API 5CT K55 Casing And Tubing For Oil &Gas

API 5CT K55 casing and tubing is a medium-strength OCTG grade manufactured according to API Specification 5CT (23rd Edition, 2020); it offers a yield strength of 55,000 psi, tensile strength of 75,000–95,000 psi, and a minimum elongation of 20%, and is available in standard sizes ranging from 4 1/2" to 8 5/8" OD with BTC, EUE, or STC threads. This grade is commonly used in shallow to medium-depth oil and gas wells under moderate-pressure, non-sour service conditions. It is widely procured by global oil and gas operators and EPC contractors for its verified mechanical performance, broad availability, and cost-effectiveness.

API 5CT K55 Chemical Composition

API 5CT K55 Mechanical Property

ISO/API Steel Casing list

ISO/API Steel Tubing list

API 5CT K55 Tolerance

API 5CT K55 Casing vs. Tubing: Sizes and Connections

We supply K55 in both configurations to meet your full well-completion needs:

K55 Casing: Used to line the borehole.

Sizes: 4-1/2" to 20".

Connections: BTC (Buttress Thread) for high tensile load; LTC (Long Thread) and STC (Short Thread) for standard sealing.

K55 Tubing: Used for oil/gas production.

Sizes: 1.050" to 4-1/2".

Connections: NUE (Non-upset) and EUE (External Upset) for enhanced joint strength.

Inspection for API 5CT K55 OCTG

Visual inspection for pipe surface
Dimension check
Mechanical test on tensile strength, yield strength and elongation
Chemical analysis
NDT test including Magnetic particle, Ultrasonic Test, Hydrostatic Test
Charpy impact test
Flattening tests
Hardness test
Drift test
Thread ends check with thread gauge and coupling check

Applications

Shallow and Medium-Depth Wells

K55 is ideal for shallow wells (<5,000 ft / 1,500 m) and moderate-pressure reservoirs.

Used in surface casing, intermediate casing, or tubing strings.

Oil and Gas Production

Suitable for both oil and natural gas wells with standard formation pressure.

Can be combined with standard drill pipe and tubing in upstream operations.

Offshore & Onshore Projects

Commonly used in onshore shallow fields in North America, Latin America, Middle East.

Offshore applications typically require higher-strength grades (J55, N80, L80) if deeper or sour service conditions.

Compatibility with Sour Gas (H2S) Environments

Standard K55 is not typically recommended for sour service.

For H2S or CO2 rich environments, L80 or N80 grades with sour-service certification are preferred.

API 5CT K55 OCTG Casing and Tubing factory

API 5CT K55 oil country tubular goods certificate

FAQ

Q: What is the primary difference between API 5CT J55 and K55?

A: While both share the same yield strength (55,000 to 80,000 psi), the key difference lies in the tensile strength. K55 requires a minimum tensile strength of 95,000 psi, whereas J55 only requires 75,000 psi. This makes K55 more suitable for deeper wells where the weight of the string imposes higher axial loads.

Q: Can K55 be used in sour service (H2S) environments?

A: Generally, no. K55 is not a "sour service" grade. For H2S environments, we recommend API 5CT L80-13Cr or C90/T95 grades, which have controlled hardness to prevent Sulfide Stress Cracking (SSC). K55 is best suited for "sweet" (non-corrosive) wells.

Q: Which thread types are available for K55 Casing?

A: We offer standard API connections: BTC (Buttress Thread) for superior tensile strength, LTC (Long Round Thread), and STC (Short Round Thread). For tubing, we offer EUE (External Upset) and NUE (Non-Upset). Premium connections (Gas-tight) are also available upon request for specific well conditions.

Q: What is the color code for API 5CT K55?

A: According to API 5CT specifications, K55 is identified by two bright green bands on the pipe body. This helps field operators quickly distinguish it from J55 (one bright green band) or N80 (one red band).

Q: What NDT (Non-Destructive Testing) methods are performed on K55 pipes?

A: Each pipe undergoes Hydrostatic testing to ensure no leaks under pressure. Additionally, we perform Ultrasonic Testing (UT) or Magnetic Particle Inspection (MPI) to detect any longitudinal or transverse defects in the steel. Drift testing is also mandatory to ensure the pipe's internal diameter allows for the passage of downhole tools.

Q: How do you prevent thread damage during long-distance sea freight?

A: We use heavy-duty plastic or composite thread protectors to safeguard the threads from impact. The pipes are also coated with a high-quality anti-rust varnish (black paint) and bundled with steel belts and dunnage to prevent shifting during transit.

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