temperature strengths (≈240±20 MPa) can be produced; most failures occur within the ceramic. Joints made with sapphire show that during bonding an initially continuous copper film undergoes a morphological instability, resulting in the formation of isolated copper-rich droplets/particles at the sapphire/interlayer interface, and extensive regions of direct bonding between sapphire and niobium. For optimized alumina bonds, bend tests at 800–1100°C indicate significant strength is retained; even at the highest test temperature, ceramic failure is observed. Post-bonding anneals at 1000°C in vacuum or in gettered argon were used to assess joint stability and to probe the effect of ambient oxygen partial pressure on joint characteristics. Annealing in vacuum for up to 200 h causes no significant decrease in room temperature bend strength or change in fracture path. With increasing anneal time in a lower oxygen partial pressure environment, the fracture strength decreases only slightly, but the fracture path shifts from the ceramic to the interface.     

Untersuchung des SwRK-Verhaltens des hochreinen martensitaushärtenden Stahles X5CrNiCuNb 17 4 PH im Vergleich zum weichmartensitischen Stahl X4CrNiMo 16 5 1 ESU in chloridhaltigen wäßrigen Medien. Teil 2: SwRK-Untersuchungen und Rißeinleitungsmechanismen

Investigations of the corrosion fatigue behaviour at a super pure martensitic stainless steel X5CrNiCuNb 17 4 PH in comparison to the soft martensitic stainless steel X4CrNiMo 16 5 1 ESR in chloride containing aqueous media — Part 2: Corrosion fatigue tests and crack initiation mechanisms The following report concerns the study of the corrosion fatigue behaviour of the soft martensitic steel X4CrNiMo 16 5 1 ESR and the precipitation hardened X5CrNiCuNb 17 4 PH in sodium solution in the temperature range between 20° and 150 °C and the determination of their general corrosion properties and the mechanism of crack propagation. Their corrosion fatigue limits were compared with each other. A comparision was also made between an electro-slag-remelted soft martensitic steel and a charge without an ESR aftertreatment. Microfractographical fracture and crack path investigation were carried out for interpretation of the experimental results. It was observed that in both super pure steels (soft martensitic and precipitation hardened) the oxidic inclusions are not responsible for the crack intiation, as it was found in the non ESR treated steels. In the 17-4 PH steel copper containing inclusions in the crack initiation areas were observed. In concentrated sodium solution pitting corrosion was found at both steels.     

Hot Salt Corrosion of titanium aluminides

There is considerable interest in the use of γ-TiAl within advanced gas turbines where they offer greater high temperature capability over conventional titanium at reduced weight. These factors would enable engines with greater thrust to weight ratio to be developed. Thus γ-TiAl offers the potential of replacing nickel based alloys within the high pressure compressor and potentially the fourth stage turbine. Service in both of these locations would require that the γ-TiAl be resistant, not only to oxidation, but hot salt corrosion. This paper presents a study of the hot salt corrosion resistance of γ-TiAl over the temperature range 500–700°C. At 700°C, laboratory tests have shown that corrosion rates in a salt ladened environment are some 20X that of equivalent oxidation for exposures out to 100 h. The morphology of attack is consistent with a corrosion mechanism involving the vapour phase transport of aluminium from within the alloy and formation of a non protective oxide scale. A model for the corrosion mechanisms is presented, involving intermediate chloride phases. The mechanism is believed to be self sustaining, requires little chloride present, and leads to the observed accelerated oxidation rates.     

Synopses of papers from other institute journals

Abstract

The corrosion behaviour of a range of readily available commercial copper based alloys was examined in three accelerated atmospheric corrosion tests: acidified salt spray, neutral salt spray at 80°C, and the GM (salt spray with thermal cycling) test. The samples exposed to the GM test evinced very little corrosion. During exposure, the weight of all the samples fluctuated in a random fashion, indicating that the corrosion products were only partially adherent and became detached from the surface at random times. The sequence of corrosion product formation on the specimen surfaces during exposure to the neutral salt spray test was very similar to that observed on coppers exposed to the atmosphere, indicating that this test can be used to give accelerated indications concerning atmospheric corrosion in humid marine regions. Four 24 h cycles of salt spray exposure are approximately equivalent to 1 year's exposure to the atmosphere. Alloying copper with phosphorus, tin, zinc, or silicon does not improve atmospheric corrosion resistance. The alloy containing 30%Zn exhibited dezincijication. The nickel silvers exbibited corrosion rates in the neutral salt spray at 80°C that were lower by a factor of at least 13 than those of the high purity coppers. For six of the alloys studied, the as received surface condition correlated with a slightly, but statistically significantly, higher corrosion rate, attributed to residual contaminants from rolling.     

Effect of the Crevice Former on the Corrosion Behavior of 316L Stainless Steel in Chloride-Containing Synthetic Tap Water

To restrain the failure of the plate heat exchanger (PHE) in customer boiler working fluid, the effect of crevice former type on the corrosion behavior of the 316L stainless steel plate was investigated using electrochemical methods and surface analyses in chloride-containing synthetic tap water (60 °C). The localized corrosion under metal–metal crevice condition was initiated more easily than that under the metal-gasket crevice condition due to the restricted mass transport at the gasket crevice mouth. However, the anodic current under the metal–metal crevice condition was lower than that under metal-gasket crevice condition at a higher anodic potential, indicating that that the metal dissolution under EPDM crevice would be higher than that under metal crevice under the accelerated corrosion condition. Because narrow crevice gap that was formed under gasket accelerated the anodic dissolution at the crevice mouth, the perforation tendency under metal-gasket crevice condition is much higher than that under metal–metal crevice condition. As a result, the crevice geometry, especially the crevice gap, mainly affected the corrosion behavior of PHE material.     

Effect of phosphate ions on electrochemical behaviour of copper in sulphate solutions

Abstract

The effect of phosphate ions on the corrosion behaviour of copper in sulphate solutions was investigated at different temperatures (293, 313, 333, and 353 K) and at different pH values (pH = 2·1, 7·2, and 12·3). A three electrode electrochemical technique was used for the measurements, using a saturated calomel electrode (SCE) for reference purposes. Both anodic and cathodic polarisation curves were established, from which the anodic and cathodic Tafel constants were determined. Corrosion potentials were determined by extra trapolation of the anodic and cathodic Tafel lines to the point of zero current density. The results showed that for a pH value of 2·1, the corrosion rate of copper showed a marked tendency to increase with increasing temperature in solutions containing either sulphate alone or sulphate plus phosphate. However, at pH values of 7·2 and 12·3, this tendency became less pronounced in solutions containing sulphate alone and in solutions containing sulphate plus phosphate together, max imum corrosion rates were greatly reduced and showed less tendency to increase with increasing temperature. Anodic and cathodic reaction mechanisms are proposed to explain the observations for the corrosion of copper.     

Anti‐tarnish treatment of brass for coinage

The anti‐tarnish film was formed on brass for coinage by 1‐phenyl‐5‐mercaptotetrazole (PMTA), which was studied by accelerated corrosion test (metallic coatings‐thioacetamide corrosion test), polarization curves and electrochemical impedance spectroscopy (EIS) in synthetic sweat solution. The accelerated corrosion test showed that PMTA exhibited better anti‐tarnish performance on brass than that of traditional anti‐tarnish agent benzotriazole (BTA). The polarization measurements showed that PMTA could be classified as a mixed inhibitor for it could restrain both anodic and cathodic reactions. EIS measurements indicated that the inhibition efficiency of PMTA on brass was over 98.4% in synthetic sweat solution. All these results showed that PMTA was an excellent anti‐tarnish agent of the brass for coinage, the optimum treating conditions of which were 0.5 gL^?1, pH = 3, 55°C–85°C, 7 min.     

Corrosion of Copper by Water of Various Temperatures and carbon dioxide contents

An investigation on corrosion of copper exposed to natural soft water with and without humic substances and at different temperatures and carbon dioxide levels is performed. The corrosion rate increases with the carbon dioxide content and is higher in water containing humic matter. For water which does not contain organic matter the corrosion rate increases with the temperature to a maximum at about 50°C and then decreases at higher temperatures. In water containing organic matter no such reductions is found. The corrosion rate is nearly constant from 50°C and up to 70°C. Pitting corrosion on copper is greatest in the temperature region where the surface corrosion is greatest. Iron seems to take part in the reaction process which leads to formation of pitting on copper.