API 5CT Grade H40 OCTG Casing is the lowest-strength steel grade specified under the American Petroleum Institute (API) 5CT standard. As a critical part of Oil Country Tubular Goods (OCTG), casing is a large-diameter pipe inserted into a newly drilled borehole to line the well, stabilize the wellbore, and prevent it from collapsing.
Because H40 has a lower yield strength, it is primarily used in shallow, low-pressure oil and gas wells or for the uppermost "surface casing" sections of deeper wells. It is highly economical for non-critical environments where high mechanical stress or corrosion is not a major concern.
Looking for the best price on surface casing? Get a factory-direct quote on API 5CT H40 today and lower your drilling costs.
API 5CT Grade H40 Specification Table
| Item | Description |
| Standard | API Spec 5CT (Latest Edition) |
| Steel Grade | H40 |
| Group | Group 1 (General purpose) |
| Product Level | PSL1 (Typical for H40) |
| Manufacturing Type | Seamless (SMLS) or Electric Resistance Welded (ERW) |
| Connection Types | STC (Short Thread), LTC (Long Thread), BTC (Buttress Thread) |
| Range Length | Range 1 (16–25ft), Range 2 (25–34ft), Range 3 (34–48ft) |
| Surface Coating | Black Paint, Anti-Rust Oil, or 3LPE/FBE upon request |
Chemical Composition (Max %)
Note: Grade H40 has very loose chemical requirements compared to higher grades; only impurities are strictly capped.
| Grade | Carbon (C) | Manganese (Mn) | Phosphorus (P) | Sulfur (S) | Silicon (Si) |
| H40 | No limit | No limit | ≤ 0.030% | ≤ 0.030% | No limit |
Mechanical Properties
| Property | Value (Grade H40) |
| Yield Strength (Min) | 276 MPa (40,000 psi) |
| Yield Strength (Max) | 552 MPa (80,000 psi) |
| Tensile Strength (Min) | 414 MPa (60,000 psi) |
| Hardness | No mandatory maximum limit |
| Elongation | Calculated based on cross-sectional area per API 5CT |
Dimensions and Tolerances Table
Standard tolerances per API 5CT for H40 Casing:
| Parameter | Tolerance |
| Outside Diameter (OD) | ± 0.75% |
| Wall Thickness (WT) | - 12.5% (No upper limit specified) |
| Weight (Single Joint) | + 6.5% to - 3.5% |
| Straightness | Max 0.2% of the total length |
| Common Sizes (OD) | 4 1/2", 5 1/2", 7", 8 5/8", 9 5/8", 10 3/4", 13 3/8", 20" |
Manufacturing Process of API 5CT H40 Casing
The production of H40 casing follows these general steps:
Raw Material: Steel billets (for SMLS) or steel coils (for ERW).
Forming:
Seamless (SMLS): Piercing a hot solid billet to form a hollow tube.
Welded (ERW): Cold-forming a steel strip into a cylinder and welding the seam using high-frequency current.
Heat Treatment: H40 is typically delivered in the As-Rolled or Normalized condition.
Straightening & Sizing: Ensuring the pipe meets the required roundness and straightness.
Threading: Cutting API-standard threads (STC/LTC/BTC) on both ends of the pipe.
Coupling Installation: Attaching the threaded coupling to one end.
Inspection: Comprehensive testing (Hydro, NDT, Mechanical).
Marking & Coating: Stenciling the API monogram and steel grade, then applying anti-corrosive paint.
Testing Requirements for API 5CT H40 Casing
Every joint of H40 casing must pass several quality control gates:
Hydrostatic Testing (Mandatory): Every pipe is filled with water and pressurized to ensure it can withstand the internal pressure without leaking.
Tensile Testing: Verifying the yield and tensile strength on samples from every heat.
Flattening Test: For ERW casing, the pipe is crushed to check the integrity and ductility of the weld seam.
Visual Inspection: Checking for surface defects, straightness, and circularity.
Dimensional Inspection: Verification of OD, Wall Thickness, and Length.
Threading Inspection: Using gauges to check thread form, pitch, and taper to ensure a gas-tight seal when connected.
Drift Test: Passing a cylindrical mandrel (the "drift") through the pipe to ensure the internal diameter is clear.
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FAQ
What is the tolerance for API 5CT casing?
The tolerances for API 5CT casing are strictly defined to ensure that the pipes can be safely connected and lowered into a wellbore. These tolerances cover outside diameter, wall thickness, weight, and length.
| Parameter | Tolerance Limit |
| Outside Diameter |
+1.00%/−0.50% (for ≥ 4.5") |
| Wall Thickness |
−12.5% (Minimum) |
| Weight (Single Joint) |
+6.5%/−3.5% |
| Straightness |
≤0.2% of total length |
| Length (Range 2) | 25 ft to 34 ft |
What thickness is API casing?
Depending on the size of the pipe, wall thicknesses generally range from 5 mm to over 16 mm (0.200" to 0.650"+).
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