# Identification of the Wear Margin of a Pipeline-Machine Subsystem
## 2 Pipeline-Machine Subsystem: Boundaries, Characteristics, Curves and Losses
Therefore, it can be assumed that wear margin of an open subsystem is not exhausted if the subsystem delivers fluid to the destination under the following conditions:  
* With capacity \(\dot{V}\) falling within the range \(\dot{V}_{2},V_{2}-\Delta\dot{V}_{2}\), at pressure \(p\) in the range of \(p_{2}\), \(p_{2}-\Delta p_{2}\) and temperature \(T\) in the range of \(T_{2}\), \(T_{2}-\Delta T_{2}\);
* With efficiency values in the range \(\eta_{\text{nom}}\), \(\eta_{\text{nom}}-\Delta\eta\);
* With failure frequency rate not exceeding a limit value;
* With an acceptable value of availability. Reliability and availability are characteristics whose measured values are determined after a specific period of subsystem use. We can only determine which characteristics of wear margin affect reliability and availability and define limit values of their measures. In the pipeline-machine subsystem, we can distinguish the following measures a priori:  
* Mass losses due to leakage of fluid outside the subsystem;
* Heat losses due to the exchange of heat between the fluid in a subsystem and the surroundings;
* Energy losses due to friction created by the flow of a liquid through the pipeline and the machine;
* Energy losses related to the conversion of energy supplied to the subsystem into the energy of the fluid. It is purposeful to divide these losses into:  
* Hydraulic losses, including fluid mass losses and losses due to friction of flowing fluid in subsystem elements;
* Thermal losses;  
Figure 2: The quality curve of the discharge pipe \(p_{d}\big{(}\dot{V}\big{)}\), rotodynamic machine \(p_{\text{rot}}\big{(}\dot{V}\big{)}\), positive displacement machine \(p_{\text{disp}}\big{(}\dot{V}\big{)}\), efficiency of the rotodynamic machine \(\eta_{\text{rot}}\big{(}\dot{V}\big{)}\), efficiency of positive displacement machine \(\eta_{\text{disp}}(p)\), operating point of discharge pipe and rotodynamic machine \(\text{OP}_{\text{rot}}\) and operating point of discharge pipe and positive displacement machine \(\text{OP}_{\text{disp}}\). * Mechanical losses, namely in the machine, in the gearbox and in the engine;
* Electric losses, including losses during the conversion of electric energy into mechanical energy. This division allows the classification of losses (neglecting thermal losses). Losses in the suction and discharge pipes are classified as hydraulic losses. Losses in the machine set are divided into hydraulic losses in the machine (pump, compressor); mechanical losses in the machine, the gear and the engine; and electric losses in the motor. Hydraulic losses in the machine add to hydraulic losses in the suction and discharge pipes. During operation, the wear margin of the pipeline-machine subsystem gets exhausted due to unavoidable processes of wear in all components of the subsystem. The main causes of pipe wall destruction are corrosion, erosion, accumulation of failures, static and pulse loads, turbulent flow of a fluid, thermal shock, ice load, etc. [18]. The wear of machine elements is due to the impact of the flowing fluid on contacting elements and friction. The final effect is an increase in losses affecting the following characteristics determining the wear margin:  
* Increase in roughness, surface flaws and wall punctures (capillary leaks) of subsystem elements;
* Increase in clearance width of the machine's moving seals and reduced tightness of valves and static sealings [19; 20; 21]. Wall punctures, sealing failures and increased clearances of pump rotor sealings [19] (radial clearance in rotor sealings of nominal value 0.4 mm and a deviation of \(-0.1\) may increase to more than 2 mm) increase mass losses of the fluid. Mass losses in the machine and discharge pipe manifest themselves as leakage of the transported fluid. In the suction pipe, another fluid may be sucked in from the surroundings. Mass losses can be measured by simultaneous measurement (two flowmeters) of mass flow rate at the beginning of the suction pipe and the end of the discharge pipe [22].