PSI - Issue 16

Oleksiy Nemchuk et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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246 Peer- review under responsibility of the 6th International Conference “Fracture Mechanics of Materials and Structural Integrity” organizers Oleksiy Nemchuk et al. / Procedia Structural Integrity 16 (2019) 245–251

Keywords: portal crane; long-term operation; degradation of mechanical and electrochemical properties ; delamination

1. Introduction

Long-term service of steel structures causes a deterioration of the initial mechanical properties of metal and, therefore, decreases their workability, as shown by Gredil (2008), Kharchenko et al. (2014), Meshkov et al. (2015), Student et al. (2018). Sea portal cranes are operated in the regime of intensive cyclic loading that leads to exhaustion of steels plasticity (Pustovoi and Reshchenko (2013), Nemchuk (2018)). Therefore these structures subject to considerable degradation which reveals itself firstly in a decrease of brittle fracture resistance. However not only mechanical loading should be taken into account during consideration of factors of operational degradation of see port installations steels. Usually marine atmosphere is considered as an aggressive environment only from the point of high corrosion rates of carbon and low alloyed steels due to their insufficient corrosion protection. However some authors, e.g. Kushida (2003) and Tsuru et al. (2005) suggested that atmospheric corrosion is the fact or of steel’s hydrogenation that could lead to its hydrogen embrittlement. This not only facilitates fatigue crack growth but also promotes intensive operational degradation of mechanical properties associated with the resistance of metal to brittle fracture. It is concerned with a development of dissipated damaging at nano- and microlevel under combined action of operational stresses and hydrogen. The main units of portal cranes are manufactured from rolled steel sheets which could be susceptible to delamination along under certain conditions, as shown by Teliovich et al. (2008) and Dolzhenko et al. (2018). A pronounced macrodelamination was also revealed by Nykyforchyn et al. (2017) and Zvirko et al. (2018) in long term operated pipeline steels, manufactured from rolled steel. This phenomenon is concerned, on the one hand, with operational degradation of steel’s mechanical properties, and, on the other hand, with hydrogenation of a pipe wall (Zvirko et al., 2017). If hydrogenating ability of atmospheric corrosion is admitted, then for steel sheets of portal cranes it also could manifest itself in lamination between fibres along rolling direction. Teliovich et al. (2008) noted that crack growth resistance of a rolled steel as one of the parameters of brittle fracture resistance, is susceptible not only to steel hydrogenation, but also to the texture of a rolled metal. Recently the electrochemical approach has been applied by Pustovoi et al. (2015), Zvirko (2017), Nykyforchyn et al. (2018) to the assessment of operational degradation of structural steels since certain electrochemical parameters were found to be sensitive to changes in the metal state in a course of its operation. This approach has been (could be?) used also for diagnostics of operational degradation of portal cranes steel. In this paper, metal state of a number of portal crane units after its long term service was analyzed on the basis of complex of mechanical, electrochemical and materials science approaches. The ob ject of the investigation is 33 year operated see portal crane “Sokol” made by “ Kranbau Eberswalde ”. Several characteristic units of the crane are distinguished (Fig. 1a) which have fabricated from rolled steel sheets of different thickness t , namely: the lower shelf of a jib ( t = 16 mm), the back shelf of a boom (12 mm), upper shelf of movable counterweight (10 mm), right side of the column, bracket area (10 mm), back side of the column above the machine deck (25 mm). Two different fragments are chosen on each unit finally having 10 types of metal samples with different operational stress levels. For the tested metal fragments, the stress range Δσ e are measured (determined) on the surface of rolled steel sheets under loading of the crane close to the operational stresses . It should be noted that the parameter Δσ e reflects only the changes in the stress state caused by the crane loading, and does not take into account stresses due to the weight of certain units. Therefore, these data are no indication of significant loading non-uniformity of different structural elements of the crane. However, when the operational degradation phenomenon is under consideration, just the parameter Δσ e is essential as a factor of plasticity exhaustion. Additionally, the investigation of mechanical properties of rolled steel sheets subjected to prolonged 2. Object, materials and methods