Does nitrogen sealing equipment fall under pressure vessels?
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There is a storage tank (100 m3) containing ethanol (a flammable medium) and an intermediate buffer tank (1 m3). Given that high-purity ethanol tends to absorb moisture and evaporate, nitrogen blanketing is planned to be used. Nitrogen blanketing can be implemented in two ways: through a vent valve or a control valve to regulate pressure. Under these two operating conditions, is it necessary to design the storage tank (or intermediate buffer tank) as a pressure vessel? Is it necessary to design it according to pressure vessel standards based on the plant’s usage requirements?
Anything below 0.1 Mpa is not considered a pressure vessel. It also depends on how local safety supervision agencies interpret and formulate the relevant regulations
It has no direct relation to whether it is a pressure vessel or not, nor to whether nitrogen sealing is used; for pressure vessels, the design pressure is what matters, while the choice of nitrogen sealing often depends on the properties of the material
The nitrogen seal pressure is generally between 2000–4000 Pa, which is less than 0.1 MPa; it is not a pressure vessel, but calculations should still be done based on the design pressure
It is not a pressure vessel, so it does not need to be designed according to pressure vessel standards. Pressure vessels refer to closed devices used for holding gases or liquids and subjected to certain pressures. They include fixed and mobile vessels whose maximum operating pressure is 0.1 MPa (gauge pressure) or higher for gases and liquefied gases, and whose maximum operating temperature is equal to or higher than their standard boiling point; such vessels also have a volume of 30 L or more and an inner diameter of 150 mm or more (for non-circular cross-sections, this refers to the largest geometric dimension of the cross-sectional boundary) ； Gas cylinders, liquefied gas cylinders, and cylinders for liquids with a standard boiling point of 60°C or lower, whose nominal working pressure at full charge is greater than or equal to 0.2 MPa (gauge pressure), and whose product of pressure and volume is greater than or equal to 1.0 MPa•L ； Oxygen chamber.
The nitrogen seal typically has a gauge pressure of around 1 KPa; it is not a pressure vessel