Volume 62 (2018): Edizione 4 (December 2018)

The paper deals with the mechanical properties of steel gas pipeline DN 500 after more than 40 years of operation. Mechanical properties of the pipeline were established by a tensile test at an ambient temperature according to the standard EN ISO 6892-1. The resistance of the pipeline against brittle failure was evaluated by using Charpy impact test according to EN 10045-1. The character of fracture surface after the Charpy test was analysed by using scanning electron microscopy. A high proportion of transcrystalline cleavage was a characteristic feature of fracture surfaces. Mechanical characteristics obtained by static tensile testing were compared with the values obtained from steel manufacturer. Higher elongation was observed in a parallel direction compared to the perpendicular direction to the axis of the pipe. The observed anisotropy of properties was related to the distribution of inclusions in the direction of the deformation of the steel sheets used for the pipeline construction.

In the modern systems of transportation of oil, gas and condensate, in the units of regasification of liquefied natural gas, two-phase flows play an increasingly important role in technological equipment used in the chemical and oil refining industry, power engineering and other industries. All available studies on the formation of gas hydrates were mainly focused on their ability to clog pipes along their entire length. While their ability to cause (initiate) corrosion remains virtually unexplored. Therefore, to increase the efficiency of industrial pipelines it is necessary to study the joint effect of hydration formation and stresses of friction on corrosion of the pipeline. The mathematical model of pipeline corrosion has been further developed by considering the influence of the gas hydrate. The influence of pressure, temperature on the speed of corrosion processes is estimated and it is shown that under the most unfavorable conditions the corrosion rate under the action of gas hydrates can increase several times.

This article presents a detail comparison of the thermal stability of the new magnesium phosphate (newberyite – MgHPO₄·3H₂O) coating with a conventional coating of zinc phosphate (hopeite – Zn₃(PO₄)₂·4H₂O). It was confirmed that dehydration of zinc phosphate (hopeite) occurs gradually (dehydration start temperature: 115 °C). The start of magnesium phosphate (newberyite) dehydration is indeed shifted to somewhat higher temperatures (about 125 °C) but the dehydration has an intense jump character. When using magnesium phosphate (newberyite) coating for further surface treatment at higher temperatures, dehydration of the coating can result in reduction of the adhesion between the phosphate/primer coatings. Under these conditions, it is recommended to use a coating of conventional zinc phosphate (hopeite) or manganese phosphate (hurealite).

Interaction of mineral solutions with solid wood leads to saturation of the wood matrix, then to the deposition of mineral particles and eventually to reaction with wood components. In this way a partially or fully mineralized wood occurs in natural or artificial conditions, whose physical-mechanical properties are influenced by the retention and by the character of the solution. Targeted application of organosilanes is based on a similar principle that reduces the intake of liquid water and thus leads to an increase in durability, however, it also causes wood corrosion and consequent decrease in mechanical parameters. In this study, penetration of commercial organosilanes-based product Lukofob 39 into solid wood was described in order to determine the extent of the mineralized part into which the solution penetrated. In this case, characteristic mineral deposits are formed in the wood matrix and its quantification by thermal analysis can be advantageously used to describe the penetration of the solution. Based on the analyses of specific samples taken from primary specimens with different exposure times in the solution, it can be stated that with the increasing exposition time the penetration depth of the solution as well as the amount of mineral deposits increase. The shifts on the thermal analysis curves also show the corrosion effects of Lukofob 39 on the basic components of wood.

Main factors affecting the corrosivity of water in water treatment plants and water towers and other storage facilities, observed types of corrosion degradation of stainless steel and the effect of manufacturing and surface treatment on their corrosion resistance are discussed. A list of stainless steel grades currently used in the field of treatment, transport and storage of drinking water is given together with some other suitable ones. Based on literature resources, optimal stainless steel grades are recommended as a function of water composition and treatment method.