Volume 39, Issue 6

A review of sacrificial Zn–Ni electroplating coatings on high-strength steels is presented. These steels are used for heavy structural applications such as landing gears, etc., that are subjected to high stresses and corrosive environments in service. The electroplating process involving aqueous electrolytes invariably produces hydrogen. The emitted hydrogen can diffuse into substrate steel, contributing to the delayed failures by hydrogen embrittlement. Microstructural inhomogeneities arising from the heat treatments and defects produced during coatings and those inherently present in the steels can trap hydrogen emitted during plating. Dissolved and trapped hydrogen can slowly diffuse to the stress concentrations or crack tips, contributing to the delayed structural failures. Baking after plating helps to eliminate hydrogen to some extent, though it may introduce some thermomechanical stresses at the bimaterial interfaces. This review discusses a) the current state of sacrificial Zn–Ni coatings, b) their protection against corrosion of the substrate, c) the associated hydrogen embrittlement predominately under cyclic loads, and d) recent advances in terms of the compositionally modulated coatings for enhanced protection.

Corrosion is the primary cause of failure of heat exchangers in industry, especially in the oil and petrochemical sector. The modes of failure related to corrosion include erosion corrosion, pitting corrosion, crevice corrosion, grain boundary corrosion, dealloying, galvanic corrosion, stress corrosion cracking, waterside corrosion, uniform corrosion, and microbially induced corrosion. Primary causes of corrosion-related failures were found to be fabrication and welding defects, presence of residual stresses, inappropriate materials selection and design, improper water chemistry/flow and poor choice of filters, presence of corrosive species such Cl − , S x− , O 2 , NH 4 + in water, nonadherence to recommended operating conditions, and noncompliance with standard practices during the shutdown. This article is a review covering only corrosion-related failures in heat exchangers.

Research on corrosion-resistant polymer coatings has attracted scientists in both academia and industry to prevent corrosion-related damage in modern industrial equipment and to extend the working life of industrial metallic surfaces. To achieve realistic applications, diverse methodologies have been designed to magnify the anticorrosion efficiency of these coatings. The current review describes the conventional and advanced methods utilized for the synthesis of corrosion-resistant polymer coatings. The main intent of this review article is to provide an overview of the design and preparation of anticorrosive polymer coatings with important examples. The promising anticorrosion applications of self-healing polymer coatings for metallic materials and alloys are highlighted. The advantage of a superhydrophobic surface to prevent the corrosion of the materials is discussed. A brief discussion over the anticorrosion mechanism of conducting polymer coatings is also provided. Finally, the current challenges and future perspectives to prolong the anticorrosion performance of these coatings are also addressed.

The corrosion performance of a newly developed corrosion-resistant rail steel (U68CuCr) was investigated and compared with that of a normally used high-speed rail steel (U71MnG) by neutral salt spray tests, electrochemical tests, X-ray diffraction analyses, and the scanning vibrating electrode technique. It was found that the weight loss and corrosion rate of U68CuCr were lower than those of U71MnG under the same corrosion conditions. In addition, due to the influence of alloying elements (copper and chromium) in U68CuCr, the rust layer was thicker and denser, resulting in a stronger protective effect. Moreover, U68CuCr had a higher corrosion potential in electrochemical tests. Finally, the dynamic corrosion process of U68CuCr in 2.2% NaCl solution mainly followed a lateral extension of corrosion. Therefore, the corrosion resistance of U68CuCr was better than that of U71MnG in the subsea tunnel environment.

The corrosion behavior and cracking susceptibility of the disbonded coating in the X80 steel pipeline were investigated by different methods. The oxygen content in the trapped solution decreased rapidly with the formation of an airtight disbonded area. The airtight system affected the electrode reaction process, resulting in the inhibition of corrosion in the center of the disbonded area and the more refined surface finish of the sample. The bottom of the disbonded area underwent a relatively intense and accelerated corrosion reaction controlled by the diffusion process. The cracking susceptibility of the X80 steel firstly decreased and then increased in the pointing direction.