API 5CT C110 Casing For Sour Service
C110 is a high-strength, Sulfide Stress Cracking (SSC) resistant steel grade. It belongs to Group 3 of the API 5CT specification.
Purpose: In typical steel, higher strength usually leads to higher sensitivity to hydrogen embrittlement and cracking in
H2SH2S
environments. C110 is engineered to maintain a high yield strength (110,000 psi) while providing the necessary toughness and chemistry to resist Sour Service (environments containing Hydrogen Sulfide).
Key Restriction: To ensure SSC resistance, C110 has a strictly mandated maximum hardness limit of 30 HRC and a controlled yield strength range to prevent the material from becoming too brittle.
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API 5CT C110 Color Code Table
C110 uses a dual-band system to distinguish it from standard P110.
| Steel Grade | Color Band (on Pipe) | Coupling Color |
| C110 | One White band + One Brown band | Entirely White with a Brown band in the center |
API 5CT C110 Chemical Composition Table (Mass Fraction %)
C110 is typically a Chromium-Molybdenum (Cr-Mo) alloy steel with strict limits on impurities to prevent cracking.
| Element | Content (%) |
| Carbon (C) | ≤ 0.35% |
| Manganese (Mn) | 0.35% - 1.20% |
| Phosphorus (P) | ≤ 0.020% |
| Sulfur (S) | ≤ 0.005% (Extremely low to prevent SSC) |
| Silicon (Si) | ≤ 0.45% |
| Chromium (Cr) | 0.40% - 1.50% |
| Molybdenum (Mo) | 0.25% - 0.85% |
API 5CT C110 Mechanical Property Table
The yield strength range for C110 is narrower than P110 to ensure precise performance control.
| Property | Units | Value |
| Yield Strength | psi (MPa) | 110,000 - 120,000 (758 - 827) |
| Tensile Strength | psi (MPa) | ≥ 115,000 (793) |
| Maximum Hardness | HRC | ≤ 30.0 (Mandatory Requirement) |
| Impact Energy | - | Based on wall thickness (usually requires low-temp testing) |
API 5CT C110 Dimensions and Sizes Chart (Common)
| OD (inch) | OD (mm) | Common Wall Thickness (mm) | Application Type |
| 4-1/2" | 114.3 | 5.21 - 16.0 | Tubing / Production Casing |
| 5-1/2" | 139.7 | 6.98 - 14.27 | Production Casing |
| 7" | 177.8 | 8.05 - 15.11 | Deep Well Casing / Liner |
| 9-5/8" | 244.5 | 8.94 - 15.11 | Intermediate Casing |
API 5CT C110 Pipe Tolerance Table
| Item | Tolerance |
| Outside Diameter (OD) | OD ≥ 4-1/2": +1.00% / -0.50% |
| Wall Thickness | -12.5% (Positive limited by weight tolerance) |
| Weight | Single Joint: -3.5% / +6.5%; Per Lot: -1.75% |
| Length | R1 (4.88-7.62m), R2 (7.62-10.36m), R3 (>10.36m) |
| Straightness | Total deviation < 0.2% of total pipe length |
Connection Types and Ends
Ends: Typically TE (Threaded and Coupled).
Connections: Because C110 is used in high-pressure sour gas wells, Premium Connections (e.g., VAM TOP, Tenaris Blue, Fox) are highly recommended. These provide "Metal-to-Metal" seals that are gas-tight, which is safer for H2S service than standard API threads.
Couplings: Must be made of seamless C110 grade stock and must undergo the same heat treatment and SSC testing as the pipe body.
Tests for API 5CT C110
Due to the hazardous nature of sour environments, C110 testing is among the most rigorous in the API standard:
SSC Testing (Sulfide Stress Cracking):
Standard: Per NACE TM0177.
Requirement: Method A (Tensile) or Method D (DCB) tests must be performed to prove the material does not crack in
H2SH2S
saturated brine.
Hardness Testing (Mandatory):
Critical: Every single joint and coupling must be hardness tested. Cross-sectional hardness traverses are required to ensure no "hard spots" exceed 30 HRC.
Metallographic Examination:
Verification of the microstructure, typically requiring a minimum of 90% tempered martensite to ensure uniformity.
NDT (Non-Destructive Testing):
100% Ultrasonic Testing (UT) and Magnetic Particle Inspection (MPI) to detect internal and surface flaws.
Hydrostatic Test:
Every joint is tested at high pressure to ensure leak-proof integrity.
Charpy V-Notch Impact Test:
Ensures the material remains tough and ductile at low temperatures to avoid brittle fracture.
API C110 Casing and Tubing factory
API 5CT C110 Oil Casing Pipe certificate
FAQ
What are the grades of API tubing
Common steel grades for API tubing include H40, J55, K55, N80, C75, L80, C90, T95, P110, and Q125; these grades are defined in accordance with the API SPEC 5CT standard and are designed to meet the strength and environmental requirements of various well conditions.
What is API spec 5CT?
API SPEC 5CT is a technical specification standard for casing and tubing published by the American Petroleum Institute (API). Used in the oil and gas extraction sector, it stipulates requirements regarding steel grades, chemical composition, mechanical properties, dimensional tolerances, and inspection procedures.
The latest edition of this standard-the 11th Edition-was published in December 2023 and establishes three Product Specification Levels (PSL):
PSL-1: Basic quality requirements, applicable to standard operating conditions.
PSL-2: Includes additional testing requirements-such as impact toughness-and is applicable to more demanding environments.
PSL-3: Designed for specific, high-risk operating conditions and imposes the most stringent requirements.
The primary steel grades covered by the standard include H40, J55, N80, P110, Q125, and sulfur-resistant grades such as L80-13Cr, each corresponding to distinct levels of strength and corrosion resistance. The international equivalent standard is ISO 11960, while the corresponding Chinese national standard is GB/T 19830.
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