API 5CT N80 is an intermediate-strength grade used in oil and gas drilling. It is known for its versatility and is often the "bridge" between lower grades (J55/K55) and high-strength grades (P110). There are two types: N80-1 and N80-Q.
N80-1: Usually normalized. It is less expensive than N80-Q but has the same yield and tensile strength.
N80-Q: Quenched and Tempered (Q&T). This heat treatment makes it more resistant to pressure and stress than N80-1.
Purpose: It is used in wells where the pressure and depth are too great for J55/K55 but do not yet require the high-cost P110.
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API 5CT N80 General Specification Table
| Item | Details |
| Standard | API Spec 5CT |
| Grade | N80 (N80-1 and N80-Q) |
| Group | Group 1 (General purpose) |
| Color Code | N80-1: One Red Band / N80-Q: One Red Band + One Green Band |
| Product Type | Casing (Pipe to line the well) & Tubing (Pipe to transport oil) |
API 5CT N80 Chemical Composition Table
API standards primarily limit the Phosphorus (P) and Sulfur (S) content for Grade N80 to ensure the purity and quality of the steel. Other elements (such as Carbon, Manganese, and Chromium) are adjusted by the manufacturer based on their heat treatment process to reach the required strength.
| Grade | Type | Phosphorus (P) | Sulfur (S) | Alloy Elements |
| N80-1 | Normalized | ≤ 0.030% | ≤ 0.030% | Not specified (adjusted by manufacturer) |
| N80-Q | Quenched & Tempered | ≤ 0.030% | ≤ 0.030% | Typically contains Cr, Mo, or Mn alloys |
API 5CT N80 Mechanical Strength Table
N80 is classified as a medium-to-high strength grade. Its most notable characteristic is its broad yield strength range and a minimum tensile strength of 100,000 psi.
| Mechanical Property | US Customary (psi) | Metric / SI (MPa) |
| Yield Strength (Minimum) | 80,000 psi | 552 MPa |
| Yield Strength (Maximum) | 110,000 psi | 758 MPa |
| Tensile Strength (Minimum) | 100,000 psi | 689 MPa |
| Hardness Limit | No mandatory limit | No mandatory limit |
| Elongation | Based on API Formula* | Based on API Formula* |
*Note: Minimum elongation is calculated based on the cross-sectional area of the specimen and the tensile strength, usually requiring 15% to 20% or higher.
Size Table: API 5CT N80 Casing (Common)
| OD (inch) | OD (mm) | Wall Thickness (mm) | Weight (lb/ft) |
| 4-1/2 | 114.30 | 5.69 - 10.16 | 10.50 - 15.10 |
| 5-1/2 | 139.70 | 6.22 - 12.70 | 14.00 - 23.00 |
| 7 | 177.80 | 6.91 - 15.11 | 20.00 - 38.00 |
| 9-5/8 | 244.48 | 8.94 - 15.11 | 36.00 - 53.50 |
| 13-3/8 | 339.72 | 9.65 - 13.06 | 54.50 - 72.00 |
Size Table: API 5CT N80 Tubing (Common)
| OD (inch) | OD (mm) | Wall Thickness (mm) | Weight (lb/ft) |
| 2-3/8 | 60.32 | 4.83 | 4.70 (EUE) |
| 2-7/8 | 73.02 | 5.51 | 6.50 (EUE) |
| 3-1/2 | 88.90 | 6.45 | 9.30 (EUE) |
| 4-1/2 | 114.30 | 6.88 | 12.75 (EUE) |
N80 Connection Types, Ends, and Couplings
| Category | Type |
| Ends | Plain End (PE), Threaded & Coupled (T&C), Beveled |
| Casing Connections | STC (Short Round Thread), LTC (Long Round Thread), BTC (Buttress Thread) |
| Tubing Connections | EUE (External Upset End), NUE (Non-Upset End) |
| Couplings | Same grade as pipe (N80), internally threaded to join two pipes. |
Applications of API 5CT N80 Casing and Tubing
Medium-Depth Wells: Ideal for wells with moderate pressures and temperatures.
Secondary Casing: Used as intermediate casing to isolate different pressure zones.
Production Tubing: In N80-Q form, it is highly effective for oil and gas production strings.
Complex Environments: Suitable for wells that require more tensile strength than J55 but where H2S is not a major factor.
API 5CT N80 Manufacturing Process
The manufacturing of N80 pipes involves several critical steps to ensure strength:
Tube Making: Can be Seamless (SML) or Electric Resistance Welded (ERW).
Heat Treatment (Crucial):
N80-1: Normalizing (heating then air cooling) or Quenching and Tempering.
N80-Q: Mandatory Quenching (rapid cooling) followed by Tempering.
Straightening: Correcting the pipe's shape.
Threading: CNC machining of API threads (LTC, BTC, EUE, etc.).
Hydro-testing: Checking for leaks under high pressure.
Quality Control of API 5CT N80
To meet API standards, N80 pipes undergo:
Dimensional Inspection: Wall thickness, OD, and length verification.
NDT Testing: Ultrasonic (UT), Magnetic Particle (MPI), and Eddy Current.
Drift Test: Passing a mandrel through the pipe to ensure clear passage.
Visual Thread Inspection: Ensuring threads are clean and meet API 5B standards.
Mechanical Testing: Tensile tests and Flattening tests.
FAQ
What is N80 material?
API 5CT N80 is a medium-high strength steel grade used for oil and gas well pipes (casing and tubing). It is considered a "workhorse" grade because it is stronger than J55/K55 but more cost-effective than high-strength grades like P110.
Here are the 3 key facts about N80:
Strength: It has a minimum yield strength of 80,000 psi (hence the name "N80").
Two Types:
N80-1: Normalized steel (more economical, general use).
N80-Q: Quenched and Tempered steel (higher toughness and better for high-pressure wells).
Identification: It is easily recognized by its color code-a Red Band painted on the pipe body.
What is the difference between N80-1 and N80Q in API 5CT casing?
The primary difference between N80-1 and N80-Q lies in their heat treatment process and toughness, even though they share the same yield strength.
Here are the 4 key differences:
Heat Treatment (The main difference):
N80-1: Usually Normalized (heated then air-cooled). It is cheaper to produce.
N80-Q: Mandatory Quenched and Tempered (heated, rapidly cooled in liquid, then reheated). This process makes the steel's structure more uniform.
Toughness and Reliability:
N80-Q has much higher impact toughness and better resistance to internal pressure. It is safer for high-stress or high-pressure environments.
N80-1 is more prone to failure in extreme conditions compared to N80-Q.
Color Identification:
N80-1: Identified by one Red band.
N80-Q: Identified by one Red band and one Green band.
Application:
N80-1: Used for general, less critical medium-depth wells.
N80-Q: Preferred for more demanding wells where better mechanical performance is required.
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