API 5CT C90 Casing Tubing
API 5CT C90 is a high-strength, controlled-yield steel grade designed specifically for Sour Service (environments containing Hydrogen Sulfide,
H2S ). It belongs to Group 2 of the API 5CT specification.
C90 is a restricted-yield grade, meaning its chemical composition and heat treatment are strictly controlled to ensure resistance to Sulfide Stress Cracking (SSC) while maintaining high tensile strength.
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API 5CT C90 Color Code Table
Color coding allows for quick identification of the pipe grade at the well site.
| Steel Grade | Color Band (on Pipe Body) | Coupling Color |
| C90 (Type 1) | One Purple band | Entire coupling painted Purple |
API 5CT C90 Chemical Composition Table (Mass Fraction %)
C90 typically utilizes a Chromium-Molybdenum (Cr-Mo) alloy design to ensure full through-thickness hardening during heat treatment, which is essential for SSC resistance.
| Element | Content (%) |
| Carbon (C) | ≤ 0.35% |
| Manganese (Mn) | ≤ 1.20% |
| Phosphorus (P) | ≤ 0.020% |
| Sulfur (S) | ≤ 0.005% |
| Silicon (Si) | ≤ 0.45% |
| Chromium (Cr) | ≤ 1.50% |
| Molybdenum (Mo) | ≤ 0.85% |
API 5CT C90 Mechanical Property Table
The yield strength of C90 is tightly restricted to a 15,000 psi window to prevent the material from being "too hard," which would increase the risk of cracking in sour environments.
| Property | Units | Value |
| Yield Strength (Min) | psi (MPa) | 90,000 (621) |
| Yield Strength (Max) | psi (MPa) | 105,000 (724) |
| Tensile Strength (Min) | psi (MPa) | 100,000 (689) |
| Maximum Hardness | HRC | ≤ 25.4 |
| Elongation | % | Calculated based on cross-section |
API 5CT C90 Size Chart (Common Sizes)
| Type | OD (inch) | OD (mm) | Wall Thickness (mm) |
| Tubing | 2-3/8" | 60.3 | 4.83 - 5.87 |
| Tubing | 2-7/8" | 73.0 | 5.51 - 7.01 |
| Tubing/Casing | 4-1/2" | 114.3 | 5.21 - 13.06 |
| Casing | 5-1/2" | 139.7 | 6.22 - 12.70 |
| Casing | 7" | 177.8 | 6.91 - 15.11 |
| Casing | 9-5/8" | 244.5 | 8.94 - 15.11 |
API 5CT C90 Tolerance Table
| Item | Tolerance |
| Outside Diameter (OD) | OD < 4-1/2": ±0.031"; OD ≥ 4-1/2": +1.00% / -0.50% |
| Wall Thickness | -12.5% |
| Weight | Single Joint: +6.5% / -3.5% |
| Length | R1: 4.88-7.62m; R2: 7.62-10.36m; R3: >10.36m |
| Straightness | < 0.2% of total pipe length |
Connections
API Connections:
LTC (Long Thread Coupled): Common for casing.
BTC (Buttress Thread Coupled): Used for heavy strings and high tension.
EUE (External Upset End): Standard for tubing.
Premium Connections:
In sour gas wells, Premium Connections (e.g., VAM TOP, Tenaris Blue) are highly recommended because they provide metal-to-metal gas-tight seals, preventing toxic H2S leaks that standard API threads might allow.
Applications
C90 is specifically utilized in:
Sour Gas Wells: Where Hydrogen Sulfide ( H2S ) is present in the reservoir fluids.
Deep Wells with Sour Conditions: Where L80 strength is insufficient to support the string weight, but C110 is not required.
Critical Wells: High-pressure, high-temperature (HPHT) wells that have a risk of environmental cracking.
Testing Requirements
Because C90 is used in hazardous H2S environments, it undergoes more extensive testing than standard grades:
SSC Testing (Sulfide Stress Cracking): Mandatory testing per NACE TM0177 to confirm the pipe will not crack in sour conditions.
Hardness Variation: Strict testing across the wall thickness to ensure no area exceeds 25.4 HRC.
Grain Size: Verification of a fine-grained structure.
NDT (Non-Destructive Testing): 100% Ultrasonic (UT) or Electromagnetic (EMI) inspection.
Hydrostatic Test: High-pressure leak testing.
Flattening Test: For welded pipes (though C90 is almost always Seamless).
API 5CT C90 OCTG Test equipments
API 5CT C90 Oil Well Pipe factory
API 5CT C90 Casing and Tubing certificate
FAQ
What are the grades of API tubing?
The primary steel grades for tubing under the API 5CT standard include H40, J55, K55, N80, C75, L80, C90, T95, P110, and Q125; these grades are suitable for various well conditions based on differences in strength, chemical composition, and service environment.
What is the ISO equivalent of API 5CT?
The ISO equivalent standard for API 5CT is ISO 11960. The full title of this standard is *Petroleum and natural gas industries - Steel pipes for use as casing or tubing for wells*; it is substantially consistent with API 5CT in terms of technical requirements and product specifications, and is widely adopted globally to facilitate international mutual recognition.
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