API 5CT K55 BTC Casing Pipe
What is API 5CT K55 BTC Casing Pipe?
API 5CT: The international standard set by the American Petroleum Institute for casing and tubing used in oil and gas wells.
K55 Grade: A medium-strength carbon steel grade. While its yield strength (55,000–80,000 psi) is identical to the J55 grade, K55 has a much higher minimum tensile strength (≥ 95,000 psi). This makes it safer for deeper wells where the weight of the pipe string is significant.
BTC (Buttress Thread Connection): A trapezoidal (buttress-shaped) thread design. It is engineered to provide high axial tensile strength, making it excellent for long, heavy casing strings. It also features "easy stabbing" during the assembly process.
Casing Pipe: Installed in the borehole to stabilize the well, isolate different formations, prevent collapse, and protect groundwater from contamination.
Need full mechanical specs and collapse pressure ratings for K55 BTC? Download the Technical Datasheet for your engineering files.
API 5CT K55 BTC Specification Chart
The following tables provide the geometric dimensions and mechanical properties for common K55 BTC specifications.
Dimensions and Wall Thickness (Common Sizes)
| Outside Diameter (OD) | Nominal Weight | Wall Thickness | Inside Diameter (ID) | Drift Diameter |
| inches (mm) | lb/ft ( kg/m ) | inches (mm) | inches (mm) | inches (mm) |
| 4-1/2" (114.3) | 11.60 | 0.250 (6.35) | 4.000 (101.6) | 3.875 (98.4) |
| 5-1/2" (139.7) | 15.50 | 0.275 (6.98) | 4.950 (125.7) | 4.825 (122.6) |
| 17.00 | 0.304 (7.72) | 4.892 (124.3) | 4.767 (121.1) | |
| 7" (177.8) | 23.00 | 0.317 (8.05) | 6.366 (161.7) | 6.241 (158.5) |
| 26.00 | 0.362 (9.19) | 6.276 (159.4) | 6.151 (156.2) | |
| 9-5/8" (244.5) | 36.00 | 0.352 (8.94) | 8.921 (226.6) | 8.765 (222.6) |
| 40.00 | 0.395 (10.03) | 8.835 (224.4) | 8.679 (220.5) | |
| 13-3/8" (339.7) | 54.50 | 0.380 (9.65) | 12.615 (320.4) | 12.459 (316.5) |
| 61.00 | 0.430 (10.92) | 12.515 (317.9) | 12.359 (313.9) |
API 5CT Pipe Body Dimensional Tolerances
| Item / Parameter | Tolerance Requirement | Remarks |
| Outside Diameter (D) | ||
| - For D<4−1/2" (114.3mm) |
±0.79 mm ( ±0.031"± ) |
Applies to smaller diameter pipes |
| - For D≥4−1/2" (114.3mm) | +1.00% / -0.50% | Standard for most casing sizes |
| Wall Thickness (t) | -12.5% | No specific upper limit; controlled by weight |
| Weight (Mass) | ||
| - Single Length | +6.5% / -3.5% | Individual pipe tolerance |
| - Carload (Bulk) | -1.75% | Tolerance for large batch orders |
| Ovality | Included in OD tolerance | Stricter for the last 1.5m of pipe ends |
Casing Length Ranges
API 5CT classifies casing into three length ranges. Range 3 is the most common for international K55 BTC exports.
| Length Range | Length (ft) | Length (m) |
| Range 1 | 16.0 - 25.0 | 4.88 - 7.62 |
| Range 2 | 25.0 - 34.0 | 7.62 - 10.36 |
| Range 3 | 34.0 - 48.0 | 10.36 - 14.63 |
K55 Mechanical Properties
| Property | Imperial (psi) | Metric (MPa) |
| Min. Yield Strength | 55,000 | 379 |
| Max. Yield Strength | 80,000 | 552 |
| Min. Tensile Strength | 95,000 | 655 |
| Wall Thickness Tolerance | -12.5% | -12.5% |
Chemical Composition (%)
| Phosphorus (P) | Sulfur (S) | Carbon (C) | Manganese (Mn) |
| ≤ 0.030 | ≤ 0.030 | Mfr. Discretion (Typ. 0.20-0.40) | Mfr. Discretion (Typ. 1.00-1.50) |
Steel Grade Identification (K55)
According to API 5CT, the color for the "55" family is Bright Green.
| Component | Color Pattern |
| Pipe Body Bands | Two Bright Green Bands |
| Coupling | Painted entirely Bright Green |
K55 BTC Inspection
| Inspection Category | Key Test Item | Main Objective |
| Material | Tensile & Yield Test | Verify K55 strength |
| Physical | Drift Test | Ensure clear internal passage |
| Threads | BTC Gauging & Triangle Mark | Ensure joint integrity |
| Integrity | EMI / Ultrasonic (NDT) | Find hidden internal flaws |
| Pressure | Hydrostatic Test | Confirm leak-proof performance |
| ID | 2 Bright Green Bands | Prevent using the wrong grade |
GNEE API 5CT K55 BTC Casing Pipe process line
GNEE API 5CT K55 BTC OCTG Casing Pipe test equipments
GNEE API 5CT K55 BTC Oil well casing pipe certificate
FAQ
What is the difference between J55 and K55?
A: They share the same yield strength, but K55 has higher tensile strength (95 ksi vs. 75 ksi). K55 is safer for strings under higher tension.
Why choose BTC over STC/LTC?
A: BTC (Buttress) offers superior axial tensile strength and can support nearly 100% of the pipe body load. It is better for deep wells and large-diameter casing.
Is K55 suitable for H2S environments?
A: No. It is a standard carbon steel. For sour service, you need L80, C90, or T95 grades.
Do you support Third-Party Inspection (TPI)?
A: Yes, we welcome SGS, BV, or Intertek to verify EMI, UT, and Hydrostatic tests at our facility.
What is the maximum depth for K55?
A: Usually for wells up to 2,000–3,000 meters, depending on the OD and wall thickness.
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