N80 EUE Oil Tubing
N80 Tubing is an oil country tubular good (OCTG) compliant with the API Spec 5CT standard.
"N80": Refers to the yield strength grade, meaning the minimum yield strength is 80,000 psi (552 MPa).
Note: There are two types: N80-1 (usually normalized) and N80-Q (Quenched and Tempered for higher uniformity).
"EUE" (External Upset End): Refers to the reinforced connection type. The wall thickness at the ends of the pipe is increased through a hot-forging process before threading. This ensures that the connection is stronger than the pipe body, preventing joint failure under heavy loads in deep wells.
Technical Specifications (Specification)
| Item | Description |
| Standard | API Spec 5CT (10th Edition) |
| Grade | N80 (N80-1, N80-Q) |
| Connection Type | EUE (External Upset End) |
| Threading Standard | API 5B (10-Round for EUE) |
| Size Range | 1.9" to 4-1/2" |
| Surface Coating | Black anti-rust paint, Internal Plastic Coating (Optional), Phosphating |
| Color Coding | N80-1 (One Red Band) / N80-Q (One Red + One Bright Green Band) |
Chemical Composition & Mechanical Properties
Chemical Composition (API 5CT Requirements)
API 5CT has limited chemical requirements for N80-1 (except for P and S), while N80-Q is more strictly controlled.
| Grade | C (%) | Mn (%) | P (max %) | S (max %) | Si (%) |
| N80-1 | Not Specified | Not Specified | 0.030 | 0.030 | Not Specified |
| N80-Q | Not Specified | Not Specified | 0.030 | 0.030 | Not Specified |
Mechanical Properties
| Property | N80 (N80-1 & N80-Q) |
| Yield Strength | 552 – 758 MPa (80,000 – 110,000 psi) |
| Tensile Strength | ≥ 689 MPa (100,000 psi) |
| Elongation | Calculated per API 5CT formula (Typically ≥ 15-20%) |
| Hardness (N80-Q) | No API limit, but generally < 22 HRC (for standard service) |
Common Size Table (N80 EUE Tubing)
| Outer Diameter (OD) | Nom. Weight (lb/ft) | Wall Thickness | Upset Diameter | Inner Diameter (ID) |
| 2-3/8" | 4.70 | 4.83 mm (0.190") | 65.89 mm | 50.65 mm |
| 2-7/8" | 6.50 | 5.51 mm (0.217") | 77.77 mm | 62.00 mm |
| 3-1/2" | 9.30 | 6.45 mm (0.254") | 93.22 mm | 76.00 mm |
| 4-1/2" | 12.75 | 6.88 mm (0.271") | 120.65 mm | 100.53 mm |
Tolerance Table
| Parameter | Tolerance |
| Outside Diameter (OD) | ±0.79 mm (For tubing ≤ 4-1/2") |
| Wall Thickness | -12.5% (Max thinning; upper limit controlled by weight) |
| Weight (per joint) | +6.5% / -3.5% |
| Straightness | Total deviation < 0.2% L; local deviation < 1.6mm/1.5m |
Features of N80 EUE Oil Tubing
High Load Capacity: N80 is roughly 45% stronger than J55/K55 grades, making it suitable for deeper wells and higher-pressure environments.
Reinforced Joint (EUE): The External Upset design increases the cross-sectional area of the threaded end. This significantly enhances the shear resistance and sealing reliability, preventing "joint pull-out" under high tension.
Versatility: N80 is the "sweet spot" grade in the industry-it offers high strength without being as brittle or expensive as higher grades like P110.
Rigorous Testing Requirements: Every joint of N80 must undergo:
Hydrostatic Test: To ensure no leakage or bursts at high pressure.
Non-Destructive Testing (NDT): Including Ultrasonic or Eddy Current testing to ensure the pipe is free of cracks.
Drift Test (Drifting): Ensuring the ID is clear for downhole tools to pass through.
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FAQ
Q1: What is the primary difference between N80-1 and N80-Q?
A: This is the most critical distinction for N80 tubing.
N80-1: Usually delivered in a Normalized condition. It is more cost-effective and suitable for standard well environments.
N80-Q: Delivered in a Quenched and Tempered (Q&T) condition. It offers superior strength uniformity and better fatigue resistance, making it more reliable for demanding well conditions.
Q2: Why is "EUE" (External Upset End) preferred over "NUE" (Non-Upset End)?
A: EUE is the industry standard for most production wells. The "Upset" process increases the wall thickness at the ends of the pipe before threading. This ensures that the joint strength is higher than the pipe body strength, preventing "joint pull-out" or failure under the high tension and pressure found in deep wells.
Q3: Is N80 EUE tubing suitable for Sour Service (H2S environments)?
A: No. N80 is a medium-to-high strength steel that is susceptible to Sulfide Stress Cracking (SSC) in H2S environments. For sour service, we recommend using L80-1, C90, or T95 grades, which are specifically designed to resist hydrogen embrittlement.
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