Advantages of heat-shrouded thermocouple WRNR3-18 in temperature measurement of high-temperature pipelines in power plants

High-temperature pipelines in power plants, such as main steam lines and reheat steam lines, are the “arteries” of unit operation. Temperature monitoring of these pipelines is directly related to unit safety—excessive temperatures or large fluctuations can cause equipment failure. Thermocouples are commonly used to monitor these pipe temperatures. The WRNR3-18 heat-shrouded thermocouple offers significant advantages over traditional prefabricated thermocouples for use on high-temperature power plant pipelines. This isn’t to say that prefabricated thermocouples are inferior, but rather that the operating conditions of high-temperature power plant pipelines are unique, and the shrink-wrap design addresses the challenges of prefabricated thermocouples in these situations. Let’s discuss the specific strengths of the shrink-wrap structure.

1. Installation and Maintenance: No Suspension, Saving the Power Plant Hassle

High-temperature power plant pipelines cannot be shut down arbitrarily. If they are shut down, the operation of the entire unit will be affected, resulting in significant losses. Installing or replacing prefabricated thermocouples presents significant challenges. The pipelines must first be drained and depressurized before the old ones are removed and replaced with new ones. The entire process is time-consuming and requires coordinated unit load reduction, making it very inconvenient for the power plant.

The WRNR3-18 heat-shrouded thermocouple is different. It comes with a separate metal sleeve, which is pre-welded to the temperature measuring point of the power plant’s high-temperature pipelines. Once the sleeve is secured, the thermocouple core inside can be removed and replaced separately. To replace the core, there’s no need to shut down the pipeline or relieve pressure—simply remove the old core from the sleeve and insert the new one, securing it. The entire process can be completed quickly, taking only a few minutes, eliminating the need for coordinated unit load reduction, significantly reducing power plant downtime and losses.

It also reduces maintenance hassles. If the protective tube of an assembled thermocouple breaks, the entire system must be removed and replaced, potentially also involving the junction box and extension wires. Shrink-wrap sleeves rarely break, and even if a problem occurs, only the core needs to be replaced, resulting in lower component costs. If you’re unsure which installation method to choose for your power plant’s piping, or if you’re unsure how to quickly replace the core, please contact us and we can provide targeted guidance.

2. High-Temperature and High-Pressure Resistance: Withstanding the “Extreme Tests” of Power Plant Piping

Power plant high-temperature piping experiences extreme temperatures and pressures. The main steam pipeline can reach temperatures of several hundred degrees Celsius, and the pressure is also high. Fabricated thermocouples are prone to problems in such environments. For example, the protective tube can deform and crack under the effects of high temperature and pressure. The sealing performance of the junction box can also deteriorate, allowing high-temperature steam to penetrate and damage internal components.

The WRNR3-18 heat-shrouded thermocouple’s shrink-wrap structure is specifically designed to withstand these extreme conditions. Its metal sheath is made of a high-strength alloy that can withstand the high temperatures and high pressures of power plant high-temperature piping. The sheath acts as a protective wall, isolating the internal thermocouple core from the high-temperature medium in the pipeline. This prevents the core from direct exposure to the extreme environment, significantly reducing the risk of damage.

In addition, the shrink-wrap seal design is more reliable. The sleeve and pipe are welded together, leaving no gaps. A dedicated seal is installed between the core and sleeve to prevent leakage of high-temperature media. The protective tube and pipe connection of prefabricated thermocouples is threaded. Under prolonged exposure to high temperature and high pressure, the threads can loosen, gradually degrading the sealing performance. In contrast, shrink-wrap thermocouples, used on high-temperature and high-pressure pipelines in power plants, ensure more stable operation of the thermocouple and reduce temperature measurement interruptions caused by component damage.

3. Vibration Resistance: Adapting to the “Continuous Vibration” of Power Plant Equipment

When a power plant is operating, the pumps, fans, and turbines within the units generate vibrations, which are transmitted to the high-temperature pipes. The protective tube and pipe connection of prefabricated thermocouples is relatively simple, typically using threads or flanges. Over time, vibration can loosen the connection, causing the thermocouple to shift. This can lead to inaccurate temperature measurement points or friction damage between the core and the protective tube, affecting temperature measurement accuracy.

The WRNR3-18 heat-shrouded thermocouple offers advantages in vibration resistance. Its metal sleeve is welded directly to the pipe, ensuring a secure weld that won’t loosen due to vibration. The internal thermocouple core is secured to the sleeve with a dedicated clip, ensuring a seamless gap between the core and sleeve, preventing vibration and wiggling. This ensures the thermocouple maintains a stable position even with continuous pipe vibration, preventing temperature measurement point drift and ensuring a more stable signal output.

Vibration-induced thermocouple failures are common in power plants. For example, after long-term use, prefabricated thermocouples can display fluctuating temperatures, often attributable to vibration-induced loosening of the protective tube. This is less common with heat-sleeve-type thermocouples, reducing the need for vibration-related maintenance and ensuring a more stable temperature measurement system.

4. Temperature Measurement Stability: Reduced Environmental Interference, More Accurate Data

High-temperature pipelines in power plants operate under complex conditions, including high temperatures, high pressures, and vibration, as well as erosion and corrosion from the media. The protective tube of a prefabricated thermocouple is in direct contact with the medium in the pipeline. Fluid erosion can cause the protective tube to thin, and corrosion can create holes in the tube. These factors can affect the thermocouple’s thermal response speed—resulting in inaccurate temperature measurements or a slow response that lags behind actual temperature changes.

The sheath of the WRNR3-18 heat-shrouded thermocouple protects against both erosion and corrosion. The sheath itself is thick and corrosion-resistant, making it less susceptible to corrosion and thinning by steam and water in the pipeline. The thermocouple core contacts only the inner wall of the sheath, transferring temperature through the sheath without direct contact with the medium. This results in a more stable thermal response and eliminates temperature lags caused by medium influences.

Furthermore, the core of a shrink-wrap thermocouple can be replaced without moving the sheath. Each replacement core returns precisely to its original temperature measurement position, eliminating any shift in the measurement point caused by disassembly or installation. Prefabricated thermocouples require repositioning each time the protective tube is replaced, which can easily lead to inconsistencies in temperature data. For power plants, accurate and stable temperature measurement data is crucial for better assessing pipeline operating conditions and avoiding misdiagnosis of faults due to inaccurate data.

5. Service Life: Replaceable Core Reduces Long-Term Costs

If the protective tube of an assembled thermocouple breaks, the entire system must be replaced—including the junction box and compensation wires—at considerable cost. Furthermore, thermocouples installed on high-temperature pipelines in power plants are frequently replaced, resulting in high long-term investment costs.

The WRNR3-18 heat-shrouded thermocouple offers a superior service life. Its core wear component is the internal thermocouple core, while the heat-shroud rarely breaks. With proper installation, the heat-shroud can last for years or even longer. Even if the core breaks, only the core needs to be replaced, not the heat-shroud. The cost of the components is significantly lower than replacing the entire assembled thermocouple. For example, some power plants’ main steam pipes, equipped with prefabricated thermocouples, need replacement about once a year or so. With the WRNR3-18 shrink-wrap thermocouple, the sheath has never been replaced, and only the core has been replaced twice. This saves significant money. Furthermore, core replacement is quick, requiring no downtime, and reduces the impact on unit operation caused by thermocouple replacement, making it more cost-effective in the long term. If your power plant wants to reduce the long-term cost of thermocouples and is unsure whether to choose shrink-wrap or prefabricated, please contact us for a cost calculation.

6. Practical Application: Shrink-wrap Thermocouples Better Meet the Needs of Power Plant High-Temperature Piping

As can be seen from the above points, the advantages of the WRNR3-18 heat-shrouded thermocouple are designed to address the pain points of power plant high-temperature piping. Power plants are afraid of downtime, hassle, and inaccurate temperature measurements. The shrink-wrap thermocouple reduces downtime during installation and maintenance, reduces failures through temperature, pressure, and vibration resistance, ensures reliable data through temperature measurement stability, and reduces costs through service life. Prefabricated thermocouples are suitable for piping with low temperatures, pressures, and vibrations, but they struggle with extreme operating conditions like those in power plant main steam and reheat steam pipes. The WRNR3-18 shrink-wrap thermocouple addresses these shortcomings, making temperature monitoring on power plant high-temperature pipes more worry-free and reliable.

However, please note that the sheath installation of a heat-shrouded thermocouple requires advance planning—the sheath must be welded during pipeline construction. If it’s added later, some pipe preparation may be required. If your power plant is retrofitting existing pipelines and you’re unsure how to install a shrink-wrap thermocouple, we can provide on-site surveys and installation design to ensure a smooth installation.

If your power plant is considering thermocouples for high-temperature pipes and is struggling to decide whether the WRNR3-18 shrink-wrap or prefabricated type is more suitable, or if you’re experiencing installation, maintenance, or temperature measurement issues with shrink-wrap thermocouples, please contact us. We not only provide genuine WRNR3-18 heat-shrouded thermocouples, but also have a professional team to provide services tailored to power plant conditions. From selection recommendations and on-site installation guidance to subsequent maintenance and commissioning, we provide a one-stop solution to your power plant temperature measurement needs, ensuring stable temperature measurement on high-temperature pipelines and supporting safe operation of the unit.

E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229
Yoyik offers various types of power plants spare parts for steam turbines, generators, boilers as below:
Differential pressure signal RC861CZ097HYR110AC
magnetic linear sensor HTD-200-3
Emergency Stop 3SJ1030-1AV
Eddy Current Sensor PR6422/103-110
intelligence Hand Operator NPDF-Q11FD3
Limit Switch WLGCA2-2
transducer for displacement measurement TDZ-1E-013
Level Indicator UHZ-10
Vibration sensor VS-068
sealed pressure sensor RC778NZ090ZSS
Temperature sensor PT 100 WZP2-001A
Control cabinet of DC electric heater 8300.D300AK-685100A
LVDT GV valve. A157.33.01.31
intelligence Hand Operator NPDF-D11D2
intelligence Hand Operator NPDF-Q10F3
indicator RCA218RZ090Z
ACTUATOR M0321rC
Excitation Voltage Converter FPVDH-V11-03
lvdt linear DET-50A
240v proximity switch TM0181-A40-B01
Speed sensor ZS-04-075-3000
lvdt linear position sensor TD4000
Electric heater ZJ-22-11(R)
probe 2401B-0.01
intelligence Hand Operator NPDF-D111
Eddy Current Sensor PR6424/011-031
Linear variable differential transformer LVDT for valve CV ZDET-50A
INTELLIGENT speed meter HY-01
Eddy Current Sensor PR6425/010-140