N80-1 may be delivered normalized, normalized-and-tempered or quench-and-tempered, while N80Q must be quench-and-tempered only. The defining point is not that Q+T is permitted for N80Q — it is that Q+T is the only permitted route. N80Q therefore guarantees a uniform tempered-martensitic microstructure, mandatory Charpy V-notch verification and tighter property consistency. For shallow to moderate sweet wells under roughly 2,500 m, N80-1 is cost-optimized; for deeper strings, cold-climate or offshore service, or where an operator specification mandates documented Q+T, N80Q is the safe selection.
| Element | C | Mn | Si | P | S | Cr | V |
|---|---|---|---|---|---|---|---|
| Typical heat analysis (representative 36Mn2V-type) | 0.34–0.38 | 1.45–1.70 | 0.20–0.35 | ≤ 0.020 | ≤ 0.015 | ≤ 0.15 | 0.11–0.16 |
API Spec 5CT fixes only the phosphorus and sulfur maxima for N80 (≤ 0.030 each in the standard table; many mills hold tighter limits as shown). Carbon, manganese, silicon, chromium, molybdenum and vanadium are defined by the manufacturer to meet the mechanical requirements and are recorded on the mill test certificate. Confirm the exact heat analysis against the order MTC.
| Property | Imperial | Metric |
|---|---|---|
| Minimum yield strength | 80,000 psi | 552 MPa |
| Maximum yield strength | 110,000 psi | 758 MPa |
| Minimum tensile strength | 100,000 psi | 689 MPa |
| Elongation under load | Per API 5CT formula (depends on wall thickness) | |
| Hardness limit (API 5CT) | None specified for N80 | |
| Charpy V-notch (N80Q) | Mandatory per batch; N80-1 optional unless specified | |
N80-1 and N80Q share the same strength minima. The practical difference is microstructure uniformity and impact-toughness consistency, not the design minimums.
| OD — inches (mm) | Nominal Weight — lb/ft | Wall Thickness — mm | Common BTC Application |
|---|---|---|---|
| 4-1/2" (114.3) | 9.50 – 11.50 | 5.21 – 6.35 | Production / slim-hole |
| 5" (127.0) | 11.50 – 24.10 | 5.59 – 12.70 | Production |
| 5-1/2" (139.7) | 14.00 – 23.00 | 6.20 – 10.54 | Intermediate / production |
| 6-5/8" (168.28) | 20.00 – 32.00 | 7.32 – 12.06 | Intermediate |
| 7" (177.8) | 17.00 – 38.00 | 6.91 – 13.72 | Intermediate / production |
| 7-5/8" (193.68) | 24.00 – 47.10 | 7.62 – 15.88 | Production / offshore |
| 8-5/8" (219.08) | 24.00 – 49.00 | 6.71 – 14.15 | Surface / intermediate |
| 9-5/8" (244.48) | 32.30 – 58.40 | 7.92 – 13.84 | Surface / intermediate (most common) |
| 10-3/4" (273.05) | 32.75 – 65.70 | 7.09 – 15.11 | Surface / intermediate |
| 13-3/8" (339.72) | 48.00 – 72.00 | 8.38 – 13.06 | Surface / conductor tie-back |
Sizes up to 20" (508 mm) and weights to about 133 lb/ft are available on request. The full API 5CT size and weight list is provided in the quotation. Drift diameter and internal diameter follow the standard for each weight class.
| Length Range | Length — m | Length — ft |
|---|---|---|
| Range 1 (R1) | 4.88 – 7.62 | 16.0 – 25.0 |
| Range 2 (R2) | 7.62 – 10.36 | 25.0 – 34.0 |
| Range 3 (R3) | 10.36 – 14.63 | 34.0 – 48.0 |
R2 is the most common supply length because it reduces connections per string; R3 is widely used for large-diameter export orders where longer joints cut running time.
| Item / Parameter | Tolerance Requirement | Remarks |
|---|---|---|
| Outside diameter, D ≤ 101.60 mm (4") | ± 0.79 mm | Small-diameter pipe body |
| Outside diameter, D ≥ 114.30 mm (4-1/2") | + 1.0% / − 0.5% | Standard for most casing sizes |
| Wall thickness | − 12.5% of nominal | No specific upper limit; controlled via weight |
| Weight — single length | + 6.5% / − 3.5% | Individual pipe tolerance |
| Weight — total order (carload) | − 1.75% | Batch-level tolerance |
| Straightness | ≤ 0.2% of total length | Last 1.5 m held to 3.18 mm |
| Ovality and pipe-end tolerance | Included in OD tolerance | Stricter control over the last 1.5 m of ends |
Tolerances are per API Spec 5CT for PSL-1; PSL-2 and PSL-3 may add supplementary requirements. Confirm against the specific PSL level on the order.
| Connection | Thread Standard | Joint Efficiency (typical) | Typical Use |
|---|---|---|---|
| STC (short round thread) | API Spec 5B | ~80 – 90% of pipe body | Shallow, low-load strings |
| LTC (long round thread) | API Spec 5B | ~90 – 98% of pipe body | Medium-depth wells |
| BTC (buttress) | API Spec 5B | ~100% of pipe body | Deep / high-tension / offshore |
| Premium | Proprietary | Gas-tight, metal-to-metal seal | HPHT, sour, deviated wells |
Every length is drift-tested, hydrostatic-tested and BTC-gauged before shipment, with NDT per the specified PSL level.
Where H₂S is present, sour-service grades such as L80 Type 1, C90 or T95 should be specified instead, in line with NACE MR0175 / ISO 15156. N80 is a conventional carbon steel without anti-sulfur formulation.
BTC stands for Buttress Thread Connection, the trapezoidal thread form machined on the pipe ends per API Spec 5B. Its wide thread flanks transfer axial and pressure loads at close to 100% of the pipe body strength, so BTC is selected for deep, large-diameter or high-tension casing strings where the joint itself must not be the weak point.
Both sub-grades share identical yield (552-758 MPa / 80-110 ksi) and tensile (minimum 689 MPa / 100 ksi) requirements, but differ on heat treatment. N80-1 may be delivered normalized, normalized-and-tempered or quench-and-tempered, while N80Q must be quench-and-tempered only. N80Q therefore gives a more uniform tempered-martensitic microstructure, mandatory Charpy V-notch verification and tighter property consistency.
The grade type suffix is a mandatory element of the full API 5CT designation. A normalized N80-1 mill can deliver against a loosely written 'N80' order, which passes every mechanical test but lacks the documented quench-and-temper record. For wells where Q+T toughness, low-temperature impact or MTC traceability matter, the PO must read 'API 5CT N80Q' with quenching and tempering declared mandatory and substitution of N80-1 not accepted.
No. N80 is a Group 1 carbon steel grade without a mandatory NACE MR0175 / ISO 15156 sour-service rating. For wells with H2S partial pressure, specify L80 Type 1, C90 or T95 under the relevant NACE MR0175 / ISO 15156 limits, and state the H2S partial pressure on the inquiry so the correct grade and test program are offered.
API 5CT N80 BTC casing is supplied from 4-1/2 in (114.3 mm) up to 20 in (508 mm) outside diameter, with nominal weights from about 9.5 to 133 lb/ft depending on size and wall thickness. Lengths follow API ranges R1 (4.88-7.62 m), R2 (7.62-10.36 m) and R3 (10.36-14.63 m), with R2 the most common for casing programs.
For the pipe body: outside diameter is plus 1.0 percent / minus 0.5 percent for D at or above 114.30 mm (or plus/minus 0.79 mm for D at or below 101.60 mm); wall thickness tolerance is minus 12.5 percent of nominal with no positive limit; single-joint weight tolerance is plus 6.5 percent / minus 3.5 percent; and straightness is within 0.2 percent of total length with the last 1.5 m held to 3.18 mm.
STC (short round thread) and LTC (long round thread) are round-thread forms per API Spec 5B with joint efficiency around 80-95 percent of the pipe body. BTC (buttress thread) uses a trapezoidal profile that reaches close to 100 percent joint efficiency and easier make-up under tension. Premium proprietary connections add gas-tight metal-to-metal sealing for HPHT, sour or highly deviated wells.
N80 BTC casing is the default specification for intermediate and production strings in sweet wells at moderate depth, typically around 1,500 to 4,000 m, where J55 or K55 no longer cover the burst and collapse design. The BTC connection is specifically chosen for high-pressure gas wells, deeper strings and offshore platforms where joint strength and tension capacity govern.
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