Are vacuum vessels considered pressure vessels or not

The relevant standards for pressure vessels are generally based on GB150 "Pressure Vessels" and "Safety Technical Supervision Regulations for Fixed Pressure Vessels". However, there is a requirement for the pressure to be greater than or equal to 0.1MPa in the vessel regulations, and GB150 also clearly lists that containers with a design pressure below 0.1MPa and a vacuum degree below 0.02MPa are not within the scope of their standard application. Therefore, many people exclude pressure vessels with design pressures below 0.1MPa, and naturally do not consider vacuum vessels used under negative pressure as pressure vessels.
However, in the third edition of Process Equipment Design, pressure vessels are divided into internal pressure vessels and external pressure vessels. Internal pressure vessels, which have an internal pressure greater than one atmospheric pressure (divided into four levels from 0.1MPa to over 10MPa); There are two types of external pressure vessels, one is those with an external surface pressure higher than atmospheric pressure and an internal surface pressure greater than surface pressure, such as deep-sea operating equipment, shell and tube heat exchangers, and the other is those with an external surface pressure higher than atmospheric pressure and an internal pressure lower than one atmosphere in a vacuum state, such as vacuum distillation towers, vacuum tanks, and so on, which is the vacuum vessel we are discussing. Therefore, in the design of process equipment, vacuum vessels are undoubtedly considered a type of pressure vessel.
For screw vacuum pump manufacturers, they prefer vacuum vessels as a type of pressure vessel. The container excluded by GB150 does not involve a vacuum degree higher than 0.02MPa. The low pressure difference of vacuum degree can be defined by referring to the atmospheric pressure vessel in JB/T4735-1997 "Steel Welded Atmospheric Pressure Vessels". In many vacuum applications, the vacuum degree is easily higher than 0.02MPa, and the internal and external pressure difference can be close to one atmospheric pressure, which is close to 0.1MPa; Moreover, in these vacuum applications, there are situations where vacuum and high pressure alternate, such as impregnation, pressure swing adsorption, etc. Therefore, according to the pressure difference, screw vacuum pump manufacturers prefer to classify vacuum containers into pressure vessels that are not governed by GB150. In practical production applications, when the true vacuum is higher than 0.02MPa, the design is carried out according to the pressure vessel standard in GB150, and when the vacuum is less than 0.02MPa, the design is carried out according to the atmospheric pressure vessel standard.