In the oil and gas industry, J55 and K55 are the most common "mid-to-low" strength tubing grades governed by the API 5CT specification.
The primary difference between them is their tensile strength: while they both begin to deform at the same pressure, K55 is much harder to actually snap or pull apart than J55.
Request a competitive quote for J55 or K55 tubing today – Get a response within 24 hours!
J55 Tubing is one of the most widely used and economical steel grades in the oil and gas industry, governed by the API 5CT specification. It belongs to Group 1 and is often regarded as the "workhorse" of drilling engineering, suitable for a broad variety of conventional well conditions.
Core Positioning: J55 is a general-purpose, medium-to-low strength steel grade. Due to its balanced yield strength and significant price advantage, it is the preferred material for shallow and medium-depth wells.
Service Environment: Primarily used in non-corrosive environments (Sweet Wells). It lacks resistance to Hydrogen Sulfide ( H2S) corrosion and is strictly prohibited for sour service.
Heat Treatment: API standards do not mandate specific heat treatment for J55; it is typically delivered in an as-rolled or Normalized (N) condition.
Applications: Widely utilized in shallow oil and gas wells, water injection wells, and conventional production wells with lower formation pressure requirements.
Technical Parameter Tables for J55
Mechanical Properties Table
| Parameter | Imperial Units (psi) | Metric Units (MPa) |
| Yield Strength - Minimum | 55,000 psi | 379 MPa |
| Yield Strength - Maximum | 80,000 psi | 552 MPa |
| Tensile Strength - Minimum | 75,000 psi | 517 MPa |
| Hardness Limit | No API requirement | -- |
| Elongation | Per API 5CT Formula | -- |
Chemical Composition Table (% Max)
Chemical requirements for J55 are relatively flexible, primarily focusing on impurity control.
| Element | API 5CT Limits (%) |
| Carbon (C) | Not Specified (typically 0.25% - 0.35%) |
| Manganese (Mn) | Not Specified (typically 1.00% - 1.30%) |
| Phosphorus (P) | ≤ 0.030 |
| Sulfur (S) | ≤ 0.030 |
| Silicon (Si) | ≤ 0.45 |
Common Dimensions & Weights Chart
J55 tubing covers all standard API sizes; the following are the most frequently used specifications:
| Nominal OD | Nominal Weight | Wall Thickness | Inner Diameter (ID) | Drift Diameter |
| inch (mm) | lb/ft ( kg/m ) | inch (mm) | inch (mm) | inch (mm) |
| 2-3/8" (60.3) | 4.60 (6.85) | 0.190 (4.83) | 1.995 (50.67) | 1.901 (48.29) |
| 2-7/8" (73.0) | 6.40 (9.52) | 0.217 (5.51) | 2.441 (62.00) | 2.347 (59.61) |
| 3-1/2" (88.9) | 9.20 (13.69) | 0.254 (6.45) | 2.992 (76.00) | 2.867 (72.82) |
| 4-1/2" (114.3) | 12.60 (18.75) | 0.271 (6.88) | 3.958 (100.5) | 3.833 (97.36) |
K55 Tubing is a medium-to-low strength oilfield tubular product compliant with the API 5CT specification. It belongs to Group 1 of the API standards. While its mechanical properties are very similar to J55, it offers an enhanced tensile strength, making it one of the most commonly used grades in oil and gas drilling.
Core Positioning: K55 is a general-purpose, non-sour service steel grade. It shares the exact same minimum yield strength as J55 but features a higher minimum tensile strength.
Key Characteristics: With a minimum tensile strength of 95,000 psi (20,000 psi higher than J55), K55 can support significantly heavier string loads. This makes it more suitable than J55 for slightly deeper well sections or applications requiring a higher tensile safety factor.
Service Environment: Designed for non-corrosive (Sweet Well) environments. It does not possess resistance to Hydrogen Sulfide ( H2S ).
Heat Treatment: Similar to J55, API standards do not mandate a specific heat treatment for K55; it is typically delivered in a Normalized (N) or as-rolled condition.
Technical Parameter Tables for K55
Mechanical Properties Table
| Parameter | Imperial Units (psi) | Metric Units (MPa) |
| Yield Strength - Minimum | 55,000 psi | 379 MPa |
| Yield Strength - Maximum | 80,000 psi | 552 MPa |
| Tensile Strength - Minimum | 95,000 psi | 655 MPa |
| Hardness Limit | No API requirement | -- |
| Elongation | Per API 5CT Formula | -- |
Chemical Composition Table (% Max)
The chemical makeup of K55 primarily focuses on controlling impurities like Phosphorus and Sulfur to ensure the material's basic toughness.
| Element | API 5CT Limits (%) |
| Carbon (C) | Not Specified (typically 0.25% - 0.40%) |
| Manganese (Mn) | Not Specified (typically 1.00% - 1.50%) |
| Phosphorus (P) | ≤ 0.030 |
| Sulfur (S) | ≤ 0.030 |
| Silicon (Si) | ≤ 0.45 |
Common Dimensions & Weights Chart
The physical dimensions for K55 are identical to J55 and follow API standards:
| Nominal OD | Nominal Weight | Wall Thickness | Inner Diameter (ID) | Drift Diameter |
| inch (mm) | lb/ft ( kg/m ) | inch (mm) | inch (mm) | inch (mm) |
| 2-3/8" (60.3) | 4.70 (7.00) | 0.190 (4.83) | 1.995 (50.67) | 1.901 (48.29) |
| 2-7/8" (73.0) | 6.50 (9.67) | 0.217 (5.51) | 2.441 (62.00) | 2.347 (59.61) |
| 3-1/2" (88.9) | 9.30 (13.84) | 0.254 (6.45) | 2.992 (76.00) | 2.867 (72.82) |
| 4-1/2" (114.3) | 12.75 (18.97) | 0.271 (6.88) | 3.958 (100.5) | 3.833 (97.36) |
Comparison Table
| Feature | J55 Tubing | K55 Tubing |
| Yield Strength (Min) | 55,000 psi (379 MPa) | 55,000 psi (379 MPa) |
| Yield Strength (Max) | 80,000 psi (552 MPa) | 80,000 psi (552 MPa) |
| Tensile Strength (Min) | 75,000 psi (517 MPa) | 95,000 psi (655 MPa) |
| Heat Treatment | None specified (usually normalized) | None specified (usually normalized) |
| Service Environment | "Sweet" wells (no H2S ) | "Sweet" wells (no H2S ) |
| Relative Cost | Most economical | Slightly higher than J55 |
| API Color Code | One Bright Green Band | Two Bright Green Bands |
Selection Guide: J55 vs. K55
| Feature | J55 Tubing | K55 Tubing | Selection Advice |
| Yield Strength | 379 - 552 MPa (55-80 ksi) | 379 - 552 MPa (55-80 ksi) | Equal: Both have the same resistance to permanent deformation. |
| Tensile Strength | ≥ 517 MPa (75 ksi) | ≥ 655 MPa (95 ksi) | K55 is Higher: K55 can withstand higher hanging weights/tensile loads. |
| Color Code | One Green Band | Two Green Bands | Used for quick identification on site. |
| Heat Treatment | Normalized or As-rolled | Normalized or As-rolled | Manufacturing processes are similar. |
| Best Application | Shallow wells, water/injection wells | Deeper wells or higher structural loads | Choose K55 if the string weight is high. |
| Cost Factor | Lowest | Slightly higher than J55 | J55 is the most economical "entry-level" grade. |
API 5CT OCTG Factory
API 5CT Oil Well casing pipe test equipments
FAQ
What is the tensile strength of J55?
The minimum tensile strength of API 5CT J55 is:
75,000 psi (517 MPa)
What is the chemical composition of API 5CT K55?
The chemical composition of API 5CT K55 is relatively flexible, as the API standard primarily focuses on its mechanical properties. However, the mandatory limits for impurities are:
Phosphorus (P): ≤ 0.030%
Sulfur (S): ≤ 0.030%
Typical manufacturing ranges (non-mandatory) include:
Carbon (C): 0.25% – 0.40%
Manganese (Mn): 1.00% – 1.50%
Silicon (Si): ≤ 0.45%
