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Help CenterSteel Pipe & Tube & Oil Pipe，H40/J55/K55、N80 (N80-1/N80Q)、L80 (L80-1/9Cr/13Cr)、C90/T95、P110、Q125
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Detailed Description of Petroleum Pipes
Petroleum pipes, also known as Oil Country Tubular Goods (OCTG), are core tubular products for oil and gas exploration and development. They mainly include four categories: casing, tubing, drill pipe and line pipe. Manufactured in accordance with API, ISO and Chinese GB standards, these pipes are designed to withstand harsh downhole conditions such as high temperature, high pressure and severe corrosion, and play a vital role in ensuring drilling safety and improving oil and gas production efficiency.
1. Product Classification & Main Applications
1.1 Casing
Application: Supports well walls, isolates different formations and prevents well collapse and fluid contamination. It is permanently installed after cementing and accounts for over 70% of the total consumption of oil country tubular goods.
Types by installation layer
Conductor Pipe: The outermost pipe, used to stabilize loose surface formations with the largest outer diameter (18-20 inches).
Surface Casing: Seals shallow aquifers to protect fresh water resources.
Intermediate Casing: Isolates complex formations including lost circulation zones, high-pressure zones and salt beds to guarantee safe drilling operations.
Production Casing: The innermost pipe connecting oil and gas reservoirs, serving as the permanent channel for oil and gas production.
Specifications: Outer diameter: 2-3/8" ~ 20" (60.3 ~ 508mm); Wall thickness: 5 ~ 20mm; Length: 8 ~ 12m.
1.2 Tubing
Application: Run inside casing, acting as the flow channel for oil and gas from the bottom hole to the ground. It is also applied for water injection, gas injection and other stimulation operations, and can be reused.
Specifications: Outer diameter: 2-3/8" ~ 4-1/2" (60.3 ~ 114.3mm); Wall thickness: 4.83 ~ 9.52mm; Length: 6 ~ 12.5m.
Thread Types: Short Round Thread (SC), Long Round Thread (LC), Buttress Thread (BC), Premium Connection (airtight & high torque resistance).
1.3 Drill Pipe
Application: Connects drill bits and surface equipment, transmits torque and drilling fluid, and bears combined loads of tension, compression, bending and torsion.
Specifications: Outer diameter: 2-3/8" ~ 6-5/8"; Wall thickness: 7 ~ 15mm; Length: 8 ~ 12m. Both ends are equipped with upset joints.
1.4 Line Pipe
Application: Used for long-distance transportation of crude oil and natural gas from wellheads to refineries or terminal stations, capable of resisting high pressure and environmental corrosion.
Specifications: DN50 ~ DN600 (2 ~ 24 inches). Available in seamless pipe, Longitudinal Submerged Arc Welded Pipe (LSAW) and Electric Resistance Welded Pipe (ERW).
2. Materials & Steel Grades (API 5CT / ISO 11960)
2.1 Common Steel Grades & Applicable Working Conditions
| Steel Grade | Yield Strength (MPa) | Applicable Environment |
|---|---|---|
| H40 / J55 / K55 | 276 ~ 379 | Shallow wells, low pressure and low corrosion conditions |
| N80 (N80-1 / N80Q) | 552 | Medium-deep wells and general working conditions; N80Q adopts quenching and tempering treatment with full non-destructive testing |
| L80 (L80-1 / 9Cr / 13Cr) | 552 | Medium-deep wells, resistant to CO₂ corrosion; 13Cr for severely corrosive wells |
| C90 / T95 | 621 ~ 655 | Deep wells with H₂S corrosion (sulfide resistant) |
| P110 | 758 | Ultra-deep wells with high pressure and high strength requirements |
| Q125 | 862 | Ultra-deep wells under extreme load conditions |
2.2 Special Materials
Sulfide Resistant Steel: C90, T95, L80-13Cr, resisting Sulfide Stress Corrosion Cracking (SSCC) caused by hydrogen sulfide.
High Collapse Resistant Steel: Manufactured with special wall thickness and heat treatment, suitable for salt beds and high-pressure formations.
Nickel-based Alloy: Inconel 718 and other grades, applied for ultra-high temperature, high sulfur and high chloride corrosive environments.
3. Executive Standards
International Standards: API SPEC 5CT (Casing and Tubing), API SPEC 5L (Line Pipe), ISO 11960
Chinese National Standards: GB/T 9711 (Line Pipe, equivalent to API 5L), GB/T 19830 (Casing and Tubing, equivalent to API 5CT)
Supplementary Standards: SY/T 6194 (Oil and Gas Transmission Pipe), SY/T 5989 (Sulfide Resistant Pipe)
4. Manufacturing Process
Seamless Pipe: Round steel billet → Heating → Piercing → Hot Rolling → Sizing → Heat Treatment (Normalizing / Quenching & Tempering) → Thread Machining → Non-destructive Testing → Anti-corrosion Treatment
Welded Pipe: Steel plate → Rolling → Welding (ERW / LSAW) → Heat Treatment → Sizing → Non-destructive Testing → Anti-corrosion Treatment
Key Processes
Heat Treatment: N80Q, L80 and P110 pipes adopt quenching and tempering to ensure excellent strength and toughness.
Non-destructive Testing: Ultrasonic Testing (UT), Magnetic Particle Testing (MT) and Eddy Current Testing (ET) to detect cracks, inclusions and other defects.
Thread Machining: API standard threads processed by CNC lathes, matched with couplings to ensure reliable sealing and connection strength.
5. Mechanical Property Requirements
Tensile Properties: Yield strength, tensile strength and elongation (≥12%) to guarantee load-bearing capacity.
Impact Toughness: V-notch impact energy (≥27J); products for low-temperature service shall pass impact test at -20℃.
Hardness: Hardness of sulfide resistant pipes shall not exceed 22HRC to avoid hydrogen embrittlement cracking.
Collapse Resistance: Excellent external pressure collapse resistance to adapt to formation pressure.
6. Anti-corrosion & Coating
Internal Coating: Epoxy Paint (EP), Fiberglass Reinforced Plastic (FRP), for corrosion resistance and flow resistance reduction.
External Coating: 3-Layer Polyethylene (3PE), Fusion Bonded Epoxy (FBE), Asphalt Coating, protecting pipes from soil corrosion and mechanical damage.
Special Anti-corrosion Solutions: 13Cr steel, duplex stainless steel and nickel-based alloy for severely corrosive working conditions.
7. Product Marking & Packaging
Marking: Steel grade, specification, standard number, heat number, manufacturer and production date are printed or stamped on pipe bodies.
Packaging: Thread protectors are installed at both ends of casing and tubing. Pipes are bundled into packs (5 ~ 10 pieces per pack) with moisture-proof and rust-proof packaging.
8. Quality Control & Acceptance
Raw Material Inspection: Re-inspection of chemical composition and mechanical properties of steel billets.
In-process Inspection: Dimensional accuracy, wall thickness deviation, surface quality and thread precision.
Final Factory Inspection: Tensile test, impact test, hardness test, non-destructive testing and hydrostatic test (≥30MPa for casing, ≥50MPa for tubing).
Acceptance Documents: Material Test Certificate (MTC), Inspection Report and Certificate of Conformity.
9. Application & Selection Recommendations
Shallow Wells (≤2000m): J55/K55 Casing + N80 Tubing, cost-effective option.
Medium-deep Wells (2000 ~ 4000m): N80Q/L80 Casing + L80 Tubing, balanced strength and corrosion resistance.
Deep Wells (4000 ~ 6000m): P110 Casing + P110 Tubing, for high pressure and high strength service.
Sour Wells: C90/T95 Casing + L80-13Cr Tubing, excellent H₂S corrosion resistance.
Long-distance Transmission Pipeline: API 5L X60/X70 LSAW Pipe with 3PE coating.
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