API 5CT N80 Oil Country Tubular Goods (OCTG) Steel
API 5CT N80 Oil Country Tubular Goods (OCTG) Steel Grade Technical
In-depth technical data for API 5CT N80 steel grade utilized in oil and gas well casing and tubing, covering chemical composition, mechanical, thermal, and electrical properties, equivalent grades, and application guidance.
Hot rolling, cold drawing, heat treatment (normalizing, quenching and tempering)
- Phone : +8618037372205
- Email : [email protected]
- WhatsApp: Contact via Whtsapp
- WeChat: +8618037372205
API 5CT N80 Oil Country Tubular Goods Steel Introduction
API 5CT N80 is a widely used steel grade for oil country tubular goods (OCTG), specifically intended for casing and tubing in oil and gas wells. It is defined by the American Petroleum Institute (API) standard 5CT. N80 steel offers a good balance of strength and toughness, suitable for a range of downhole environments. The grade N80 is available in two types: N80-1 and N80-Q, distinguished by heat treatment process. N80-1 may be supplied in the as-rolled, normalized, normalized and tempered, or quenched and tempered condition, while N80-Q must be quenched and tempered. The material exhibits a minimum yield strength of 552 MPa (80 ksi) and minimum tensile strength of 689 MPa (100 ksi), providing reliable performance in medium-depth wells. The chemical composition is relatively open, primarily controlled by maximum phosphorus and sulfur limits, allowing manufacturers to optimize strength and toughness through alloy design and heat treatment. N80 is not inherently resistant to sour service (H2S), so additional testing is required for such applications.
API 5CT N80 Oil Country Tubular Goods Steel Chemical Composition
API 5CT only imposes strict limits on phosphorus and sulfur for N80 grade. Other elements such as carbon, manganese, silicon, chromium, nickel, molybdenum, and copper are not specified but are typically controlled by the manufacturer to achieve the required mechanical properties. The following table lists the guaranteed maximum limits per the standard. The composition is not fixed; manufacturers may use different alloy designs within the framework of meeting the specified strength and toughness. For sour service applications, stricter controls on hardness and chemistry may be required by supplementary requirements.
| Element | Standard Value (max %) | Remarks |
|---|---|---|
| Phosphorus (P) | 0.030 | Product analysis per API 5CT |
| Sulfur (S) | 0.030 | Product analysis per API 5CT |
| Other elements (C, Mn, Si, Cr, Ni, Mo, Cu, etc.) | Not specified | Controlled by manufacturer to meet mechanical properties; typical carbon equivalent ranges may apply for Q&T grades |
API 5CT N80 Oil Country Tubular Goods Steel Thermal and Electrical Properties
The following physical properties are typical for medium-carbon steel grades used in OCTG applications, such as N80. These values are not part of the API 5CT specification but are useful for engineering calculations. Actual properties may vary slightly depending on the specific chemical composition and heat treatment.
| Property | Typical Value | Unit | Test Condition / Remarks |
|---|---|---|---|
| Density (ρ) | 7850 | kg/m³ | At 20°C |
| Modulus of Elasticity (E) | 205 | GPa | At 20°C |
| Shear Modulus (G) | 80 | GPa | At 20°C |
| Poisson's Ratio (ν) | 0.3 | — | At 20°C |
| Thermal Expansion Coefficient (α) | 11.7 × 10⁻⁶ | /°C | 20–100°C |
| Thermal Conductivity (λ) | 50 | W/(m·K) | At 20°C |
| Specific Heat Capacity | 460 | J/(kg·K) | At 20°C |
| Electrical Resistivity (ρ_e) | 0.15 | µΩ·m | At 20°C |
API 5CT N80 Oil Country Tubular Goods Steel Mechanical Properties
The mechanical properties of API 5CT N80 steel are required to meet specified tensile and elongation limits. Yield strength is measured as 0.5% extension under load (EUL). The following table presents the mandatory tensile requirements. Elongation values are determined by the formula A = 1940 * S^0.2 / U^0.9 for round bar specimens, where S is specimen cross-sectional area in square inches and U is tensile strength in ksi. For a typical transverse round bar specimen of 0.350 in diameter (area 0.096 in²) and U=100 ksi, the minimum elongation is approximately 19%. Actual values depend on wall thickness and specimen geometry.
| Property | Required Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH 0.5% EUL) | 552 - 758 | MPa | Transverse or longitudinal, room temperature |
| Yield Strength (ReH 0.5% EUL) | 80 - 110 | ksi | same |
| Tensile Strength (Rm) | ≥ 689 | MPa | room temperature |
| Tensile Strength (Rm) | ≥ 100 | ksi | same |
| Elongation (A) | ≥ 19 | % | Transverse round bar specimen, diameter 0.350 in, gauge length 2 in; applies to wall thickness ≤ 0.500 in |
| Elongation (A) | ≥ 24 (approx.) | % | Longitudinal round bar specimen, same dimensions; values may vary |
API 5CT N80 Oil Country Tubular Goods Steel Fully Equivalent Material Grades and Standards
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| International | ISO 11960:2011 | N80 | Identical technical requirements to API 5CT |
| Europe | EN ISO 11960:2011 | N80 | Adopts ISO 11960 |
| China | GB/T 19830-2011 | N80 | Equivalent to ISO 11960, same grade N80 |
| Russia | GOST R 53366-2009 (ISO 11960) | N80 | Harmonized with ISO |
API 5CT N80 Oil Country Tubular Goods Steel Application Introduction
API 5CT N80 steel is primarily employed in the construction of oil and gas well boreholes as casing and tubing strings. Casing lines the wellbore to prevent collapse and isolate formations, while tubing conveys hydrocarbons to the surface. The grade is suitable for wells with moderate pressures and non-sour conditions. N80 can also be used for downhole tools and accessories where high strength and good impact toughness are required.
Product Applications: Seamless casing pipes, Seamless tubing pipes, OCTG coupling stock, Pup joints and accessories
Processed into products: Casing joints, Tubing joints, Couplings, Crossovers, Liner hangers, Production packers, Downhole mandrels
Application industries: Oil and Gas Exploration & Production, Geothermal Drilling, Mining and Groundwater Wells (limited)
API 5CT N80 Oil Country Tubular Goods Steel Similar and Alternative Material Grades
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA/International | API 5CT | L80 Type 1 | Similar strength range but with higher chromium (typically 9% Cr) for CO₂ corrosion resistance; also restricted hardness for sour service. |
| USA/International | API 5CT | C95 | Higher strength grade, yield 95 ksi min, suitable for deep wells, though less common. |
| USA/International | API 5CT | T95 | High strength with sour service capability (restricted hardness); yield 95 ksi min, better for H₂S environments. |
| China | GB/T 19830-2011 | L80-1 | Equivalent to API 5CT L80, for corrosive service. |
Notes:
For sour service environments containing H₂S, supplementary requirements per API 5CT Annex H (Sour Service) must be specified, which includes hardness limits (max HRC 22) and sulfide stress cracking (SSC) tests. N80 is generally not considered a sour service grade without such qualification. Always verify the specific manufacturing process and heat treatment for N80-1 vs N80-Q according to the purchase order. The use of N80 steel as pipeline (line pipe) is not covered by API 5CT; for line pipe, refer to API 5L standard. The term "Pipeline Steel Coil" in the prompt likely refers to coiled tubing, which is a continuous length of tubing used for well intervention and can be manufactured to N80 grade under API 5ST (coiled tubing standard) but more commonly under API 5CT for discrete joints.
- Share
