Electrochemical Method for the Diagnostics of Degradation of Steels of Marine Portal Cranes
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ELECTROCHEMICAL METHOD FOR THE DIAGNOSTICS OF DEGRADATION OF STEELS OF MARINE PORTAL CRANES O. O. Nemchuk1, 2 and O. I. Zvirko3
UDC 621.875.5:620.193
We develop an electrochemical method aimed at the evaluation of in-service degradation of the mechanical properties of rolled steels of the frames of marine portal cranes. The regularities of decrease in the impact toughness of steels and their polarization resistance are analyzed. The correlation between these parameters forms a basis for the development of a nondestructive method aimed at prediction of the state of metal according to its brittle-fracture resistance. A series of engineering solutions is proposed for the practical realization of this method. Keywords: reloading equipment, rolled steel, in-service degradation, impact toughness, electrochemical method.
Introduction The serviceability and service life of portal cranes are determined by the technical state of their metal structures made of rolled steels. Long-term operation worsens the mechanical properties of these carbon and lowalloy steels. However, the characteristics of brittle-fracture resistance deteriorate most intensely [1–3], which increases the hazard of uncontrolled failures of these structures. In general, the discovered features of degradation of the rolled steels of portal cranes agree with the regularities of the in-service loss of physicomechanical properties of structural steels, including pipe steels made of sheet rolled steels for the oil-and-gas complex [4–8]. These steels are characterized by the dependence of their mechanical characteristics on the direction of cutting of tested specimens relative to the direction of rolling, as well as by the high sensitivity of the characteristics of in-service degradation to the texture of the metal [9–11]. This is explained by the facilitated formation of microdelaminations between the matrix and elongated rolled nonmetallic inclusions in the process of operation [11, 12]. The marine portal cranes operate under the conditions of intense cyclic loading. Therefore, it is possible to assume that just this factor is responsible for the decrease in the brittle-fracture resistance of steels. However, in recent years, the action of marine atmosphere is regarded as the cause of hydrogenation of these structures [13], which increases the degree of damage in the bulk of the metal and, hence, intensifies the process of degradation of the mechanical characteristics [14, 15]. On the other hand, the destructive role played by hydrogen in the formation of microdelaminations in the direction of rolling of steel is obvious [16]. Therefore, it can be expected that the cyclically deformed metal of cranes may lose its initial properties as a result of in-service hydrogenation. For the analysis of the in-service degradation of the steels of portal cranes, it is reasonable to apply nondestructive methods of diagnostics. As a promising procedure, we can mention the so-called electrochemical (EC) method 1 2 3
Odesa National Marine University, Odesa, Ukraine. Correspo
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