## 2 Dataset of Simulated Leakage in a Seeded Boiler Tube  
In a coal-burning thermal power plant, the steam vaporized from feedwater by heat energy from fuel combustion rotates the turbine to generate electricity. To simulate the leak process in a boiler tube, an elaborate experimental apparatus was built to collect the leakage signal. The general scheme of the system is depicted in Figure 1. The feedwater was circulated by a pump between the tube membrane and the tank. Before flowing into the lower drum, water was preheated by steam from the upper drum. The lower drum fed feedwater that was vaporized into steam, which was temporarily stored in the upper drum. In advance, bituminous pulverized coal was directed through the nozzle into the combustion or furnace. To protect the sensor from heat damage caused by fire and hot gas when the furnace was in a positive pressure situation and ensured the sensitivity of the sensor. Most leak detection testbeds weld waveguides onto the boiler tube membrane and through the case, unused soot blower ports, or penetrations in the inspection doors. Both airborne and structure-borne techniques were used to measure the leakage signal. In airborne applications, microphones were attached by hollow waveguides to the furnace medium space. For the structure-borne measurement, piezoelectric transducers were attached to AE-type waveguides. The waveguide housed the AE sensor assembly with integrated head amplifiers to reduce the loss of the AE energy in the measurement, along with the essential components required for its sustained operation, such as isolation valves, heat-insulated spacers, and heat-insulated couplings.  
The leakage phenomenon in the boiler tube was simulated by seeding four pinholes, which were located at four different positions in the boiler's tube. The four pinholes were disposed at random position in the tubes as the occurrence of faults is random. The positions of the seeded pinholes are depicted in Figure 1, where the pinholes are depicted by red stars. The testbed was installed using seeded pinholes with different sizes: 0.6 mm, 1 mm, and 2 mm in diameter. The detailed installation of each pinhole on the boiler membrane is illustrated in Figure 2. The measuring points with waveguides were located near the source of the leakage hole to get a better AE signal. The leakage level was controlled by manipulating the flow passage with a valve. Each pinhole state could be remotely controlled by solenoid valves, which were attached to the pinhole. The valves needed to open and close the pinholes to simulate tubes in different operating conditions: leak and normal. First, the valves were held in the closed state during the process of collecting AE signals for the normal condition. For the normal condition, AE signals were recorded for one minute. These signals were segmented into multiple one-second signals. Furthermore, valves were opened to record the signals related to the leakage phenomenon. Signals were recorded for two minutes in the leak state. The AE signals were recorded using wideband differential AE sensors (WDI-AST) and data acquisition devices with a peripheral component interconnect (PCI-2). To increase the number of impacts between the fuel powder and the tube membrane, the fuel stream was composed of a mixture of steel elements and pulverized coal. A detail of the setup is illustrated in Figure 2, and the data specification is also presented in Table 1 below.  
Figure 1: The overall scheme of the boiler tube leak detection testbed.