Mária Hagarová

Corrosion Degradation of Steel Pipes in Indirect Cooling Circuit of Gas Cleaning

The paper deals with corrosion damage to steel pipes which were a part of the indirect cooling circuit of gas cleaning. The pipes were made from steel ASTM A106 Gr.B. The outer surface of pipes of the inside part of the circuit was affected by flue gases with mean temperature of approximately 1200 °C. The pipes of the outside part of the circuit were exposed to outer environment with mean temperature of about 25 °C. The cooling water flowing in these pipes had mean temperature of about 20 °C and contained a corrosion inhibitor based on zinc chloride (with addition of hydrochloric acid, phosphoric acid and PBTC). Flow rate of cooling water was 3700 m3/h, its total volume 1500 m3, and the pressure of cooling water was 600 kPa. The achieved thickening of cooling water was N=4. Side filtering was accomplished by a filter DPF 4000. The pipes of the cooling circuit were welded to each other, which initiated stress stimulating development of cracks on the outer surface of pipes in the heat-affected zone, Fig.1. The existing technological conditions resulted in formation of deposits on the outer pipe surfaces. Their presence changed thermal conditions in steel pipes.

Corrosion Characteristics of Transit Pipeline API 5L X60

The paper deals with the determination of corrosion rate to the natural gas pipeline API 5L X60 in Trnava region. Linear polarisation resistance method (exposure time 1 hour) was used for investigation the corrosion rate of exposed samples in the environment (top, middle and lower part of soil excavation and distilled water). The corrosion rate was also determined by measuring the weight loss of the steel samples. The exposure time for the measurement method of the weight loss of metallic materials accounted 120, 288, 528 hours. These outputs helped to identify the most suitable environment for the tested metallic material. Top and middle part of soil excavation was situated in the least aggressive environment. On the other hand, the lower part of soil excavation was situated in the most aggressive environment for API 5L X60.

Some Possibilities of Evaluation of Corrosive Resistance of Metal and Non-Metal Coatings

The study investigated the possibilities of determination of corrosion resistance of metal and non-metal (organic) coatings deposited to steel surface in the corrosion environment. To determine the corrosion rate of metal PVD coating based on Ti, we used the method involving measurement of polarization conductivity. Corrosion resistance of galvanic Ni or Ni-Co coatings was determined by measuring free corrosion potential ESCE (against that of saturated calomel electrode SCE), or by means of potentiodynamic polarization relationships according to Tafel. These methods provided the basic corrosion characteristics: corrosion potential Ecorr, instantaneous corrosion rate jcorr and polarization resistance Rp. Corrosion resistance of organic coating Woerodur, which was applied by pressure spray to the substrate pre-treated in various ways, was tested in a salt-fog environment. After the exposure to the respective environment we evaluated the appearance of coating. The aim of the study was to point out to the availability of methods suitable for evaluation of corrosion resistance of coatings, and to the possibilities of their application under real practical conditions.

Structure Characterisation of Electrodeposited Ni-Co Alloy

This paper is focused to structure characterization of two differently electrodeposited Ni-Co alloys on the copper surface. The chemical composition of the layers was determined by the EDX analysis in the scanning electron microscope. Phase analysis was realized by diffraction in the transmission mode using synchrotron radiation. Diffraction patterns also show the preferred orientation in the coating with saccharine addition.

Properties of Ni-Co Alloy Coating Prepared from Sulphate Bath

The paper deals with nickel – cobalt coatings on the copper substrate prepared by electroplating process. The different Co content in the alloy coating depending on chemical composition of sulphate electrolyte and current density. The microstructure and composition of Ni-Co coating were observed with use of light and scanning electron microscopy. The mechanical properties were determined with use of the test according to EN ISO 6892-1:2009 standard and means of a Vickers microhardness tester. The results showed that under the same bath composition and technological parameters of process the Ni-Co alloy coating exhibited laminated structure. Their strength and hardness of the deposited coatings were higher than those for the Ni coatings.

The Influence of Current Density on Tribological Behavior Ni-Co Electroplated Coatings

Nowadays, more and more scientific studies deal with the formation of electroplating alloy coatings due to the possibility of combination and share content type metal – forming alloy. To produce coatings that fulfil pre-defined specific requirements is possible by a suitable combination of process conditions. The paper deals with the study of tribological properties of Ni-Co coatings that were prepared by electrodeposition technique from sulphate electrolyte on the copper substrate. Effect of current density on the properties of electroplated coatings was determined via a morphology characteristics and micro-hardness of coating′surface. The tribological behaviour of Ni – Co coatings was described by friction coefficient using the pin-on-disc method.

Structural Properties of Ni-Co Electroplated Coatings Studied by X-Ray Micro-Beam

In this article we focused to influence of current density on the structure parameters evaluated by microdiffraction experiment in transmission mode using synchrotron radiation. For this purpose the coatings of Ni-Co alloy were deposited on the Cu substrate using different current densities during the electrodeposition process. The results of the microdiffraction experiment showed the structure uniformity of the coatings along their thickness, as well as changes in the structure parameters depending on the used current density during the deposition process.

Evaluation of Local Mechanical Properties of Thin Coatings Prepared by PVD Evaporation

The contribution deals with evaluation of mechanical properties of thin hard coatings prepared by ARC evaporation on steel substrate K110. In this paper TiN and AlTiCrN are comparatively studied. The thickness of TiN and AlTiCrN coatings was evaluated using the calotest, GDOES and nanohardness was also measured. The results show that AlTiCrN coatings posses higher hardness and Young´s modulus than simple monolayer TiN coatings. The substrate-coating interface was without failures, which confirmed excellent adhesion properties of the system. Due to their specific properties, the coatings appear suitable for use in practical operations.