A problem that plagues even experienced instrument technicians; please proceed to analyze the causes
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:Victory: Thermocouple A :victory: Thermocouple B. Since it’s not possible to draw a diagram, a simple representation is shown above. Please refer to the following explanation and then analyze the issue: 1. The oil and gas flow from left to right, passing through a long pipeline (DN150); the distance from point A to point B is approximately 200 meters. 2. The temperature at point A is 416°C, but it rises to 420°C upon reaching point B. Under normal circumstances, the temperature should decrease as it moves from A to B. 3. In previous operations, the temperature at point A was always higher than that at point B, but now the situation is reversed; this is unclear. 4. Steps taken to resolve the issue: (1) The DCS malfunction was resolved, and measurements were taken using FLEKE equipment, confirming that the temperature at point A was indeed lower than that at point B. (2) When the thermocouples were removed, it was found that they were not clogged and their surfaces were clean, with no problems detected. (3) Both thermocouples had their internal elements replaced, but the problem persisted. (4) The process engineers analyzed the situation and said that there was definitely no issue with the process itself; the temperature should decrease as the oil and gas move further. All of us, who are experts in instrumentation, have tried to find the cause, but we’ve been unable to do so. We hope that experienced users can help analyze what might be causing this issue.
Processing steps: (1) Troubleshoot the DCS issue; use FLEKE for measurements on-site, and it is confirmed that the value at point A is lower than that at point B. (4) Analyze the reasons from a process perspective – the analysis indicates that there are absolutely no problems with the process; it’s somewhat contradictory to think that the oil and gas levels should keep dropping. This is the actual situation, so how is it possible not to understand it? In terms of manufacturing processes, it sometimes indeed goes against common sense. . . Perhaps some factors have just not been discovered. .
Based on the way the original poster handled it, it seems that temperature at point A is indeed lower than that at point B. Swap the thermocouples at A and B and then check the temperature display. If you wait any longer, there is an issue with the response time. How about using an armored thermocouple? Find a skilled craftsman to take a look.
Use the same 500-degree mercury thermometer to measure the temperatures at points A and B.
Is this pipeline insulated, or has other materials mixed in?
Some things are unexplainable; swap the two thermocouples around, and maybe that will solve the problem. We have encountered similar problems before as well.
“DCS troubleshooting: measurements were taken on-site using FLEKE, and it was indeed found that the value at point A was lower than that at point B. Could you be more specific? Where do the temperature changes of these two thermocouples occur, at the site or in the control cabinet? On-site temperature variations: if the temperature environment is high, it can cause fluctuations in temperature. Or try replacing the thermocouple and see.
1. Send a signal to the DCS on-site to rule out issues with the DCS or the wiring. 2. Equip a standard thermocouple to see how the temperatures at both locations are displayed If the above two steps have been carried out and no problems were found, it can be basically determined that it is not an issue with the instrument
Use the same thermocouple to measure the temperature and see if it’s the same; this will help determine whether there’s an issue with the thermocouple. If both the thermocouple and the DCS configuration cards are fine, then the process team should check again to see if there’s any problem. That’s the only possibility!
According to the original poster, there should be no problem with the instrument. If the two thermocouples are swapped and temperatures at points A and B still show the original values, then it can be confirmed that there is no problem with the instrument. The original poster had better explain the production process again.
If I were to handle it: 1. Determine the actual temperature at the inspection points of the process pipeline. Other temperature measurement methods can be used for comparison, such as thermal resistance or infrared. This is a fundamental premise: if the pipeline temperature is already lower for A than for B, then there is no need to check the instruments. 2. If the pipeline temperature is normal, then check the measurement stage. Such as insertion depth, transducer unit, primary element, temperature compensation, etc. The main confusion at present stems from the fact that the fundamental premise of the actual pipe temperature has not been clarified. It is recommended to start checking from this aspect.
First, disconnect the transmitter and measure the millivolt value. If A is less than B, then the error is too large; if A is greater than B, proceed with further checks.
I think we should look for the cause in terms of the manufacturing process, such as whether there are any fittings on this pipe.
As the people upstairs said, first swap the two thermocouples to see if the problem still persists; if it does, then it indicates that the issue isn’t with the instrument. Check whether the settings of the DCS channels for the two thermocouples are the same (range, delay time, etc.). Next, consider the installation location of the thermocouple. Is there anything attached to the armored thermocouple that could cause inaccurate measurements? If the problem persists, it’s a process issue.
I’ve encountered similar situations before as well; there’s basically no good way to solve it. It’s only 4 degrees difference – that’s normal! The process might just be like that.
It is necessary to check whether the insertion depth of the thermocouples is the same, whether the ambient temperature is the same, and whether the compensation is correct. The simplest approach is to confirm that the process is stable, and then use the same thermocouple to measure the temperatures at two different points to see if the problem can be identified. :victory:
As the original poster said, using both setups should be fine; the issue lies in the installation location. As mentioned by the poster, the distance from point A to point B is about 200 meters, and that’s where the problem lies. Take a look at the surrounding environment as well. Check whether the signal cables are of poor quality; over time, it’s possible that the resistance of one of the cables between those two points becomes too high. This is based on my years of experience in installations! Last edited by Ah, the sea on 2009-4-7 19:24.]
Did the medium vaporize after transmission?
The poster did not provide information on the process equipment related to this pipeline, making it difficult to analyze the situation. It is necessary to check whether the pressure in the pipeline has increased compared to before, as well as whether the flow rate has risen If point B is near a pressure-relief device or container, this is possible
What is the oil and gas pipeline of this device? What medium?