# Microscopic Analysis of Structure and Wear for Metallic Materials Using SEM
## 2 Materials and Methods
### Steel Pipes for Aqueous Media and Their Internal Surfaces  
As a material, steel is one of the most used materials for the installation and production of traditional hot water heating pipes. It has the necessary and expected material properties that ensure good resistance to operating pressures. Pipes made of steel are sufficiently strong and durable, thus preventing the permeability of the medium. At the same time, they make it possible to withstand expansion changes and deviations from the specified geometry. The potential strength of steel and its ductility are based on the mass percentage of carbon. Higher percentages of carbon mean stronger and harder steel. On the other hand, it is less malleable. Relating to the material for pipes of heating systems, low-carbon steel is used for the production of pipes because the steel with a high carbon content has a reduced melting point. Within the scope of standards, defining carbon steel, other elements can be used, e.g., chromium, tungsten, manganese, cobalt, and molybdenum, as additional or alloying elements that can improve the material properties. For the assembly of heat-carrying medium distributions for hot water heating, the following materials have been used still: black steel pipes, carbon steel with external galvanization, and copper [6; 7; 8].  
The internal surfaces of steel pipes, which interact with the water medium, represent a critical aspect of their further functionality and service life. These surfaces are in direct contact with water of different purity and temperature, which can affect the internal material surface of pipes. Their importance is based on the following:  
* The material integrity--the internal surfaces of the pipes ensure or provide the mechanical strength and stability of metal hydraulic components;* The impact on material properties--the nature of the microstructure and the occurrence of the undesirable phases (inclusions) affect resistance to load and degradation;
* The corrosive change in materials--both internal and external surfaces are susceptible to corrosion, which can lead to material degradation and a reduction in overall service and lifetime [6; 7].  
Steel pipes used for liquid media are exposed to various types of wear and temperature changes. The prediction of future degradations is based on the identification of the following:  
* The corrosion layers--if the corrosion areas relating to the internal surfaces of the pipes are critical, they can lead to degradation of the base material and a reduction in service and lifetime. The identification of these layers is essential to prevent the spread of corrosion and the initiation of cracks that propagate into the inside layers of the pipe wall;
* The cavitation and its effects on the material--microscopic volumes of material are torn out by cavitation as a result of pressure changes in the microlocations of the water medium. The present corrosion with cavitation can significantly weaken the pipe walls and change their geometry. This phenomenon can have serious consequences for changing the mechanical properties of the material, which can lead to component failure [7; 9].  
Research and analysis of these processes taking place on the inner surfaces of metal materials, such as pipes, allow for a better understanding of their reaction to real operating conditions. As long as all aspects that can affect the occurrence of material failure are mapped, it is possible to develop measures to optimize their performance and in-service conditions as well as lifetime.