What are the causes and treatment methods of thermocouple tube rupture?

Thermocouples may inevitably experience sleeve rupture during use, which directly affects reliable and safe operation. By investigating the phenomenon of thermocouple tube rupture, identify the cause. The main reasons for the rupture of thermocouple sleeves are as follows:

1. The thermocouple sleeve is subjected to high-speed fluid impact, resulting in excessive load and stress exceeding the limit, leading to sleeve rupture;

2. Processing defects in the thermocouple sleeve itself can lead to stress concentration and easily cause sleeve fracture;

3. Excessive pipeline vibration causes fatigue damage to the thermocouple sleeve;

When the fluid flows through the thermocouple sleeve, it induces vibration of the thermocouple sleeve, that is, resonance between the natural frequency of the thermocouple sleeve and the frequency of fluid vortex shedding. This resonance phenomenon can accelerate the damage speed of the thermocouple sleeve, leading to fracture.

Based on the above situations that can easily cause the rupture of thermocouple sleeves, we have conducted research and found that the occurrence of thermocouple sleeve rupture can be reduced through the following methods.

1) Strictly control the insertion depth of thermocouple sleeves. As the insertion depth increases, the force on the protective sleeve increases by a factor of square. So, when we measure temperature, we only need to insert the thermocouple sleeve into the isothermal zone of the fluid, without inserting it into the center point of the pipeline. This is beneficial for shortening the length of the temperature gauge bag cantilever and achieving the effect of reducing the amplitude at its endpoints.

2) Optimize the selection of thermocouple sleeve diameter while ensuring the necessary strength of the thermocouple sleeve. As the diameter of the thermocouple sleeve increases, the force on the pocket increases linearly. Therefore, when selecting the diameter of the pocket, it is necessary to ensure the strength of the sleeve while avoiding the resonance hazard zone as much as possible.

3) Change the cross-sectional shape and process its surface into a structural form, so that the fluid does not produce vortex shedding phenomenon.

4) Strictly control the quality of maintenance, conduct material inspection of thermocouple sleeves, and also carry out non-destructive testing to prevent abnormal accidents such as weld cracking and fracture.

5) When the system is put into operation, avoid sudden opening of valves on the pipeline. At the moment when the valve is first put into operation, the thermocouple sleeve will bear a large one-way force. Therefore, when the system is first put into operation, the valve should be slowly opened to gradually increase the system pressure and minimize the pressure difference between the front and back of the thermocouple sleeve to avoid sleeve fracture accidents caused by excessive one-way force.