Volume 62 (2018): Edizione 3 (July 2018)

The basic regularities in deformation and fracture of pipe steel X65 are revealed by testing specimens from the pipe fragment cut during the repair of the “Soyuz” gas main after 30 years of operation. It is shown that the pipe steel slightly changes its properties when the gas main is operated under the influence of working stresses and environmental factors. Structural degradation and micro-defects accumulated in the pipe wall were scattered, indicating that the material retains sufficient plasticity that allows it to resist fracture processes and the nucleation of macrocracks.

Generally, organic coatings which contain zinc ferrites are able to protect metal substrate, most often low-carbon steel, by inhibition mechanism. Conductive polymers are using a system of conjugated double-bonds to transfer a charge over the chain thereby providing their own electrical conductivity in the organic coatings. The charge from the chain in combination with the iron substrate generates electrons to the formation of passivation products on the surface of paint film. This paper is focused on combination of zinc ferrite with conductive polymer and using of synergic effect of these two components. The organic coatings were formulated from hematite and specularite on pigments concentration line 5, 10, 20 and 25 wt.% for better recognizing of the effectiveness of zinc ferrite component. The content of the conductive polymer was consistently set at 3 wt.% in each organic coating. A solvent-based epoxy-ester resin was used as a binder. The physico-mechanical and corrosion tests were performed for all samples. The corrosion signs were evaluated on the surface of coating and also on the surface of metal substrate. In the end, the efficiency was compared alone zinc ferrite and alone polymers and also their combinations.

High sensitivity of lead to organic compounds leads to degradation of historical lead objects stored in the depositories of museums or archives. High concentration of organic compounds in the atmosphere of depositories is caused by degradation of organic materials (wood, glue, leather, paper). Organic materials are stored together with lead objects or they are used as a packaging material. This study was aimed on the influence of packaging material properties to aggressiveness towards lead with different state of surface by the resistometric method. The results showed that aggressiveness of packaging material is determined by a complex influence of material properties. The presence of corrosion products on the lead surface significantly increases its sensitivity to organic compounds.

Aluminium alloy AA5083 is prone to intergranular corrosion in marine environments. In an attempt to reduce the intergranular corrosion, AA5083 was subjected to friction stir processing (FSP). The FSP experimental trials were conducted as per face-centered central composite design with three levels of variation in FSP process parameters viz. tool rotation speed (TRS), tool traverse speed (TTS) and tool shoulder diameter (SD). Intergranular corrosion susceptibility of the processed specimens was assessed by performing nitric acid mass loss test. The mass loss of the specimens was correlated with the intergranular corrosion susceptibility as per the standard ASTM G67-13. The experimental results indicate that FSP had significantly reduced the intergranular corrosion susceptibility of the AA5083 alloy. Soft computing techniques namely Artificial Neural Network, Mamdani Fuzzy system, and Sugeno Fuzzy system were used to predict the intergranular corrosion (IGC) susceptibility (mass loss) of the friction stir processed specimens. Among the developed models, Sugeno fuzzy system displayed minimum percentage error in prediction. So Sugeno fuzzy system was used to analyze the effect of friction stir processing process parameters on the IGC of the processed specimens. The results suggest that stir processing of AA5083 at a TRS of 1300 rpm, TTS of 60 mm/min and SD of 21 mm would make the alloy least susceptible to intergranular corrosion.

The influence of deformation on electrochemical properties of Q235 steel is studied. The uni-axial tension of the steel is conducted on universal testing machine to get a series of strain, 0.07%, 6%, 11% and 24%, respectively. The deformation process for strain of 0.07% is controlled by load, and the others are controlled by displacement correspondingly. Afterward, the tests of potentiodynamic polarization and electrochemical impedance spectroscopy are conducted for the deformed steel in 0.01 mol.dm⁻³ NaCl solution. The results showed that plastic deformation leads to crystalline grains refine and elongate, and crystalline boundary increases, it induces more corrosive possibility and lower corrosive resistance; the corrosion potential of Q235 steel becomes more negative with the increase of deformation amount, and the corrosion current density increases with the amount of deformation; the corrosion resistance decrease with the increase of deformation seriously.