Electrochemical corrosion characteristics of Ni-Resist type 2 in sea water containing ferrous sulphate

Abstract

The corrosion characteristics of Ni-Resist type 2 alloy in sea water have been determined in relation to dissolved oxygen (DO) content, pH, and concentration offerrous sulphate (injected to inhibit corrosion of copper based alloy condenser tubes). The alloy underwent uniform cathodically controlled corrosion so that relatively high pH and low DO provide an acceptable environment. Compared with similar pH conditions in the absence of added iron, Fe²⁺ dosing of aerated sea water to ≤100 ppm at pH<5 increased the corrosion rate, whereas dosing at 1000-2400 ppm (pH<5) decreased it. Addition of ferrous sulphate to deaerated sea water further suppressed the already low corrosion rates in this medium. Even under aggressive conditions of anodic polarisation, the alloy showed near uniform attack of the major constituent metals, leaving, however, a graphitised surface. The possible stagnation of a concentrated ferrous sulphate solution injected into the condenser circulating cooling water system has been considered. It is also concluded that ferrous sulphate dosing does not alter the stress corrosion cracking susceptibility of the alloy.     

Corrosion behaviour investigation of 460 low alloy steels exposed in the natural deep-sea environment

ABSTRACT

The corrosion behaviours of 460 low alloy steels were investigated by the field exposure corrosion experiments with various long periods and 1200–3000?m depths in the natural deep-sea environment. XRD analysis results indicate that corrosion products of β-FeOOH, γ-FeOOH and Fe₃O₄ increase and the corrosion product of α-FeOOH decreases with the exposure sea depth extending. Electrochemical experiment results reveal the corrosion status is aggravated with the exposure sea depth extending: corrosion potentials shift negatively to a minimum self-corrosion potential of ?0.590?V (vs. SCE) and charge transfer resistances decrease to a minimum of 278?Ω?cm². Corrosion behaviours analysis shows that the average corrosion rate decreases with the time increasing and reaches a maximum value of 101?μm?a^?1. The maximum pitting depth varies between 63.0?μm and 138?μm. Gray relational analysis shows that the corrosion rate of 460 steel is most influenced by the pressure and dissolved oxygen concentration of deep sea, exhibiting a positive correlation relationship.     

Influence of iron addition on corrosion layer built up on 70Cu-30Ni alloy in sea water

Abstract

The effect of additions of iron on the corrosion behaviour of a 70Cu–30Ni alloy in sea water was studied by electrochemical methods and corrosion tests. Iron additions of 0·5 and 2% increased the average corrosion resistance of the alloy. This beneficial effect is due to the formation of a layer containing a large quantity of nickel and iron oxides. A disadvantage of iron additions is the possibility of pit and crevice formation as a result of segregation of nickel-iron rich precipitates at grain boundaries.     

Chromate passivation of hot dipped Zn25Al alloy coatings

Abstract

A low concentration chromate passivation treatment has been successfully applied to a new type of hot dipped Zn2 5Al alloy coating, and the corrosion resistance of the chromate passive film has been assessed using the copper accelerated acetic salt spray (CASS) test, electrochemical measurements, and sea water immersion testing. The results showed that the corrosion resistance of the Zn2 5Al alloy coating was significantly better after the chromate passivation treatment. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses showed that the composition (at.-%) of the low concentration chromate passive film was: 5·5S–3·4Na–11·8C–7·9Ti–41·6O–1 3·7Cr–16·0Zn. Aluminium was not found in the film, which is attributed to the dissolution behaviour of the Zn2 5Al alloy coating in acidic chromate solution.     

Effect of sulphides on corrosion of Cu–Ni–Fe–Mn alloy in sea water

Abstract

The corrosion behaviour of Cu–30Ni–2Fe–2Mn commercial alloy (similar to C71640) in quiescent, hermetically closed sulphide polluted and unpolluted natural sea water at 25°C was investigated. The corrosion resistance was examined using free corrosion and electrochemical tests and the surface film was characterised by chemical analysis and X-ray photoelectron spectroscopy. The different susceptibilities to corrosion were closely linked to the initial sulphide concentration; the accelerated attack occurring with an initial sulphide concentration of 4 ppm correlated with the amount of dissolved oxygen in solution and with the chemical composition of the corrosion layer.     

Cathodic protection requirements for high strength steel in sea water assessed by potentiostatic weight loss measurements

Abstract

A potentiostatic weight loss technique has been used to compare the corrosion rates of Weldox 700 high strength low alloy steel exposed to both natural and sterile sea water at potentials ranging from the free corrosion condition to - 1000 mV (SCE). Anodic polarisation curves with Tafel constants of 54 and 64 mV per decade were fitted to the data and the minimum levels of protection required to limit the corrosion rate to 0·001 mm per year were found to be - 770 and - 790 mV (SCE) in natural and sterile sea water, respectively. Lower corrosion rates occurred in filtered natural sea water than in sterile sea water but the highest rates were recorded on specimens ex posed to a seabed sediment. The reasons for this behaviour are discussed in terms of the biofilms and the numbers of sulphate reducing bacteria present on the surfaces.     

Effects of Pb and Cu additives on microstructure and wear corrosion resistance behaviour of PM Al–Si alloys

Abstract

The wear and wear corrosion resistance behaviour of Al–20Si–XPb–YCu (X=0–10 wt-%, Y=0–3 wt-%) alloys fabricated by a powder metallurgy (PM) technique and subsequent heat treatments were evaluated by a block on ring tribotest. The microstructure of all aluminium alloys was observed by optical microscopy and scanning electron microscopy with X-ray energy dispersive spectroscopy. The effects of applied potentials and environments including dry air and 3.5 wt-%NaCl aqueous solution were studied. The results of microstructure analysis indicated that Pb exhibited a bimodal distribution in the Pb containing alloys, and Cu particles become to form the intermetallic phase CuAl₂. Furthermore, the hardness rises significantly for both Pb and Cu containing alloys only after solid solution quenching treatment. The wear and corrosion results showed that the addition of both lead and copper would improve the wear resistance but lead to a higher corrosion rate whereas heat treatment had a beneficial effect of reducing the corrosion rate of most alloys with the exception of Al–Si alloy. Furthermore, by comparison of all alloys after heat treatment, the wear corrosion resistance of Al–Si alloy was inferior to the other alloys; consequent additions of Pb and Cu further improved its wear corrosion resistance. Moreover, at an anodic potential, the wear corrosion rate and current density of both Al–Si and Al–Si–Cu alloys containing particle Pb decrease significantly owing to a corrosion product layer composed of Al, O and Pb elements.     

Influence of Surface Condition on the Corrosion of Aluminium Brass

Abstract

The corrosion behaviour of aluminium brass, with four different surface treatments (highly and lightly oxidised, pickled and sandblasted), was studied in natural sea water, both stagnant (aerated) and flowing.

Electrochemical measurements and weight loss determinations showed that the oxide film produced during industrial annealing had little effect on the corrosion rate as compared with a pickled surface, in both stagnant and flowing conditions. Sandblasted surfaces were inferior.

Measurements of currents flowing in galvanic couples formed between oxidised and stripped metal were small and decreased with time, but the oxidised surfaces appeared to be slightly more vulnerable than the pickled ones to localised corrosion. Some further work is needed here.     

Papers to be presented at Eurocor '77

Abstract

Despite numerous studies on atmospheric corrosion of copper and copper based alloys, the corrosion induced release processes of individual alloy constituents suffer from significant knowledge gaps. This investigation comprises metal release rate measurements of copper, zinc and tin from some copper based alloys including brass (20 wt-%Zn) and bronze (6 wt-%Sn), and their pure alloying metals, copper, zinc and tin. Data have been generated during a 2·5 year urban field exposure in Stockholm, Sweden and parallel laboratory investigations in a specially designed rain chamber using artificial rain. Brass shows significantly lower annual release rates of both copper and zinc compared to pure metal sheets of its alloy constituents. Zinc is preferentially released compared to copper. Dezincification of brass occurs both at field and laboratory conditions, a process influenced by rain characteristics. Alloying with tin does not largely reduce the release rate of copper from bronze compared to pure copper. No measurable amount of tin is released from the bronze surface.     

Preparation and electrochemical corrosion behaviour of 3D large-sized nanocrystalline copper bulk in solutions with chloride ions

ABSTRACT

A 3D large-sized nanocrystalline (NC) copper bulk was prepared by inert gas condensation and in situ warm compress, the density of which was 99.51% of theoretical value. Electrochemical methods and XRD、EDS、SEM technique were used to investigate the anodic polarisation behaviour of NC copper in solutions with chloride ions. NC copper exhibited a different anodic polarisation behaviour from its coarse-grain (CG) counterpart in 0.47?wt-% NaCl solution. No second passivity was observed for NC copper, while there was a notable second passivity for CG copper. Compared with CG copper, the corrosion resistance of NC copper decreased. The anodic polarisation behaviour of NC copper changed significantly when 10^4?ppm Cl^? was added in 0.3% Na₂SO₄ solution. Attributed to the CuCl protective film on NC copper, the critical current intensity decreased and the decreasing rate of anodic current intensity lowed notably in activity-passivity zone.     

Indoor atmospheric corrosion of copper and steel under heat trap conditions in Cuban tropical climate

Abstract

Corrosion behaviour of copper and steel under heat trap conditions in Cuban tropical climate is reported. Temperature and humidity reach higher values than those reported for traditional outdoor and indoor conditions. Annual calculated time of wetness is in the range corresponding to outdoor or ventilated sheds. This behaviour is not reported for other indoor conditions. Sulphur compounds deposition rate is higher than chloride deposition rate at all corrosion stations. Main corrosion products formed on steel and copper are goethite and brochantite respectively. No significant differences in the statistical influence of exposure time and time of wetness on atmospheric corrosion process of copper and steel under heat trap conditions are determined.     

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.

     

Corrosion of CuNi30Fe in artificial solutions and natural sea water: influence of biofouling

Abstract

The electrochemical behaviour of CuNi30Fe in natural sea water, artificial sea water, NaCl+Na₂SO₄, and NaCl solutions has been compared. Potentiodynamic polarisation curves, open circuit potential versus time plots, and current transients were recorded. Significant differences between the electrochemical responses of the alloy in the electrolytes used were detected. Corrosion products after various exposure times in-natural sea water and in artificial solutions were analysed using SEM and EDAX. Attachment of micro-organisms after exposure in natural sea water was examined by SEM. The effect of biofilms at early stages of formation on the corrosion process was also studied. The protective characteristics of the complex layers formed on the CuNi30Fe surface were found to be altered by microbial adhesion to the metal surface.     

Fatigue behaviour of 8090-Al-Li alloy in chloride containing environments

The effect of an environment containing chloride on the fatigue behaviour of a 8090 Al Li Mg Cu alloy was studied. Results were compared with those obtained on a traditional 2024 Al Cu Mg alloy. Fatigue and corrosion-fatigue tests were carried out both on smooth specimens and riveted samples. In order to assess the corrosion behaviour of the materials and their susceptibility to stress corrosion cracking, potentiodynamic polarization and slow strain rate tests were carried out. Results showed a remarkable effect of the aggressive environment on the fatigue behaviour both of the innovative 8090 alloy (in T8 ageing conditions) and on the traditional clad 2024 alloy (in T3 natural ageing conditions), though the former showed slightly better behaviour. Nevertheless, in the presence of rivets the reduction in fatigue strength in the aggressive environment was negligible. Slow strain rate tests showed premature fractures under anodic polarization above the pitting potential and with a strain rate of 10⁻⁶ s⁻¹, only for the 8090 T8 alloy.     

Corrosion behaviour of bronze in urban environments: influence of tin content

Abstract

In this paper, the influence of the tin content on the corrosion behaviour of copper alloys was investigated. Three different bicomponent bronze alloys were exposed to a natural urban environment. The kinetic corrosion processes and the patina properties were monitored using the open circuit potential, electrochemical impedance spectroscopy and spectrocolorimetry. Results show that the bronze corrosion behaviour improves upon increasing the tin content. In addition, the mechanism of the patina formation is different for the three alloys.     

Stress corrosion in copper–nickel alloys: influence of ammonia

Abstract

The test results from an earlier investigation by the author on the mechanical behaviour of a low nickel nickel-copper alloy exposed to a solution of 3·5%NaCl + 10%MgCl₂ with and without ammonia indicated that the presence of 1% ammonia alters the failure mode and affects the load bearing capacity of the material. In the present investigation, further tests have been conducted on the same alloy to study its mechanical/corrosion behaviour on exposure to an aqueous solution of ammonia in comparison with exposure to a similar solution of ammonia containing 3·5%NaCl + 10%MgCl₂. A constant displacement rate of 9·6 × 10^-3 μ m s^-1 was used and the concentration of ammonia was maintained at 5%. On exposure to the 5% aqueous ammonia solution, the mechanical properties of the alloy were degraded significantly and the material exhibited a brittle stress corrosion type of failure. However, on exposure to 5% ammonia in the presence of 3·5%NaCl + 10%MgCl₂, there was less change in failure mode relative to that in air and a significant improvement in the mechanical properties of the material compared with those in aqueous ammonia. This indicates that the presence of MgCl₂ and/or NaCl can be beneficial when low nickel copper alloys are exposed to ammonia. This paper presents the experimental results and observations from the recent tests, and discusses the relative roles of ammonia and NaCl/MgCl₂ in determining the mechanical properties and modes of failure in a low nickel content copper-nickel alloy.     

The effect of manufacturing process induced near-surface deformed layer on the corrosion behaviour of AA2198-T851 Al–Cu–Li alloy

ABSTRACT

The effect of the near-surface deformed layer on the corrosion behaviour of AA2198-T851 Al–Cu–Li alloy has been investigated using microscopy and electrochemical techniques. This shows that a deformed layer developed by rolling was more active but only exhibited superficial attack compared to a mechanically polished surface, which produced severe localised corrosion associated with the presence of hexagonal T1 particles. The rolled surface became increasingly corrosion resistant with time, but when coupled, galvanically enhanced severe localised corrosion sites developed on the surface over time.     

Microbially influenced corrosion and inhibition of nickel–zinc and nickel–copper coatings by Pseudomonas aeruginosa

The present study describes the effect of Pseudomonas aeruginosa on the corrosion rate of nickel–zinc and nickel–copper alloy coatings. The presence of bacteria was associated with decreases in R_ct values, suggesting that P. aeruginosa promoted the corrosion of nickel–copper alloy coatings. However, R_ct values of nickel–zinc coatings increased in response to bacterial inoculation, corresponding to a decrease in corrosion rate for nickel–zinc alloy coatings. Our results suggest that the activity of P. aeruginosa facilitated the corrosion of nickel–copper alloy, while serving a protective function for the nickel–zinc alloy.     

Thermomechanical treatment and corrosion resistance correlation in the AA2198 Al–Cu–Li alloy

ABSTRACT

The influence of T3, T8 and T851 thermomechanical treatments on the microstructure and corrosion resistance of the AA2198 was investigated. Differential scanning calorimetry and scanning electron microscopy were used for microstructural characterisation, whereas electrochemical methods were employed to analyse the corrosion behaviour of the alloy. The morphology and composition of constituent particles were similar for the T3 and T8 thermomechanical treatments but varied in the T851. There was an inverse relation between T1 phase density and corrosion resistance. The T3 treatment with the highest corrosion resistance was the one with the lowest density of T1 phase. The mechanisms of corrosion varied with the thermomechanical treatments.     

Study of passive film on stainless steels and high grade nickel base alloy using X-ray photoelectron spectroscopy

Abstract

In the present study an assessment has been made of the air formed passive film and the passive film existing after a short exposure to a synthetic sea water environment on austenitic (UNS S31603), superaustenitic (UNS S31254 and UNS S32654) and superduplex (UNS S32760) stainless steels and a Ni base alloy (UNS N06625) using X-ray photoelectron spectroscopy. Assessment of their corrosion behaviour has been made through use of electrochemical accelerated tests supported by post-test microscopy. The passive film on the Ni base (low Fe) UNS N06625 alloy is remarkably similar to those formed on the high Cr and Mo stainless steels. It has been demonstrated that the Fe/Cr ratio in the passive film is dependent on alloy composition and on the conditions to which the material has been exposed, and a general correlation between passive film constitution and corrosion resistance is evident.