API 5CT C95 Casing is a high-strength steel grade within the Group 2 category of the API 5CT specification. It is specifically designed for deep oil and gas wells that require high tensile strength and high collapse resistance.
Unlike C90 or T95, C95 is generally not a "Sour Service" grade (it is not specifically restricted for H2S resistance by NACE MR0175 unless special requirements are met), but it offers significantly higher yield strength than J55, K55, and N80. It is primarily used in deep-well environments where high mechanical loads are the primary concern.
Color Code of API 5CT C95 Casing & Tubing
Grade C95 is identified by the color Brown.
| Grade | Pipe Body Paint Band | Coupling Paint Color | Coupling Band Color |
| C95 | One Brown Band | Brown | None (Solid Brown) |
API 5CT C95 Casing Pipe Specification
| Parameter | Specification |
| Standard | API Spec 5CT / ISO 11960 |
| Product Specification Level | PSL-1, PSL-2, PSL-3 |
| Heat Treatment | Quenched and Tempered (Q+T) |
| Forming Process | Seamless (SML) or Electric Resistance Welded (ERW) |
| Pipe Type | Casing and Tubing |
API 5CT C95 Chemical Composition (Mass Fraction, %)
| Element | Requirement (Max %) | Role in C95 Steel |
| Carbon (C) | 0.45% | Provides strength and hardenability |
| Manganese (Mn) | 1.90% | Increases strength and toughness |
| Phosphorus (P) | 0.030% | Kept low to prevent brittleness |
| Sulfur (S) | 0.030% | Kept low to prevent internal cracking |
| Silicon (Si) | 0.45% | Used as a deoxidizer during melting |
| Chromium (Cr) | Not Specified* | Usually added for deep hardenability |
| Molybdenum (Mo) | Not Specified* | Usually added to improve strength at depth |
API 5CT C95 Mechanical Properties
| Property | Imperial Units | Metric Units |
| Yield Strength (Minimum) | 95,000 psi | 655 MPa |
| Yield Strength (Maximum) | 110,000 psi | 758 MPa |
| Tensile Strength (Minimum) | 105,000 psi | 724 MPa |
| Yield to Tensile Ratio | Not specified by API | Typically 0.85 - 0.92 |
| Hardness (Typical Range) | 25 - 30 HRC | 255 - 285 HBW |
| Hardness (Maximum) | N/A | 312 HBW / 32 HRC (approx.) |
| Elongation (Min %) | Calculated by formula | Calculated by formula |
Grade C95 Oil Well Drilling Casing Tube Hierarchy
This table shows where C95 fits within the API 5CT groups.
| Group | Grades | Characteristics |
| Group 1 | H40, J55, K55, N80 | General purpose, low-mid strength |
| Group 2 | L80, C90, T95, C95 | Controlled Yield Strength |
| Group 3 | P110 | High strength |
| Group 4 | Q125 | Highest strength |
API 5CT C95 Petroleum Casing Pipe Dimension Chart (Popular Sizes)
| OD (Inches) | Weight (lb/ft) | Wall Thickness (in) | Drift Diameter (in) |
| 5-1/2" | 17.00 | 0.304 | 4.767 |
| 7" | 26.00 | 0.362 | 6.151 |
| 7" | 32.00 | 0.453 | 5.969 |
| 9-5/8" | 40.00 | 0.395 | 8.679 |
| 9-5/8" | 53.50 | 0.545 | 8.379 |
| 13-3/8" | 72.00 | 0.514 | 12.191 |
Hardness of Grade C95 Oil Well Drilling Tube
While C95 is not a "sour service" grade, it still has hardness requirements to ensure material uniformity.
| Metric | Value |
| Typical Hardness Range | 25 - 30 HRC |
| Max Hardness (Customer Spec) | Often requested at
≤32≤32 HRC |
| Testing Requirement | Mandatory for PSL-2 and PSL-3 |
Testing & Inspection of API 5CT C95 Casing Pipes
Inspection levels increase with PSL (Product Specification Level) requirements.
| Test Item | Standard / Method | Requirement |
| Visual Inspection | API 5CT | Surface defects, straightness |
| Dimensional Check | Calipers/Micrometers | OD, Wall, Length, Weight |
| Hydrostatic Test | API 5CT | 100% joints must pass |
| Non-Destructive (NDT) | UT (Ultrasonic) / MPI | Required for PSL-2/PSL-3 |
| Tensile Test | ASTM A370 | Verify Yield & Tensile |
| Flattening Test | API 5CT | Checks ductility (for ERW/SML) |
| Impact Test | Charpy V-Notch | Mandatory for PSL-2/PSL-3 |
API 5CT C95 Casing Connections Table
| Connection Type | Abbreviation | Thread Profile | Seal Mechanism | Performance Characteristics |
| Short Round Thread | STC | 8 Round Threads/Inch | Thread Interference (Grease) | Used for shorter casing strings and low-tension applications. |
| Long Round Thread | LTC | 8 Round Threads/Inch | Thread Interference (Grease) | Offers better tension strength than STC; very common for C95 tubing/casing. |
| Buttress Thread | BTC | Trapezoidal (Square-like) | Interference & Shoulder | High tensile strength and excellent collapse resistance; standard for deep casing. |
| Premium Connection | VAM / New VAM | Proprietary (Wedge/Special) | Metal-to-Metal Seal | 100% gas-tight; used in high-pressure or deviated wells. |
| Premium Connection | Tenaris Hydril | Proprietary (Blue/MS) | Metal-to-Metal Seal | Superior torque and bending resistance for complex drilling. |
| Extreme Line | XC | Integrated Thread | Metal Seal & Shoulder | Flush or semi-flush joints; used when clearance is limited (slim-hole). |
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FAQ
What are the grades of oil well casing?
Group 1 includes grades H40, J55, K55, N80, and R95, which are suitable for general-purpose applications in less demanding environments. Group 2: Comprises grades L80, C90, T95, and M65, designed for restricted yield strength and often used in sour service (hydrogen sulfide-rich) environments.
What is the difference between casing and tubing in an oil well?
Purpose: Casing provides structural integrity, isolates formations, and protects groundwater. Tubing primarily aims to transport oil and gas from the reservoir to the surface, protecting the casing from production fluids. Size: The casing is a larger-diameter tubular, typically 4.5" to 30" or more.
What are common problems with casing?
The casings are normally subjected to material degradation, varying local loads, induced stresses during stimulation, natural fractures, slip and shear during their installation and operation leading to different kinds of casing failure modes.
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