Band 36, Heft 4

The present manuscript reviews state-of-the art models of hydrogen-assisted cracking (HAC) with potential for application to remaining life prediction of oil and gas components susceptible to various forms of hydrogen embrittlement (HE), namely, hydrogen-induced cracking (HIC), sulfide stress cracking (SSC), and HE-controlled stress corrosion cracking (SCC). Existing continuum models are compared in terms of their ability to predict the threshold stress intensity factor and crack growth rate accounting for the complex couplings between hydrogen transport and accumulation at the fracture process zone, local embrittlement, and subsequent fracture. Emerging multiscale approaches are also discussed, and studies relative to HE in metals and especially steels are presented. Finally, the challenges that hinder the application of existing models to component integrity assessment and remaining life prediction are discussed with respect to identification of model parameters and limitations of the fracture similitude, which paves the way to new directions for further research.

Suitable application of techniques for detection and monitoring of microbiologically influenced corrosion (MIC) is crucial for understanding the mechanisms of the interactions and for selecting inhibition and control approaches. This paper presents a review of the application of electrochemical and surface analytical techniques in studying the MIC process of metals and their alloys. Conventional electrochemical techniques, such as corrosion potential ( E corr ), redox potential, dual-cell technique, polarization curves, electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) analysis, and microelectrode techniques, are discussed, with examples of their use in various MIC studies. Electrochemical quartz crystal microbalance, which is newly used in MIC study, is also discussed. Microscopic techniques [scanning electron microscopy (SEM), environmental SEM (ESEM), atomic force microscopy (AFM), confocal laser microscopy (CLM), confocal laser scanning microscopy (CLSM), confocal Raman microscopy] and spectroscopic analytical methods [Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS)] are also highlighted. This review highlights the heterogeneous characteristics of microbial consortia and use of special techniques to study their probable effects on the metal substrata. The aim of this review is to motivate using a combination of new procedures for research and practical measurement and calculation of the impact of MIC and biofilms on metals and their alloys.

Traditionally, controlling corrosion has been managed by various methods like cathodic protection, process control, reduction of the metal impurity content and application of surface treatment techniques as well as incorporation of suitable alloys. However, the use of corrosion inhibitors has proven to be the easiest and cheapest method for corrosion protection and prevention in acidic media. These inhibitors slow down the corrosion rate and thus prevent economic losses due to metallic corrosion on industrial vessels, equipment or surfaces. Many researchers have recently focused on corrosion prevention methods using organic inhibitors for mild steel in acidic solutions to mimic industrial processes. This paper arranges for an overview of types of corrosion, corrosion process and mainly recent work done on the application of quinolone derivatives as corrosion inhibitors for different metals.

The inhibition efficiency of Atlas cedar essential oil (ACEO) as a green corrosion inhibitor on steel in 1 m hydrochloric acidic was studied. The effects of temperature and the concentration of the ACEO inhibitor on the inhibition efficiency were studied. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to test the performance of the inhibitor. We found that the inhibition efficiency of ACEO exceeded 88% at 1 g/l at 298 K and increased with increasing concentration. The evaluation of activation and thermodynamic parameters reveals that the organic molecules of cedar essential oil and its fractions act by chemical adsorption on the metal surface. The adsorption of the inhibitor on the surface of steel is in a good agreement with the Langmuir adsorption isotherm. Increasing concentration of the corrosion inhibitor enhances the surface coverage and formation of a protective film.

The relationship between the passivation period of Si-containing steel and oxygen concentrations was investigated by conducting the oxidizing experiments employing four different oxygen concentrations on a simultaneous thermal analyzer (STA) at a heating temperature of 1260°C. The results show that the duration of passivation period increased with the increasing oxygen concentration. Moreover, the passivation period occurred at the oxygen concentrations ranging from 2.0 vol.% to 3.0 vol.%, whereas no visible passivation period was observed at the oxygen concentrations ≤1.5 vol.%. In addition, the oxidation mass gain versus time followed a linear relationship before the passivation period, which lasted for about 20 min when the mixed binary atmosphere was introduced into the sample chamber right from the beginning of the heating process.

The effect of soft cations (Na + , K + , NH 4 + ) on the corrosion behavior of carbon steel in chloride (Cl − ) media was investigated using various electrochemical and nonelectrochemical techniques. Data revealed that the corrosion rate is higher in the case of ammonium chloride solution following the order NH 4 + >K + >Na + . The polarization and electrochemical impedance spectroscopy (EIS) measurements indicated a significant influence of cations on both the corrosion rate and the mechanistic reaction pathway of carbon steel dissolution in Cl − media. The EIS measurement showed two time constants in all the cases. Electrical equivalent circuit was employed to model the EIS data. The surface morphology and the corrosion products were also analyzed. It was found that the hydration energy of cations and the initial pH of the solution play a critical role in describing the effect of cations present in Cl − media on carbon steel corrosion.

Physical vapor deposition (PVD) multilayered coatings with titanium nitride and chromium nitride top layers were deposited on UNS S17400 alloy in an attempt to improve the corrosion and corrosion-wear resistance of this stainless steel in corrosive environments. The coatings were produced in an industrial chamber by cathodic arc PVD on heat-treated and mechanically polished stainless steel specimens. The microstructures of the substrates and coatings were characterized by X-ray diffraction and scanning electron microscope equipped with an energy-dispersive X-ray spectroscopy system. To evaluate the corrosion and corrosion-wear resistance, reciprocating-sliding tribometer and electrochemical tests were conducted in 3.5% NaCl solution. The results showed that nitride coatings possess, in general, better corrosion and corrosion-wear resistance compared with bare S17400 substrates. Specimens with CrN top coating revealed a typical compact structure and superior corrosion resistance compared with substrate and TiN top coating. However, the sliding motion damaged the surface with some microcracks on the coating, which act as the diffusion channels for NaCl solution; both TiN and CrN top coats experienced approximately similar behavior in corrosion-wear open-circuit potential testing.