Casing couplings ensure the continuity of downhole casing through threaded connections. They play a crucial role in oil well structures by reinforcing the wellbore and sealing oil and gas reservoirs, and their service life directly impacts the overall lifespan of the oil well. According to API 5CT standards, casing couplings are manufactured using carbon steel or alloy steel, with common materials including special steel grades such as L80-13Cr. The manufacturing process encompasses blank preparation, thread forming, and surface treatment. They are widely used in the construction of deep wells and complex well structures in major domestic oilfields such as Shengli Oilfield and Changqing Oilfield, and are compatible with various thread types such as STC, LTC, and BTC.
Technical Standards:
According to API SPEC 5CT standard, the manufacturing of bushing couplings must meet the following technical requirements:
Material Mechanical Properties: Rockwell hardness HRC22-32, yield strength ≥552MPa (N80 steel grade)
Thread Parameters: 1/16 taper, 8 threads/inch pitch, tooth height tolerance ±0.002 inches
Surface Treatment: Copper plating thickness ≥0.008mm, color-coded identification system specifies the colored area
Size Range: Covers 4-1/2 inch to 20 inch bushing sizes, wall thickness tolerance ≤±12.5%
Processing Technology:
The processing of sleeve couplings includes two main stages: blank preparation and finishing:
Blank Forming: Hot-rolled seamless steel pipes are used and normalized. The machining allowance for the outer diameter of the blank is controlled within 1.5-3mm.
Thread Machining: Threads are machined using CNC machine tools according to API 5B standards, equipped with a three-coordinate measuring machine system to ensure accuracy.
Surface Treatment: The current density of the copper plating process is controlled at 3-5A/dm², and the coating adhesion is ≥15MPa.
Finished Product Inspection: 100% magnetic particle testing and thread gauge inspection are implemented.
Applications
In drilling engineering practice, casing couplings are mainly used in the following scenarios:
Deep Well Casing Suspension: When using a spindle-type suspension system, the coupling directly bears the weight of the casing string, forming a metal-to-metal seal.
Complex Well Structures: Horizontal wells and extended reach wells require high-torsion couplings with torque capacity meeting API standards.
Corrosive Environment Operations: 13Cr material couplings meet API standard service life requirements in CO₂/H₂S-containing oil and gas fields.
Rapid Installation Needs: Simple snap-fit couplings allow for single-person connection operations.
