How are blind flanges installed and removed? Will it cause a leak when removed?

It’s not quite appropriate to post this thread in this section. I’ve seen how others install blind plates: first, the process valve on the upstream side is closed, then a few screws on one side of the flange are removed, the blind plate is inserted between the flanges, and finally the screws are reinstalled. The disassembly process is the reverse of assembly, and the washer also needs to be replaced. As for the issue of leaks, any risk factor can exist during the maintenance of chemical plants.

The installation of a blind flange is similar to its removal: first, ensure that there is no liquid in the pipeline and that it is not in use; second, close the valve behind the flap, then slowly loosen the bolts between the flanges to allow any remaining fluid in the pipeline to drain out, after which the blind flange can be installed； The same is true when removing the blind flange. Whether it is disassembly or installation, it is essential to use proper pads; otherwise, material leakage is likely to occur. Generally, a work permit is required to do this kind of work. Otherwise, safety accidents are likely to occur.

Before installing the blind flange, the valve located upstream in the pipeline should be closed first. Then, the bolts of the flange are removed, the gasket is taken out, the blind flange is installed, and a new gasket is placed in its place. Since the sealing surface of a gasket that has been compressed tightly gets damaged, it is necessary to use a new gasket to prevent leaks. After that, the bolts of the flange are tightened again, and a soap solution is used to check for leaks

When removing the blind flange: First, confirm the process and cut off the material flow. For residual liquids (gases) inside pipes or equipment, wear appropriate protective gear and have supervision in place, depending on the pressure and the medium involved. Loosen the bolts slowly, making sure that the first opening is not directed at anyone (it’s best to point it downward). Use a container to catch the liquid in order to prevent contamination of the floor, platform, or other equipment. After gradually reducing the pressure, remove the blind flange. When installing the blind flange: clean the sealing surface thoroughly (to avoid any secondary radial scratches), replace the gasket (placing it in the center), tighten the bolts symmetrically, open the material valve, bring it to the operating pressure, and hold it at that pressure for 5 minutes; if no leaks are detected, it is considered acceptable.

In fact, after a proper blind flange is removed and a orifice plate needs to be installed, especially in cases where the pipe is thick and has a high pressure rating, the gap left after removing the blind flange is large; without an orifice plate, high stress can lead to leaks. For an 8-shaped blind flange, it’s only necessary to change its orientation. Whether removing or installing a blind flange, there is only one principle: close the manual valves before and after the blind flange to release all pressure from that area. Use protective equipment when dealing with toxic or corrosive substances, and employ explosion-proof tools when working with flammable or explosive materials. Keep proper records of the installation and removal of the blind flange.

When installing a blind flange, first close the valves that are located above it, and then use the drain valve to discharge any remaining liquid to the flare or wastewater tank for disposal. Then, to tighten the flange screws, generally only one of the upper screws is removed, and a blind plate is installed. Note that the old gasket should be placed on the side far from the valve, while the new gasket should be placed on the side close to the valve. The final configuration is: valve—new gasket—blind flange—old gasket. In my opinion, there is no need to replace the gasket in the section far from the valve, as it is the end closest to the valve that provides sealing; all that needs to be done is tighten the screws, applying force diagonally. The removal process is similar to the installation process; at this time a new gasket should be used. As it’s the first time someone is moving in, please forgive any mistakes that may occur. . .