K type armoured thermocouple is the common solution to the problem of common problems and deal with the release date: 2019 - 05 - 21 reading

K type armoured thermocouple 10 common fault analysis and recommendations: 1. After thermal cycle use easy break line inspection found that there are many accidentally wire break reason: when more than outer diameter of armoured thermocouple temperature limit, armoured thermocouple casing material, insulation material and the thermocouple wire, because of the difference of expansion coefficient of each, cause excessive extension thermocouple wire and wire. Solution: increase the armoured thermocouple diameter, change with the distance between the protection tube, set aside space with the temperature, reduce the thermocouple wire stress. 2. At 800 ℃ hydrogen furnace show low value anomaly thermocouple conduction, insulation resistance check seen without exception. Test results under 800 ℃ measurement result is the same with the users. Reason: although there are metal thermocouple wire outer casing protection and atmosphere completely cut off, the hydrogen can be through the casing wall and pipe residual oxygen reaction, make its casing oxygen concentration is available for nickel chrome selective oxidation and chromium, cause substantial decrease in thermoelectric emfs. Solution: use no oxidation film of light silk, assemble with thermocouple protection tube and anti-oxidation structure or add oxygen titanium getter. It is recommended to use titanium getter armoured thermocouple. 3. Using temperature is 470 ℃, 30 h, + 4. 6 ℃ error. Check under 400 ℃, its error is small. Reason: for K type thermocouple short-range order transformation phenomenon, if in a specific temperature range 450 ~ 600 ℃, so in a short period of time, atomic arrangement changes the thermoelectric emfs. But the phenomenon is reversible, through above 900 ℃ heat treatment, can restore the original correction. The solution: short-range order transformation is one of the characteristics of material itself, is inevitable, it is recommended to use N type thermocouple. 4. Users regularly check, error has great changes. Insert depth of different, measurement carried out within a certain range, the results found that change. Causes: when inserting depth is not at the same time, due to deterioration of thermocouple, in the groove and slot ( The atmosphere) Part of a temperature gradient between, so have a great error. Solution: insert part in furnace thermocouple degradation, has reached the life, suggest to replace thermocouple or using a fixed device to ensure a uniform depth of the insert. 5. The service life of the year, in the flange welding, armoured thermocouple fracture. Chromic acid and phosphoric acid steam were found to exist in the measuring system. Microscopic analysis found that the armoured thermocouple breaking part, through wall crack. The crack morphology is transgranular model through crystal. Reasons: being measured gas condensation under the flange, due to the residual stress formed during welding, make its appear corrosion crack. Solution: install socket in the flange, armoured thermocouple fixed. 6. Temperature 980 ℃, use after 3 months of temperature indicating wobbly, when make the break. If the temperature is too high, the offline status. When the temperature drops, has shown in value. Testing a pair is found to be broken, broken section microscope observation, found that the coarse grains, there are traces of brittle fracture. Reason: when armoured thermocouple temperature measurement under large temperature gradient, by armoured thermocouple wire and casing expansion coefficient is different, cause I bear too much stress. Due to the high temperature and low temperature part of grain growth is different, so produce the intergranular brittle fracture. Solution: when installing armoured thermocouple increase the supporting tube, to reduce armoured thermocouple temperature gradient. 7. Before the installation thermocouple don't conduction. Found the terminal part of the core wrapping have caused serious damage to break. Reason: when wiring or remove wire wrapping, appear damage caused by. Solution: to improve the operator expertise. 8. The instrument shows low temperature. Temperature characteristic test no abnormalities. Reason: thermocouple positive and negative polarity reverse solution: change the polarity. 9. Measurement of high temperature and high pressure water temperature ( 400℃、10MPa) Time: 2 ~ 3 months crack of armoured thermocouple crack section using an electron microscope observation. Reason: identified as general austenitic stainless steel is related to the chloride ion type transgranular crack caused by stress corrosion. Solution: recommended with excellent corrosion resistance, high nickel content of the material. 10. Use after six months, temperature swing, value for insulation resistance. Armoured thermocouple part wall thinning, appear crack, fall off and found that insulation near crack. Causes: in the vibration environment, with armoured thermocouple temperature measuring devices, and due to the friction vibration, make armoured thermocouple wall thickness thinning, steam from the damaged parts in armoured with internal insulation materials reaction, cause the volume expansion, due to internal pressure, expanded into secondary cracks. Solution: install the fixed screw, to prevent vibration armoured thermocouple.