API 5CT N80 Casing And Tubing Pipe
Product Introduction
API 5CT N80 casing and tubing is a medium-to-high strength oil well tubing manufactured according to American Petroleum Institute (API) standards. It is widely used in deep wells and oil and gas extraction in complex geological environments to support the wellbore (casing) and transport oil and gas (tubing), offering excellent tensile strength and overall cost-effectiveness.
API 5CT N80 Casing Pipe Chemicals and mechanical strength
The chemical composition details of N80 steel are as follows: (unit: %), carbon content 0.28-0.32 (0.22-0.29 for outer diameters greater than 9 5/8 inches/244.48 mm), silicon content 0.17-0.37, manganese content 1.30-1.45 (1.3-1.60 for outer diameters greater than 9 5/8 inches/244.48 mm), maximum chromium content 0.25, maximum nickel content 0.20, maximum copper content 0.20, vanadium content 0.07-0.12, maximum phosphorus content 0.025, maximum sulfur content 0.020.
Yield strength for N80 type Q and type 1, is 552 Mpa to 758 Mpa. Tensile strength minimum shall be 689 Mpa.
Outside diameter: 5 1/2", 6 5/8", 7", 7 5/8", 7 3/4", 8 5/8", 9 5/8", 10 3/4", 11 3/4", 13 3/8", 16", 18 5/8", 20"
Thickness: 14 LB/FT to 106.59 LB/FT, 0.244" to 0.875"
API 5CT N80 OCTG Casing Tube Classification and Manufacturing Process
N80Q must undergo quenching + tempering, while N80-1 uses normalizing or normalizing + tempering - this is the root cause of all performance differences.
| Classification Dimension | Details |
| Manufacturing Method | Seamless vs ERW/HFW - N80 also available as HFW casing |
| Thread Type | STC (Short Thread Coupling) vs LTC (Long Thread Coupling); per SY/T6194-96 |
| Economy Grade N80 | Optimized heat treatment to reduce cost while exceeding API 5CT requirements |
| Production Flow | Continuous Casting → Piercing & Rolling → Quenching & Tempering / Normalizing →Surface Treatment → 100% NDT |
API 5CT N80 oil tubing Metallographic Structure
This is the fundamental reason distinguishing N80-1 from N80Q:
| Grade | Typical Microstructure | Defect Risks |
| N80-1 | Ferrite (F) + Pearlite (P) + Minor Bainite (B) → P+F or B+P+F | Coarse network ferrite, lamellar martensite (severely reduces impact toughness), overheated Widmanstätten structure, surface decarburization |
| N80Q | Tempered Sorbite dominant | More uniform structure, superior toughness |
API 5CT N80 oil tubing Quality Inspection Items
API 5CT mandates far more than just tensile testing:
| Inspection Item | Standard Reference | Notes |
|---|---|---|
| Hydrostatic Test | API 5CT | Mandatory - verifies pressure-bearing capacity |
| Flattening Test | GB246 / API 5CT | Verifies collapse resistance |
| Tensile Test | GB228 / ASTM E8 | UTS, Yield Strength, Elongation |
| Impact Test (Charpy) | ASTM E23 | Mandatory for N80Q; N80-1 PSL-1 may be exempt |
| Hardness Test | ASTM E18 / E10 | N80 ≤ 241 HB |
| SSC Test (Sulfide Stress Cracking) | NACE TM0177 | Mandatory for sour service |
| Magnetic Particle Testing (MT) | ASTM E709 / E3024 | 100% surface + end inspection |
| Ultrasonic Testing (UT) | ASTM E213 | Internal defect detection |
| Grain Size Determination | ASTM E112 | Controls microstructural uniformity |
| Drift Test (Caliper) | API 5CT | Minimum drift diameter = Nominal ID − 3.18 mm (casing D<244.5mm) |
API 5CT N80 OCTG Casing Tube Length Ranges
Domestic casing is random length, typically 8~13m; pipes ≥6m allowed but ≤20% of total.
| Range | Designation | Interval |
| R-1 | 4.88 ~ 7.62 m | Short pipe |
| R-2 | 7.62 ~ 10.36 m | Medium length (domestic mainstream: 8~13m) |
| R-3 | ≥ 10.36 m | Long pipe |
| Tubing | 6.10~7.32m / 8.53~9.75m | - |
API 5CT N80 OCTG Casings Corrosion Resistance
| Corrosion Type | N80 Performance | Notes |
| CO₂ Corrosion | Moderate | Normalizing heat treatment slightly improves resistance |
| H₂S Corrosion (SSC) | Requires SSC test verification | Higher Cl⁻ concentration → weaker resistance |
| General Corrosion | Meets conventional service | Cr 2~5% economy anti-CO₂ tubing as alternative |
API 5CT N80 casing pipe certifications
aPI 5CT N80 OCTG casing process line
FAQ
1.What thread types are available for N80 casing? Which one is best?
N80 casing is available with STC, LTC, BTC , and premium connections. STC is the most common and cost-effective. LTC offers better sealing. For demanding environments, premium connections are highly recommended for faster makeup, no cross-threading, and superior bending resistance.
2.What inspections are mandatory for N80 casing under API 5CT?
All N80 casing must pass hydrostatic test, flattening test, tensile test, 100% MT (surface + ends), UT, and drift test. N80Q requires mandatory Charpy impact test. Sour service additionally requires SSC test per NACE TM0177.
3.What is the difference between N80-1 and N80Q? Which one should I choose?
The core difference is heat treatment. N80-1 uses normalizing with ferrite + pearlite microstructure, lower toughness, and lower cost. N80Q uses quenching + tempering with tempered sorbite microstructure, significantly higher toughness, and superior SSC resistance. Choose N80Q for sour service, H₂S, or ultra-deep wells. Choose N80-1 for conventional non-sour wells where cost is the priority.
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