Thread Content
How should instruments be insulated and protected from freezing in winter? In winter, as temperatures drop gradually, phenomena such as freezing, solidification, and crystal formation often occur when the medium is conveyed through pipelines to the transmitter. The extremely low ambient temperatures exceed the normal operating temperature range of the instruments used, which directly affects the accuracy of the measurements displayed by these instruments. Various instruments used to measure pressure, flow rate, liquid level, temperature, etc., typically use liquids as the medium for measurement. Affected by low temperatures, these instruments are more prone to measurement errors, and in severe cases, it may lead to safety incidents such as poisoning, fires, and explosions. In summary, it is particularly important to protect instruments from cold and freezing conditions. Some large-scale instrument users took preventive measures well in advance; for example, power plants, water treatment plants, as well as oil and chemical enterprises all established cold and frost prevention protocols suitable for their own operations. To prevent freezing of instruments and their measurement pipelines, objects that require heating and insulation include: transmitters installed inside instrument enclosures, external float-type level transmitters or other types of level transduction units installed outdoors, as well as the detection and measurement pipelines for instruments such as pressure, differential pressure, and flow meters. To prevent instrument failures in low-temperature conditions, the following measures are typically taken: I. Selection measures (1) Choose instruments equipped with insulation devices. Based on the category, purpose of the instrument, and the location where it is intended to be installed, the insulation and anti-freezing requirements for that instrument are determined, and then submitted to the manufacturer for handling. (2) Signal remote transmission instruments and display meters must meet the requirements for low-temperature environments; those equipped with isolation fluids need to satisfy the requirements regarding the low-temperature performance of such fluids. (3) Metal rotameters, electric target flowmeters, positive displacement flowmeters, mass flowmeters, etc. generally do not require separate heating. (4) When selecting a model, the primary considerations are generally the practicality and cost-effectiveness of the instrument. Practicality refers to ease of maintenance and accurate measurement, while cost-effectiveness simply means it being inexpensive. The two should be combined; it is not appropriate to choose mass flow meters, metal rotors, electric targets, etc., solely for the sake of convenience and reduced maintenance. Therefore, selecting the right model is also a measure to prevent freezing and condensation. Furthermore, when installing instruments, proper consideration should be given to preventing freezing and condensation; for example, the pressure transfer pipes should be as short as possible, regular inspections and cleaning should be carried out, and heating systems should be made available – otherwise, no matter how well the instruments are selected, it will be of no use. (5) In some areas in the north, the temperature difference between day and night is extremely large; temperatures can drop to below -20 degrees at night. If this issue is not addressed through proper product selection, it results in a poor cost-performance ratio, making it uneconomical. Choosing insulation and heat tracing, along with maintenance methods such as routine inspections and sewage discharge, are the best solutions to prevent freezing. II. Insulation Measures Use insulating materials to provide insulation, that is, wrap the parts of the instruments that are prone to freezing or sensitive to cold with such materials. When winter arrives, it is necessary to conduct inspections and regularly remove waste material to prevent damage to the insulation material of the packaging. III. Heat tracing measures 1. Steam heat tracing measures Using steam from pipes for heating and insulation. Before supplying steam for insulation in winter, check whether the steam insulation pipeline is unobstructed or blocked. 2. Insulation protection box measures (1) The electric heating tube type insulation box consists of three main components: the box body, the heater, and the instrument holder. Its structural format is the same as that of a regular protection box; the difference lies in the fact that it is equipped with an electrical heating device inside. The electric heating device consists of an electric heating tube and a temperature controller; there is a socket on the side of the box. Once power is supplied, the interior of the box heats up to the desired temperature, after which the temperature controller turns on the power to continue raising the temperature. Through repeated operation, the temperature inside the box can be maintained within a certain range. (2) Steam pipe heating insulation box, whose heating pipes are made of metal tubes in an S-shaped structure; the top and bottom of the box are welded to the heating pipes using welded plate joints, and the heating pipes are installed inside the box with steam entering from the top and exiting from the bottom, thereby achieving heating through the circulation of steam within the pipe chambers. Heat tracing tube materials are generally divided into two types: copper tubes and seamless steel tubes (carbon steel). 3. Electric heating strip measures Electric heat tracing insulation technology is a new type of heating technique that converts electrical energy directly into thermal energy. By installing insulated cables, wrapping the heating tape around the instruments, or sticking it inside the instrument cabinet (but be careful with the length of the heating tape used to ensure it is appropriate and cost-effective). A single-phase constant-power electric heating tape suitable for use in heating, anti-freezing, and insulation of pipes, valves, and pump bodies, or for maintaining the process temperature of instrument pipelines. It has a constant heat generation per unit length; its output power does not change with variations in ambient temperature. The length required for use is proportional to the power level. It can be cut as needed during installation, but at least one heating section (i.e., 2.5 meters) must be retained. The outer woven layer serves to transfer and dissipate heat, and it also functions as a safe grounding element to prevent static electricity. It is mainly used for anti-freezing and insulation of various pipes and instruments, with a maximum maintainable temperature of 150°C. Note: Heating and insulation for liquid pipelines where strict temperature control is required (a temperature controller must be used). There is another product available on the market: a soft-packaged electric heat tracing sleeve, designed specifically for heating instruments in spaces with limited space. It is explosion-proof and is mainly installed on the pressure transfer tubes of instruments as well as at valves. IV. Maintenance Measures 1. Installation Measures Select an appropriate installation location: a dry place free from rain, snow, and water leakage. 2. Inspection measures As needed, a designated person conducts daily technical checks and takes appropriate actions to ensure that the insulation materials are not damaged and that the steam pipelines are not blocked. 3. Alarm measures As needed, small audio-visual alarm devices can be installed to detect steam leaks or power outages, thereby facilitating the identification of potential issues related to insulation and anti-freezing measures and enabling timely correction of those issues. 4. Inspection measures The person responsible for instrument maintenance in the area conducts regular inspections along the predetermined routes. During inspections, it is necessary to check whether the valves of the insulated pipelines are functioning properly, whether the insulation boxes are in good condition, whether the drain devices are working correctly, whether the insulation material packaging is intact, and whether the components responsible for electric heating are functioning properly. Conduct thorough inspections of the instruments in the freeze-proofing equipment and keep records of these inspections; maintain the instruments as well as the insulation and freeze-protection measures in a dry, intact, and clean condition, and address any issues related to insulation and heating that arise on site promptly.