Pitting Corrosion in Copper Tubes – Cause of Corrosion and Counter-Measures

Abstract

An investigation of failures of hard-drawn copper water pipes (phosphorus-deoxidised copper) in service due to pitting corrosion was conducted from November, 1962 to February, 1965. Fifteen cases were reported. All those about which information could be obtained came from hot water installations and occurred in water with a low pH (≤7) and a HCO_3- content of, at the most, 100 mg/l but generally below 50 mg/1. Failures not due to pitting corrosion (i.e. caused by erosion and corrosion or corrosion fatigue) occurred in waters with a higher pH and higher HCO₃- content.

A laboratory investigation into the ability of the corrosion products to counteract further corrosion in different types of water was also carried out, using an electrolytic cell which, in principle, was a model of an active pit in a copper tube. This led to the following conclusions, which are in good agreement with the results obtained from the examination of service failures:

If the pH value of the water is high enough, the copper dissolved by the corrosion can be precipitated as basic copper salt. At low pH values such precipitation does not take place.

If the [HCO₃^?]/[SO₄^2?] ratio in the water is high, dissolved copper can be precipitated as basic copper carbonate in the neighbourhood of the corrosion site and counteract further corrosion.

At a low [HCO₃^?]/[SO₄^2?] ratio, crusts of basic copper sulphate will be precipitated at some distance from the corrosion site and may lead to a high corrosion rate.

Pitting is not likely to occur in hot water tubes of hard copper if the pH is ≥ 7·4 and the [HCO₃^?]/[SO₄^2?] ratio ≥1 (the concentrations given in mg/1). The critical values mentioned are approximate and may be adjusted in the light of future experience.     

Corrosion behavior of magnesium and magnesium alloys

The automotive industry has crossed the threshold from using magnesium alloys in interior applications such as instrument panels and steering wheels to unprotected environment such as oil pan, cylinder head and wheels. The expanding territory of magnesium leads to new challenges.mainly environmental degradation of the alloys used and how they can be protected. The present critical review is aimed at understanding the corrosion behavior of magnesium and magnesium alloys in industrial and marine environments, and the effect of microstructure, additive elements and inhibitors on the corrosion mechanism.     

Corrosion and fatigue in micro-sized Ni cantilever beams

The Ni microcantilevers were fabricated by femtosecond laser. The corrosion behavior of the micro-sized Ni cantilever beams was studied by electrochemical noise and a newly developed fatigue testing method. The results show that the micro-sized specimens exhibit general corrosion behavior under the studied corrosion condition, whereas the ordinary-sized plates exhibit the localized corrosion behavior. The critical load amplitude of the micro-sized Ni specimens under corrosion fatigue status was determined to be 15 mN. The maximum bending loads, which were measured by fatigue tests, decrease gradually prior to final fracture. Corrosion fracture first occurs in the range of notch with a higher tensile bending stress, and exhibits clear evidence of trans-columnar fracture. The variation of maximum bending loads with time agrees with that creep deformation of the micro-sized Ni specimens can easily occur at room temperature, which implies that the micro-sized Ni specimens appear to have an improved resistance towards total crack as compared with the ordinary-sized Ni specimens.     

High Temperature Corrosion and Protection of Titanium Alloys and TiAl Intermetallics

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Corrosion and high-temperature oxidation of AM60 magnesium alloy

The corrosion and high-temperature oxidation characteristics of AM60 Mg alloy in different environments were investigated by immersion test, electrochemical polarizing analysis and differential thermal analysis （DTA）/thermo gravimetric （TG） experiments. The influence of aging heat treatment on the corrosion resistance of AM60 Mg alloy was studied. AM60 Mg alloy shows better corrosion resistance in sea water than in 3.5%（mass fraction） NaCI solution. The corrosion resistance after aging for 24 h is better than that of both as-cast and aging for 48 h. Corrosion resistance of Mg alloy is controlled by microstructure, composition of a-matrix. Precipitation offl phase along the grain boundaries acts as a barrier that decreases corrosion rate, whereas the decrease of aluminum content of a phase causes an increase in the corrosion rate. The DTA and TG curves of heating process in air are characterized with combustion after 590℃. When heated in helium, the curves show two endothermic peaks and a remarkable evaporation of magnesium. As for isothermal DTA and TG experiments, mass increment caused by oxidation does not happen till 520 ℃.     

Corrosion and radiation resistance of “Bochvaloy” nickel-chromium alloy

The structure, properties, and corrosion and radiation resistances of Bochvaloy nickel-chromium alloy are studied. Under neutron irradiation to a dose of 35 dpa the alloy experiences inconsiderable low-temperature radiation-induced embrittlement. Its corrosion resistance in various aggressive media is several orders of magnitude higher than that of stainless steels. The alloy is well adaptable to manufacture and possesses enhanced strength and ductility parameters as compared to austenitic steels and alloys.     

Corrosion behavior of tantalum and its nitride in alkali solution

The corrosion behavior of tantalum and its nitrides in stirring NaOH solutions was researched by potentiostatic method, cyclic voltammetry and XPS. The results showed that the corrosion products were composed of Ta2O5 and NaTaO3. The corrosion reaction formula of tantalum and its nitrides was written according to cyclic volt-ampere curves. The electric charge transfer coefficient and the electric charge transfer number were calculated.     

High-Temperature Corrosion Resistance of Al–Re and Re Coatings

The oxidation behavior in air at 1473 K, and sulfidation behavior in a H2S–H2 gas mixture with a sulfur partial pressure of 10^–2 Pa at 973 K of Al–Re coated CMSX-4 were studied. Investigation on the sulfidation behavior of the Re-coated CMSX-4 was carried out in a H2S–H2 gas mixture with a sulfur partial pressure of 10^–2 Pa at 973 K. The experimental results show that a Re-rich alloy layer was formed between an -Al₂O₃ layer and the inner concentration zone of Ta and Ti for the CMSX-4 single crystal alloy with an Al–Re coating after oxidation. The Re-rich alloy layer containing Cr, W, Ni, Co, and Mo effectively inhibited the outward diffusion of alloying elements and the inward diffusion of Al. The Al/Re-coated CMSX-4 single crystal alloy had excellent sulfidation resistance; the Re-rich alloy layer, containing W, Ti, Ta, and Mo, which formed during the sulfidation process and located between the alumina scale and the CMSX-4 base alloy, plays a role in inhibiting the outward diffusion of alloying elements. The sulfidation resistance of CMSX-4 single-crystal alloy is greatly improved by a Re coating on the CMSX-4 alloy surface; this is attributed to a Re–Cr–W alloy layer that retarded the outward diffusion of cations and the oxide layer containing Ta, Ti, and Al, which inhibited the inward penetration of sulfur.     

International Standards in Corrosion of Metals and Alloys. The Activities of ISO/TC 156 “Corrosion of Metals and Alloys”

We continue to inform readers about the activities of the Technical Committee Corrosion of metals and alloys of the International Organization for Standardization (ISO/TC 156). The work program of the Committee for 2000 is given. The scheme of the participation of specialists in corrosion in the activity of the Committee, as well as the procedure of submitting draft standards for the development as International standards, is shown.     

Corrosion behavior and surface treatment of superlight Mg–Li alloys

Mg–Li alloy, as a superlight metallic engineering material, shows great potential in the fields of aerospace and military due to its high specific strength, better formability, and excellent electromagnetic shielding performance. The research process of Mg–Li alloys is reviewed and three main problems are pointed out. Aimed at the poor corrosion resistance of Mg–Li alloys, the corrosion behavior is mainly summarized. The surface treatment technologies, including electroplating, electroless plating, plasma spraying, molten salt replacement, conversion coating, anodizing, micro-arc oxidation, organic coating, and organic–inorganic hybrid coating, are introduced in detail. Finally, the future development of corrosion and protection of Mg–Li alloys is discussed.     

Corrosion properties ofAZ31 magnesium alloy and protective effects of chemical conversion layers and anodized-coatings

The corrosion properties of AZ31 magnesium alloys were studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy（E1S） techniques, meanwhile, the protective properties of two environmentally protective types of chemical conversion layers and anodized coatings of AZ31 magnesium alloys were also discussed. The component of chemical conversion bath is NaH2PO4·12H2O 20 g/L, H3PO4 7.4 mL/L, NaNO2 3 g/L, Zn（NO3）2·6H2O 5 g/L and NaF 1 g/L, and components of the anodization bath is Na2SiO3 60 g/L, C6H5Na3O7·2H2O 50 g/L, KOH 100 g/L and Na2B4O7·2H2O 20 g/L. The results show that the corrosion resistance of AZ31 magnesium increases with the increase of pH value of the corrosive medium. For the chemical conversion layer acquired at 80 ℃, 10 min is the best processing time and the charge transfer resistance of the chemical conversion layer is enhanced nearly by 10 times. The optimum processing time for the anodization of AZ31 is 60 min, the charge transfer resistance value of the anodized sample at the early immersion stage is nearly 26 times of that of the blank sample and the corrosion type of the anodized samples is pitting.     

Corrosion and Electrochemical Behavior of β-W CVD Coatings in NaCl Solution

Protection of Metals and Physical Chemistry of Surfaces - The paper presents the results of a study of the corrosion-electrochemical behavior of coatings based on the metastable phase of tungsten...     

Effect of Pyrrole and N-Methylpyrrole Coatings on Corrosion Resistance of Mild Steel

COATING ON THE SURFACE of metals bypolymeric materials have been widely used inindustries for the protection of this materials against ofcorrosion[1-4].Electropolymerization is an effective technique forthe surface coating of various conductive materialswith wide variety of polymers with various thick nesses[5].Recently,electropolymerization of pyrrole on steelsubstrates has been investigated with the aim ofproducing uniform and strongly adherent coatings[6-9].It was found that only lim…     

Corrosion and electrochemical behavior ofAZ31D magnesium alloys in sodium chloride

The corrosion and electrochemical behavior of extruded AZ31D magnesium alloys in NaCl solution were investigated using SEM, XRD and electrochemical method. It is found that AZ31D is susceptive to Cl^- ion, and the open circuit potential shifts to more negative values with increasing chloride concentration. Pitting occurs at corrosion potential and corrosion area enlarges with enhanced polarization. Tafel slopes of the cathode branches in different testing solution are almost the same. Cl^- concentration affects cathode course slightly. High frequency capacitive loops shrink with the increase of Cl^- concentration. Corrosion initiates from the grain boundary and spreads to entire surface with time.     

Corrosion resistance of electrodeposited RE-Ni-W-P-SiC-PTFE composite coating in phosphoric and ferric chloride

1 Introduction During process, store and use in various kinds of environment, corrosion, wear, fatigue and rupture may happen in all materials and products. These kinds of failure and damages widely occur in industries, causing enormous losses to nationa…     

Corrosion Behavior of Ψ and β Quasicrystalline Al–Cu–Fe Alloy

Two nanostructured Al–Cu–Fe alloys, Al64Cu24Fe12 and Al62.5Cu25.2Fe12.3, have been studied. Icosahedral quasicrystalline(w) Al64Cu24Fe12 and crystalline cubic(b) Al62.5Cu25.2Fe12.3cylindrical ingots were first produced using normal casting techniques. High-energy mechanical milling was then conducted to obtain w icosahedral and b intermetallic nanostructured powders. Electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization were used to investigate the electrochemical corrosion characteristics of the powders in solutions with different p H values. Current density(icorr), polarization resistance(Rp), and impedance modulus(|Z|) were determined. The results showed that regardless of p H value, increasing the solution temperature enhanced the corrosion resistance of the both phases. However, the electrochemical behavior of the w phase indicated that its stability depends on the submerged exposure time in neutral and alkaline environments. This behavior was related to the type of corrosion products present on the surfaces of the particles along with the diffusion and charge-transfer mechanisms of the corrosion process.     

Investigations on the Corrosion Behaviour and Structural Characteristics of Low Temperature Nitrided and Carburised Austenitic Stainless Steel

The wear resistance of austenitic stainless steels can be improved by thermo-chemical surface treatment with nitrogen and carbon. However, it is possible that the corrosion resistance will be impaired by the precipitation of chromiumnitrid or -carbide. The present contribution deals with investigations of the corrosion behaviour and structural characteristics of a low temperature nitrided and carburised austenitic stainless steel.The material investigated was AISI 316L (X2CrNiMol7-12-2) austenitic stainless steel. A commercial plasma-nitriding unit (pulsed dc) was used for the nitriding and carburising process. Additional samples were treated by the gasoxinitriding process for a comparison between plasma- and gasoxinitriding. The nitrided and carburised layer of austenitic stainless steel consists of the nitrogen or carbon S-phase (expanded austenite), respectively. X-ray diffraction investigations show the typical shift of the peaks to lower angles, indicating expansion of the fcc lattice. Also the X-ray diffraction technique was employed to study the residual stresses in the nitrogen and carbon S-phase. The corrosion behaviour of surface engineered samples was investigated with electrochemical methods. Anodic potentiodynamic polarisation curves were recorded for testing the resistance against general corrosion (in H2SO4) and pitting corrosion (in NaCl).     

Corrosion behavior of B30 Cu-Ni alloy and anti-corrosion coating in marine environment

The corrosion behavior of B30 Cu-Ni alloy in a sterile seawater and a SRB solution was investigated. The results show that the corrosion potential of specimen in the SRB solution is much lower than that in the sterile seawater. The polarization resistance of specimen in the SRB solution decreases quickly after a period immersion and becomes much lower than that in the sterile seawater. It is concluded that the SRB accelerates the corrosion process of B30 Cu-Ni alloy greatly. An anti-corrosion electroless Ni-P coating was produced and applied to the alloy. The results show that specimens coated with Ni-P plating exhibit favorable corrosion resistance property in SRB solution. Severe pitting corrosion appears on the uncoated specimens in the SRB solution when the coated specimens are still in good condition. The anti-corrosion mechanism of Ni-P plating was analyzed. It is concluded that coating the B30 Cu-Ni alloy with electroless Ni-P plating is an effective technique against the attack of SRB in marine environment.     

Morphology,Texture and Corrosion Behavior of Nanocrystalline Copper–Graphene Composite Coatings

This article discusses morphology, texture and corrosion behavior of electrodeposited Cu–graphene composite coatings on mild steel. This study demonstrates that a metal–graphene composite coating, in which graphene is incorporated into a suitable metal matrix, is an effective way to harness the anti-corrosive potential of graphene in producing anti-corrosive coatings for corrosion-prone materials such as steel. Enhanced corrosion resistance of such metal–graphene coatings can facilitate reductions in the requisite coating thickness and material costs in a given coating application. Cu–graphene composite coatings were electrodeposited from sulfate-based acidic electrolytic baths consisting of uniform dispersions of electrochemically exfoliated graphene. Incorporation of graphene into a Cu matrix promoted finer coating morphology, reduction in crystallite size and a strong <220> texture, which subsequently made these composite coatings about 43% more corrosion resistant in 3.5% NaCl when compared to pure Cu coatings. Enhanced corrosion resistance of the composite coatings was indicated by the corrosion potential which increased with the amount of incorporated graphene.     

Corrosion and tribological properties of nanocrystalline pulse electrodeposited Ni–W alloy coatings

Ni–W alloys with different tungsten content and grain size under 50?nm were prepared by means of pulse current and pulse reverse current electrodeposition. The alloys were analysed using various methods (EDX, SEM and XRD). The electrochemical (open circuit potential, corrosion current density) and tribological (coefficient of friction and wear rate) characteristics were evaluated. Tungsten content in the alloys influences grain size which is responsible for the quality of the coating and the corrosion and tribological properties. When the content of tungsten in the Ni fcc lattice is lower than 5?at.-% W, the corrosion resistance increases. When the content of W is higher than 5?at.-%, the corrosion resistance decreases. The relationship between tribological properties and W content is the reverse of that experienced with corrosion properties.