API 5CT C95 Oil Country Tubular Goods (OCTG)
API 5CT C95 Oil Country Tubular Goods: High-Strength Casing & Tubing for Sour Service
Detailed technical data for API 5CT C95 oil special pipe: chemical composition, tensile and impact properties, thermal and electrical physical properties, complete equivalents and similar grades, application guide.
Heat treatment (quenching and tempering or normalizing and tempering at the option of the manufacturer); forming by hot-rolling or cold-drawing; welding only for welded pipe grades as per PSL requirements.
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API 5CT C95 Oil Country Tubular Goods Introduction
API 5CT C95 is a controlled yield strength, high-strength steel grade specified for oil country tubular goods (OCTG) primarily used in casing and tubing for oil and gas wells. It exhibits a minimum yield strength of 95 ksi (655 MPa) and is designed for sour service and high-pressure environments. Its chemical composition is carefully balanced to ensure excellent hardenability and resistance to hydrogen sulfide stress cracking (SSC). This grade is characterized by:
- Reliable mechanical properties with mandatory Charpy V-notch impact testing at low temperatures.
- Stringent limits on impurities like phosphorus and sulfur for improved toughness.
- Availability in seamless and welded forms under various delivery conditions, including heat treatment to attain the specified properties.
API 5CT C95 Oil Country Tubular Goods Chemical Composition
The chemical composition for API 5CT C95 is specified to maximise mechanical properties and resistance to sulfide stress cracking. The alloy design generally uses a carbon-manganese or chromium-molybdenum base. Precise limits are defined in API 5CT Table C.1. Tramp elements such as phosphorus and sulfur are tightly restricted to ensure low-temperature toughness and weldability. All values are maximum unless otherwise noted.
| Element | Mandatory Limits (%) | Remarks |
|---|---|---|
| Carbon (C) | ≤ 0.45 | For PSL-1; may be further restricted for PSL-2 |
| Manganese (Mn) | ≤ 1.90 | |
| Silicon (Si) | ≤ 0.45 | Optional element, often 0.15–0.35 for deoxidation |
| Phosphorus (P) | ≤ 0.030 | For PSL-1 (lower for PSL-2: ≤ 0.020) |
| Sulfur (S) | ≤ 0.030 | For PSL-1 (lower for PSL-2: ≤ 0.010) |
| Chromium (Cr) | ≤ 1.50 | Depending on manufacturer, typically 0.80–1.20 for enhanced hardenability |
| Molybdenum (Mo) | ≤ 0.75 | Often 0.15–0.40 for temper resistance |
| Nickel (Ni) | ≤ 0.99 | Limited for sour service; some variants may contain up to 0.25 |
| Copper (Cu) | ≤ 0.35 | Residual control |
| Vanadium (V) | ≤ 0.20 | Optional grain refiner |
| Niobium (Nb) | ≤ 0.05 | Optional micro-alloying |
| Titanium (Ti) | ≤ 0.05 | Optional |
| Aluminum (Al) | 0.020–0.080 (if used as grain refiner) | Only when specified; total Al |
API 5CT C95 Oil Country Tubular Goods Thermal and Electrical Physical Properties
The physical properties listed are typical for a quenched and tempered low-alloy steel of C95 grade. These values are not specification requirements but serve as engineering guidelines for thermal and electrical design. Values are valid at room temperature unless otherwise noted. Actual properties may vary slightly with exact chemistry and heat treatment.
| Property | Typical Value | Unit | Test Condition / Temperature |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | At 20 °C |
| Modulus of Elasticity (E) | 205 | GPa | At 20 °C; tension |
| Shear Modulus (G) | 80 | GPa | At 20 °C, estimated from E and Poisson ratio |
| Poisson's Ratio (ν) | 0.29 | - | At 20 °C, in elastic range |
| Thermal Expansion Coefficient (α) | 11.7 | 10⁻⁶ /°C | Mean coefficient between 20 °C and 100 °C |
| Thermal Expansion Coefficient (α) | 12.5 | 10⁻⁶ /°C | Mean coefficient between 20 °C and 300 °C |
| Thermal Conductivity (λ) | 48.5 | W/m·K | At 20 °C |
| Thermal Conductivity (λ) | 45.5 | W/m·K | At 100 °C |
| Thermal Conductivity (λ) | 40.0 | W/m·K | At 300 °C |
| Specific Heat Capacity (Cp) | 460 | J/kg·K | At 20 °C; typical for low alloy steel |
| Electrical Resistivity (ρ_e) | 0.22 | µΩ·m | At 20 °C, typical for heat treated steel |
API 5CT C95 Oil Country Tubular Goods Mechanical Properties
Mechanical properties are determined on specimens machined from the pipe body. The yield strength range and tensile strength minimum are mandatory for C95. Elongation is calculated by the formula e = 1944 A0.2 / U0.9 (psi units) or e = 625 000 A0.2 / U0.9 (metric). Charpy impact requirements depend on product specification level and ordering conditions; commonly, transverse specimens at 0 °C or −20 °C are tested. Hardness is limited to ≤ 25.4 HRC (or equivalent) for sour service compliance.
| Property | Standard Requirement | Unit | Test Condition / Remarks |
|---|---|---|---|
| Yield Strength (0.2% offset, ReH) | 95 – 110 | ksi | Tensile test at room temperature; full-section specimen per API 5CT |
| Yield Strength (0.2% offset, ReH) | 655 – 758 | MPa | Tensile test at room temperature |
| Tensile Strength (Rm) | ≥ 105 | ksi | Tensile test at room temperature |
| Tensile Strength (Rm) | ≥ 724 | MPa | Tensile test at room temperature |
| Elongation (A) | Calculated per API formula | % | Minimum elongation depends on cross-sectional area and tensile strength; typically 12-18% for common sizes |
| Charpy V-notch Impact Energy (KV₂) | ≥ 20 (average); ≥ 15 (single) | J | Transverse specimen at 0 °C, PSL-1; product specification may require different temperature and values |
| Charpy V-notch Impact Energy (KV₂) | ≥ 27 (average); ≥ 20 (single) | J | Transverse specimen at 0 °C, typical PSL-2 sour service requirement |
| Hardness | ≤ 25.4 | HRC | For sour service (H₂S conditions); equivalent HBW 255 max |
| Bend Test | No cracking or opening | - | As per API 5CT for material qualification, if specified |
| Hardness Variation | ≤ 3.0 | HRC | Maximum difference across the wall thickness for C95 in sour service |
API 5CT C95 Oil Country Tubular Goods Direct Equivalent Standards and Substitutable Grades
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| International / ISO | ISO 11960:2011 | C95 | Identical technical content to API 5CT C95; fully interchangeable within scope |
| USA | API 5CT | C95 | Original specification |
| Russia | GOST 632-80 | K (approximate equivalent) | GOST grade "K" is often referenced for 95 ksi strength, but chemistry and toughness may differ; not identical without supplementary agreement |
| China | GB/T 19830 | C95 | Equivalent to API 5CT C95, adopted as Chinese standard for petroleum casing |
| Norway / International | NORSOK M-123 | C95 | Used for offshore applications; references ISO/API grades with additional NORSOK requirements |
API 5CT C95 Oil Country Tubular Goods Application Introduction
API 5CT C95 is a workhorse grade in the petroleum industry, designed for high-pressure and sour gas environments. Its controlled yield range ensures reliable performance without excessive hardness that could lead to cracking in H₂S service. Below are typical sectors and products:
Product Applications: Production casing for crude oil and natural gas wells, Intermediate and surface casing strings, Tubing strings for high-pressure production, Liner hangers and accessories, Slotted liners for sand control, Coupling stock and pup joints
Processed into products: Pipe body (plain-end casing and tubing), Couplings (standard, special clearance, semi-premium), Integral joint connections, Perforated or slotted casing sections, Bridge plugs and packer mandrels (machined from C95 pipe), Flow control devices (sliding sleeves, nipples)
Application industries: Oil & Gas Upstream (drilling and completion), Geothermal energy extraction, Underground gas storage, Mining (borehole casing for deep exploration), CO₂ injection wells for carbon capture and storage (CCS)
API 5CT C95 Oil Country Tubular Goods Similar / Nearby Substitute Materials
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA / Global | API 5CT | T95 | Higher yield strength (95–110 ksi) and improved corrosion resistance; used in more severe sour service where C95 is borderline; tensile and toughness requirements similar |
| USA / Global | API 5CT | L80 | Lower yield strength (80–95 ksi) but good sour service performance; often used in less demanding pressure conditions |
| USA / Global | API 5CT | N80 Type Q | Lower strength level (80–110 ksi) but with quenched and tempered condition; may replace C95 in some well designs if strength reduction is acceptable |
| USA / Global | API 5CT | C90 | Similar strength but with higher resistance to sulfide stress cracking; can be used where C95 may not meet NACE MR0175/ISO 15156 limits |
| Europe | EN 10216-2 / EN 10210 | P355N (P355NH) / S355J2H | Structural steel grades with lower strength (~355 MPa), not for downhole service; chemical and physical properties differ significantly, only for non-OCTG applications |
| Japan | JIS G 3441 | SCM435TK (modified) | Quenched and tempered alloy steel tubes with similar 95 ksi yield, but not API certified; may be used for mechanical applications in place of C95 if permitted |
Notes:
- Sour Service Compliance: C95 must meet the requirements of NACE MR0175/ISO 15156 for H₂S-containing environments when ordered for sour service. This typically implies maximum hardness of 22 HRC for carbon and low alloy steels, but C95 is often limited to 25.4 HRC per API 5CT. Additional hydrogen-induced cracking (HIC) testing may apply.
- Product Specification Levels (PSL): API 5CT C95 is available in PSL-1 (basic requirements) and PSL-2 (additional testing, tighter chemical limits, and mandatory NDE). PSL-2 is mandatory for sour/offshore applications.
- Dimensional Tolerances: OD and wall thickness tolerances align with API 5CT tables, with extra drift requirements for certain sizes to ensure passage of downhole tools.
- Cold Sizing: Some grades may be cold-sized after heat treatment; for C95, a stress relieving heat treatment is usually required to avoid residual stresses that could affect SSC resistance.
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