In winter, as the temperature gradually decreases, when the measured medium is transmitted to the transmitter through the measuring pipeline, phenomena such as freezing, solidification, and crystallization often occur when the ambient temperature is too low. Due to the low ambient temperature, it exceeds the normal working temperature range of the instrument used, directly affecting the accuracy of the instrument measurement display. And various instrument points such as pressure, flow rate, liquid level, temperature, etc., whose measuring medium is mostly liquid, are more susceptible to measurement errors due to low temperature, and in severe cases, may cause safety accidents such as poisoning, fire, and explosion.

In summary, the anti cold and anti freezing work of instruments and meters is particularly important. Some users of large instruments and meters have taken early measures to cope with the situation, such as power plants, water plants, petroleum, chemical industries, etc., which have formulated suitable anti cold and anti freezing work systems for their own enterprises. Let's explore how winter instrument users should perform instrument antifreeze work.

Antifreeze treatment is required for instruments and instrument measurement pipelines. The objects that require heat tracing and insulation mainly include transmitters installed inside the instrument insulation box, external float type liquid level transmitters or other forms of outdoor installed liquid level transmission units, as well as detection and measurement pipelines for pressure, differential pressure, flow and other instruments. Prevent such accidents from occurring through selection or other means. The measures usually taken include: selection, insulation and heat tracing, maintenance (point inspection, sewage discharge), etc.

1、 Selection measures

(1) Choose instruments with insulation devices. Based on the type, purpose, and intended installation location of the instrument, propose the insulation and antifreeze requirements for the instrument, and then submit them to the manufacturer for processing.

(2) Signal remote transmission instruments and display heads should consider the requirements of environmental temperature resistance, and isolation fluid with isolation fluid should consider the requirements of environmental temperature resistance.

(3) Metal rotor flow meters, electric target flow meters, volumetric flow meters, mass flow meters, etc. generally do not require separate heat tracing.

(4) When selecting, the primary consideration is generally the practicality and economy of the instrument. Practicality refers to easy maintenance and accurate measurement, while economy means affordability. The two should be combined with each other, and mass flow meters, metal rotors, electric targets, etc. should not be used solely for convenience and maintenance free purposes. So the correct selection is also a measure to prevent freezing and condensation. In addition, when installing instruments, full consideration should be given to their anti freezing and anti condensation properties, such as keeping the pressure conduit as short as possible, conducting frequent inspections and sewage discharge, and facilitating heat tracing. Otherwise, even the best selection will not be effective.

(5) In some places in the north, the temperature difference between day and night is too large, and it can reach over -20 degrees at night. If we solve this problem in terms of selection, the cost-effectiveness is quite high and not cost-effective. The solution to antifreeze is to choose insulation and heat tracing, maintenance (point inspection, sewage discharge) and other methods.

2、 Thermal insulation measures

Insulate with insulation materials, that is, wrap the parts of the instrument that are prone to freezing or afraid of freezing with insulation materials. During winter, it is necessary to inspect and regularly discharge pollutants to prevent damage to the insulation materials of the packaging.

3、 Heat tracing measures

1. Steam tracing measures

Use pipe steam heating for insulation. Before delivering steam during winter insulation, it is necessary to check whether the steam insulation pipeline is unobstructed or blocked. Steam is available 24 hours a day, so it should not be too hot. Sometimes, the amount of insulation steam should be adjusted according to changes in weather temperature to prevent the evaporation of condensate in the transmitter's pressure tube caused by high temperature from affecting the transmitter's operation, or the freezing of condensate in the transmitter's pressure tube caused by low temperature from affecting the smooth operation of the transmitter.

2. Insulation protection box measures

a、 The electric heating tube heat tracing insulation box consists of three main parts: the box body, the heater, and the instrument bracket. Its structural form is the same as that of the protection box, except that the box is equipped with an electrical heating device. The structural form is shown in the figure. The electric heating device is composed of electric heating tubes and a temperature controller. There are sockets on the side of the box body. When the power is turned on, the box is heated to the desired temperature, and then the temperature controller is turned on to continue heating. By repeatedly working, the temperature inside the box can be maintained within a certain range. The main parameters of its constant temperature heater are:

⑴ Rated voltage 200V.50Hz

⑵ Rated power 300-500W

⑶ Temperature control can be customized by the user

⑷ The constant temperature heater can also be made into an explosion-proof type

There are three types of materials for electric heating tubes: copper tube, carbon steel tube, and stainless steel tube.

b、 Steam pipe heat tracing insulation box, the heat tracing pipe is made of metal pipes in an S-shaped structure The upper and lower parts of the box are welded with a welded through plate joint and a heat tracing pipe. The heat tracing pipe is installed inside the box to achieve heating by circulating steam inside the tube. There are generally two types of materials for heat tracing pipes, namely copper pipes and seamless steel pipes (carbon steel).

c、 Adding another layer of insulation cotton to the key instrument box and sealing it with glue at the door of the insulation box and the inlet and outlet of the pipeline can achieve better insulation and antifreeze effect on the instrument system.

3. Electric heating belt measures

Electric heat tracing insulation technology is a new type of heating technology that directly converts electrical energy into thermal energy. Install insulated cables, wrap the heat tracing tape around the instrument or stick it inside the instrument cabinet (but pay attention to the length of the heat tracing tape used and ensure it is economical and moderate).

A single-phase constant power electric heating belt suitable for heat tracing, antifreeze, and insulation of pipelines, valves, and pump bodies, or for maintaining the process temperature of instrument pipelines. The heat generation per unit length is constant, and the output power is not affected by changes in ambient temperature. The length and power are proportional, and can be spliced arbitrarily during installation, but a heating joint (at least 2.5m) must be retained. The outer woven layer has heat transfer and dissipation functions, and can also serve as a safe grounding for anti-static. Mainly used for antifreeze and insulation of various pipelines and instruments, with a maximum maintenance temperature of 150 ℃. Attention: Heat tracing and insulation for liquid pipelines with strict temperature control requirements (temperature controllers must be used).

There is another product on the market, which is a soft packaged electric heat tracing protective cover, specifically designed for instrument heat tracing in relatively small spaces, explosion-proof, mainly installed at the pressure pipe section and valve of the instrument.

4、 Maintenance measures

1. Installation measures

Reasonably choose the installation location: a dry, rain and snow free place.

2. Inspection measures

When conditions permit, a dedicated person shall conduct daily technical confirmation and disposal of whether the insulation material is damaged and whether the steam pipeline is blocked.

3. Alarm measures

If conditions permit, sound and light alarm devices can be installed for steam leakage or power outage status to facilitate the detection and timely remediation of hidden dangers in insulation and antifreeze measures.

4. Inspection measures

The regional instrument maintenance responsible person shall conduct regular inspections according to the predetermined inspection route. During the inspection, it is necessary to check whether the insulation pipeline valves are normal, whether the insulation box is normal, whether the drainage device is normal, whether the insulation material packaging is intact, and whether the electrical heating and power supply components are normal. Key inspections should be carried out on instruments that are prone to freezing, and inspection records should be kept. Dry, complete, and clean maintenance should be carried out on the instruments and their insulation and anti freezing measures to promptly solve insulation and heat tracing problems that occur on site.