Volume 39, Issue 5

Fossil fuels like coal, oil and natural gas are continuously being used for electricity generation. However, combustion of fossil fuels has raised environmental concerns which have forced the world to search for alternative sources of energy like geothermal, solar and biomass energy. Biomass is a carbon-based fuel, readily available in many parts of the world, highly volatile with less sulphur and nitrogen content, its ash possesses the property of absorbing carbon dioxide emissions, co-firing of biomass and coal increases thermal efficiency, it creates employment opportunities and provides a better way of utilization of agricultural waste. However, chlorine species from biomass combustion results in corrosion of boiler tubes at high temperature. In this review, challenges like fouling, agglomeration, gaseous emissions, emission of heavy metals, low heating value, storage and transportation problems and high temperature corrosion have been discussed, which can limit the flexibility, economy and reliability of biomass boilers. Each of these challenges has a relatively satisfactory solution except for hot corrosion, which has been addressed through several approaches with varying success and those approaches have been presented in this review. It is recommended that the implementation of the discussed remedies can surely provide efficient, economical and ecological biomass combustion.

For decades, zinc- and aluminum-based coatings have been considered the best material choice for steel corrosion protection since they may act as a protective barrier and show sacrificial behavior. These coatings are often prepared by galvanizing methods. However, their application by thermal spraying techniques (wire arc spraying, WAS and flame spraying, FS) has been proved as a cost-effective solution for the preparation of long-term corrosion-resistant coatings. This review selectively collects the most relevant information about the application and performance of these two techniques on Zn and Al coatings for corrosion protection. The report summarizes separately the Zn and Al data from the effect of the spraying parameters on coating properties on the one hand, and the results shown in long-term studies carried out in relevant and real exposure conditions, on the other. Finally, this review includes a description and comparison of the most recent advances found out with the novel and emerging spray technique, cold gas spray, for the deposition of Zn and Al coatings for corrosion protection purposes. Nevertheless, the use of this technique has not reached the stage of wide industrial application yet and therefore its long-term performance is unknown, which suggests that there is still room for further development.

This paper presents a research on the corrosion behavior of Ti-15-3 alloy overlapped with aluminized PVC film in salt spray. It was found that severe corrosion occurred on aluminized PVC film in the coupled regions because of crevice corrosion and/or galvanic corrosion whereas Ti-15-3 alloy in the coupled regions experienced minor corrosion. Scanning electron microscope and Energy-dispersive X-ray spectroscopy analyses demonstrated the corrosion products adhered to the surface of Ti-15-3 alloy within the crevice. To evaluate the effect of aluminized PVC film on the crevice corrosion of Ti-15-3 alloy in salt spray condition, it is necessary to compare with the corrosion resistance of Ti-15-3 overlapped with polytetrafluoroethylene (PTFE) in different neutral salt spray. Further, the tests were performed by electrochemical impedance spectroscopy and potentiodynamic polarization. Combining the graphical model, an in-depth understanding of the crevice and galvanic corrosion mechanism of Ti-15-3 alloy overlapped with aluminized PVC film has been revealed.

In order to reveal the corrosion of a ship hull in flowing seawater, which is difficult to study under experimental conditions, a numerical method was adopted. Firstly, the numerical model of seawater flow field around the hull was established and computed, and the hydraulic characteristics of the flow field such as velocity, pressure, and oxygen concentration distribution were got. The distribution of oxygen has a great influence on corrosion. Generally speaking, where the oxygen concentration is higher, the corrosion rate is higher. The results show that the oxygen concentration is higher at the rear of the hull bottom surface. Next, a corrosion model was founded based on the above calculation. Through the calculation of the corrosion model, the mass transfer coefficient and corrosion rate distribution on the hull surface were obtained and the final conclusion was got flow accelerated corrosion (FAC) mechanism was revealed. The conclusion is as follows: Comparatively speaking, the corrosion rate of the middle and rear part of the bottom and the middle part of the sideboard is higher. Generally speaking, the corrosion rate increases with the increase of flow rate.

Anodic protection (AP) is one of the corrosion control methods that has been widely used in the manufacture, storage, and transport of sulfuric acid. The present paper gives a brief review of the history, some applications, and a case study of failure causes and remedial actions of AP in a sulfuric manufacturing plant. The AP system consists of a direct current source, cathodes, reference electrodes, and signal conditioning electronics. In a sulfuric manufacturing plant, for AP of 316L piping (as an anode), platinized titanium (Pt/Ti) and Hastelloy B-2 were used as reference and cathode electrodes, respectively. After seven years of operation of the AP system in the sulfuric acid plant, a section of the protected pipelines has severely corroded. The study of the system showed that the reference electrodes, which were titanium-electroplated with platinum, lost their stability in the acid with the loss of coating and caused overprotection. However, the system could not control the pipe’s potential in the AP situation. In this condition, accelerated corrosion of the cathodes and pipes has also occurred.

The diamond-like carbon (DLC) films were successfully fabricated on the surface of 13Cr super martensitic stainless steel by plasma enhanced chemical vapour deposition, and the microstructure changed with the variation of pulse voltages of the high pulse power supply. The microstructure of the DLC films was characterized by atomic force microscope, and the corrosion behavior of the films in a high Cl − environment was analyzed by open circuit potential, polarization curve and electrochemical impedance spectroscopy. It is found that the substrate corrosion occurred first for the DLC films with open pores, followed by a substrate surface passivation before the final corrosion failure. The DLC film with closed pores can effectively prevent Cl − from attacking the substrate before the corrosion pits formed at the local defects.

The corrosion behavior of duplex stainless steel 2205 DSS and 2507 DSS in simulated flue gas condensate of a waste incineration power plant at 180 °C was compared by micro-area electrochemical testing, surface and weight loss analysis. The results showed that the corrosion resistance of the two stainless steels decreased with the increase of Cl − concentration. After 48 h of corrosion, when the Cl − concentration was not less than 6 g·L −1 , active sites where current density increased suddenly appeared on the surface of 2205 DSS, accompanied by the obvious increase of surface roughness and the weight loss. The lowest Cl − concentration that caused the appearance of active sites on the surface of 2507 DSS was 20 g·L −1 , with less surface corrosion products and lower degree of general corrosion.