API 5CT K55 LTC Casing Pipe
API 5CT K55 LTC casing is a balanced, high-tensile carbon steel tubular engineered for medium-depth wells, featuring a yield strength of 55,000 to 80,000 psi (379–552 MPa) and a minimum tensile strength of 95,000 psi (655 MPa), which provides significantly higher axial load capacity for heavy pipe strings compared to the J55 grade.
Utilizing a Long Round Thread (LTC) connection with 8 threads per inch and a 60° V-shape thread profile, this product offers superior joint integrity and seal performance over Short Round Threads (STC) in non-sour drilling environments. Manufactured in strict accordance with API 5CT standards-including a -12.5% wall thickness tolerance and mandatory 100% hydrostatic testing-it is identified by two bright green bands on the pipe body, ensuring high structural reliability when used as surface or intermediate casing in shallow to medium-depth boreholes.
Need a precise dimension chart for LTC connections? Download the K55 LTC Specification Guide for your engineering files.
API 5CT K55 LTC casing Chemical Composition (%)
According to API 5CT standards, the chemical requirements for Grade K55 focus primarily on limiting harmful impurities. The specific chemical composition is determined by the manufacturer to ensure the material meets the required mechanical properties.
| Element Name | Symbol | Requirement (%) |
| Phosphorus | P | ≤ 0.030 |
| Sulfur | S | ≤ 0.030 |
| Carbon | C | 0.20 - 0.40 (Typical value) |
| Manganese | Mn | 1.00 - 1.50 (Typical value) |
API 5CT K55 LTC casing pipe Mechanical Properties
The mechanical properties of K55 provide a significant advantage over J55 in applications involving high tensile loads.
| Property | Imperial Unit (psi) | Metric Unit (MPa) |
| Yield Strength | 55,000 - 80,000 | 379 - 552 |
| Min. Tensile Strength | ≥ 95,000 | ≥ 655 |
| Min. Elongation | Per API 5CT calculation formula | Per API 5CT calculation formula |
| Hardness | No maximum specified | No maximum specified |
API 5CT K55 LTC Casing Size Chart
LTC connections are widely used in the following common specifications:
| Outside Diameter (OD) | Nominal Weight | Wall Thickness (WT) | Inside Diameter (ID) | Drift Diameter |
| inches (mm) | lb/ft ( kg/m ) | inches (mm) | inches (mm) | inches (mm) |
| 4-1/2" (114.3) | 11.60 (17.26) | 0.250 (6.35) | 4.000 (101.6) | 3.875 (98.4) |
| 5-1/2" (139.7) | 15.50 (23.07) | 0.275 (6.98) | 4.950 (125.7) | 4.825 (122.6) |
| 17.00 (25.30) | 0.304 (7.72) | 4.892 (124.3) | 4.767 (121.1) | |
| 7" (177.8) | 23.00 (34.23) | 0.317 (8.05) | 6.366 (161.7) | 6.241 (158.5) |
| 26.00 (38.69) | 0.362 (9.19) | 6.276 (159.4) | 6.151 (156.2) | |
| 9-5/8" (244.5) | 36.00 (53.57) | 0.352 (8.94) | 8.921 (226.6) | 8.765 (222.6) |
| 40.00 (59.53) | 0.395 (10.03) | 8.835 (224.4) | 8.679 (220.5) |
API 5CT K55 LTC OCTG casing Dimensional Tolerances
| Measurement Item | API 5CT Tolerance Requirements |
| Outside Diameter (OD) | For D≥4−1/2": +1.00% / -0.50% |
| Wall Thickness | -12.5% |
| Weight (Mass) | Single length: +6.5% / -3.5%; Carload: -1.75% |
| Straightness | Full length ≤ 0.2%; Pipe ends ≤3.2mm (1/8") |
| Length | Range 1, 2, or 3 (Typically Range 3: 10.36m - 14.63m) |
API 5CT K55 LTC oil well casing Inspection Items
Hydrostatic Test: Performed on every length of pipe to verify no leaks under high-pressure conditions.
Drift Test: Passing a standard drift mandrel through the full length of the pipe to ensure a clear internal passage.
Visual Inspection: Checking the pipe surface for cracks, scabs, and mechanical damage.
Non-Destructive Testing (NDT): Primarily Electromagnetic Induction (EMI) or Ultrasonic Testing (UT).
Thread Inspection: Checking thread lead, taper, height, and the LTC hand-tight standoff position.
Color Identification: Grade K55 must be marked with two bright green bands (on the pipe body and coupling).
GNEE API 5CT K55 LTC Oil well casing pipe process line
GNEE API 5CT K55 LTC Casing Pipe test equipments
GNEE API 5CT K55 LTC OCTG Pipe certificate
FAQ
What is the practical difference between K55 LTC and J55 LTC?
A: The primary difference is the tensile strength. While both share the same yield strength (55,000 to 80,000 psi), K55 has a minimum tensile strength of 95,000 psi, whereas J55 is only 75,000 psi. This means K55 LTC is far more resistant to breaking under the massive weight of a long pipe string in deeper wells, offering a higher safety margin.
Why choose LTC (Long Round Thread) over STC (Short Round Thread) for K55?
A: LTC has a longer threaded section than STC. This increased thread engagement significantly enhances the joint tensile strength. Since K55 is a high-tensile steel grade, using LTC allows you to fully utilize the material's mechanical properties. Additionally, LTC provides better leak resistance under high-tension loads compared to STC.
Can K55 LTC threads be connected to STC threads?
A: No. Although both are 8-round threads with a 60° V-shape profile, the lengths of the coupling and the thread section on the pipe are different. Mixing them will lead to seal failure, reduced load capacity, or a complete "pull-out" of the joint.
Is K55 LTC casing suitable for H2S (Sour Service) environments?
A: No. K55 is a standard carbon steel and is not treated for Sulfide Stress Cracking (SSC). Using it in "sour" environments containing
H2SH2S
will lead to brittle failure of the pipe. For sour service, you should choose L80-1 or higher corrosion-resistant grades.
Do you support Third-Party Inspection (TPI) for K55 LTC?
A: Yes. We regularly work with international agencies such as SGS, BV, or Intertek. Customers typically request TPI to verify Ultrasonic Testing (UT), Magnetic Particle Inspection (MPI), hydrostatic test data, and chemical composition reports.
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