H40 is the lowest grade defined in API Specification 5CT, 11th Edition. At 276 MPa (40 ksi) minimum yield, it is specified for applications where depth, pressure, and corrosion requirements sit well below what higher grades must handle — conductor pipe, surface casing in shallow onshore wells, and non-structural water well casing are its primary homes. The grade costs less because it requires no heat treatment and carries no alloy requirements beyond basic P and S limits.
The procurement risk with H40 is not that the grade fails to meet its specification — it is that the grade gets specified for applications that have grown beyond its ceiling without anyone updating the casing design. Procurement teams inherit H40 from legacy well designs or regional practice, and the grade ends up in strings where the collapse or burst requirements have crept above what 40 ksi yield can support.
ZC Steel Pipe supplies H40 casing primarily for conductor pipe packages destined for onshore wells in East Africa and South Asia, typically in 20-inch and 30-inch OD for the large-diameter conductor section, and in 13-3/8-inch for surface casing in shallow wells with maximum set depth under 600 m.
What Is H40 Casing?
H40 is a Group 1 OCTG casing grade per API Specification 5CT, 11th Edition. "H40" designates the minimum yield strength in ksi — 40 ksi, or 276 MPa. Unlike the sour-service and high-strength grades in API 5CT, H40 has no required heat treatment, no chromium or molybdenum chemistry restriction, and no hardness limit. It is supplied in whatever condition the mill chooses — typically as-rolled or normalised, depending on the steel chemistry selected.
The wide yield range — 276 to 552 MPa (40 to 80 ksi) — is characteristic of a grade that sits at the commodity end of the OCTG specification. A mill can ship any yield between those limits and be fully compliant. This is relevant to string design: the minimum design value to use in collapse and burst calculations is always 276 MPa (40 ksi), even if the MTC shows a higher actual yield.
API 5CT does not assign a mandatory color band to H40. The grade may carry a black band at the manufacturer's option, or no color marking at all. In practice, many shipments arrive without any color identification, which places the entire burden of grade verification on the stencil and the MTC.
Mechanical Properties
| Property | H40 | J55 (comparison) | N80-1 (comparison) |
|---|---|---|---|
| Min yield strength | 276 MPa / 40 ksi | 379 MPa / 55 ksi | 552 MPa / 80 ksi |
| Max yield strength | 552 MPa / 80 ksi | 552 MPa / 80 ksi | 758 MPa / 110 ksi |
| Min tensile strength | 414 MPa / 60 ksi | 517 MPa / 75 ksi | 689 MPa / 100 ksi |
| Max hardness (HRC) | None specified | None specified | None specified |
| Heat treatment | None required | None required | Normalised or Q+T |
| Sour service | No | No | No |
| Color code | None / black (optional) | One bright green band | One red band |
Source: API 5CT, 11th Edition.
The gap between H40 and J55 is meaningful in shallow-well design. J55's minimum yield of 379 MPa (55 ksi) gives 37% more collapse and burst resistance at the design floor than H40's 276 MPa (40 ksi). For wells that are borderline on collapse resistance in the conductor or surface string, that margin can determine whether the design passes without a wall thickness increase.
For the complete API 5CT grade ladder including tensile, hardness, and chemistry requirements, see the API 5CT specification tables →
To match a casing grade to your well conditions, use the AI Pipe Grade Selector →
What we see on conductor pipe orders: Most H40 purchase orders we receive do not specify a PSL level. API 5CT defaults to PSL-1 when no PSL is stated, which means no Charpy impact testing and no supplementary test requirements. For conductor pipe this is usually acceptable — the conductor is typically not a pressure-containing string — but we always confirm with the buyer before manufacturing begins, because some project specifications require PSL-2 documentation even for conductor pipe in deepwater-adjacent locations.
Chemical Composition
API 5CT does not restrict carbon, manganese, molybdenum, chromium, niobium, nickel, copper, or silicon for H40. The only chemistry requirements are:
| Element | H40 limit |
|---|---|
| Phosphorus (P) | 0.030% max |
| Sulfur (S) | 0.030% max |
| All other elements | Not restricted by API 5CT |
This is the least restrictive chemistry profile in the entire API 5CT grade table. A mill producing H40 can use whatever C-Mn steel chemistry achieves the required yield and tensile without heat treatment. The practical consequence is that two heats of H40 from different mills can have substantially different carbon and manganese contents while both being fully API-compliant. For most conductor and surface casing applications this does not matter — the grade is not being selected for weldability or toughness. For applications where field welding of the casing will occur (e.g. conductor joints welded rather than threaded), the actual carbon content matters and should be confirmed with the mill before ordering.
Standard Applications
Conductor pipe: The most common H40 application. The conductor is the outermost pipe in the well, set at 30–150 m to isolate near-surface groundwater and provide structural support for the wellhead. Load requirements are modest: the conductor carries the weight of the BOP stack and surface equipment, not wellbore pressure. H40 meets these requirements at minimum cost.
Surface casing in shallow onshore wells: In onshore wells with total depth under 600–800 m and no gas shows at surface, H40 is often the base case for the surface string. The string is cemented to surface and sees relatively low burst loads unless the well encounters shallow gas.
Water well casing: Water well drilling uses large-diameter, low-pressure casing where structural requirements are limited to resisting overburden collapse and maintaining borehole integrity. H40 is widely used for municipal and agricultural water well casing in this context.
Construction and geotechnical borehole casing: Temporary casing for foundation investigation, environmental monitoring boreholes, and soil stabilisation applications uses H40 because cost dominates the selection and the pipe is typically recovered after use.
Depth and Load Limits
H40's practical depth limit for surface casing is approximately 600–800 m in most onshore well designs, assuming standard well fluid densities and no shallow gas overpressure. Beyond this, collapse resistance at the design floor of 276 MPa (40 ksi) begins to require wall thicknesses that erode the cost advantage over J55.
The critical load limit is collapse pressure, not burst. Conductor and surface casing are typically set in formation with hydrostatic annular load. As set depth increases, the external pressure load on an uncemented or partially-cemented string grows, while H40's collapse resistance — a function of yield strength and D/t ratio — remains fixed.
Burst limits become relevant when shallow gas is present. A well that encounters gas at 200 m TVD with formation pressure gradient of 0.1 psi/ft generates approximately 2.9 MPa (420 psi) formation pressure at surface. For 13-3/8" casing at 68 lb/ft, H40's burst resistance (using minimum yield) is approximately 11.0 MPa (1,600 psi), giving a design factor of 3.8× against that specific load — adequate. But if gas migration reaches the wellhead or the safety factor is specified at 1.33× or higher, the allowable working pressure narrows quickly.
Worked Calculation: Collapse Resistance for 13-3/8" H40 Surface Casing
A common surface casing design uses 13-3/8" × 54.5 lb/ft. At this weight, the wall thickness is 8.71 mm (0.343") and OD is 339.7 mm (13.375").
The D/t ratio = 13.375 / 0.343 = 39.0
At D/t ≈ 39, the approximate yield-strength collapse pressure using the simplified formula P_yp = 2 × Y_min × (t/D) / (1 − t/D):
P_yp = 2 × 40,000 psi × (0.343 / 13.375) / (1 − 0.343/13.375) = 80,000 × 0.02564 / 0.97436 = 2,105 psi (14.5 MPa)
This is the minimum collapse resistance at the H40 design floor. Actual collapse resistance from the plastic collapse formula at this D/t is somewhat higher (typically 10–25% above yield-strength collapse), but API 5CT string design uses the lower bound.
For comparison, the same 13-3/8" × 54.5 lb/ft in J55 (Y_min = 55,000 psi):
P_yp = 80,000 × (55,000/40,000) × 0.02564 / 0.97436 ≈ 2,895 psi (20.0 MPa)
J55 provides 37% more collapse resistance at the design floor for the same pipe geometry. In a well with set depth of 600 m and mud weight of 1.5 sg, the external hydrostatic load is 8.8 MPa (1,277 psi). H40 passes at 14.5 MPa with a design factor of 1.14 — marginal against the API-recommended 1.0× minimum, and uncomfortably low if any safety margin is specified above 1.0×.
H40's wide yield range (276–552 MPa) means the actual pipe you receive may have a yield well above the 276 MPa design floor. Mills producing H40 from high-carbon C-Mn heats routinely ship material at 380–450 MPa actual yield. This does not change the design — engineers must use the specified minimum — but it does explain why H40 pipe in the field often performs better than the design assumes. The risk of design on actual yield rather than minimum yield is that a future order from a different mill ships material closer to 276 MPa, and the actual collapse performance drops without warning.
When NOT to Use H40
Wells with any H2S exposure. H40 has no hardness limit and is not qualified for sour service under NACE MR0175 / ISO 15156. Even trace H2S at high partial pressure can cause sulfide stress cracking (SSC) in uncontrolled-hardness carbon steel. Any string that contacts produced fluid in a H2S environment requires a sour-service grade — minimum L80-1.
Deep wells or high-pressure formations. H40's 276 MPa (40 ksi) minimum yield supports conductor and shallow surface casing. For wells where the surface string must be set deeper than 800 m, or where formation pore pressure requires a mud weight above 1.4 sg, collapse and burst margins against the minimum yield become very thin. Step up to J55 at minimum, or N80 where depth-driven loads are significant.
Wells with shallow gas potential. If the well prognosis identifies shallow biogenic gas or any gas-bearing formation above the production casing shoe, the surface casing must contain a gas influx to surface. H40's minimum burst resistance for common surface casing sizes can be insufficient for uncontrolled gas at surface pressure, particularly for strings in the 20-inch and 24-inch range where wall thickness is low relative to OD.
Sour service water injection. Produced water injection wells that handle water with dissolved H2S — even at low concentration — cannot use H40. This is common on fields where produced water is co-mingled and the H2S level varies seasonally or by well. Assume sour conditions unless water chemistry testing proves otherwise.
High-temperature steam or thermal wells. Steam injection wells (SAGD, cyclic steam stimulation) expose surface and production casing to repeated thermal cycling. H40's absence of heat treatment requirements means microstructure is not controlled for thermal fatigue resistance. Use N80Q or higher for thermal well applications.
Strings requiring premium connection performance. Premium connections are designed for specific pipe body mechanical properties. Where the connection's structural rating is based on the pipe body yield, an H40 pipe body — at minimum yield well below J55 or N80 — reduces the effective connection rating below what the premium connection manufacturer assumes. Most premium connection qualification testing is conducted on J55 and higher grades.
Purchase Order Guidance
Minimum required PO content
A complete H40 casing purchase order should specify:
- Standard: API Specification 5CT, 11th Edition
- Grade: H40
- Size: OD in inches, weight in lb/ft (e.g., 13-3/8", 54.5 lb/ft)
- End finish: STC, LTC, or BTC (or plain end if coupling is ordered separately)
- PSL level: PSL-1 or PSL-2
- MTC type: EN 10204 3.1 (mill-certified) or 3.2 (third-party witnessed)
- Delivery condition: typically as-rolled — state if normalised is required
Procurement trap
A purchase order that reads only "API 5CT H40 casing, 13-3/8" 54.5 lb/ft" — without specifying an end finish — allows the mill to ship plain-end pipe. Plain-end H40 cannot be run in a well without field threading or separate coupling supply. This is a common error on conductor pipe orders where the buyer assumes BTC is the default. It is not: API 5CT requires the purchaser to specify the connection type.
The correct PO line reads: "API Specification 5CT, 11th Edition, Grade H40, 13-3/8" 54.5 lb/ft, BTC, PSL-1, EN 10204 3.1 MTC."
MTR verification checklist
On receipt of the mill test report for H40 casing, verify:
- Standard reference is "API Specification 5CT, 11th Edition" — not an older edition or equivalent
- Grade marked as "H40"
- Yield strength ≥ 276 MPa (40 ksi) — reject if below
- Yield strength ≤ 552 MPa (80 ksi) — reject if above (overstrength is an API 5CT non-conformance)
- Tensile strength ≥ 414 MPa (60 ksi)
- P ≤ 0.030%, S ≤ 0.030%
- Heat number on MTC matches heat number stencilled on pipe body
- Connection type matches order (STC/LTC/BTC)
Failure mode: grade misidentification at the yard
Because H40 carries no mandatory color marking, it is the OCTG grade most likely to be misidentified at a pipe yard. A shipment of H40 and J55 arriving without clear color differentiation — both possibly arriving with no bands or one band depending on manufacturing batches — can be sorted only by reading the stencil or checking the MTC. Yards that store pipe by connection type and OD without checking grade have run J55 conductor jobs with H40 pipe and vice versa. The diagnostic: pipe body stencil must read "H40" in clear lettering near the pin end, and the MTC heat number must be traceable to that stencil. If pipe at the yard shows a faded or absent stencil, do not run it without re-confirming grade against the bundle MTC.
For the complete API 5CT grade comparison and collapse/burst resistance tables, see the API 5CT specification tables → and use the AI Pipe Grade Selector → to compare H40 against J55 or N80 for your well conditions.
Frequently Asked Questions
What is H40 casing used for?
H40 casing is used primarily for conductor pipe, surface casing in shallow low-pressure wells, and non-structural water well casing. Its 276–552 MPa (40–80 ksi) yield range suits applications where depth does not exceed roughly 600–800 m and wellhead pressures are below 7 MPa (1,000 psi). It is also used for construction-sector soil casing and temporary borehole casing where mechanical loads are well below the grade ceiling.
What are the H40 casing yield and tensile strength requirements?
Per API Specification 5CT, 11th Edition, H40 has a minimum yield strength of 276 MPa (40 ksi), a maximum yield strength of 552 MPa (80 ksi), and a minimum tensile strength of 414 MPa (60 ksi). API 5CT does not specify a hardness limit for H40. No heat treatment is required — the grade is typically supplied in the as-rolled or normalised condition.
Does H40 meet sour service requirements?
No. H40 is not a sour service grade under API 5CT or NACE MR0175 / ISO 15156. It has no hardness restriction, which means it can be supplied with hardness levels well above the HRC 22 threshold that NACE MR0175 sets for carbon steel in H2S service. If the well has any H2S, even trace levels at high pressure, H40 is not acceptable for any string that contacts the produced fluid.
Can H40 be used for conductor casing?
Yes — conductor pipe is H40's primary OCTG application. The conductor is set at shallow depth (typically 30–150 m), cemented, and carries little more than the weight of the BOP stack and any annular loads from the drilling fluid. H40's yield and collapse resistance are sufficient for these loads, and no heat treatment is required, which keeps cost low. For conductor sizes above 20-inch OD at depths beyond 150 m, verify collapse resistance explicitly.
What is the color code for H40 casing?
API 5CT gives H40 no mandatory color band, or optionally a black band at the manufacturer's discretion. In practice, many mills ship H40 with no color marking at all. This makes pipe identification at the yard entirely dependent on stencil markings and the mill test certificate. Always verify grade identity from the MTC and stencil, not from the absence of a color band.
What is the difference between H40 and J55 casing?
H40 has a minimum yield of 276 MPa (40 ksi) versus J55's minimum of 379 MPa (55 ksi). J55 also has a higher minimum tensile: 517 MPa (75 ksi) versus H40's 414 MPa (60 ksi). Both grades have no hardness limit and require no heat treatment, but J55 costs marginally more. For any well deeper than 600 m or with wellhead pressure above 7 MPa, the strength differential matters. J55 is the better choice for shallow wells where collapse or burst calculations are borderline.
What PO language is required to order H40 casing?
A purchase order for H40 casing should specify: API Specification 5CT, 11th Edition; grade H40; pipe size (OD and weight per foot); end finish (STC, LTC, or BTC); PSL level; and whether EN 10204 3.1 or 3.2 MTC documentation is required. Specifying only 'H40 casing' without an end finish allows the mill to ship plain end pipe, which cannot be run without separate coupling machining.
Can H40 casing be used in water injection wells?
H40 can be used in the surface string of a water injection well where the well is shallow and injection pressures are low. For disposal or injection wells that penetrate corrosive formations, carry significant wellhead pressure, or inject treated produced water with H2S traces, H40 is not appropriate. The grade has no corrosion resistance beyond standard carbon steel, and its lack of a hardness limit means it is not qualified for any H2S exposure.
How do I verify H40 casing on arrival at the yard?
On yard receipt, verify: (1) stencil marking on pipe body reads 'H40' along with size, weight, and mill code; (2) MTC confirms API 5CT 11th Edition compliance, grade H40, minimum yield 276 MPa, minimum tensile 414 MPa, and PSL level; (3) coupling markings match the pipe body grade and connection type; (4) no color band is required, so rely entirely on stencil and MTC. Reject any pipe where stencil and MTC disagree on grade, or where the MTC does not reference API 5CT.