Volume 38, Issue 6

The state of art in alternating current (AC)-induced corrosion in pipelines is reviewed. Growing pipeline networks and their co-location with high-voltage (HV) transmission networks have brought into focus the issue of induced AC corrosion on the pipeline networks. Induced AC corrosion may quickly and severely affect the integrity of pipeline networks, especially considering that a number of such pipelines are transporting huge quantities of hazardous fluids. Any breach in pipeline integrity due to AC corrosion may result in disastrous consequences. In the last 30 years, it has been established that the induced AC corrosion can affect the buried pipeline integrity severely. During operations, the resistive as well as inductive coupling with transmission lines pose a significant risk of pipeline corrosion. The literature is reviewed to put together various issues and factors responsible for AC-induced corrosion in pipelines. The various publications on induced AC corrosion are reviewed to identify characteristics of AC-induced corrosion and major factors that determine the severity and impact of AC-induced corrosion. The areas have been identified wherein scope exists for additional studies on AC corrosion.

Twinning-induced plasticity (TWIP) steels are increasingly receiving wide attention for automotive applications due to their outstanding combination of ductility and strength, which can largely be attributed to the strain hardening effect, formation of mechanical twins during straining, and the presence of manganese (Mn) as an alloying element. However, the premature cracking and sudden failure frequently experienced by the TWIP steels under the combined action of tensile stress and corrosion environment remain a challenge for many material scientists and experts up till now. Driven by this challenge, an overview of the stress corrosion cracking (SCC) susceptibility of high-Mn TWIP steels (under the action of both mechanical loading and corrosion reaction) is presented. The SCC susceptibility of the high-Mn TWIP steels is specifically sensitive to hydrogen embrittlement, which is a major factor influencing the SCC behavior, and is a function of the hydrogen content, lattice-defect density and strength level. Besides, the corrosion susceptibility to hydrogen embrittlement may be reduced by suppressing the martensite in the TWIP steels by carbon additions. This review further discusses in detail the precipitation strengthening mechanisms as well as the corrosion behavior of TWIP steel by mechanism.

One of the promising applications of magnesium and magnesium alloys is their use as biodegradable implants in biomedical applications. The pH around an orthopedic implant greatly affects the degradation kinetics of biodegradable Mg–Ca alloys. At the location of a fracture, local pH changes, and this has to be considered in the optimization of implant materials. In this study, the effect of the pH of a physiological buffer on degradation of a Mg–0.8Ca alloy was studied. The pH of Hank’s balanced salt solution (HBSS) was adjusted to 1.8, 5.3 and 8.1. Degradation of a Mg–0.8Ca implant was tested using immersion test and electrochemical techniques. Immersion tests revealed an initial weight gain for all samples followed by weight loss at extended immersion time. Weight gain was highest at acidic pH (1.8) and lowest at alkaline pH (8.1). This was in agreement with results from electrochemical polarization tests where the degradation rate was highest (7.29 ± 2.2 mm/year) at pH 1.8 and lowest (0.31 ± 0.06 mm/year) in alkaline medium of pH 8.1. The pH of all HBSS buffers except the most acidic (pH 1.8) reached a steady state of ∼pH 10 at the end of the two-month immersion period, independent of the initial pH of the solution. Corrosion products formed on the sample surfaces were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and X-ray diffractometry (XRD), revealing the formation of magnesium and calcium phosphates with distinct morphologies that were different for each of the pH conditions. Thus, pH of physiological buffers has a significant effect on the degradation and corrosion of Mg–Ca alloys used for biomedical applications.

This study reports a facile method to prepare silica-coated graphene oxide nanoflakes (SiO 2 –GO). Results of X-ray diffraction analysis, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and atomic force microscopy reveal that silica was successfully coated on the GO flakes. The effect of SiO 2 –GO nanosheets on the corrosion protection and barrier performance of the epoxy coating was investigated in this work. Results indicate that the mechanical properties of all coatings added with GO and SiO 2 –GO were significantly improved. Furthermore, electrochemical impedance and Tafer polarisation curves showed that added 0.5 wt% SiO 2 –GO nanoflakes into zinc-rich epoxy coating could greatly improve the anti-corrosion performance of the sample, and the corrosion protection efficiency increased from 67.01 to 99.58%.

The relatively limited data for the corrosion and pitting of high nickel alloys are reviewed herein and time-dependent trends developed for exposures in marine and atmospheric environments. Data sets for average or ‘uniform’ corrosion losses that are sufficiently extensive show topological consistency with the bimodal functional model previously observed for steels and various copper-nickel and aluminum alloys. Trends for localized corrosion (pit or crevice depth) plateau after earlier rapid growth over several years. The present observations add support to the concept that there is a change in corrosion behavior with extended temporal exposure and that this is generally consistent for many alloys. They also reinforce that shorter-term observations of maximum corrosion or pit depth usually is unsuited for extrapolation to, and prediction of, longer-term corrosion as typically important for practical infrastructure applications.

The effect of small amounts of chalcogen alloying elements (S, Se and Te) on the oxidation resistance (OR) of Cu has been investigated at 300–800 °C in 0.1 MPa oxygen atmospheres. Compared to pure copper, the addition of S, Se and Te could effectively improve the OR below 600 °C mainly owing to the chalcogen-element inclusions which hinder the diffusion of Cu. However, it becomes weak above 800 °C. In contrast, the failure at 800 °C is associated with the absence of those inclusions. The results are discussed in detail by the thermodynamic methods.