API 5CT N80 Casing Pipes
Product Information
API 5CT N80 casing is a type of steel pipe mainly used in oil well drilling to support the wellbore during and after drilling, so as to ensure the smooth operation of the oil well and extend the overall service life after well completion. API 5CT N80 oilfield casing pipes are divided into two types: N80-1 and N80-Q. Both grades feature identical chemical composition and mechanical properties, with the only difference lying in their heat treatment processes.During heat treatment, N80-1 steel undergoes normalizing and tempering, while N80Q steel undergoes quenching and tempering. Therefore, N80Q steel has higher compressive strength and internal pressure strength than N80-1 steel. Designers should clearly specify whether N80-1 or N80Q steel is being selected for the shell.
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API 5CT N80 Casing Pipe chemical composition
| element | N80-1 / N80-Q Requirements |
| C | 0.34～0.38% |
| Si | 0.20～0.35% |
| Mn | 1.45～1.70% |
| P | ≤0.020% |
| S | ≤0.015% |
| V | 0.11～0.16% |
| Cr / Ni / Cu / Mo | ≤0.20% |
| Al | ≤0.020% |
API 5CT N80 oil well casing steel pipe Mechanical properties
| Performance indicators | Required value |
| Minimum yield strength | 552～758 MPa |
| tensile strength | ≥689 MPa |
| elongation | ≥18% |
| Brinell hardness | ≤241 HB |
| Impact toughness | Lateral -20℃ ≥34J (N80-Q requires higher performance) |
| hydrostatic test | Calculated using the formula p=(2·f·YSmin·t)/D, no leakage is observed after holding the pressure for ≥5 seconds. |
API 5CT N80 OCTG Casing Specifications and dimensions
| parameter | scope |
| outer diameter | 114.3 mm ～ 508 mm(4.5"～20") |
| Wall thickness | 5.21 mm ～ 16.13 mm |
| length | R-1: 4.88～7.62m ／ R-2: 7.62～10.36m ／ R-3: ≥10.36m |
| outer diameter tolerance | ＜114.3mm：±0.79mm;≥114.3mm：+1.0%/-0.5% |
| Wall thickness deviation | 0 ～ -12.5% |
| Single piece weight deviation | +6.5% / -3.5% |
| curvature | ≤0.2%L,end1.5m≤3.18mm |
API 5CT N80 oilfiled casing pipes End connection type
| Buckle type | Thread type | Sealing | Applicable Scenarios |
| STC | Short round thread | Ordinary | conventional wells and shallow wells |
| LTC | Long round thread | Good | Medium to deep wells, requiring good sealing |
| BTC | Offset trapezoidal thread | Excellent | High-pressure gas wells, deep wells, offshore platforms |
| EU/NU/PL | oil pipe end | - | Pipeline products |
Differences between API 5CT N80-1 and N80Q
Heat Treatment Process (Core Difference)
N80-1: Adopts normalizing + tempering (N&T) process. The pipe is heated, air-cooled, normalized, and then tempered to stabilize its basic mechanical properties. This is a common low-cost heat treatment method for conventional oilfield pipes.
N80Q: Forced to use quenching and tempering (Q&T) process. The pipe is quenched as a whole and then tempered at high temperature. The "Q" in the grade designation represents the quenching process, which is the most fundamental technical difference between it and N80-1.
Application Scenarios
N80-1: Applied to shallow and medium-depth conventional wells with stable pressure, non-sour and non-alternating load conditions, serving as cost-effective general-purpose OCTG pipes.
N80Q: Suitable for medium-deep high-pressure wells, fatigue load wells, and mild sour service wells that require high toughness and high structural reliability.
API Standard Color Marking
N80-1:Single bright red band marking.
N80Q:Composite marking of one bright red band plus one green band, which is visually distinguishable for field identification.
API 5CT N80 casing pipe certifications
API 5CT N80 OCTG casing process line
FAQ
1.What are the application fields of API 5CT N80 products?
API 5CT N80 oil casing is widely used in the exploration and development projects of onshore conventional oilfields and gasfields. It can be used as surface casing, intermediate casing and production casing, suitable for drilling scenarios such as medium and shallow oil and gas wells, coalbed methane wells and shale gas well.
2.How is the corrosion resistance of API 5CT N80 products?
API 5CT N80 is a common carbon alloy casing steel grade without special formula for sulfide resistance or carbon dioxide corrosion resistance. It has decent basic resistance to atmospheric corrosion and ordinary formation fresh water corrosion, and can be used in neutral and fresh water formation conditions without hydrogen sulfide and high concentration CO₂.
3.What is the difference between API 5CT N80 and L80?
API 5CT L80 is specially designed for sour service with excellent sulfide stress corrosion resistance, while API 5CT N80 is a conventional carbon steel grade without anti-sulfur performance; N80 is more cost-effective for ordinary non-acidic wells, and L80 is preferred for high-sulfur and corrosive well conditions.
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