API 5CT is a specification issued by the American Petroleum Institute (API) that defines the technical requirements for steel casing and tubing used in oil and gas drilling operations.
API 5CT is applicable to the following grades: H40, J55, K55, N80 (Type: 1 or Q), R95, L80 (Type: 1, 3Cr, 9Cr, or 13Cr), C90, T95, C100, P110, Q125
API 5CT Connections:
SC: short round thread casing
LC: long round thread casing
BC: buttress thread casing
NU: non-upset tubing
EU: external upset tubing
LJ: integral tubing
API 5CT J55 casing specification
Outer Dimensions: 6.0mm -219.0mm
Wall Thickness: 1.0mm -30mm
Length: R1(4.88-7.62m), R2(7.62-10.36m), R3(10.36-14.63m)
Thread type: Short round thread, Long round thread, Buttress thread
J55 Casing Tubing Steel Color Code: a bright green band
J55 Coupling Color Code: entire green coupling + a white band
Application: Transportation of gas, water, oil and natural gas.
API 5CT J55/K55 casing and tubing manufacturing types
API 5CT J55 casing and tubing are produced as seamless (SMLS) or electric resistance welded (ERW/HFI) pipes. Seamless pipes offer high strength and reliability, while ERW pipes provide cost efficiency and good dimensional accuracy. They can be supplied in as-rolled, normalized, or normalized and tempered conditions.
API 5CT J55 casing and tubing heat treatment
API 5CT J55 casing and tubing can be supplied in different heat treatment conditions depending on manufacturing methods and service requirements. Common conditions include:
As-rolled (AR): Supplied without additional heat treatment, suitable for general low-pressure wells.
Normalized (N): Heated above the critical temperature and air-cooled to refine the grain structure, improving toughness and uniformity.
Normalized and Tempered (N&T): Further heating after normalization to enhance strength, ductility, and impact resistance.
API 5CT J55 Chemical Composition
| Grade | C | Si | Mn | P | S | Cr | Ni | Cu | Mo |
| API 5CT J55 | 0.34-0.39 | 0.20-0.35 | 1.25-1.50 | 0.020 | 0.015 | 0.15 | 0.20 | 0.20 | / |
| Steel Grade | Yield Strength (Mpa) | Tensile Strength (Mpa) | Total elongation under load % |
| API 5CT J55 | 379-552 | ≥517 | 0.5 |
| Item | Allowable tolerance | |
| Outer diameter | Pipe body | D≤101.60mm±0.79mm |
| D≥114.30mm+1.0% | ||
| -0.5% | ||
| Wall thickness | -12.5% | |
| Weight | Single piece | +6.5%+3.5% |
| Total weight | -1.75 |
| Outer Diameter | Wall Thickness | Weight | Grade | Threaded | Length | |
| in | mm | kg/m | lb/ft | |||
| 4 1/2″ | 114.3 | 14.14-22.47 | 9.50-11.50 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 5″ | 127 | 17.11-35.86 | 11.50-24.10 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 5 1/2″ | 139.7 | 20.83-34.23 | 14.00-23.00 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 6 5/8″ | 168.28 | 29.76-35.72 | 20.00-24.00 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 7″ | 177.8 | 25.30-56.55 | 17.00-38.00 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 7 5/8″ | 193.68 | 35.72-63.69 | 24.00-42.80 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 8 5/8″ | 219.08 | 35.72-72.92 | 24.00-49.00 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 9 5/8″ | 244.48 | 48.07-86.91 | 32.30-58.40 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 10 3/4″ | 273.05 | 48.73-97.77 | 32.75-65.70 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 11 3/4″ | 298.45 | 62.50-89.29 | 42.00-60.00 | J55 | LTC/STC/BTC | R1/R2/R3 |
| 13 3/8″ | 339.72 | 71.43-107.15 | 48.00-72.00 | J55 | LTC/STC/BTC | R1/R2/R3 |