Pressure vessels are essential equipment in many industries. They are used to store or transport gases, liquids, and other substances. Depending on their structure, pressure, volume, and working environment, pressure vessels can be divided into simple pressure vessels and fixed pressure vessels. Let's break down the design requirements, material choices, and application standards for each type.
Simple Pressure Vessels
Simple pressure vessels are mainly used for storing or transporting gases, liquids, and other materials. Their design is straightforward and they are used in situations with lower pressure and smaller volumes. These vessels are built to be reliable and meet strict safety standards to avoid leaks, ruptures, or other risks during normal use.
1. Design Requirements
Pressure and Volume: Simple pressure vessels are designed for pressures up to 1.6 MPa and volumes no larger than 1000 liters. The product of pressure and volume must be at least 2.5 MPa·L but no more than 1000 MPa·L.
Common Media: These vessels typically store air, nitrogen, or steam from medical distilled water.
Temperature: The operating temperature should range between -20°C and 150°C.
2. Key Components
Connection Parts: Simple pressure vessels have connections like threaded joints, flange sealing surfaces, and other specialized connectors. These parts link the vessel to external pipes or equipment.
Pressure-Resistant Sections: The pressure caps for openings and their fasteners must be able to handle the internal pressure and maintain a seal.
Welded Joints: The welds between non-pressurized parts and the vessel body should be strong and sealed.
Safety Accessories: Safety valves, rupture disks, pressure gauges, and water level indicators protect the vessel from overpressure or abnormal conditions.
3. Material Selection
Simple pressure vessels are usually made from steel that's been hot-rolled or normalized. The carbon content shouldn't exceed 0.25%, and the levels of phosphorus and sulfur shouldn't be higher than 0.045%.
The minimum tensile strength is typically below 540 MPa. A common material used is Q235-B.
4. Purchasing Standards
A simple pressure vessel is typically one with a volume of 1 m³ or less and a pressure of 10 kg (or less). Q235-B is commonly used for these vessels.
5. Safety and Reliability
Safety is crucial for simple pressure vessels. They must be built with quality materials and manufacturing processes to avoid leaks or ruptures. These vessels should also be reliable and perform safely throughout their lifespan.
Fixed Pressure Vessels
Fixed pressure vessels are designed for larger volumes and higher pressures. They are used to store or process gases, liquefied gases, and high-temperature liquids in industries such as petrochemical, energy, and metallurgy. These vessels must be strong, durable, and able to handle extreme conditions like high pressure and temperature.
1. Design Requirements
Pressure and Volume: Fixed pressure vessels are designed for volumes of at least 30 liters, with an inner diameter of at least 150 mm. The working pressure is typically above 0.1 MPa. The product of pressure and volume must be at least 2.5 MPa·L.
Common Media: These vessels store gases, liquefied gases, and liquids at temperatures above their normal boiling points.
Temperature and Performance: Fixed pressure vessels have stricter temperature and performance requirements compared to simple pressure vessels.
2. Key Components
Connection Parts: Fixed pressure vessels connect to external pipelines or equipment through welded joints, threaded joints, or flange seals. The strength and sealing of these connections must be strictly controlled.
Pressure-Resistant Sections: Pressure caps for openings and their fasteners must withstand internal pressure without rupturing or leaking.
Welded Joints: Welds between non-pressurized parts and the vessel body must meet strength standards to ensure stability and sealing.
3. Material Selection
Fixed pressure vessels are typically made from low-alloy steel or stainless steel, such as Q345R or stainless steel 304.
These materials need to be strong and resistant to corrosion to handle different pressures and temperatures.
4. Safety and Reliability
Just like with simple pressure vessels, safety is crucial for fixed pressure vessels. The welding quality, material strength, and sealing of connections must meet strict standards to ensure these vessels can safely handle high pressure and temperature over time.
Design and Production Requirements
The design and production of both simple and fixed pressure vessels differ in areas like material selection, manufacturing processes, and structural design. Regardless of the type, ensuring safety and stability during operation is always the top priority. Here's a closer look at the requirements for designing and producing these vessels.
1. Production Design
Simple Pressure Vessels: These vessels typically have a volume of 1 m³ or less and a pressure of less than 1.6 MPa. The design should focus on simplicity and safety, with typical media being inert gases like air or nitrogen.
Fixed Pressure Vessels: These vessels are designed for larger volumes and higher pressures. The design must account for factors like the operating environment, pressure fluctuations, and temperature changes to ensure they remain stable and safe over long periods.
2. Safety and Quality Control
Manufacturers must follow strict quality control guidelines during production. From materials selection to welding techniques and sealing tests, every step must be thoroughly checked to make sure the pressure vessel meets safety standards.
3. Environmental and Sustainability Considerations
As environmental concerns continue to grow, both simple and fixed pressure vessels must be designed with sustainability in mind. Manufacturers should choose environmentally friendly materials and processes, avoid harmful substances during production, and increase the recyclability of the vessels. This is becoming an important trend in modern pressure vessel design.
Conclusion
Simple and fixed pressure vessels have different design requirements and applications. Simple pressure vessels are used for lower pressure and smaller-volume needs, focusing on ease of design and safety. Fixed pressure vessels, on the other hand, are used for high pressure and large-volume applications, requiring more complex and detailed design. Whether simple or fixed, the key factors in both types are safety, reliability, and material selection. By following strict design, production, and quality control standards, manufacturers can ensure that pressure vessels will operate safely and efficiently in various conditions.
