Production tubing is the innermost tube in a completed well — the conduit through which oil, gas, and condensate flow from the reservoir to surface. Selecting the correct grade and size is a multi-variable engineering decision that spans reservoir conditions, production rate targets, corrosion environment, completion design, and economic optimization over well life. Selecting the wrong grade creates either a safety risk (insufficient corrosion resistance in H₂S) or unnecessary cost (over-specified CRA tubing in a sweet well).
This guide covers the four key production tubing grades that ZC Steel Pipe supplies — N80Q, L80-1, T95, and L80-13Cr — together with the complete API 5CT tubing size range, connection types, and purchase order requirements. ZC supplies seamless production tubing from 1.050" through 4½" OD for export to Africa, the Middle East, South America, and Southeast Asia.
Grade Selection: Matching Steel to the Well Environment
Before specifying a tubing size, establish which grade is required. Grade selection is driven by three well conditions in priority order:
Step 1 — Is H₂S present?
H₂S at even low partial pressures triggers sulfide stress cracking (SSC) in standard carbon steel tubing. NACE MR0175/ISO 15156 defines the threshold at which materials must be qualified for sour service.
- H₂S absent or below threshold → N80Q is the standard choice for medium-depth sweet wells
- H₂S present at any significant level → minimum L80-1 is required; T95 if higher yield is needed
Step 2 — What is the CO₂ partial pressure?
When H₂S is absent but CO₂ is significant, carbon steel tubing corrodes rapidly. Corrosion inhibitors are the first line of defense; if inhibition is unreliable or impractical, a chromium-bearing grade is required.
- Mild CO₂, inhibited → N80Q with inhibition program is commonly used
- High CO₂ partial pressure, sweet → L80-13Cr tubing for its 12–14% chromium content, which forms a protective oxide layer
- CO₂ with H₂S → 13Cr grade limit applies; if H₂S exceeds the 13Cr safe operating envelope, Super 13Cr or duplex must be evaluated
Step 3 — What yield strength does the well design require?
Once the corrosion environment determines whether the grade must be sour-qualified or CRA, the structural design loads determine the minimum yield strength:
| Grade | Min–Max Yield | Sour Service | CO₂ Grade | Heat Treatment |
|---|---|---|---|---|
| N80Q | 552–758 MPa (80–110 ksi) | No | No | Q+T only |
| L80-1 | 552–655 MPa (80–95 ksi) | Yes | No | Q+T only |
| T95 | 655–758 MPa (95–110 ksi) | Yes | No | Q+T only |
| L80-13Cr | 552–655 MPa (80–95 ksi) | No (CO₂ only) | Yes | Q+T only |
Source: API Specification 5CT, 11th Edition (December 2023), Table C.24
N80Q and T95 share the same 80–110 ksi and 95–110 ksi windows respectively, but N80Q is general service (sweet) and T95 is sour-qualified. When H₂S rules out N80Q and the structural design needs more than 95 ksi, T95 is the required grade — there is no other sour service grade in the 95–110 ksi window in the standard API 5CT system.
For the full mechanical properties table, see the API 5CT specification tables →
Mechanical Properties of Key Tubing Grades
| Property | N80Q | L80-1 | T95 | L80-13Cr |
|---|---|---|---|---|
| Min yield strength | 552 MPa (80 ksi) | 552 MPa (80 ksi) | 655 MPa (95 ksi) | 552 MPa (80 ksi) |
| Max yield strength | 758 MPa (110 ksi) | 655 MPa (95 ksi) | 758 MPa (110 ksi) | 655 MPa (95 ksi) |
| Min tensile strength | 689 MPa (100 ksi) | 655 MPa (95 ksi) | 724 MPa (105 ksi) | 655 MPa (95 ksi) |
| Max hardness HRC | Not specified | 23.0 | 25.4 | 23.0 |
| Max hardness HBW | Not specified | 241 | 255 | 241 |
| Cr content | Not specified | Not specified | 0.40–1.50% | 12.0–14.0% |
| Mo content | Not specified | Not specified | 0.25–0.85% | Not specified |
Source: API 5CT 11th Edition, Tables C.24 and C.26
Note on L80-13Cr: Despite carrying the L80 hardness limit (23.0 HRC / 241 HBW), L80-13Cr is classified by API 5CT as a CO₂ corrosion grade, not a sour service grade. Do not specify it for wells where H₂S is present.
API 5CT Production Tubing Sizes
Production tubing sizes are designated by OD in inches, following a legacy numbering system that ranges from 1.050" to 4½". The most commercially significant sizes are 2 3/8", 2 7/8", and 3½":
Most Common Production Tubing Sizes
| OD (in) | OD (mm) | Wall (mm) | ID (mm) | NU lb/ft (kg/m) | EU lb/ft (kg/m) |
|---|---|---|---|---|---|
| 2 3/8 | 60.32 | 4.83 | 50.66 | 4.60 (6.85) | 4.70 (6.99) |
| 2 3/8 | 60.32 | 6.45 | 47.42 | 5.80 (8.63) | 5.95 (8.85) |
| 2 7/8 | 73.02 | 5.51 | 62.00 | 6.40 (9.52) | 6.50 (9.67) |
| 2 7/8 | 73.02 | 7.01 | 59.00 | 7.80 (11.61) | 7.90 (11.76) |
| 2 7/8 | 73.02 | 7.82 | 57.78 | 8.60 (12.80) | 8.70 (12.95) |
| 3 1/2 | 88.90 | 6.45 | 76.00 | 9.20 (13.69) | 9.30 (13.84) |
| 3 1/2 | 88.90 | 9.52 | 69.86 | 12.70 (18.90) | 12.95 (19.27) |
| 4 1/2 | 114.30 | 6.88 | 100.54 | 12.60 (18.75) | 12.75 (18.97) |
| 4 1/2 | 114.30 | 8.56 | 97.18 | 15.20 (22.62) | — |
Source: API 5CT 11th Edition Table C.19. NU = non-upset; EU = external upset. Weight shown is nominal with threads and coupling.
Smaller Tubing Sizes (Slim-Hole and Recompletions)
| OD (in) | OD (mm) | Wall (mm) | ID (mm) | NU lb/ft (kg/m) |
|---|---|---|---|---|
| 1.315 | 33.40 | 3.38 | 26.64 | 1.70 (2.53) |
| 1.660 | 42.16 | 3.56 | 35.04 | 2.30 (3.42) |
| 1.900 | 48.26 | 3.68 | 40.90 | 2.75 (4.09) |
| 1.900 | 48.26 | 5.08 | 38.10 | 3.65 (5.43) |
Source: API 5CT 11th Edition Table C.19. Smaller sizes used primarily for slim-hole completions, shallow wells, and recompletions.
2 3/8" vs 2 7/8" — The Most Common Decision
2 3/8" (60.32 mm OD) is the default for most oil wells and moderate-rate gas wells. The 4.83 mm wall variant (NU: 4.6 lb/ft) is the most widely stocked global size. It fits inside 5½" casing with adequate annular space for cementing equipment and allows standard wireline tools. It is the first choice unless production rate calculations require a larger bore.
2 7/8" (73.02 mm OD) is preferred for higher-rate gas wells, higher-volume oil wells with artificial lift, and wells where downhole tools (ESPs, gas lift mandrels) require larger internal clearance. The 5.51 mm wall (NU: 6.4 lb/ft) is the lightest common weight; 7.01 mm wall is the standard for most production applications.
3½" (88.90 mm OD) is used for high-rate gas wells, gas condensate wells requiring large bore, and ESP installations where pump size demands larger tubing OD. It requires at least 7" casing to be run safely.
4½" (114.30 mm OD) is a special application size for very high-rate wells, horizontal wells with large-bore completions, and ESP installations with large-diameter pumps. Requires 9 5/8" or larger production casing.
Connection Types: NU, EU, and IJ
API 5CT defines three standard connection configurations for production tubing:
| Connection | Description | When to Use |
|---|---|---|
| NU (Non-upset) | Same OD at body and threaded end; separate coupling | Shallow to medium depth, lower pressure, cost-sensitive |
| EU (External upset) | Increased OD at threaded ends; separate coupling | Standard choice for production depths; stronger thread |
| IJ (Integral joint) | No coupling; pin one end, box other end | Slim-hole wells, through-tubing completions, restricted clearance |
EU vs NU — the practical choice: EU is preferred for most production tubing applications because the upset section provides a thicker thread engagement area, giving higher connection tensile efficiency and better gas-tightness. NU is adequate for shallow wells with low burst and tensile loads and is slightly lower cost. For sour service wells, EU is typically specified regardless of depth to maximize connection integrity.
IJ connections eliminate the coupling OD entirely, which matters when the tubing must pass through a tubing hanger, downhole safety valve, or slim-hole completion tool with a restricted minimum OD. IJ connections have lower tensile efficiency than EU and are not the standard choice for normal wells.
For further detail on API 5CT connection standards and torque requirements, see the API 5CT specification tables →
Size and Grade Selection Matrix
| Well Type | Recommended Size | Recommended Grade | Reason |
|---|---|---|---|
| Sweet oil, medium depth | 2 3/8" EU | N80Q | Standard choice, lowest cost for sweet service |
| Sweet oil, high rate | 2 7/8" EU | N80Q | Larger bore for volume |
| Sweet gas, medium rate | 2 3/8" EU | N80Q | Gas-tight connection needed |
| Sweet gas, high rate | 3½" EU | N80Q or L80-1 | Large bore, conservative grade |
| Sour oil, mild H₂S | 2 3/8" EU | L80-1 | NACE MR0175 required |
| Sour gas, high pressure | 2 7/8" EU | L80-1 or T95 | Depends on burst/collapse loads |
| Deep sour well | 3½" EU or 2 7/8" EU | T95 | L80 insufficient, sour required |
| CO₂ gas condensate | 2 3/8" EU | L80-13Cr | Sweet CO₂ corrosion control |
| Slim-hole recomplete | 1.9" IJ | L80-1 or N80Q | Clearance-constrained |
To match your grade and size to specific reservoir and well conditions, use the AI Pipe Grade Selector →
Purchase Order Guidance
Sweet service (N80Q):
- Standard: API 5CT N80Q, [OD] × [lb/ft], Range 2, EU connection
- PSL: PSL-1 (PSL-2 for gas wells or when operator spec requires)
- MTC: EN 10204 3.1
- Thread: API 8rd EUE or per project specification
- Heat treatment: Confirm Q+T records on MTC (do not accept N80-1 substitution on an N80Q order)
Sour service (L80):
- Standard: API 5CT L80 Type 1, [OD] × [lb/ft], Range 2, EU connection
- PSL: PSL-2
- Max hardness: 22 HRC on PO (NACE MR0175 limit; stricter than API's 23 HRC maximum)
- MTC: EN 10204 3.2 with per-joint hardness records
- Thread compound: H₂S-compatible
- Supplementary SR15C (HIC testing per NACE TM0284) if combined CO₂ + H₂S environment
Sour service (T95):
- Standard: API 5CT T95, [OD] × [lb/ft], Range 2, EU connection
- PSL: PSL-2
- MTC: EN 10204 3.2 with per-heat chemistry (confirm Cr ≥ 0.40%, Mo ≥ 0.25%) and per-joint hardness records
- SR15A (SSC testing per NACE TM0177) if project specification requires laboratory qualification
CO₂ service (L80-13Cr):
- Standard: API 5CT L80 13Cr, [OD] × [lb/ft], Range 2, premium connection
- Note: Standard API BTC thread compounds are not compatible with 13Cr — a premium connection with appropriate thread compound is required
- Weight correction: Apply 0.989 density correction factor for 13Cr weight calculations
- MTC: EN 10204 3.1 with Cr chemistry confirmation (12.0–14.0%)
Procurement trap — tubing OD vs coupling OD: EU tubing has a larger coupling OD than the pipe body OD. The 2 3/8" EU coupling OD is approximately 2.910" (73.91 mm), significantly larger than the 2.375" (60.32 mm) pipe body. Always confirm that the coupling OD fits through the casing packer bore, tubing hanger, and any downhole tools before ordering. Ordering tubing by pipe body OD without accounting for coupling OD is a common error that results in the tubing string being unable to reach total depth.
ZC Steel Pipe supplies API 5CT production tubing in N80Q, L80-1, T95, and L80-13Cr grades across the standard size range. PSL-2, EN 10204 3.2 MTC, and third-party inspection are available. Contact us with your well profile, grade, OD, weight, connection, and quantity for technical review and commercial terms.