Measuring the effect of high-temperature media on pressure transmitters and pressure gauges

Alas, you just won’t give up until you hit a wall. Sometimes you can understand things in a simpler way: if someone tells you that your hand can handle temperatures of 60 degrees, and you insist on trying to touch water at 100 degrees, then it’s only natural that you’ll get burned. For example, in the case of pressure gauges, when the temperature is high, there are issues related to the linearity of the spring tube, as well as the wear resistance of the small gears inside under high temperatures. Additionally, the oil used in the transmitter is affected by thermal expansion and contraction

At 100 degrees, pressure transmitters can be installed directly on the pipeline. We have those plug-in types with flanges that contain isolation fluid, as the medium forms salts which can cause the conduits to get clogged. But the isolation fluid must not be affected by thermal expansion and contraction at room temperature to the measurement temperature.

1. When the medium in the pipeline is at 100 degrees Celsius, installing the transmitter directly may damage its sensor due to heat transfer. Moreover, operating the transmitter at such high temperatures for an extended period will accelerate its aging process and reduce its lifespan. 2. In the second question, \"pressure\" was replaced with a pressure gauge; by the same logic, why are laboratory temperature and humidity specified in the measurement management regulations? Different temperatures result in varying degrees of deformation of the spring tube under stress, and excessively high temperatures can also cause damage to the precision gear and wire components inside the spring tube; therefore, it is not recommended to install pressure gauges directly. Appendix: In either case, direct installation will not affect the operation of the pressure gauge at that moment, but it is not conducive to long-term use and may cause irreversible damage to the transmitter/pressure gauge.

The poster’s question reminds me of something my supervisor once said: “What will happen if electrical systems are not made explosion-proof in explosion-proof areas?” I was speechless at that moment. Do you mean that if an explosion-proof area isn’t made explosion-proof, it will definitely explode? During our maintenance work, there were still people smoking in the maintenance facility (an explosion-proof area), but nothing happened to us. 1. There are many measures to deal with high temperatures; for example, measuring the vapor and using condensation tanks, or constructing very long ducts. I’ve also seen others with heat sinks. 2. Hazards of not using it: it affects usability, accuracy, and service life. It’s hard to determine the extent; it also depends on how high the temperature is.

There is a statement in the petrochemical regulations stating that when measuring the pressure of media at temperatures above 60°C, cooling measures such as the use of condensation coils are required. Many years ago, we didn’t do it this way here. Reason: 1. The pressure guide tube is a \"dead tube\" with no flow of fluid; the heat from the medium reaches the instrument body through heat conduction. This process of heat transfer is slow and the amount of heat transferred is small, and moreover this heat is cooled by the surrounding air (even if the ambient temperature is 60 degrees). It can be estimated roughly as follows: at 400 degrees with a medium, a 3/4\" pressure valve plus 1/2\" pipes, it won’t be hot to the touch beyond 500 mm. Thinking about it the other way around, if the temperature of the pressure relief valve is high, wouldn’t that become a \"ignition source\" for the gas? 2. Gas phase changes generate a large amount of heat; substances such as steam or methanol have high phase change heats, which can damage instruments. So, use a condensation bend to cool and \"store\" the condensate, allowing it to come into contact with the instruments, while the condensate is at essentially ambient temperature. The main function of the condensation bend is indicated in red. So I have a question: Question 1: For example, when measuring gas with a medium temperature of 100°C, what hazards might arise if I use a pressure transmitter that is installed directly via flanges, without any cooling measures such as a condensation ring or long pressure transfer tubes? Gas at 100°C does not require condensation or bending as long as there is no phase change. A high temperature indicates a leak in the pressure guide tube system, as the flowing gas carries a large amount of heat. The pressure guide tube should be as short as possible. Question 2: For example, when measuring a gas with a medium temperature of 100°C, what harm can occur if I install a pressure gauge directly with a short tube without using a condensation coil? As answered above, a condensation bend is not required. Keep the pressure gauge piping as short as possible; if it is too long, it will vibrate. Pay special attention to high-temperature liquids. If the device is brought online with a gradual increase in temperature (for example, using hot oil), the valve should be opened to allow cold oil to enter the instrument first, before hot oil is used ； If the high-temperature liquid is to be introduced directly into the device, first close the valve assembly and slightly open the root valve to allow the liquid to cool down; once the temperature is appropriate, then open the valve assembly. High-temperature liquids are rarely introduced directly into the device, otherwise the pipes cannot withstand the stress due to the too rapid increase in temperature. The most common means of introducing high temperature directly is steam, and that is also done in a gradual manner. @jiaguoyun @Big Horse with Big Bow

Regarding the original poster’s question, I’d like to add a few words as well: 1. According to the installation specifications for instruments, when the temperature of the medium is above 60°C, a condensation ring must be used with the pressure gauge. This standard is established for gauges whose Bourdon tubes are made of brass, as brass has a low melting point; when the temperature rises, brass softens, which prevents the Bourdon tube made of brass from undergoing elastic deformation, or in other words, it loses its ability to deform elastically. This leads to inaccurate measurements, and in more severe cases, it can cause damage to the gauge. That’s how the standard specifies 60°C with a condensation ring. 2. Nowadays, the diaphragm material used in most pressure gauges is 316 stainless steel. Its price is not very high compared to that of brass diaphragms, and it is generally acceptable. Since 316 stainless steel can withstand higher temperatures than brass, discussions with well-known manufacturers of pressure gauges have shown that diaphragms made of this material can maintain good elastic properties at temperatures up to 120°C. When selecting 316 material pressure gauges, no condensation ring is required when the medium temperature is not higher than 100°C. 3. For pressure gauges installed directly, since there are no primary valves or pressure lead pipes, the temperature of the medium inside the gauge’s spring tube is more \"close\" to the temperature in the pipeline or equipment. In such installations, it is essential to ensure that the medium temperature does not exceed 60°C or 100°C. This is something to keep in mind. 4. For pressure gauge transmitters, since they contain electronic components, the maximum operating temperature for such components is generally 75°C. This requirement can be found in the instruction manuals of various brands of electronic instruments; there, the recommended ambient temperature is usually also no more than 75°C (for higher-quality manufacturers). Therefore, for pressure gauge transmitters, when installed directly, the temperature of the medium inside the transmitter’s measurement chamber is more \"close\" to that of the medium in the pipeline. When the medium temperature exceeds 75°C, it can cause the electronic components to operate beyond their allowable operating temperature; this may lead to accelerated aging of the instrument in mild cases, or even complete damage to the instrument in severe cases. This issue is similar to the requirements for integrated temperature transmitters. 5. Therefore, for pressure gauge transmitters, it is best to use the pressure tube installation method, as this ensures the appropriate operating temperature for the transmitter. When the pressure tapping pipe is short and the temperature of the medium is high, such as in the case of steam, a condensation tank is required instead of a condensation elbow, as the condensation tank is more reliable than the condensation elbow. So, the original poster’s question should be clear now. The reason I wrote so much is that I read the replies above, and none of them addressed the root cause of this problem, nor did they explain the original intent behind these rules. The above is for your reference!

It’s explained very clearly; great, thank you

The experts have already explained all the reasons and negative consequences in great detail; I can only share my own opinion. Action must be taken, as failing to do so will affect the equipment’s service life.

Thank you! Thank you! The language is easy to understand

Simply put, it’s because they’re afraid that the gauge diaphragm will get damaged by heat. What’s there to discuss? If your instrument’s measuring components can withstand high temperatures and corrosion, then you can certainly choose any installation method you prefer, provided that those components are indeed capable of withstanding such conditions. The vast majority of instruments we use function properly at temperatures between -30 and 60 degrees. If you were to measure a substance at 100 degrees Celsius, what do you think would be the consequences of taking such a direct measurement?