Instrumentation: [Weekly Question] Week 40 of 2011: Measures and materials for preventing freezing in instrument pipelines

1. Location and industry type: Kaifeng, Henan; chemical production. 2. Heat tracing method and key points: copper tube wrapping, heat tracing with 0.4MPA steam; it is necessary to ensure no dead zones exist and that condensate water can be effectively recovered. 3. Specifications of insulation material: ordinary silicate insulation cotton, covered with aluminum foil -

1. Location and industry type: Yichang, Hubei – chemical manufacturing. 2. Methods and key points for heat tracing: Prevent freezing of instruments and the pipelines used for measurement; measures include selecting appropriate devices, using insulation for heat tracing, and carrying out maintenance tasks such as regular inspections and sewage removal.         In winter, when the medium to be measured is conveyed through the measurement pipeline to the transmitter, phenomena such as freezing, solidification, and crystal formation can occur when the ambient temperature is too low. Since such low temperatures exceed the normal operating temperature range of the instruments used, it directly affects the accuracy of the measurements displayed by those instruments. To this end, it is necessary to take anti-freezing measures for instruments and their measurement pipelines. The components that require heating and insulation mainly include transmitters installed within 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. Avoid such accidents through proper selection or other means.     The measures typically taken include: selection, insulation and heat tracing, maintenance (spot inspections, drainage), etc.   　  I. Selection measures: Choose instruments equipped with insulation devices. Based on the category and purpose of the instrument, as well as the location where it is intended to be installed, the insulation and anti-freezing requirements for that instrument are determined, and these requirements are then submitted to the manufacturer for handling.     　In some areas in the north, the temperature difference between day and night is extremely large; at night, temperatures can drop below -20 degrees. Addressing this issue through product selection would result in a poor cost-performance ratio, making it uneconomical. On the other hand, using insulation and heating systems, along with maintenance measures such as regular inspections and waste removal, are the best ways to prevent freezing.     　II. Insulation measures Use insulation materials to insulate, that is, wrap the parts of the instrument that are prone to freezing or sensitive to cold with such materials. When winter arrives, inspections should be carried out and waste should be removed regularly to prevent damage to the insulation material of the packaging.    　 III. Heat tracing measures 1. Steam heat tracing measures That is, 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. It is best to keep the steam flowing 24 hours a day, but not at too high a temperature. Sometimes it is also necessary to adjust the amount of steam supplied based on changes in weather and temperature, in order to prevent condensation inside the transmitter’s pressure tubes from vaporizing due to high temperatures, which could affect the transmitter’s operation, or to prevent the condensation from freezing due to low temperatures, which could also hinder proper functioning of the transmitter.     　2. Insulation protection box measures a. The electric heating tube-based insulation box consists of three main components: the box body, the heater, and the instrument holder. Its structural design is similar to that of a regular protection box; the difference lies in the presence of an electrical heating device inside the box. As shown in the diagram, the heating device is made up of electric heating tubes and a temperature controller. There are sockets on the sides of the box body, and once power is supplied, the temperature inside the box rises to the desired level. Once this temperature is reached, the temperature controller continues to supply power to keep the temperature high. Repetitive operation is used to keep the temperature inside the box within a certain range. The main parameters of its constant-temperature heater are as follows: ⑴ Rated voltage: 200V, 50Hz; ⑵ Rated power: 300–500W; ⑶ The control temperature can be set by the user; ⑷ The constant-temperature heater can also be designed as an explosion-proof version; ⑸ There are three types of materials for the heating elements: copper tubes, carbon steel tubes, and stainless steel tubes.     b. Steam pipe heating insulation box: The heating pipes are made of metal tubes in an S-shaped configuration. The top and bottom of the box are welded to the heating pipes using welded plate joints; these heating pipes are installed inside the box with steam entering from the top and exiting from the bottom, and heating is achieved through the circulation of steam within the pipe channels. Heating tube materials are generally divided into two types: copper tubes and seamless steel tubes (carbon steel).     c. Adding another layer of insulation material to the key instrument cabinets, and sealing the openings of these cabinets as well as the inlet and outlet pipelines with glue, can achieve a better insulation and anti-freezing effect for the instrument system.     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. Install insulated cables; wrap the heat tracing tape around the instruments or stick it inside the instrument cabinet (be careful to choose a length for the heat tracing tape that is appropriate and cost-effective).   　  A single-phase constant-power electric heating tape suitable for heating, anti-freezing, and insulation of pipes, valves, and pump bodies, or for maintaining the process temperature of instrument pipelines. It features 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 at will 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: Heat tracing 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 in 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: When conditions permit, a dedicated person shall conduct daily technical checks and take necessary actions to determine whether the insulation materials are damaged or whether the steam pipelines are blocked.     　3. Alarm measures: Where possible, install small audio-visual alarm devices that detect steam leaks or power outages, to facilitate the identification of potential issues related to insulation and anti-freezing measures and their prompt correction.     　　 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. 3. Specifications and models of insulation materials: The specific details are unclear.

1. Location and industry type: Hunan, chemical production. 2. Heat tracing method and key points: Steam-insulated pipelines. 3. Specifications of insulation material: Ordinary insulation cotton

Reply to 1# Baghdad: 1. Location and industry type: Sichuan, oil refining and chemical industry }& V2 d8 u* h 2. Method of heat preservation and key points: Steam for insulating the pipelines) b5 g% k0 s$ r$ S 3. Specifications of insulation materials: Seamless steel pipes, insulating rock wool, iron sheets, steam traps (or returning water to the main return pipe)

Reply to 1# Baghdad: 1. Anhui’s petrochemical industry; 2. Low-pressure steam is used for instrumentation pipelines; 3. Ordinary insulation cotton and glass cloth are used for protection

1. Location and industry type: Huizhou, Guangdong; advanced processing of propylene. 2. Heating method and key points: steam copper tube heating, with insulation cotton added； When high standards are required, steam copper pipes should be fitted with thermal paste and insulation foam. 3. Specifications for insulation materials: Ordinary rock wool, with a thickness of 30–50 mm. 1. Location and industry type: Yangzhou, Jiangsu; acrylic deep processing. 2. Method of heat tracing: The same as above; however, when high standards are required, a dedicated instrument insulation box should be used, with steam heat tracing and insulation in place, along with temperature control. 3. Specifications for insulation materials: These are usually ready-made products from manufacturers and can be used directly. Insulation materials may include rock wool, aluminum silicate, etc

This post was last edited by denghl on 2012-12-12 21:04. In Shandong’s chlor-alkali industry, electric heating and steam heating are used for heating purposes. The protective materials used are as follows: for electric heating, stainless steel tubes are employed, covered with ordinary silicate insulation material, and then enclosed in a thin aluminum alloy sheet. For steam heating, composite silicate tubes are used; these tubes are tied together with galvanized iron wire, covered with a thin aluminum alloy sheet, fixed using M4 self-tapping screws, and the gaps between the components are filled with adhesive.

1. Location and industry type: Shandong, oil refining and chemical industry. 2. Heat tracing method and key points: Steam-insulated pipelines. 3. Specifications of insulation material: Ordinary insulation cotton, covered with aluminum foil

Location: Yan’an, Shaanxi Province. Industry: Refining and petrochemicals. Methods and key points for heat tracing: 1. The vast majority of instruments that require heat tracing are insulated using steam; for this purpose, 18x3 seamless tubes are used to convey low-pressure steam. A drain valve is installed on the return line, while the condensate is sent to the condensate recovery system. The pipes are wrapped with insulating rock wool, which is then covered with glass cloth and painted. When performing heat tracing, it is necessary to maintain a certain distance between the heat tracing pipes and the pressure measurement wires, in order to prevent the medium inside these wires from vaporizing due to excessive temperatures. When wrapping both the heat tracing pipes and the pressure measurement wires with insulating rock wool, it should be done loosely enough to allow heat air to circulate; it should not be wrapped too tightly, as this would prevent heat from reaching the pressure measurement wires. If the transmitter is equipped with a steam-heated insulation box, the insulation layer inside the box must be properly protected; if it is damaged, it should be replaced promptly. In windy and cold weather, the door of the instrument box should be kept closed. If the transmitter does not have a insulation box, when using steam for heating, the heating pipeline must reach the diaphragm box of the transmitter, but it should not be too close to it; an outer insulation layer should be used. Similarly, the insulation layer should form a cavity to ensure that sufficient hot air can flow within it. Heating the diaphragm box is intended to prevent the medium there from freezing, while maintaining a certain distance is necessary to avoid excessive temperatures that could lead to inaccurate measurements or damage to the diaphragm box. 2. In some transmitters, the temperature of the medium being measured is quite high, such as in steam systems. For these instruments, it is possible to use self-heating methods, taking into full account the length of the pressure lead wires; the temperature of the pipeline can be used to heat both the transmitter and the pressure lead wires. With this heating method, the pressure lead wires should be short, and insulating material must be used in a way that creates a cavity, so that the heat from the pipeline can reach the farthest points. It is also advisable for the transmitter to be located above the heat source. 3. Electric heating: Some of the pipelines in our factory are equipped with electric heating. The details regarding electric heating and the maintenance of such heating systems are clearly stated on the 3rd floor, so there is no need to repeat them here.

1. Location and industry type: Sichuan, chemical manufacturing. 2. Method of heat preservation and key points: Steam insulation mixed in. 3. Specifications of insulation materials: Seamless steel pipes, insulating rock wool, aluminum foil