Views: 0 Author: Site Editor Publish Time: 2025-01-02 Origin: Site
Steel casings are essential auxiliary equipment in rotary drilling rig operations. They are widely used in pile foundation construction, especially in soft soil, water-rich, or complex geological conditions. Their primary functions include protecting the borehole, preventing collapse, stabilizing the borehole wall, and guiding drilling tools. The fabrication and installation of steel casings directly affect the success of the construction process, and thus require adherence to specific principles and standards. Below is a detailed explanation of the principles of steel casing fabrication, installation, and related precautions.
Material Selection
Steel casings are typically made of high-quality Q235 or Q345 carbon steel to ensure excellent strength, rigidity, and durability. The material should be free of visible rust, cracks, or other defects to meet construction requirements.
Precise Dimensions
The diameter and wall thickness of the steel casing should be designed based on geological conditions and project specifications. Generally, the inner diameter of the casing should be 200–300 mm larger than the drill bit diameter to allow smooth tool operation while providing sufficient support. The wall thickness typically ranges from 8 to 20 mm; thinner walls may deform, while thicker walls increase costs and weight.
Welding Quality
The casing should adopt a full-weld seam process, ensuring the welds are smooth, free of cracks, and voids. The welding quality must meet construction standards. Anti-corrosion treatment should follow the welding process to extend the casing’s service life.
Flat Ends
The upper and lower ends of the casing should be flat. The lower end should be chamfered through cutting or machining, allowing the casing to penetrate the soil more smoothly during installation while minimizing soil disturbance.
Verticality Control
The casing must be installed vertically, with a deviation typically controlled within 1%. Any inclination may lead to borehole deviation or tool jamming, affecting construction quality. Tools such as cranes and levels can assist in correcting the casing’s verticality.
Depth of Installation
The installation depth should be determined based on geological conditions and design requirements, generally 1.5–2 times the casing diameter below the surface. For collapsible soil or water-abundant areas, the depth should be increased appropriately to provide better support and sealing.
Sealing Treatment
After installation, seal the casing by filling it with bentonite slurry or other sealing materials to prevent groundwater or mud intrusion and stabilize the borehole wall further.
Segmental Installation
For deep boreholes, segmental installation is recommended. The casing can be fabricated in sections, typically 3–6 meters each, and joined during installation to meet depth requirements. The joints should be securely connected with flanges or welds, ensuring proper sealing and strength.
Ground Preparation
Before installation, level the ground to ensure the casing stands firmly and to avoid tilting due to uneven surfaces.
Prevent Casing Displacement
During installation, the casing may shift due to groundwater buoyancy or geological disturbances. To prevent this, use sandbags, weights, or support systems to secure the casing.
Regular Inspection
After installation, regularly check the stability and sealing of the casing. If looseness or sealing failure is detected, address it promptly to avoid construction issues.
Mud Circulation Protection
Maintain an appropriate slurry level inside the casing to balance groundwater pressure, preventing borehole collapse and further stabilizing the borehole environment.
The fabrication and installation of steel casings are crucial steps in rotary drilling rig operations. Proper fabrication and standardized installation effectively prevent issues such as borehole collapse or tool jamming, improving construction efficiency and quality. During actual operations, fabrication and installation plans should be adjusted based on geological conditions and design requirements. Adherence to relevant construction standards and specifications ensures the smooth progress of the project.
