Shell Design of Skirt Supported Vessels

Introduction

Skirt supported vessels are commonly used in various industries, such as oil and gas, chemical, and petrochemical, for storing and processing fluids under pressure. The shell design of these vessels plays a crucial role in ensuring their structural integrity and safe operation. This topic will cover the key concepts, principles, and considerations involved in the shell design of skirt supported vessels.

Importance of Shell Design in Skirt Supported Vessels

The shell design of skirt supported vessels is essential for several reasons. Firstly, it ensures the structural stability and integrity of the vessel, preventing any potential failures or accidents. Secondly, it helps in determining the appropriate material selection, shell thickness, and reinforcement requirements. Lastly, a well-designed shell contributes to the overall efficiency and cost-effectiveness of the vessel.

Fundamentals of Shell Design in Skirt Supported Vessels

Before diving into the specifics of shell design in skirt supported vessels, it is important to understand the fundamentals. This includes knowledge of the vessel's characteristics, loadings, stresses, material selection, and reinforcement requirements.

Key Concepts and Principles

Skirt Supported Vessels and Their Characteristics

A skirt supported vessel is a type of pressure vessel that is supported by a cylindrical skirt attached to its bottom. The skirt provides stability and support to the vessel, allowing it to withstand the internal and external pressures. Skirt supported vessels are commonly used for large storage tanks, reactors, and other process equipment.

Shell Design Considerations for Skirt Supported Vessels

The shell design of skirt supported vessels involves several considerations to ensure their structural integrity and safe operation. These considerations include:

1. Loadings and Stresses on the Shell: The shell is subjected to various loadings, such as internal and external pressures, wind loads, seismic loads, and thermal expansion. It is essential to analyze and calculate the stresses induced by these loadings to determine the required shell thickness and reinforcement.

2. Material Selection for the Shell: The material selection for the shell depends on factors such as the process fluid, operating temperature and pressure, corrosion resistance, and cost. Common materials used for skirt supported vessel shells include carbon steel, stainless steel, and alloy steel.

3. Shell Thickness Calculation: The shell thickness is calculated based on the allowable stress limits and the applied loadings. The calculations involve determining the hoop stress and longitudinal stress, considering factors such as the vessel's geometry, internal and external pressures, and material properties.

4. Shell Reinforcement and Stiffening: Depending on the vessel's size, shape, and operating conditions, additional reinforcement and stiffening may be required to enhance its structural integrity. This can include the use of stiffening rings, gussets, or other structural elements.

Skirt Design Considerations for Skirt Supported Vessels

In addition to the shell design, the skirt design of skirt supported vessels is equally important. The skirt provides support and stability to the vessel, transferring the loadings to the foundation. The following considerations are crucial for the skirt design:

1. Skirt Length and Diameter: The skirt length and diameter are determined based on the vessel's weight, dimensions, and the required stability. The length should be sufficient to provide adequate support and prevent excessive deflection.

2. Skirt Support Structure: The skirt support structure, which includes the legs or columns, should be designed to withstand the loadings and provide stability to the vessel. Factors such as the material, size, and arrangement of the support structure need to be considered.

3. Skirt Attachment to the Shell: The attachment of the skirt to the shell should be carefully designed to ensure a strong and rigid connection. This can be achieved through the use of welds, bolts, or other mechanical fasteners.

4. Skirt Stiffness and Flexibility: The skirt should have sufficient stiffness to support the vessel's weight and resist any deflection or deformation. However, it should also have some flexibility to accommodate thermal expansion and contraction.

Step-by-step Walkthrough of Typical Problems and Solutions

This section will provide a step-by-step walkthrough of typical problems encountered in the shell design of skirt supported vessels and their solutions. Two common problems will be discussed:

Problem 1: Determining the Required Shell Thickness for a Skirt Supported Vessel

To determine the required shell thickness, the following steps are typically followed:

1. Calculation of Internal and External Pressures: The internal and external pressures acting on the shell are calculated based on the process conditions and design codes.

2. Calculation of Hoop Stress and Longitudinal Stress: The hoop stress and longitudinal stress induced by the pressure are calculated using appropriate formulas and equations.

3. Determination of Required Shell Thickness: The required shell thickness is determined based on the stress limits specified by design codes and standards.

Problem 2: Designing the Skirt Support Structure for a Skirt Supported Vessel

The design of the skirt support structure involves the following steps:

1. Calculation of Skirt Support Loads: The loads acting on the skirt support structure, such as the weight of the vessel, contents, wind loads, and seismic loads, are calculated.

2. Selection of Appropriate Skirt Support Structure: Based on the calculated loads and other design considerations, an appropriate skirt support structure is selected. This can include options such as legs, columns, or a combination of both.

3. Design of Skirt Attachment to the Shell: The attachment of the skirt to the shell is designed to ensure a strong and rigid connection. Factors such as the load distribution, weld design, and material compatibility are considered.

4. Verification of Skirt Support Structure: The designed skirt support structure is verified against the calculated loads and other design criteria to ensure its adequacy and safety.

Real-world Applications and Examples

Skirt supported vessels find extensive applications in various industries. Some real-world applications include:

Skirt Supported Vessels in the Oil and Gas Industry

1. Offshore Platforms and FPSOs: Skirt supported vessels are commonly used in offshore platforms and floating production storage and offloading (FPSO) units for storing and processing oil and gas.

2. Onshore Storage Tanks: Skirt supported vessels are used for large storage tanks in onshore oil and gas facilities.

Skirt Supported Vessels in the Chemical Industry

1. Reactors and Pressure Vessels: Skirt supported vessels are widely used in the chemical industry for reactors and pressure vessels used in various chemical processes.

2. Storage Tanks for Hazardous Chemicals: Skirt supported vessels are used for storing hazardous chemicals, ensuring their safe containment and preventing any environmental or safety hazards.

Advantages and Disadvantages of Shell Design of Skirt Supported Vessels

Advantages

1. Cost-effective Solution for Large Vessels: Skirt supported vessels offer a cost-effective solution for storing and processing large volumes of fluids under pressure. The skirt provides stability and support, eliminating the need for additional support structures.

2. Enhanced Stability and Support: The skirt support structure enhances the stability and support of the vessel, allowing it to withstand external loadings such as wind and seismic forces.

3. Easy Installation and Maintenance: Skirt supported vessels are relatively easy to install and maintain compared to other types of vessels. The skirt provides a stable base for the vessel, simplifying the installation process.

Disadvantages

1. Limited Flexibility in Design: Skirt supported vessels have certain limitations in terms of design flexibility. The skirt attachment and support structure restrict the vessel's shape and dimensions.

2. Increased Complexity in Fabrication and Construction: The fabrication and construction of skirt supported vessels can be more complex compared to other types of vessels. The design and fabrication of the skirt attachment and support structure require careful consideration and expertise.

Conclusion

In conclusion, the shell design of skirt supported vessels is crucial for ensuring their structural integrity, stability, and safe operation. The key concepts and principles discussed in this topic provide a foundation for understanding the design considerations and solutions for skirt supported vessels. By following the step-by-step walkthrough of typical problems and solutions, engineers can effectively design and analyze skirt supported vessels for various applications.

Summary

This topic covers the key concepts, principles, and considerations involved in the shell design of skirt supported vessels. It discusses the importance of shell design, the fundamentals of shell design, and the key considerations for both the shell and skirt design. The content also includes a step-by-step walkthrough of typical problems and solutions, real-world applications and examples, and the advantages and disadvantages of shell design in skirt supported vessels.

Analogy

Imagine a skirt supported vessel as a tall and slender dancer performing on a stage. The shell design is like the dancer's costume, providing support, stability, and flexibility. The skirt represents the support structure, ensuring the dancer's balance and preventing any wobbling or falling. Just as a well-designed costume and support structure enhance the dancer's performance, a well-designed shell and skirt support structure enhance the vessel's stability and safe operation.