The 8-character blind plate is a kind of pipe fitting, which is mainly for convenient maintenance. You can paint the upper part of the "8" in black to see the specific shape. It's half blind and half iron. Usually used for pipeline flanges that need to change the flow. The material is mainly carbon steel, stainless steel and alloy.
It is usually used in pipelines with large diameters. At ordinary times, one end of flange is used to occupy space to keep the pipeline unimpeded. When necessary, the other end is replaced with a blind plate of the same thickness to cut off the pipeline. Avoid forced expansion of pipeline due to temporary replacement of other blind plates, affecting the whole system.