API SPEC 5CT is a technical specification standard for oil casing issued by the American Petroleum Institute (API), mainly used in the oil and gas extraction field. This standard specifies the steel grade system, chemical composition, mechanical properties, dimensional tolerances, and other technical indicators for casing and tubing. The standard covers more than ten steel grades, including H40, J55, N80, and P110, and sets strict limits on the content of elements such as carbon, manganese, and phosphorus, and sets specific requirements for mechanical properties such as tensile strength (≥517-965MPa) and yield strength (379-965MPa).
Common specifications for API 5CT oil casing include:
Outer diameter range: 114.3 mm to 508 mm
Material grades: J-55, K-55, N-80, L-80, C-90, C-95, P-110, Q-125
Thread types: BTC, LTC, STC
Lengths: R1, R2, R3
Scope
1. This International Standard specifies the delivery technical conditions for steel pipes (casing, tubing, plain-end casing liners, and short sections), couplings, and accessories.
2. This International Standard applies to four groups of products including the following steel grades:
Group 1: All casing and tubing (plain casing and tubing) of H, J, K, and N steel grades
Group 2: All casing and tubing (corrosion resistant) of C, L, M, and T steel grades
Group 3: All casing and tubing (high strength) of P steel grade
Group 4: All casing (high strength) of Q steel grade
3. Definitions
Casing: A pipe run from the surface into a drilled wellbore as a liner.
Tubing: A pipe run into a well for production or injection of fluids.
Coupling: A cylindrical body with internal threads used to connect two threaded pipes.
Coupling Semi-finished Product: Unthreaded blank material used to produce one coupling.
Coupling blanks: Seamless thick-walled tubes or mechanical tubes used in the production of coupling semi-finished products.
Dimensional Specifications
The standard clearly defines the product's geometric dimensions:
Outer Diameter Tolerance:
≤101.60mm, allowable deviation of ±0.79mm
≥114.30mm, subject to a tolerance zone of +1.0%/-0.5%
Wall Thickness Deviation controlled within the range of 0 to -12.5%
Length Classification:
Casing is classified into three categories: 4.88-7.62m, 7.62-10.36m, and 10.36-14.63m.
Tubing length standard is 6.10-9.75m.
Quality Inspection Requirements
The standard system includes eight testing items:
Hydrostatic pressure test to verify sealing performance
Flattening test to detect plastic deformation capacity
Sulfide stress corrosion cracking test to assess corrosion resistance
Tensile test to ensure mechanical properties meet standards
Surface defect removal depth must not exceed 12.5% of the nominal wall thickness
End Processing and Thread Parameters
The standard specifies detailed requirements for pipe end processing:
Processing methods are divided into three types: flat end (PL), thickened end (EU), and threaded end (NU).
Thread parameters include: Taper requirement 1:16; Pitch tolerance ±0.051mm; Tooth height deviation ±0.051mm;
Coupling types include five categories such as standard couplings and special intermittent couplings.
