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

The inhibitive action and adsorption behaviour of pomegranate leave extract (PGLE) on corrosion of carbon steel in 1M HCl solution at 293-333 K was investigated through chemical (weight loss measurements), electrochemical (potentiodynamic polarisation) and surface analysis [Fourier transform infrared (FTIR) and X-ray diffraction (XRD)] methods. Results obtained shows that the adsorption of PGLE molecules on the C steel surface obeyed the Langmuir adsorption isotherm and acts as mixed type inhibitor for C steel in 1M HCl with anodic as its dominant inhibitor at high concentration. The inhibitory property of the extract was discussed in terms of the mechanism by which its components adsorb onto the C steel surface. Activation energy of corrosion and other thermodynamic parameters such as standard free energy, standard enthalpy and standard entropy of the adsorption process as well as FTIR and XRD examinations of the electrode surface revealed that the corrosion inhibition of C steel in 1M HCl in the presence of PGLE is mainly controlled by the physical adsorption process.

This paper presents a novel system to protect the reinforced steels from corrosion in the underwater zone by removal of the dissolved oxygen. The factors that influence the corrosion processes such as the pH value and the dissolved oxygen concentration were monitored for 48 hours in this system. And the effects of the dissolved oxygen consumption under different output currents and flow rates were compared. Then the corrosion rate of the steels under protection using this system was monitored for 100 hours. At last, a contrastive analysis was conducted between the scanning electron microscope surface morphologies of two bare steel specimens immersed in the underwater zone for 30 days with and without protection. The results showed that the pH value would increase and the dissolved oxygen concentration would decrease in the novel system, which is beneficial to protect the steels. The dissolved oxygen concentration could be reduced to a low value when the output current and the flow rate are appropriate. Steels could be well protected in the system presented in the paper.

Flux-cored arc welding (FCAW) is an automatic welding process widely employed to join duplex stainless steel (DSS) structures in industrial plants because of its high productivity. However, when multiple passes are performed, this process can lead to the formation of non-metallic inclusions originating from the slag in the fusion zone. In this case, the welded joint can be repaired using the same welding process. Some regions next to the heat-affected zone are not removed during the repairing operation. Thus, these regions are subjected to repeated welding cycles and to a high heat input, which can cause microstructural alteration that impairs the corrosion resistance of the welded material. The aim of this work was to study the corrosion resistance of 2304 DSS plates joined using the FCAW process and repaired using the same process. The influence of the repair procedure on the corrosion resistance of the welded joints was evaluated using potentiodynamic polarisation and chronoamperometric curves, which allow the determination of the critical pitting temperature of the samples. The microstructure obtained after each repair cycle was evaluated using optical microscopy and scanning electron microscopy. The results showed that the corrosion resistance was depressed as the number of repair cycles increased.

The mixtures of hydrochloric acid and hydrogen peroxide were employed as the environmental friendly pickling solution for 430 hot-rolled stainless steel in this study. Increase of HCl concentration accelerates the corrosion rate of base metal, however aggravates the intergranular attack in sole hydrochloric acid solution. Addition of oxidant (H₂O₂) boosts the corrosion potential of stainless steel significantly resulting in the change of electrode action. At high oxidant content (0.6 mol l⁻¹ H₂O₂), a corrosion product film accumulates onto the surface and the corrosion is then governed by the mass-transport at the film/stainless steel interface. The random dissolving of metal ions because of the film leads to brightening of stainless steel surface and the local corrosion is suppressed.

This work studies the influence of various parameters, such as temperature and humidity, fly ash content and chloride concentration, on the relationship between half-cell potential and the corrosion level of rebar in concrete. Results show that the half-cell potential decreases with an increase in temperature under the same corrosion level of rebar, and half-cell potential decreases with an increase in corrosion level of rebar under the same temperature. The half-cell potential decreases with an increase in chloride concentration and increases with an increase in fly ash content when fly ash content is lower than 50% under the same corrosion level of rebar, and the half-cell potential decreases with an increase in the corrosion level of rebar under the same chloride concentration and fly ash content.

The paper reports the results of an experimental research devoted to the study of the damage mechanism of steel in contact with fresh flowing cementitious mixtures. It focuses on the damage caused by both erosion and corrosion. Weight-loss tests, potentiodynamic tests and electrochemical impedance spectroscopy tests were carried out on stationary and rotating cylindrical/disk electrodes, on steels with different hardness, composition and microstructure – ranging from carbon steel to manganese steel and stainless steel. The electrochemical tests were performed in fresh fluid mortar designed to grant sufficient workability retention up to 24 h. The specimens were observed after exposure by means of scanning electron microscope to evaluate damaging morphologies. The effect of rotating speed on damage and corrosion mechanisms is discussed in the present investigation. It was noticed that the corrosion contribution to the total damage was negligible at high rotational speed due to prevailing erosion. The results point out that corrosion rate rises with the rotational speed but it remains determined by the anodic process and re-passivation kinetic of the steel in the alkaline medium, without reaching conditions of oxygen-limiting current density.

In this paper, a ring form electronic resistance (ER) sensor system was developed for the study of under-deposit corrosion (UDC) caused by mineral deposit in pipeline conditions. The corrosion status of different locations along the pipeline circle direction and the galvanic current between the deposit-covered area and the bare steel area were monitored by the conjunction of the ER method and electrochemical noise technique. The performance of inhibitor ethylene diamine tetra methylene phosphonic acid sodium (EDTMPS) on UDC was studied by both the electrochemical method and the ring form ER sensor system. The measurement results demonstrated that the inhomogeneous distribution of the rust layer will cause heterogeneous corrosion patterns in the pipeline. Though EDTMPS showed an excellent inhibition effect for the corrosion of both deposit-covered steel and bare steel in electrochemical tests, it failed for the inhibition of UDC in the pipeline working conditions and serious localised corrosion beneath the sand particle was monitored by the sensor system.

Corrosion behaviour of the liquid-phase sintered SiC ceramics (LPS-SiC) was studied through exploration of weight loss, strength reduction and morphology evolution of the SiC specimens etched in the room-temperature/70°C 6.12 mol/L (20 wt-%) NaOH aqueous solutions. As a comparison, corrosion of the reaction-bonded SiC ceramics (RB-SiC) was also investigated. The results show that corrosions of the SiC specimens mainly contain homogeneous dissolution of the secondary-phase oxides in the LPS-SiC and that of Si in the RB-SiC, and peel-off of the SiC particles, resulting in increase of the surface roughness, weight loss and strength reduction of the SiC ceramics. As dipped in the 70°C NaOH solution, corrosion pores and channels form in the sublayer, leading to rapid increase of weight loss and strength reduction of the LPS-SiC. No matter in the room-temperature or 70°C NaOH solution, the LPS-SiC always has a higher corrosion resistance than the RB-SiC.

In this work, X-ray diffraction and Mössbauer spectroscopy techniques were used to characterise and carry out a comparison of the corrosion products obtained during the pigging activities in two sour-hydrocarbon-transporting pipelines located in the Gulf of Mexico: the first one being a gas pipeline and the other one a crude oil pipeline. The results indicate that for these specific conditions, there are differences between the corrosion products formed in each pipeline. Iron sulphides and oxides were the main corrosion products and their presence is directly related to the operating conditions prevailing in the pipelines as well as to the hydrocarbon quality. As for the sour gas pipeline, higher concentrations of greigite and pyrite were observed, whereas more proportions of magnetite, mackinawite and marcasite were found in the sour crude oil pipeline. The most important parameters in the formation of the different types of corrosion products are the water content, hydrogen sulphide concentration and oxygen presence in the system.