Installation Methods for Large Storage Tanks: Top-Down vs. Bottom-Up

 
During the construction of large storage tanks, the choice of installation method directly impacts the quality, efficiency, and safety of the project. Different types of storage tanks and construction environments require specific installation techniques to ensure smooth execution and long-term stability. This article delves into two common installation methods for large storage tanks: the top-down method and the bottom-up method. It provides a detailed analysis of their working principles, specific procedures, and suitable scenarios to help engineers make the best choice in practical operations.

Top-Down Method for Large Storage Tanks

 
The top-down method is a traditional approach used in constructing large storage tanks, particularly floating roof tanks. The core of this method involves starting from the bottom of the tank and installing the wall panels layer by layer upwards.

1. Construction Principles and Steps

 
Understanding the construction principles and steps of the top-down method is crucial for applying this technique effectively in practice.
 
Tank Bottom Construction: Begin with the installation of the tank's bottom plate, ensuring it is firmly connected to the foundation. The bottom plate is usually welded from steel sheets, and its stability is the foundation of the entire tank structure.
Installing the First Ring of Wall Panels: The first ring of wall panels is installed on the bottom plate. These panels are vertically aligned and welded to the bottom plate, forming the basic structure of the tank.
Layer-by-Layer Installation: Subsequent rings of wall panels are installed layer by layer on the first ring, continuing upwards until the topmost wall panels are in place. Each layer requires welding to ensure structural stability and sealing.

2. Specific Installation Methods

 
Different installation techniques can be applied within the top-down method to adapt to various construction environments.
 
Internal Scaffolding Method: Scaffolding is erected inside the tank, usually supported by brackets on the inner side of the wall panels. Platforms are placed on the scaffolding to create a work area, facilitating the installation and welding of each ring of wall panels. This method provides convenient working space for the construction crew.
External Scaffolding Method: External scaffolding is set up outside the tank wall. The construction process is similar to the internal scaffolding method, but the key advantage here is that it does not occupy internal space, allowing more flexibility for internal operations.
Water Floating Method: This method utilizes a floating platform that rises with the water level inside the tank. The floating platform serves as a stable work platform for installation and welding, effectively reducing the need for high-altitude operations.
 
The top-down method is a common choice in tank construction due to its clear structure, intuitive operation, and broad applicability, especially for floating roof and conventional tanks.

Bottom-Up Method for Large Storage Tanks

 
The bottom-up method operates in the reverse order of the top-down method and is typically used in ground-level construction. This method minimizes the risks associated with high-altitude operations and enhances safety and efficiency, making it particularly suitable for large tanks, especially dome-roof tanks.

1. Construction Principles and Steps

 
The following steps outline the bottom-up method's construction principles and procedures.
 
Tank Bottom Construction: Begin by constructing the tank's bottom plate to ensure its stability.
Installing the Top Ring of Wall Panels: The top ring of wall panels is installed on the bottom plate and secured in place. At this stage, the top ring is positioned but not connected to the bottom plate.
Sequential Lifting and Installation: Using hydraulic lifting equipment, the top ring is raised, allowing the next ring of wall panels to be installed and welded underneath. This process continues until the first ring of wall panels is assembled and welded.
Final Welding: After completing the installation of all wall panels, the major weld seam between the tank wall and the bottom plate is executed to ensure overall structural integrity and sealing.
Accessory Installation: During the lifting process, wind-resistant rings, reinforcement rings, and other accessories are installed in sync with the wall panels, enhancing the tank's stability and durability.

2. Specific Installation Methods

 
Several techniques are used in the bottom-up method to suit different construction conditions.
 
Hydraulic Jacking Method: The top ring of wall panels is installed first, and hydraulic jacks are used to lift the panels in sequence. Each ring is assembled and welded as it is lifted, ensuring high efficiency and precision, making it ideal for large storage tanks.
Pole Assembly Method: This method involves using lifting poles for hoisting the assembly, working from top to bottom. It is simpler and often used for smaller tanks.
Inflation Lifting Method: Compressed air is introduced into the tank, creating enough pressure to lift the tank body. Once the desired height is reached, wall panels are welded. This method reduces labor and material costs and is widely used in constructing large dome-roof tanks.
Mechanical Lifting Method: Electric hoists are used to lift the wall panels in sequence, followed by welding. This method is efficient and stable, making it suitable for large tanks.
 
Both the top-down and bottom-up methods have their advantages and limitations. The choice of method depends on the type of storage tank, construction environment, and project requirements. The top-down method is widely applicable, especially for floating roof tanks, due to its clear construction process and intuitive operation. The bottom-up method, on the other hand, is safer and more efficient for ground-level construction, particularly for dome-roof tanks with complex structures. Advanced techniques like the inflation lifting method and water floating method offer time-saving and labor-saving benefits and have been widely adopted in large storage tank construction. Selecting the appropriate installation method based on specific project needs can significantly improve construction quality and efficiency.