Key factors and safety regulations for pressure vessel and storage tank design

1. Introduction
Pressure vessel tanks are devices capable of withstanding a certain pressure and used to store gases or liquids. They are widely used in industries such as petrochemicals, natural gas, power generation, metallurgy, pharmaceuticals, and food. They often store high-pressure, high-temperature, flammable, explosive, or toxic media. Therefore, the rationality of their design directly determines the safety and service life of the equipment.

Ignoring key factors during the design phase or failing to adhere to relevant safety regulations can lead to serious accidents such as leaks and explosions during operation, resulting in significant casualties and economic losses. Therefore, scientific design and strict adherence to safety standards are prerequisites for ensuring reliable operation of storage tanks.

2. Key Design Factors
Working Pressure and Temperature

Design pressure: The design should be based on the maximum operating pressure the tank can withstand, with sufficient safety margin.

Design temperature: Not only should the normal operating temperature be considered, but also temperature fluctuations during startup, shutdown, and extreme weather conditions.

Example: Liquefied natural gas (LNG) storage tanks must operate at extremely low temperatures (approximately -162°C). Therefore, cryogenic steel or composite materials must be used to prevent accidents caused by brittle fracture. Storage Medium Characteristics
Flammability and Explosiveness: Gas storage tanks for propane and butane require explosion-proof devices and strict sealing designs.
Corrosiveness: Corrosive liquids such as sulfuric acid and hydrochloric acid place extremely high demands on tank materials, often using stainless steel or corrosion-resistant coatings.
Toxicity: When storing gases such as ammonia and chlorine, in addition to material selection, additional double-walled shells or emergency spray systems are required as safety measures.
Material Selection
Carbon steel: Low cost, suitable for normal temperature and pressure or low-pressure storage tanks, but has poor corrosion resistance.
Stainless steel: Offers excellent corrosion and temperature resistance, suitable for industries such as food, pharmaceuticals, and chemicals, but is more expensive.
Alloy steel: Used in high-temperature and high-pressure environments, such as power plant boiler storage tanks.
Composite materials: In recent years, they have been increasingly used in applications requiring lightweight and corrosion-resistant materials.
Structural Design
Common structures include vertical, horizontal, spherical, and cylindrical. Spherical tanks can withstand relatively uniform internal pressure and are commonly used to store liquefied gases. Thickness Design: Based on wall thickness calculation formulas (such as those provided by ASME and GB150), ensure that the wall thickness can withstand pressure while avoiding material waste.
Welding Process: The weld is the weakest link, requiring strict quality control and non-destructive testing.
Manufacturing and Processing
Welding Quality Control: Radiographic testing (RT), ultrasonic testing (UT), penetrant testing (PT), and magnetic particle testing (MT) are used to ensure weld quality.
Heat Treatment: Thick steel plates require overall heat treatment after welding to relieve stress and prevent brittle fracture.
Forming Processes: For processes such as cold coiling and hot pressing, ensure that the steel plate does not produce cracks or excessive residual stress after forming.

3. Safety Regulations and Standards
International Standards
ASME Boiler & Pressure Vessel Code (American Society of Mechanical Engineers): The most widely used pressure vessel design code worldwide, covering the entire design, manufacturing, and inspection process. API 650/620 (American Petroleum Institute): Primarily used for the design and construction of large-capacity storage tanks. API 650 applies to atmospheric pressure tanks, while API 620 applies to cryogenic and low-pressure tanks.

Chinese Standards
GB 150 "Pressure Vessels": China's core pressure vessel design standard.
GB/T 151 "Shell and Tube Heat Exchangers": Detailed regulations for heat exchange pressure vessels.
TSG 21 "Regulations on Safety Technical Supervision of Stationary Pressure Vessels": Safety management regulations from design, manufacturing, to operational inspection.

Design Safety Margin

Stress Analysis: Finite Element Analysis (FEA) is used to calculate stress distribution in various components to ensure a reasonable safety factor.

Load Considerations: In addition to internal pressure, external factors such as earthquakes, wind loads, and snow loads must also be considered.

Safety Accessories

Safety Valve: Prevents tanks from operating under overpressure.

Rupture Disc: Releases pressure in extreme conditions to protect the tank.

Pressure Gauge and Level Gauge: Monitor operating status in real time. Automatic Control and Alarm System: Utilizes sensors and PLCs to enable remote monitoring and accident warnings.

4. Inspection and Maintenance
Pre-shipment Inspection: Includes a hydraulic pressure test (to verify pressure bearing capacity) and an airtightness test (to prevent leaks).
In-Service Inspection: Ultrasonic thickness testing and corrosion rate monitoring are used to assess equipment degradation.
Periodic Inspection: Regular and comprehensive inspections are required in accordance with laws and regulations (such as the Regulations on Safety Supervision of Special Equipment).
Lifecycle Management: A full lifecycle archive for the storage tank is established, documenting design, manufacturing, operation, and maintenance data to facilitate risk assessment.