Contact the process team and obtain permission. Confirm that disassembly will not trigger other interlock actions. Process the work ticket according to regulations.
Conduct a risk analysis regarding the medium, pressure, temperature, etc. Wear protective gear and use explosion-proof tools when necessary. It is best to work in pairs for mutual supervision.
The double-flange differential pressure transmitter consists of a differential pressure transmitter, capillary tubes, and two flanges with sealing diaphragms. The sealing diaphragm prevents the medium in the pipeline from directly entering the differential pressure transmitter. It connects to the transmitter via capillary tubes filled with liquid (usually silicone oil). When the diaphragm is pressurized, it undergoes minute deformation, which is transmitted through the capillary liquid to the transmitter, where it is processed and converted into an output signal.
Flange inspection:
- Check the seal between the flange and the equipment for leaks. Inspect the connection between the flange and capillary tubes, as well as between the capillary tubes and the transmitter, for liquid leaks.
- After removing the flange, carefully clean any debris from the flange diaphragm and check for deformation, damage, corrosion, or scaling.
- For units with isolation tanks, replace the medium in the tank and check for corrosion inside the tank, especially at the bottom weld and the nozzle area. Ensure that the upper vent valve operates normally and check for any plugs.
- After disassembly, perform a pressure test on the primary valve and check for internal leaks, as well as corrosion on the valve plate and inner wall. Replace parts if necessary.
- Check the valves on the isolation liquid line, including gate valves and threaded globe valves, for proper operation and ensure no internal leakage.
- Be careful not to damage the diaphragm surface. Since the diaphragm protrudes by about 1mm, placing it face down can scratch the surface.
- After disassembly, inspect the corrosion of the pressure port on the equipment and the sealing surface of the flange. Record the condition of bolts and gaskets, and store the flange diaphragm and transmitter properly.
Transmitter inspection:
- External inspection: Check the transmitter casing for damage, corrosion, or other issues, and address any problems promptly.
- Internal inspection: Open the transmitter cover and check the sealing ring for damage; replace if necessary. Inspect the circuit board and other components for proper functioning.
- Check the wiring connections for integrity and inspect for corrosion at the terminals.
- Check the condition of the flexible conduit and junction boxes for cracks, ensure the panel display functions normally, and verify that sunshade and rain protection are intact.
Installation precautions:
- Avoid passing welding current through the transmitter or allowing welding slag to splash onto the diaphragm or sealing surface when welding during site piping.
- When measuring liquid level, the minimum liquid level (zero point) should be set at least 50mm above the center of the high-pressure side diaphragm.
- Ensure that the high- and low-pressure flanges are installed correctly and not reversed.
- To minimize the effect of ambient temperature differences, bundle the high- and low-pressure capillaries together and secure them to prevent damage from wind or vibration. If the capillaries are too long, coil them and secure them without twisting or pressing them. Do not apply excessive force to the capillaries.
- Replace flange gaskets and bolts if corroded. Clean the flange sealing surface before installation.
- Ensure that the gaskets and flanges are aligned, bolts extend through the flange, and the flange gap is even.
- After installation, perform a pressure test to check for leaks in isolation liquid lines or use a manual pressure pump for systems without isolation. Check for leaks in the primary valve before pressurizing the process equipment.
- Ensure proper wiring of the transmitter. If the cable connections are oxidized, clean the oxidation before reconnecting. Replace damaged flexible conduits with cable glands and ensure proper waterproofing.
- For new or modified transmitters, set the parameters properly, especially the measurement interface. Check the zero point and range for correctness, verify display settings, and confirm proper signal transmission to the control room. Ensure everything is functioning correctly before commissioning.
Pressure testing: Conduct pressure tests to confirm no leaks once conditions are met.
