Corrosion Engineering,Science and Technology: The International Journal of Corrosion Processes and Corrosion Control

In order to separate the effects of a specific microbial species (Pseudomonas) in sea water on carbon steel, a comparative study of the corrosion and mechanical properties of AISI 1045 carbon steel in natural sea water, sterile sea water and Pseudomonas inoculated sea water was carried out using tensile testing, mass loss experiments and microscopy. The results of mass loss showed that the corrosion rate of the specimens in the single Pseudomonas system was faster than that in sterile sea water but slower than in natural sea water. Microscopy revealed that a loose corrosion product layer formed on the surface of carbon steel, and micropitting corrosion occurred underneath the corrosion product. Energy dispersive X-ray analysis of this deposit indicated that iron and oxygen were the main components, and a large amount of carbon, which most likely originated from the bacteria and its exopolymer, could also be detected. The tensile strength of carbon steel was reduced by the action of Pseudomonas, but hydrogen embrittlement was not found.

When carbon steel is subjected to atmospheric corrosion, the surface texture of the base metal becomes rougher due to corrosion attack. In this study, three-dimensional surface roughness analysis of the base metal of carbon steel samples exposed outdoors was performed to investigate this aspect of atmospheric corrosion. Corrosion loss was found to depend mainly on the number of days of exposure, the carbon content of the base metal and the core void volume. A high correlation coefficient was obtained, which suggests that analysis of surface texture can also be used as a means for determining atmospheric corrosion degradation.

Nitrocarburising is a well known process developed to improve superficial hardness and wear resistance of steels; a subsequent post-oxidation step is often useful to enhance the corrosion resistance. In this work, an additional step was evaluated: nitrocarburised and post-oxidised parts were impregnated in lubricant oil in order to improve their wear and corrosion resistance. The effectiveness of this new treatment, in terms of corrosion resistance, was assessed for two steels, 20MnCr5 and 42CrMo4, using two different oils. The results obtained from corrosion tests show that the impregnation treatment increases the corrosion resistance, in both acidic and chlorurated media.

The ASME AS-240TP-316L stainless steel in the form of a sheet 3 mm in thickness and the ASTM SA-516 grade 60N steel substrate are joined by explosion cladding. The objective of this paper is to evaluate the electrochemical behaviour of a cladding plate of carbon–manganese steel and stainless steel 316L when compared to non-cladding plate 316L steel. The effect of the cladding process on the corrosion resistance was evaluated in a medium of aqueous solution of sulphuric acid. Anodic potentiodynamic polarisation curves were obtained to study the passivation behaviour of the cladding plate. Electrochemical impedance spectroscopy was performed to elucidate the corrosion mechanism of the cladding plate. The non-cladding ASME AS-240 TP-316L steel showed a higher corrosion potential, a lower passivation current density and a higher polarisation resistance, exhibiting a higher corrosion resistance than cladding 316L steel.

The kinetics of carbide free layer formation in a process heater tube made of Fe–Ni–Cr austenitic steel during high temperature service exposure has been studied. An integrated scanning electron microscopy–energy dispersive spectroscopy–electron backscatter diffraction system was used for microstructural and compositional analysis of the investigated alloy tubes. A diffusion based model has been proposed to estimate the surface temperatures based on the widths of the respective carbide free layers. The model would be useful to predict the chromium concentration profiles at various times to prevent catastrophic failure of the material.

The rust layer formed on carbon steel after 1 year exposure to Qinghai salt lake atmosphere was characterised by the following complementary techniques: X-ray diffraction, infrared transmission spectroscopy, scanning electron microscopy and energy dispersive X-ray. The crystalline components of the rust layers consisted primarily of β-FeOOH, γ-FeOOH and iowaite [Mg₄Fe(OH)₈OCl.4H₂O]. δ-FeOOH, ferrihydrite and amorphous rust were also found. Most corrosion products were contained in the inner layer, while foreign particles were mainly distributed in the outer layer. Energy dispersive X-ray and linear scanning results indicated that Cl and Mg elements were rich in the whole rust layer, in which case they will have had an important influence on the corrosion process of carbon steel in the salt lake atmospheric conditions.

316L stainless steel in environments with high chlorine content suffers localised corrosion. In this study, hybrid sol–gel based anticorrosive protective coatings were developed and deposited on 316L stainless steel substrates. The effect of incorporating different compositions of silica in polymethylmethacrylate (PMMA) sol–gel coatings on the aqueous corrosion resistance of 316L stainless steel in 5 wt-% aqueous NaCl electrolyte was evaluated. Analysis shows that the coatings are uniform, crack free and well bonded to the substrate. Organic–inorganic phases exhibited good compatibility. In addition, the adhesion strength of PMMA–silica hybrid coatings to the surface was found to be higher than the pure system PMMA coating. The anticorrosive properties were evaluated by electrochemical noise and visual test according to ASTM D610 (rusting degree) and ASTM D714 (blistering degree). Coatings with 75 wt-%PMMA–25 wt-% silica possessed the best corrosion performance among the coating specimens.

The present work investigated the characteristics and mechanism of corrosion product films and the corrosion rates of standard and microalloyed ‘antisulphur’ steels in H₂S/CO₂ containing oilfield environments at various temperatures. The resistance of antisulphur steels to CO₂/H₂S corrosion was highlighted to provide information for material selection in sour oilfields. The corrosion rates were calculated by weight loss carried out in a high temperature and high pressure autoclave. Meanwhile, the surface morphologies of corrosion product films were studied using scanning electron microscopy with energy dispersive spectrometry. The results indicated that the corrosion product films became more protective, and the corrosion rates of chromium containing antisulphur steels substantially decreased, with increasing temperature. H₂S corrosion dominated the corrosion process under the test conditions. In addition, antisulphur steels P110S and N80SS were found to be superior to common steel P110 in CO₂/H₂S corrosion environments especially at temperatures below 120°C. A model for corrosion product film formation and damage was produced.

A composite structure comprising high strength titanium (Ti) alloy core and a high surface area pure Ti coating can be ideal for implant applications. In this work, the corrosion behaviour of pure Ti coatings composed of porous top layer (∼100 μm) and dense bottom layer (∼500 μm) obtained by cold spray method has been investigated. The porous top layer satisfies the high surface area requirement for the implant and the dense bottom layer ensures a good corrosion protection of the substrate and also good bond strength. In order to further improve the corrosion and mechanical property of cold sprayed Ti coatings, heat treatment (850°C for 5 h) was applied. Electrochemical potentiodynamic and electrochemical impedance spectroscopy (EIS) measurements were used to characterise the electrochemical corrosion behaviour of the cold sprayed Ti coatings in Hanks’ solution. For comparison, the corrosion and mechanical properties of annealed and un-annealed wrought Ti substrates were also investigated. Our results showed that the as sprayed Ti coatings exhibited a relatively lower corrosion resistance than those for pure Ti substrate. However, post-spray heat treatment improved the corrosion resistance to a level close to that of the bulk material. Furthermore, EIS studies revealed that the newly formed dense and structurally stable oxide layer on the surface of the coating during potentiodynamic scanning was beneficial to the corrosion behaviour.

The impacts of tensile stress on the non-linear electrodissolution behaviour of carbon steel were investigated in an aqueous solution of 5M phosphoric acid. The frequency of the current oscillations within the transpassive potential region increases slightly when the elastic deformation was introduced to the electrode by applying tensile stress, but the oscillatory mode is essentially unchanged. The elastic deformation could induce the current oscillations in the passive potential region that was not observed on stress free state. This fact suggests that the tensile stress can reduce the stability of passive film. Immediately after the tensile stress exceeds the yield strength, the oscillatory mode changes into a chaotic one with high frequency and recovers the original state gradually. This phenomenon resembles the consequence due to the injection chloride to the electrode/electrolyte interface and implies that the plastic deformation may result in the formation of more defective passive films.