# Microscopic Analysis of Structure and Wear for Metallic Materials Using SEM
## 1 Introduction  
Nowadays, metallic materials play a crucial role in a wide range of industrial applications and construction. Their material properties, such as strength, resistance, and thermal conductivity, make them irreplaceable in the production of various components and technical objects (TOs). In this context, it is important to have a deeper understanding of metallic materials so that their potential can be effectively used to prevent unwanted phenomena. The external environment can cause chemical, mechanical, or physical changes in metallic materials, which become initiators of future degradation. The aim of the experimental part of the presented work is to analyze the materials that were used and are used in practice for the assembly of hot water pipes from the Zilina location. The analyses were carried out on an electron microscope SEM. Internal surfaces of pipes from new and hot water heating pipes used for several years were mainly monitored. Attention was paid to wear caused by the flowing medium, mainly the occurrence and progression of corrosion both on the outer and inner surface of the selected pipes and the chemical composition of the applied layers. There are various studies on the corrosion of metallic materials, such as pipes. For example, [PERSON] et al., in an article on the effects of corrosion on the mechanical properties of welded carbon steel pipes, state that using the galvanostatic method, the deepest corroded point between the weld zone andthe base metal region was observed on the samples. This indicates that the corrosion was concentrated due to the difference in the microstructure [1]. Welding is a common method used in the assembly of hot water heating and district heating pipes [2]. In the carbon steel welding process, the heat-affected zone (HAZ) is formed by several microstructures that differ from the base metal [3]. [PERSON] et al. pointed out in the article that standard corrosion phenomena are not sufficient to explain all cases of pipeline failures. The authors performed new metallographic investigations on galvanized steel pipes and on the zinc coating itself. The results showed the frequent occurrence of defects in the welding, such as blisters or cracks, and also in the coating. Cracks were identified in the coating, near the substrate, and sometimes inside the substrate. They also observed important irregularities in the thickness of the coating, with the coatings not meeting the European standard (which specifies a minimum thickness of 55 \(\upmu\)m on the inside of galvanized steel pipes and 28 \(\upmu\)m for welding). Corrosion can also be accelerated by a high level of chlorides and sulfates in water, and an increase in temperature or pH of the water [4]. Currently, there are many types of materials in the heating technology market, which must also be verified according to the quality of the microstructure, which will affect their service life. Three years ago, the replacement of hot-water heating riser pipes in a six-story dormitory building in Zilina was addressed. At that time, the old steel distribution sys-tems, which were installed in the 1970s, were replaced (almost 50 years in operation), and they re-used seamless steel pipes joined by flame welding. Reconstruction of two more riser pipes in the dormitory building is planned in the near future. From this resolved issue, based on the comparison of detailed knowledge about the investigated materials, it will be possible to propose or recommend the material for the conditions of the given reconstruction. Considering that this work deals only with metal pipes, it will be important to pay attention to their microstructure. Changes in the internal surfaces of pipes and their wear and tear have a major impact on their functionality and service life. The solution to this issue is current and necessary for engineers, designers (in the field of construction and reconstruction of medical-technical installations), and scientists in the development and production of new products.