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In thermal power plants, thermocouples installed on the pipe walls of the furnace are usually fixed to the wall either by using threaded mounting blocks or by welding a base to the wall and then securing the thermocouple with threaded clamps. To improve the accuracy of temperature measurement, the author has improved the method of installing thermocouples on the furnace wall; this article shares this practical approach for installing such thermocouples. Among tube rupture accidents that occur during boiler operation, overheater and reheat gas overheating-induced tube ruptures rank first. A tube rupture accident will reduce the availability of the equipment and increase power generation costs. Therefore, monitoring the operating temperature of the metal in the heated surfaces plays a significant role in preventing overheating and improving the reliability of power generation equipment. Therefore, the quality of the furnace wall thermocouple installation will directly affect the monitoring of boiler operation. Thermal power plant boilers have numerous monitoring points for the temperature of their superheaters and reheaters. Based on my experience with various units, the installation of thermocouples on the walls of the superheating and reheating steam pipes can be roughly divided into two methods: one involves using heat collection blocks to secure the thermocouples with screws ； Secondly, a stainless steel tube is welded to the pipe wall; at the rear end, a threaded armored thermocouple is connected using a collar, after which the insulation layer is attached. Furthermore, issues such as insufficient length of the thermocouples and an unreasonable design location for the control unit have led to disordered arrangement, thereby complicating maintenance tasks. Based on past installation and maintenance experiences, I have analyzed the methods used for installing thermocouples on the boiler walls and proposed improvements, in the hope of enabling better monitoring and maintenance of the unit. In the unit installations I have been involved in, the heat electrode WRN2-191/PD05, mounted using collector blocks, has been used for installing heat electrodes on the furnace walls at various power plants, including Zunyi Power Plant in Guizhou, Shuanghe Hydropower Plant in Guangdong, and Liyujiang Power Plant in Hunan. This type of installer is used by most power plants, as the large contact area between the thermocouple and the wall of the pipe being measured allows for more accurate temperature readings, resulting in better reliability. However, in terms of ease of maintenance, although dual thermocouples are currently used for measuring the furnace wall temperature, if both of them get damaged, it becomes more difficult to replace them. Firstly, the thermocouple is fixed to the heat collection block with screws; when it needs to be replaced, it is necessary to wait until the boiler has cooled down, remove the outer protective cover and insulation material of the boiler, and the installation environment must still have a relatively high temperature. Secondly, after prolonged operation of the boiler, the screws used to secure the armored thermocouples soften or rust in high-temperature conditions, making it difficult or even impossible to remove those screws. In such cases, it is necessary to install new heat collection elements nearby, which involves welding issues related to high-pressure pipes. So personally, I think this installation method has some shortcomings. Of course, the main purpose of installing furnace wall thermocouples is to ensure the reliability of operational monitoring; therefore, without considering maintenance, this method remains the most reliable. http://yunrun.com.cn/upload/201811/26/201811261709265507.png Improvements to the installation method of thermocouples on the furnace walls of thermal power plants. yunrun.com.cn/tech/2265.html The second method for measuring wall temperature uses a regular φ12×2mm stainless steel tube as the protective cover for the thermocouple, which is then fixed in place using threaded couplings. Taking Boilers No. 3 and No. 4 at Meizhou Huai Gang Power Plant as an example, φ12×2mm stainless steel tubes are used for installing the wall thermocouples; these tubes are welded vertically to the pipeline under inspection and extend out through the insulation layer. At the end of the protective sleeve, a clamping fitting is used to secure the armored thermocouple. This installation method greatly facilitates the replacement of thermocouples, allowing them to be replaced easily without shutting down the boiler or removing the insulation layer. However, there are also some issues: during operation, it was often found that the wall temperature measurements were inaccurate. We first checked whether the compensation of the thermocouple was sufficient and whether the thermocouple itself was damaged; we also checked for any loose connections, but no abnormalities were found. Finally, we examined the insertion depth of the thermocouple and discovered that there was a significant distance between the front end of the thermocouple and the surface being measured, resulting in a loss of contact. This is due to the vibrations that occur during boiler operation, as well as thermal expansion and contraction. The protective sleeve used for the thermocouple is a stainless steel tube with dimensions of φ12×2mm, having an inner diameter of 8mm, while the diameter of the thermocouple itself is 5mm. After installation, there is still a 3mm gap inside the protective sleeve. Under the effects of vibration and expansion, this gap causes the measuring end of the thermocouple to be further away from the surface, leading to inaccurate temperature measurements in some cases. To address the shortcomings of the two commonly used methods mentioned above, the author presents their own views on the installation of furnace wall thermocouples, suggesting some minor modifications. Taking Meizhou Heshuyuan Power Plant as an example, the design and installation method of the thermocouples used for measuring the wall temperature of Units 3 and 4 is basically the same as that at Huai Gang Power Plant. After discussions with the design institute, the owner, the supervisor, and the manufacturer, my installation method was approved: the protective sleeve was replaced with a φ12×3 mm stainless steel tube to facilitate maintenance; the angle at the end used for detection was set at 30° to increase the contact area between the end tip and the tube wall. Additionally, two observation slits of 1–2 mm were made along the axis of the protective sleeve to allow checking whether the armored thermocouple was installed in place during installation. This installation method offers three improvements over the second installation method: first, the original stainless steel protective tube has been changed from φ12×2mm to φ12×3mm, which reduces the available space inside the protective tube for the armored thermocouple after it is installed, allowing for a tighter fit and reducing external influences during operation ； Secondly, the stainless steel protective sleeve is installed at an angle of 30° instead of vertically, which reduces the distance between the measuring end of the thermocouple and the tube wall, increases the heating area, and improves measurement accuracy ； Third, an observation slit is provided at the welded end of the sheath tube, allowing for clear inspection during installation to verify whether the thermocouple is properly installed. In addition to the fixation of the furnace wall thermocouples, their length also has a significant impact on operation and maintenance. Furnace wall thermocouples generally use 100×75 mm wire grooves to lead the wires to the steel frame platform in a somewhat concentrated manner; in this case, the thermocouples must have sufficient length to reach the steel frame platform, and attention must also be paid to the arrangement of the connection terminals. In previous construction projects, due to the insufficient length of the furnace wall thermocouples, or an improper design and installation location of the controller unit, some of the thermocouples could not be connected to the controller unit in one go; this is why compensation wires are used. Due to the cluttered wires inside the cable tray, it poses certain difficulties in checking the wires after installation. Therefore, for the sake of operational stability and ease of maintenance, compensation wires should be avoided as much as possible. When the furnace wall thermocouples are led to the connection points on the controller, brackets should be used to arrange the terminals of the thermocouples in layers and label them; this way, when it is necessary to inspect or replace a particular circuit, the desired thermocouple can be easily located from the outside of the terminals. It should be noted that when such improvements are necessary during construction, it is essential to first consult the relevant departments; work can only proceed after obtaining approval from the designers, manufacturers, owner, and supervisor. Author: Li Wanghua, Guangdong Thermal Power Engineering Co., Ltd., China Energy Engineering Group