## 2 Materials and Methods
### Creep Test Laboratory  
The laboratory consists of 89 single-sample creep test machines and four two-chamber multi-sample creep test machines. As a result, nearly 900 samples can be tested simultaneously in the laboratory [24]. The single-sample creep test machines are shown in Figure 1a, and the multi-sample creep test machines are shown in Figure 1b.  
Figure 1: (a) One-sample creep test machines, (b) multi-sample creep test machines.  
The laboratory focuses mainly on the research of steel and metal alloys. The results of the research are applied in the energy [25], petrochemical [26], and aerospace industries, as well as in other industries where the material used is exposed to high stress and high temperature [27]. Creep tests are conducted over a long period of time. The duration of a single test can range from tens of hours to even decades. The test preparation and conduct process is described in the standard Metallic materials--Uniaxial creep testing in tension--Method of test (ISO 204:2023) [28]. In order to meet the requirements of the standard, the laboratory has been completely automated. One of the requirements is to conduct creep testing continuously. Due to this fact, the laboratory has been equipped with a diesel generator to ensure the availability of electricity in the event of its loss in the mains. The power of the generator was specified with some margin to match the power of the laboratory, where all the creep test machines are running, and the air conditioning system is in operation. The typical average load generated by the laboratory does not exceed 60 kW, while the rated power of the generator is 75 kW. This shows that the generator has been selected with a reserve of approximately 25% of power [29]. These calculations were carried out for average power values, not taking into account the number and type of electricity loads connected to the grid. A creep test machine consists of two systems: a heating system and a system responsible for generating a constant force. Thus, a typical creep test machine consists of a furnace in which the test specimen is placed, a lever system to which the test specimen is attached at one end, and a scale with weights at the other end [30; 31]. The cited standard ISO 204:2023 requires that the temperature along the length of the test specimen and during the test is constant. The permissible temperature deviation is \(\pm 3\)\({}^{\circ}\)C for test temperatures below 600 \({}^{\circ}\)C. Due to such strict requirements, the furnaces of single-sample creep test machines are built as a three-zone system, using three electric heaters. Considering the number of machines used, the dimensions of the furnaces are limited, which consequently limits the space for the heaters. The placement of the resistance heaters in a small space, with the requirement to operate at high temperatures for long periods of time while being powered by 230 V mains voltage, results in their power rating being significantly higher than the typical power needed for the test. In the case under consideration, the power of the single furnace heater of the three-zone creep test machine is 1400 W, while the power of the lower heater, at a test temperature of 900 \({}^{\circ}\)C, does not exceed 400 W. The multi-sample machines are equipped with sixteen heaters for each heating chamber. There are 389 heaters connected to the electrical grid in the laboratory, respectively: 143 for phase L1, 130 for phase L2, and 116 for phase L3. Switching on all the heaters simultaneously would require a power source of 545 kW.