A Comprehensive Introduction to N80 Oil Casing Pipe

N80 oil casing pipe is a key piece of equipment used to support the wellbore during oil drilling. It is categorized by application as guide pipe, surface casing pipe, technical casing pipe, and reservoir casing pipe. It is primarily made of N80 steel grade, with chemical composition requirements for sulfur and phosphorus content below 0.045%. Production standards comply with API 5CT and SY/T6194-96.

N80 Oil Casing Pipe Production Process

This casing pipe is manufactured using either hot rolling or cold drawing processes. During production, defects are detected through online flaw detection. Quality inspection is performed in a physical and chemical laboratory equipped with eddy current and ultrasonic flaw detection equipment. Finished products undergo flattening, tensile, and hydrostatic tests.

Anti-corrosion measures include the installation of rubber rings and centralizers. Packaging is done with steel wire or steel strapping, and protective rings are installed on exposed threads.

N80 Oil Casing Pipe Chemical Composition

Carbon (C): 0.26%–0.34%. Manganese (Mn): 0.60%–0.90%.

Silicon (Si): 0.10%–0.35%.

Phosphorus (P) and Sulfur (S): These two elements are typically present in low concentrations (<0.03%).

Molybdenum (Mo): For N80 casing pipe, an appropriate amount of Mo can improve its stability under high temperature and pressure conditions.

Material Properties of N80 Oil Casing Pipe

1. Strength and Toughness

N80 oil casing pipe has a high tensile strength, typically around 80,000 psi (approximately 550 MPa), capable of withstanding the high pressure environments found in oil and gas wells. Its yield strength is generally around 55,000 psi (approximately 380 MPa), demonstrating good load-bearing capacity.

2. Corrosion Resistance

Although N80 oil casing pipe has relatively low corrosion resistance, alloying elements such as Mo enhance its corrosion resistance to a certain degree in oil and gas well environments, making it suitable for drilling operations in general environments.

3. Fatigue Resistance

N80 oil casing pipe exhibits excellent fatigue resistance under long-term, high-frequency pressure fluctuations, effectively withstanding cyclic loads and vibration.

4. Heat Treatment Performance

N80 oil casing pipe typically undergoes heat treatment (such as normalizing or tempering), which imparts excellent overall mechanical properties, especially in high-temperature environments, ensuring long service life during drilling and production.

Oil Casing Pipe Specifications

Specs range from 114.3mm to 508mm.

Thread types include long round, short round, and trapezoidal threads.

Performance parameters include elongation of 0.5%; yield strength of 552-758 MPa; and tensile strength of 689 MPa.

Lengths are available in R-1 (4.88-7.62m), R-2 (7.62-10.36m), and R-3 (≥10.36m).

Tolerance Requirements for N80 Oil Casing Pipe

According to the API 5CT standard, tolerance requirements for N80 oil casing pipe typically include the following:

1. Outside Diameter Tolerance

The outside diameter tolerance is typically ± 0.125 inches (3.175 mm).

Excessive outside diameter tolerances may affect casing pipe installation and sealing.

2. Wall Thickness Tolerance

The wall thickness tolerance is typically ± 12.5% (for OCTG casing with an outside diameter less than 10 3/4 inches).

For casing with larger outside diameters, the wall thickness tolerance may vary.

3. Length Tolerance

The length tolerance is typically between ± 5 mm and ± 10 mm.

4. Straightness and Curvature

Casing pipe straightness is typically required to be high, and curvature is typically required to be no more than 1/2 inch (12.7 mm) per 6 meters to prevent bending during installation.

5. End Tolerance

The end tolerance of casing pipe is typically controlled within ± 1/16 inch (1.6 mm).

Applications of N80 Oil Casing Pipe

1. Drilling

During the drilling process, N80 oil casing pipe is primarily used to connect the drill collar and drill bit and transmit drilling power. It also supports the wellbore during drilling to ensure smooth drilling.

2. Post-Completion Well Operation

N80 oil casing pipe is also used to maintain the normal operation of the entire well after completion, providing support and protection.

3. Workover, Fracturing, and Other Operations

During downhole oil well operations, N80 oil casing pipe can also be used as part of downhole tools for workover, fracturing, and other operations.

4. Other Applications

N80 oil casing pipe is also widely used in other areas of the oil industry, such as oil pipelines and oil well tools.

FAQ

1. How To Choose Between J55 And N80 Oil Casing Pipe?

If the well conditions are relatively simple, J55 oil casing pipe will meet the requirements.

If the well conditions are complex, or if higher strength and corrosion resistance are required, N80 oil casing pipe should be selected.

2. What Are The Advantages of N80 Oil Casing Pipe?

N80 oil casing pipe offer high dimensional accuracy, excellent weld toughness, good extrusion resistance, easy quality control, and low cost.

Summary

N80 oil casing pipe, with its excellent performance and wide range of applications, are an ideal choice for the oil drilling industry.