How does the eight-character blind plate in the picture mean normally open?

The normally open state is to shut down or cut off the equipment from the system and isolate it with a blind plate. According to relevant public information, normally open blind plate equipment or pipelines are generally used when the device is started or stopped, and normally open equipment is used during normal production. When the equipment shuts down or cuts off the system, use a blind plate to isolate it. 8-shaped blind plate is a kind of pipe fittings, that is, half is blind plate and half is iron ring. Commonly used for pipeline flanges that need to change the process, the materials are mainly carbon steel, stainless steel and alloy, which can be selected according to the pipeline pressure grade and pipeline medium.