## 3 Results and Discussion
### Critical Roughness Parameters for Leakage Detection
The mechanism of building the tightness between the heterogenous sealing surfaces on the basis of conducted studies parameters _Sq_, _Sp_, _Sa_, _Sz_, and _Spc_, revealed that despite the increase in the pushing force, the lower tightness was due to the homogenous surfaces. This is a result of the impossible filling of free spaces by the material of the second sample among the peaks or ridges and valleys toward each other. Moreover, it is difficult to try to eliminate sharp peaks or to match them to the flat contact surface of the other element. A correlation was noted that despite the increasing value of the applied force, it is not possible to completely eliminate the unevenness of the surface geometry and leakage, which was characterized by sharp peaks. In this case, there are always left micro-deformations that have experienced material strengthening and are an obstacle to filling the free surfaces between the components to be joined, which lead to the increased leakage in their area. Figure 11: The value of leakage \(Q\) as a function of the surface topography parameter _Sa_ for a constant compressive force of 2280 N.  
Analyzing the results of subsequent tests, in which one of the parts belonged to code group B, and the other part of the pair samples had the surface parameters of one of the other groups, the influence of the topography parameters _Sq_, _Sp_, _Sa_, _Sz_ and _Spc_ on the leakage values was observed. The tests were carried out for a compressive force equal to 2280 N. The influence of the difference in the topography parameter Sa and its influence on the leakage value is shown in Figure 13. It was observed that for the pair of samples in which the second surface was characterized by higher values, the leakage value increased. However, when the second sample had lower values, the leakage remained at the same level. The surface parameters _Sz_, _Sq_, _Sp_, and _Spc_ show a similar relationship. Figure 12: The value of leakage \(Q\) as a function of the difference in the value of the surface topography parameter Sa for a constant compressive force of 2280 N for the base surface with a value of _Sa_ = 5.24 μm. Figure 13: The value of leakage \(Q\) as a function of the difference in the value of the surface topography parameter Sa for a constant compressive force of 2280 N for the base surface with the value _Sa_ = 3.29 μm. If the difference in the value of the surface topography parameters is smaller than the base surface with the following values of parameters: \(Sq=3.92\)\(\upmu\)m, \(Sp=9.1\)\(\upmu\)m, \(Sz=15\)\(\upmu\)m, \(Sa=3.29\)\(\upmu\)m, and \(Spc=14,779\)\(1/\)mm, then the tightness remains at the same level. However, in the case of applying surfaces with sharper peaks than the base surface, there was a rapid increase in leakage values, since the contact area between the surfaces was smaller. By analyzing successive measurement results of a pair of samples, one of which was characterized by parameters belonging to code group D, while the other sample was characterized by the surface parameters of one of the other code groups, a relationship was found between the leakage values and the values of the surface topography parameters \(Sq\), \(Sp\), \(Sa\), \(Sz\), and \(Spc\) for a compressive force equal to 2280 N. This influence is presented for the parameter \(Sa\) in Figure 14. On the basis of the results, it was observed that for the sets containing samples with higher values, there was an increase in leakage values for the difference greater than 2\(\upmu\)m for the \(Sa\) parameter. Below the thresholds indicated, and when the second pair had a parameter with a lower value, the leakage test results remained at the same level. The surface parameters \(Sz\), \(Sq\), \(Sp\), and \(Spc\) show a similar relationship.