Comprehensive Guide to Pressurized Tanks | MECH FIX ZONE

 

How to design pressurized Tanks and what are the ASME standards

Introduction

Pressurized tanks are essential in industries such as oil and gas, chemicals, pharmaceuticals, and power plants. These tanks store gases and liquids under pressure, requiring careful design to ensure safety and efficiency. This blog covers the fundamental design principles and the American Society of Mechanical Engineers (ASME) standards that govern the construction of pressurized tanks.

1. Key Considerations for Designing Pressurized Tanks

Designing a pressurized tank involves various factors to ensure structural integrity and compliance with industry regulations. Below are the primary considerations:

a. Purpose and Operating Conditions

• Define the type of fluid (gas or liquid) to be stored.
• Identify the operating pressure and temperature.
• Consider the environmental conditions such as external temperature, corrosion factors, and seismic activity.

b. Material Selection

• The material must withstand pressure, temperature variations, and corrosion.
• Common materials include carbon steel, stainless steel, and alloy steels.
• The ASME Boiler and Pressure Vessel Code (BPVC) specifies suitable materials.

c. Wall Thickness and Shape

• The required thickness is calculated based on internal pressure and material strength.
• Cylindrical and spherical shapes are commonly used as they efficiently distribute stress.

d. Design Pressure and Temperature

• The design pressure should be higher than the operating pressure to include a safety margin.
• Temperature considerations must include both normal operation and potential thermal expansion effects.

e. Stress Analysis

• Tanks experience internal pressure, external loads, and possible cyclic loading.
• Finite Element Analysis (FEA) can be used to evaluate stress distribution.

f. Safety Features

• Pressure relief valves to prevent overpressure scenarios.
• Reinforced supports and anchorage to prevent structural failure.

2. ASME Standards for Pressurized Tanks

ASME has established codes and standards to regulate the design, fabrication, testing, and inspection of pressure vessels.

a. ASME Boiler and Pressure Vessel Code (BPVC)

• ASME Section VIII: Deals with the design and construction of pressure vessels.
• Division 1: Covers simpler design with safety factors for general industrial applications.
• Division 2: Includes more rigorous design with advanced stress analysis techniques.
• Division 3: Focuses on high-pressure applications beyond 10,000 psi.

b. Welding and Fabrication Standards

• ASME Section IX defines welding qualifications and procedures.
• Ensures the quality of welds under high-pressure conditions.

c. Inspection and Testing Standards

• Hydrostatic and Pneumatic Testing: Ensures vessels can withstand pressure without leaks.
• Non-Destructive Testing (NDT): Methods like ultrasonic, radiographic, and magnetic particle testing are used to detect flaws.

3. Steps in Designing a Pressurized Tank

Step 1: Define Requirements

• Determine the type of fluid and pressure/temperature limits.
• Establish compliance with ASME codes.

Step 2: Material Selection

• Choose a suitable material that meets ASME standards.
• Consider corrosion resistance and mechanical properties.

Step 3: Calculate Wall Thickness

• Use ASME formulas to determine the required thickness.
• Consider joint efficiency and safety factors.

Step 4: Design Structural Components

• Design nozzles, manways, and support structures.
• Ensure proper reinforcement at stress concentration points.

Step 5: Conduct Stress Analysis

• Use software like ANSYS or SolidWorks for FEA simulations.
• Verify compliance with ASME stress limits.

Step 6: Fabrication and Welding

• Follow ASME Section IX for welding procedures.
• Perform visual and NDT inspections.

Step 7: Testing and Certification

• Conduct hydrostatic or pneumatic testing.
• Obtain ASME certification to validate compliance.

Conclusion

Designing pressurized tanks requires careful attention to safety, material selection, and regulatory compliance. The ASME BPVC standards provide the necessary framework to ensure tanks operate reliably under high-pressure conditions. By following a structured design approach, engineers can develop safe and efficient pressure vessels for various industrial applications.