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Instrumentation is one of the common devices in chemical plants. Previous articles by Xiao 7 have covered topics related to its selection and troubleshooting; today, we will discuss the matters that need attention during the installation of instruments. The installation of instruments in industrial plants involves the detection of temperature, pressure, flow rate, and level; process analysis and data display; as well as automatic regulation and control. To ensure that all these functions operate properly, proper installation is crucial. Below is a detailed explanation of this. Precautions before installation: 1. Before installing the instrument, the process pipelines should be purged to prevent ferromagnetic substances remaining in the pipes from adhering to the instrument, which could affect its performance or even damage it. If unavoidable, a magnetic filter should be installed at the inlet of the instrument. The instrument itself does not participate in the gas purging prior to commissioning, to avoid damaging it. 2. Before installing the gauge in the process pipeline, check for any damage to it, and open the housing to remove the filler that holds the pointer in place. 3. The installation style of instruments can be vertical or horizontal; in the case of vertical installation, it is necessary to ensure that the angle between the instrument’s central vertical line and the vertical line itself is less than 2° ； If installed horizontally, the angle between the instrument’s horizontal center line and the horizontal line should be less than 2°. 4. The pipes upstream and downstream of the instrument should have the same diameter as that of the instrument; the connection flanges or threads must match those of the instrument. The length of the straight pipe section upstream of the instrument should be 5 times its nominal diameter, while the length of the straight pipe section downstream should be 250 mm or more. 5. Since the instrument transmits signals through magnetic coupling, in order to ensure its performance, no ferromagnetic materials are allowed to be present within at least 10 cm around the installation site. 6. Instruments for measuring gases are calibrated at a specific pressure; if the gas is released directly into the atmosphere at the outlet of the instrument, a pressure drop will occur at the float, resulting in distorted data. Under such operating conditions, a valve should be installed at the outlet of the instrument. 7. Instruments installed in pipelines should not be subjected to stress; the inlet and outlet of the instruments should have appropriate pipeline support to keep them in a state of minimal stress. 8. When installing instruments with a PTFE (polytetrafluoroethylene) lining, extra care must be taken. Since PTFE deforms under pressure, the flange nuts should not be tightened excessively. 9. For instruments with LCD displays, try to avoid direct sunlight on the display during installation to extend the lifespan of the LCD. 10. When measuring low-temperature media, a jacketed type should be selected. Precautions during installation: 1. Avoid making openings in the instruments on the shaped pipes. 2. Pay attention to the length of the straight sections before and after the flow meter. 3. For flowmeters such as electromagnetic and mass flowmeters that require grounding, grounding shall be carried out in accordance with the instructions. 4. When welding process pipelines, the grounding wire should be kept away from the instrument itself to prevent the grounding current from flowing through the instrument and causing damage to it. 5. During process welding, prevent the grounding current from flowing through the capillary pressure tubes of single and double flanged instruments. 6. For medium and high-pressure pressure transfer pipes, if argon arc welding or socket welding can be used, such methods shall be employed. When the wind speed is >2 m/s, wind protection measures should be taken; otherwise, flux-cored welding wires should be used. When the wind speed is >8 m/s, wind protection measures are mandatory; otherwise, welding must be stopped. 7. Pay attention to the installation direction of the pressure tapping port for the flow meter’s throttling device. 8. Hot bending of stainless steel pressure guiding pipes is strictly prohibited ； It is strictly prohibited to bend the pressure lead pipe flat. 9. The installation locations of the instrument pressure conduits, air ducts, and wire conduits should be such that they do not interfere with future process operations; they should be kept away from areas subject to high-temperature corrosion, and they must be fixed securely ； For the wire raceway running downward from above, its lowest lead-out end must be lower than the wiring entry point of the connected instrument ； A drip tee should be added at the lowest point of the conduit ； Y-type or conical explosion-proof sealing joints should be added near the instrument side ； A drain (sludge) valve should be installed at the lowest point of the main instrument air line. 10. For the copper gaskets used in instruments, if they have not been annealed, they should be annealed before use. Attention should also be paid to the allowable temperature, medium, and pressure conditions for gaskets made of various materials. 11. Within the on-site instrument wiring box, grounds from different grounding systems must not be connected together; the shielding wires of all instruments should be connected to their respective upper and lower shielding layers separately, and it is strictly prohibited to twist these together for connection. 12. When the instruments are in a location that makes them difficult to observe or maintain, obtain the consent of Party A before changing their position or installing a platform. 13. Joints are strictly prohibited in the middle of the instrument wires; in case of special circumstances, approval from Party A must be obtained, and proper records of such modifications must be kept. Joints in compensation wires should be made by welding or crimping. 14. Stainless steel welds should be subjected to pickling, passivation, and neutralization treatment. 15. Instruments and fittings that require degreasing must be subjected to degreasing treatment in strict accordance with the relevant specifications. After degreasing, these instruments and fittings should be properly sealed and stored to prevent secondary contamination during storage and installation. 16. Stainless steel pipelines must not come into direct contact with carbon steel. 17. Galvanized and aluminum alloy cable trays must not be cut or drilled using electric or gas welding; mechanical methods such as toothless saws and specialized drilling tools should be used instead for cutting and making openings. 18. Stainless steel pipes must not be cut or drilled using electric or gas welding; plasma or mechanical cutting and drilling methods should be employed instead. 19. Wiring ducts, cabinets, panels, etc., for instruments with a voltage greater than 36V shall be grounded; the threads of the grounding wiring ducts shall be treated with conductive paste ； The threads of the wiring ducts for instruments with a voltage of 36V or less should be treated to prevent rust ； The exposed thread should not be more than one thread. 20. The instrument conduit in explosive hazard areas should maintain electrical continuity. 21. For insulated instrument circuits with voltages below 100 volts, a 250V insulation resistance tester should be used to measure the insulation resistance, which should be ≥5 megohms. 22. Aluminum alloy cable trays should be bridged with short-circuit wires, while galvanized cable trays should be secured with no fewer than two anti-loosening screws. Trays within 30 meters in length must be reliably grounded at both ends; for lengths exceeding 30 meters, an additional grounding point should be added every 30 meters. 23. When instrument wires of different grounding systems or instrument wires and power wires share the same tray, they should be separated by a metal partition. 24. Gas welding is strictly prohibited in the installation and processing of dashboards, cabinets, boxes, and benches; welding should not be used for fixation, and mechanical drilling methods are preferred for making holes. 25. The blind ends for instrument heating and return water should not be greater than 100 mm. 26. A pipe cap to prevent valve leakage should be added at the lower outlet of the transmitter drain valve (especially in explosion-proof areas). 27. One end of instruments, their conduit pipes, and pressure guiding pipes should be fixed to the thermal expansion zone (such as towers or accessories that expand along with the towers), while the other end should be fixed to the non-thermal expansion zone (such as safety protection rooms). When connecting the instruments, it is necessary to leave a certain amount of thermal expansion allowance for flexible pipes, conduit pipes, and pressure guiding pipes, based on the actual site conditions. 28. Tower-mounted cable trays and conduit pipes should be equipped with thermal expansion joints or flexible connections according to the actual conditions on site. Other: 1. For copper pipes, socket welding, sleeve welding, or clamping shall be used; for aluminum pipes, sleeve welding shall be employed. The oxide layer must be removed prior to welding. 2. Special attention should be paid when the measuring pipeline is connected to the measuring instrument. Pipelines for gas media and low-boiling-point liquid fluids should be installed upward ； Pipelines for transporting ordinary liquids should also be installed upward. 3. For the pressure guiding tube used to measure liquids, in order to reduce measurement errors and improve accuracy, it should be laid horizontally for a sufficient distance (greater than 500 mm) outside the container, along the level of the lowest liquid surface. This ensures that the horizontal position at the bottom of the liquid level changes. 4. The pressure guiding pipe at the bottom of the liquid level should extend into the interior of the liquid container, with its opening facing downward, to prevent impurities from clogging it and affecting measurements. 5. Location of the gas outlet above the liquid container. It should be selected in a location where fluid flow and fluid impact within the container can be avoided. After exiting the vessel, the pressure guide pipe should be laid vertically upward to a certain height (generally more than 150 mm), and then laid horizontally. 6. The installation of pressure guiding pipes shall comply with the technical standards for installing instrument pressure guiding pipes in large-scale air separation units. The bending radius of the pressure guiding pipes shall be R = 5D. Inside the cold box, the pressure guiding pipes shall be installed in accordance with “HTA1107-93, Technical Requirements for Installation of Large-Scale Air Separation Units”, with a bending radius of R = 10D. 7. The materials of the sensing elements and pressure guiding pipes of instruments must comply with the material requirements of the process pipelines or equipment. In particular, before installation, all sensing elements and pressure guiding pipes used for measuring corrosive and toxic media must be checked one by one. 8. The welding technical requirements for the primary elements of instruments and the pressure guiding pipes of instruments must be consistent with those for process pipelines or equipment. 9. In instrument installation within tank farms and processing areas with explosion-proof requirements, strict attention must be paid to such requirements as explosion protection and grounding. When connecting protective conduits to field instruments, instrument cabinets, junction boxes, and distribution boxes, proper sealing must be ensured; all work shall be carried out strictly in accordance with the design specifications. Source: Internet