Choosing a suitable high-temperature resistant electric contact pressure gauge for pressure monitoring and interlock protection in processes such as refining, cracking, and liquefaction has always been an important task for accurate and safe measurement in project engineering. The electric contact pressure gauge is not only “pressure reading”, but also a “sentinel” for protecting the safe operation of the device. Incorrect selection can result in damage to the instrument panel, or even unplanned parking or safety accidents.
The five factors of “medium, temperature, protection, contact, and installation” are crucial when selecting a high-temperature resistant electric contact pressure gauge.
1.Firstly, the most important factors are high temperature resistance and impact resistance
This is the primary consideration factor, which must be viewed from two levels: the “header” and the “liquid receiving part”.
Regarding the selection of liquid receiving materials (diaphragm/spring tube):
2.316/316L stainless steel: This is the most basic and universal choice, with acceptable corrosion resistance, but its strength will decrease at high temperatures.
For example, in working conditions where the project temperature is below 300 ° C, the medium is clean hydrocarbons, water vapor, air, nitrogen, and the chloride ion content is extremely low (usually<50ppm). For example, general fuel gas, circulating water, and non acidic oil products. You can choose 316/316L stainless steel.
Monel alloy: It has better corrosion resistance for high-temperature sulfur-containing media, such as acidic gases in oil refining. For example, applicable temperature: -100 ° C to 480 ° C. Resistant to seawater corrosion, with better performance than stainless steel in reducing media (such as hydrofluoric acid, hydrochloric acid, alkaline solution), hydrofluoric acid alkylation device, seawater cooling system, alkaline environment: such as alkali washing tower.
Hastelloy C276: Suitable for strong corrosion and high temperature environments, it is the preferred choice for high corrosion conditions such as cracking equipment.
Tantalum: It has excellent corrosion resistance, but is expensive and often used in special corrosive conditions. For example, applicable temperature: -196 ° C to about 1000 ° C (forming a protective film on the surface in an oxidizing atmosphere), high temperature, high corrosion: such as the quench oil/quench water system of an ethylene cracking unit (containing organic acids, bromides, etc.).
Suitable for high chloride ion environments such as seawater injection systems and desalination units. Wet chlorine gas environment. Flue gas desulfurization (FGD) system, etc.
Filling fluid (damping fluid):
This must be filled. Dry meters are strictly prohibited from being used in high temperature and vibration environments. Filling fluid (such as silicone oil or fluorine oil) can effectively lubricate the movement, shock absorber, prevent pointer shaking, and take away some heat, protecting the electrical contact mechanism inside the meter head.
Temperature resistance level: Ordinary silicone oil can withstand temperatures of about 200 ℃, while high-temperature silicone oil can reach temperatures above 300 ℃. When selecting, the temperature resistance level of the filling liquid must be higher than the maximum temperature of the process medium.
Effects of heat dissipation devices:
Heat sink/condenser/siphon: If the temperature of the medium exceeds the temperature tolerance limit of the instrument itself (for example, if the medium temperature is 300 ℃, the instrument temperature tolerance is only 85 ℃), a heat dissipation device must be installed. A radiator is the most commonly used option, which reduces the temperature entering the header by increasing the heat dissipation area.
Electric contact magnetic assisted vs. inductive form:
In refining equipment, magnetic assisted electrical contacts are the absolute mainstream.
Magnetically Coupled Electrical Contact:
It uses the coupling effect of magnetic steel to drive the action of electrical contacts, and the contacts and pointers are isolated.
Its advantages include vibration resistance, anti shake, large capacity, and long lifespan. In places with high vibration such as the pump outlet, compared to ordinary contacts, it is more prone to misoperation (ignition), but magnetic assisted type does not. If you are in the refining industry, please choose magnetic assistance, especially interlocking protection circuits.
Ordinary electrical contact (Direct Acting):
The pointer of a regular electric contact pressure gauge directly drives the micro switch.
However, it is prone to misoperation under vibration conditions, with small contact capacity and short working time.
If it is only used in non vibration, non critical, and alarm only work environments, ordinary electrical contacts can be selected.
In the oil refining and chemical industry, where every inch of land is precious, reliability always comes first. A regular electric contact pressure gauge is like a fragile “glass cup”, while a magnetic assisted electric contact pressure gauge is a sturdy “stainless steel insulated cup”. Although it is a bit more expensive, it allows you to sleep soundly while the device is running, avoiding unplanned parking caused by a false alarm. Its value far exceeds the difference of a few hundred dollars.
Installation and maintenance
Selection of installation method:
Radial direct installation: the most commonly used, but pay attention to the orientation of the dial for easy observation.
Axial edge installation: suitable for panel installation.
Universal/Turnaround Installation: Suitable for situations where the viewing angle is limited.
Process connection:
The standard is 1/2 “NPT or M20 × 1.5. If the medium is prone to crystallization and blockage, an open flange connection or diaphragm sealed pressure gauge should be selected to avoid blockage of the pressure tap“
How to choose based on the example projects below:
The catalytic cracking unit (FCCU) of a refinery in the Middle East is the core unit of refining, which breaks down heavy oil into light oil (gasoline, diesel, etc.). Its reaction regeneration system has high temperature (>600 ℃), large pressure fluctuations, strong abrasion of catalyst (solid powder), and contains high-temperature oil and gas, which is flammable and explosive. The ambient temperature in the Middle East during summer can reach 55 ° C, with smoke (including catalyst dust) medium at high temperatures and operating pressure of 0.25 MPaG
Operating temperature: 280 ° C, explosion-proof area: Zone 1, Group IIA, T3 (high ambient temperature, pay attention to temperature rise)
The problem with the project is that the medium temperature is 280 ° C, far exceeding the limit of ordinary pressure gauges (usually resistant to temperatures of 85 ° C).
Solution:
Choose a high-temperature resistant electric contact pressure gauge, and the temperature resistance level of the gauge head should be higher than the ambient temperature (at least 85 ° C).
Install a heat sink (Syphon/Snuber): Install a circular heat sink (commonly known as a “pig tail pipe” or “condenser ring”) between the pressure tap and the instrument, using natural convection of air to dissipate heat and reduce the temperature of the medium entering the meter head to below 85 ° C. This is the standard practice for such working conditions.
Filling fluid: High temperature silicone oil (temperature resistance>300 ° C) must be filled to lubricate the movement, shock absorber, and assist in heat dissipation.
2. Liquid receiving material and anti blocking design
Problem: The medium contains catalyst dust, which is prone to wear and blockage of the pressure tap.
Solution:
Liquid receiving material: 316 stainless steel is selected for the spring tube and joint. Although the sulfur content of Middle Eastern crude oil may be high, the medium here is regenerated flue gas, which has relatively weak corrosiveness, and 316SS is sufficient to cope with it.
Anti blocking design: Choosing a diaphragm sealed pressure gauge (Chemical Seal) with a flushing ring/open flange connection is a better solution. Diaphragm can isolate catalyst dust outside the pressure sensing system, avoiding blockage of the pressure tube. If the budget is limited, at least a pulse damper (Snuber) should be installed before the pressure tap, which can buffer pressure pulsation and prevent dust from directly impacting the spring tube.
3. Electrical contact form (core)
Problem: The pressure fluctuation and vibration at the outlet of the main fan are large, and ordinary electrical contacts are prone to misoperation (shaking can cause frequent on-off of contacts, burn contacts, or mistakenly send parking signals).
Solution:
Mandatory selection of magnetically coupled electrical contacts. Its magnetic coupling design can effectively resist vibration interference, ensuring that the contact will only move stably when the pressure truly reaches the set point, avoiding false interlocking parking.
4. Explosion proof and electrical parameters
Problem: Middle Eastern projects typically follow IEC/ATEX or local oil company standards (such as Aramco standards).
Solution:
Explosion proof rating: Ex d IIC T6 Gb (explosion-proof type, suitable for Zone 1). Due to the high ambient temperature of 55 ° C, special attention should be paid to the “maximum surface temperature” T6 (85 ° C) of the instrument, which must be higher than the ambient temperature and leave a margin.
Electrical interface: M20 x 1.5 cable sealing joint, protection level IP66 (to cope with sandstorm weather in the Middle East).
Contact capacity: set to 220VAC, 5A. This contact does not directly drive high-power equipment, but is connected to the DI card or intermediate relay of the DCS/ESD system, so the 5A capacity is more than sufficient.
5. Install accessories
Installation method: Radial direct installation (Bottom Mount).
Valve group: equipped with three valve group or five valve group for online isolation, drainage and calibration.
In high-temperature and high-pressure conditions such as refining and cracking, electric contact pressure gauges are not only measuring tools, but also the “last line of defense” for device safety. When selecting, “high temperature resistance, vibration resistance, corrosion resistance, and high reliability” are the core principles. It is necessary to accurately match the contact material according to the composition of the medium, prioritize the use of magnetic assisted electrical contacts to resist on-site vibration interference, and ensure that the explosion-proof and protection levels meet strict environmental requirements. The correct selection can effectively avoid unplanned parking, ensure long-term stable operation of the device, and its value far exceeds the price of the instrument itself.