Corrosion protection properties of copper‐ and carbon‐containing polyethylene films in humid air climates

The corrosion protection properties of commercially available polyethylene (PE) films containing copper and carbon were investigated and compared with pure PE films of comparable thickness. The composition of these films was analyzed by thermoanalysis and atom emission spectroscopy (ICP‐AES). Electrochemical impedance spectroscopy (EIS) and packaging tests were used to determine the ability of copper‐ and carbon‐containing PE films to protect mild steel against corrosion in humid air climates. For the here‐investigated samples, no electrochemical activity of copper could be found under these conditions. In contrast to the added copper only the inserted carbon decreased the surface resistance. Additional abrasive tests imply that copper is encapsulated inside the films. For all samples, the permeability to vapor and the insertion of water were similar to the copper and carbon free reference film. The tests in the climate cabinet revealed that mild steel samples packed in copper‐ and carbon‐containing films reached the same degree of corrosion than those in the reference films.     

New surfactants N‐alkyl‐N,N‐dimethyl‐N‐(3‐thienylmethylene)ammonium bromides: Preparation and anticorrosion evaluation

A new series of N‐alkyl‐N,N‐dimethyl‐N‐(3‐thienylmethylene)ammonium bromides (designated as NTA‐n, n = 8, 10, 12, 14, and 16) were synthesized. The electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization showed that NTA‐n could protect availably X70 steel from attack of HCl with an inhibition efficiency of about 95%. And the inhibition ability follows the following sequence: NTA‐8 < NTA‐10 < NTA‐12 < NTA‐14 < NTA‐16, suggesting that prolonging alkyl chain may enhance the inhibition capacity of the molecules. Theoretical investigation backs up well the experiment results. The correlation of theoretical calculation with the experiment results illustrated clearly double logarithmic relations between the corrosion current and the computed quantum chemical parameters such as the highest occupied molecular orbital energy (), energy gap (ΔE), molecular volume ( ν), electronegativity ( χ), the total energy of iron crystal with the adsorbed inhibitor molecule ), the interaction energy of Fe (1 0 0) surface and inhibitor molecules (), while an equation resembling Hammet relation was existed between the corrosion currents and the fraction of electrons transfer (ΔN). These linear correlations suggest the relation of the inhibitor structure with its inhibition activity: long alkyl chain and electron donating groups in NTA‐n will enhance the corrosion efficiency.     

Early‐stage oxidation behavior of Co‐rich high‐temperature alloys

The long‐term oxidation performance of an alloy is critically linked to the early‐stage oxidation behavior of high‐temperature alloys. This study investigates early‐stage oxidation behavior in terms of oxidation kinetics, scale evolution, and residual stresses developed within a scale of the commercially available cobalt‐rich alloys: HAYNES® 188, 6B, 25, and HR‐160® and a newly developed nitride‐dispersion strengthened NS‐163® alloy (HAYNES®, HR‐160®, NS‐163® are registered trademarks of Haynes International, Inc). Short‐term isothermal oxidation exposures were conducted in flowing air at 982 °C for durations of 1–50 h. Oxidation kinetics was assessed by weight‐change behavior, which showed that 188 alloy exhibited the lowest weight‐gain, while for similar times HR‐160 alloy underwent weight‐loss. SEM/EDS analysis was performed to characterize oxides formed in these alloys, while stresses developed in the oxides of different alloys were measured using synchrotron X‐ray radiation. The results in this paper clearly demonstrated the effects of alloy composition on the scale evolution and the amount of stresses developed in oxides.     

Barrier and self‐healing coating with fluoro‐organic compound for zinc

The barrier and self‐healing abilities of a corrosion‐protective coating with a fluoro‐organic compound for zinc was investigated. Several types of fluoro‐organic compounds, having different terminal groups and various numbers of carbon atoms, were coated on a pure zinc plate by dip coating. A fluoro‐organic compound having the terminal group of COF showed excellent barrier resistance, which increased as the number of carbon atoms in the compound increased. The optimal conditions — concentration of fluoro‐organic compound in the solution and the pH of the solution — were determined for coating, based on those that demonstrated more ability than chromate conversion coating. Monitoring the corrosion resistance of a scratched specimen in corrosive solution and observing the surface appearance of the specimen after the corrosion test confirmed the self‐healing ability of the coating with the fluoro‐organic compound. The fluoro‐organic coating had excellent self‐healing ability — equivalent to that of a chromate conversion coating. The self‐healing effect of the coating appeared to be due to the release of the fluoro‐organic compound as a result of the pH increase caused by cathodic reaction in the corrosion process, and the formation of a film on the defect.     

Microbiologically influenced corrosion of X60 carbon steel in CO2‐saturated oilfield flooding water

The corrosion behavior of X60 carbon steel in CO₂‐saturated oilfield flooding water inoculated with sulfate‐reducing bacteria (SRB) was investigated using polarization curves and electrochemical impedance spectroscopy (EIS). With the propagation of SRB in the flooding water, the pH values of flooding water increased quickly in the initial 2 days and remained relatively steady during the later stage. Polarization curves showed that the corrosion current density decreased during the first 10 days due to the protection of corrosion products and SRB‐biofilms, and then increased possibly due to the partial detachment of the corrosion products and the biofilms. EIS analysis also showed that the charge transfer resistance increased initially and then decreased with exposure time. In the beginning of corrosion, the anodic dissolution of X60 steel was dominated by CO₂. After the formation of SRB‐biofilms, part of FeCO₃ corrosion products was converted to incompact FeS precipitates by SRB bio‐mineralization. Thus, the dispersed iron sulfide in SRB‐biofilms and X60 steel base may constitute a galvanic couple, accelerating the localized corrosion of the steel base in the flooding water.     

An in‐situ FT‐IR investigation of the anodic behaviour of WC‐Co hardmetal

An in‐situ FT‐IR spectroelectrochemical and voltammetric study of the corrosion of a WC‐Co hardmetal grade is reported in this communication. A slightly acidic sulphate solution is considered. The potential‐ and time‐dependent anodic formation of CO₂ and Co(OH)₂ can be followed with the variation of the vibrational spectra. The formation of CO₂ occurs at the same potential at which tungsten oxidation starts to be detected and the breakdown of passivity can be observed by electrochemical methods. Our results suggest that a threshold potential exists for the oxidation of WC in WC‐Co, giving rise to the concomitant oxidation of tungsten and carbon at more noble potentials than those typical for the oxidation of the individual elements.     

Electrochemical and mechanical behaviour of Sn‐2.5Ag‐0.5Cu and Sn‐48Bi‐2Zn solders

In this paper, two tin‐based alloys (Sn‐2.5Ag‐0.5Cu and Sn‐48Bi‐2Zn) are proposed as new lead‐free solders. Alloys have been developed by melting pure elements. Samples have been evaluated in terms of microstructure, corrosion resistance and mechanical features. Corrosion tests have been performed in 3% NaCl solution by polarization curves and electrochemical impedance spectroscopy (EIS). SEM observations and EDS analysis were carried out on samples before and after corrosion tests. Static monotonic tensile tests have been performed on three specimens for each alloy. SEM and EDS analysis revealed the presence of Sn‐Ag and Sn‐Cu intermetallic compounds within the Sn‐Ag‐Cu alloy. As a result of corrosion test, the Sn‐Ag‐Cu alloy showed a better corrosion resistance with respect to Sn‐Bi‐Zn. Both alloys evidenced good mechanical properties higher than the traditional Sn‐Pb system. Sn‐Ag‐Cu seems to be a suitable soldering material.     

X‐ray micro‐computed tomography analysis of accumulated corrosion products in deep‐water shipwrecks

Accumulated corrosion products from two different shipwrecks which had lain on the seabed (2.5 km depth) for 73 years were systematically analysed by three‐dimensional imaging at high resolution using X‐ray micro‐computed tomography. Complementary surface and chemical characterization experiments were conducted to identify the morphological structure of the corrosion products. Goethite was observed as the main corrosion phase found in both the wreck's corrosion products. However, other corrosion products such as silica, lepidocrocite, maghemite, magnetite, benyacarite, jarosite and amorphous materials were noticed using Fourier transform infrared spectroscopy, Raman spectroscopy and X‐ray diffraction. In addition, mineralized microbial structures were also observed as significant constituents of the corrosion products. However, there were significant differences between samples from the two shipwrecks including porosity, distribution and volume percent of the corrosion products components. The mechanism of different corrosion products formation was proposed and discussed in detail.     

An ultra‐sulfur Hastelloy alloy C‐4

The effect of sulfur on solidification‐segregation and corrosion resistant properties of Hastelloy C‐4 corrosion‐resistant alloy was studied. It was found that strict controlling the content of sulfur can reduce the width and temperature interval of the solid‐liquid biphase region and the segregation degree of the alloy, resulting in a higher corrosion resistance. An improved low segregation Hastelloy C‐4 corrosion resistant alloy was developed.     

Thermo‐mechanical fatigue – the route to standardisation (“TMF‐Standard” project)

Thermo‐mechanical fatigue (TMF) data are needed for dimensioning of safety‐critical parts, e.g. in power generation and in transportation by air, rail and road, and for designing of components, which operate at higher levels of efficiency and safety for longer periods of time. However, the current lack of a validated international standard for TMF leads to non‐reproducibility of TMF data with negative implications on the design and economy of operation of many components. While a preliminary draft TMF standard has been written under the auspices of the International Standards Organisation (ISO), the “TMF‐STANDARD” project addresses this issue at the European level, within the GROWTH programme of Framework Programme 5 funded by the European Commission. The R&D work in the TMF‐Standard project has been started with the preparation of an inventory of institutions in the EU and the pre‐accession states that perform TMF testing, and the testing methods and procedures which they apply. Afterwards, extensive pre‐normative testing work has been carried out, the results of which have been considered in the drafting of a preliminary Code‐of‐Practice (CoP) that forms the base for the current validation round robin testing. The results of the validation tests are going to be subjected to statistical analysis, in order to substantiate the formulation of a validated CoP on strain‐controlled TMF testing. The present paper summarizes the main objectives and achievements obtained so far within the TMF‐Standard project, and gives an outlook on the further activities of the project.     

Sulfate‐reducing bacteria‐assisted hydrogen‐induced stress cracking of 2205 duplex stainless steels

The paper presents the results of a laboratory investigation of the microbiologically assisted hydrogen‐induced stress cracking (HISC) of 2,205 duplex stainless steel (DSS). The testing of susceptibility toward HISC was performed with two different methods. Precharged in sulfate‐reducing bacteria (SRB), inoculated medium samples were subjected to slow strain‐rate testing in artificial seawater. In situ constant load tests were performed directly in SRB‐inoculated medium under hydrogen charging at 70% of the ultimate tensile strength. Samples tested in the biotic (SRB) conditions showed a considerable loss of ductility as compared to those tested in sterile conditions. Quantitative characteristics of fracture surfaces indicated increased susceptibility to HISC of biotic samples, therefore, suggesting a role of SRB in promoting hydrogen damage of DSS.     

Corrosion characteristics of the wrought Ni‐Cr‐Mo alloys

This paper concerns the wrought, nickel‐chromium‐molybdenum (Ni‐Cr‐Mo) alloys, a family of materials with a long history of use in the chemical process industries. Their attributes include resistance to the halogen acids and resistance to pitting, crevice attack, and stress corrosion cracking in hot, halide salt solutions. The purpose of this paper is to characterize the performance of the Ni‐Cr‐Mo alloys in several key chemicals, using iso‐corrosion diagrams. These indicate the expected corrosion rates over wide ranges of concentration and temperature. Furthermore, the differences between individual Ni‐Cr‐Mo alloys, and their behavior relative to the stainless steels are defined. The data indicate benefits of both a high chromium content and a copper addition, as used in Hastelloy® C‐2000® alloy.     

Oxidation behaviour of Fe‐Cr‐Al alloys during resistance and furnace heating

The behaviour of thin Fe‐Cr‐Al heating element strips was investigated with respect to the oxidation limited life times and geometrical changes during resistance and furnace heating. For this purpose, isothermal and cyclic oxidation tests varying in their total exposure time and cycle duration were performed in the temperature range 1050–1200 °C. Specimens subjected to rapid cyclic, resistance heating revealed shorter life times than calculated for specimens subjected to isothermal exposure. The life times were found to increase with increasing cycle duration and hence decreasing number of cycles for a given time at temperature. This life time decrease is related to an “hour glass” waviness of the specimens, which develops during prolonged thermal cycling. The development of this plastic deformation also occurred during furnace heated, thermal cycling tests. A two‐step mechanism is introduced combining an oxidation kinetics related time to the onset of significant waviness with an enhancement of this waviness as a result of a ratcheting effect. The latter seems to strongly depend on the number of cycles and on the plastic deformation generated during each cycle rather than on the total time at temperature. The development of an “hour glass” waviness leads to an enhanced aluminium depletion due to an increase of the specimen surface area. Additional deformation phenomena like “hot tube” or “corkscrew” behaviour occur during the resistance heating tests. These are related to a temperature gradient that develops over the specimen width due to the poor aspect ratio of the specimens.     

Correction of chloride threshold concentration and time‐to‐corrosion due to reinforcement presence

Reinforcement presence affecting corrosion threshold concentration, C_t, determination and time‐to‐corrosion, T_i, has been investigated. Elevated C_t and decreased T_i due to reinforcement physical obstruction on the path of chloride ingression into concrete has been examined with finite element modeling. Results indicated that reinforcement with larger size, better corrosion resistance, less cover thickness, or a more flat leading edge causes more pronounced T_i reduction. Experimental results exposed aggregate content discrepancy within reinforced bar vicinity zone. According to this finding, a multi‐shell chloride diffusion model, in which specific chloride ion diffusivity in each shell surrounding bar presents, is proposed. The C_t results of proposed model are discussed along with those acquired from traditional one‐dimensional model, in which chloride diffusion follows Fick's second law without considering reinforcement presence, and two‐dimensional model with the effect of reinforcement physical obstruction regarded.