Although OCTG Pipe and Line Pipe are both essential steel pipes in the energy industry, they serve very different purposes. Their distinctions lie in definition, performance requirements, structural design, and applicable standards. The comparison can be made across five core dimensions:
1. Core Definition & Application
OCTG Pipe (Oil Country Tubular Goods): Used directly in oil and gas well operations, acting as the “skeleton and channel” of the well. It covers the entire lifecycle of drilling, cementing, completion, and production. Key types include:
Drill pipe (transmits drilling power)
Casing pipe (supports the well wall, prevents collapse)
Tubing (lifts oil and gas to the surface)
These pipes must withstand harsh downhole conditions such as high pressure, high temperature, and corrosive environments.
Line Pipe: Designed for long-distance transport of fluids including crude oil, natural gas, refined products, and water. It forms the backbone of energy “transportation channels.” Applications include onshore pipelines, subsea pipelines, and municipal utility systems. The focus is on stable, long-distance transmission with minimal pressure fluctuations.
2. Performance Requirements
Pressure Resistance
OCTG: Must handle extreme downhole pressures (≥30MPa).
Line Pipe: Operates at moderate transmission pressures (10–15MPa), with emphasis on stability and leak prevention.
Corrosion Resistance
OCTG: Resistant to corrosive well fluids (H₂S, CO₂, brine); often requires special steel grades (e.g., N80Q) or coatings, and HIC resistance.
Line Pipe: Focuses on soil and seawater corrosion; typically uses external anti-corrosion coatings like 3PE.
Mechanical Strength
OCTG: High strength and fatigue resistance are essential. Grades like P110 casing and S135 drill pipe are common.
Line Pipe: Prioritizes toughness and weldability for extensive field welding; common grades include API 5L B and X65.
Temperature Performance
OCTG: Designed for high-temperature stability (>150°C); low-temperature toughness is less critical except for polar wells.
Line Pipe: Pipelines in cold climates must ensure impact toughness at -40°C to avoid brittle failure.
3. Structure & Specifications
OCTG Pipe: Mostly seamless; connections use specialized threads (e.g., API trapezoidal threads). Lengths typically range from 9–13m, with smaller diameters (2–13¾ inches). Some pipes, such as drill pipe, feature body upsets for added durability.
Line Pipe: Predominantly welded (ERW or SSAW), with seamless used in high-pressure lines. Supplied in 6–12m lengths, diameters can exceed DN2000. Designed with smooth walls and simple weld ends for field joining.
4. Standards & Certification
OCTG Pipe: Governed by API 5CT (casing/tubing) and API 5D (drill pipe). Testing covers not only mechanical properties but also thread accuracy, sealing, airtightness, and corrosion resistance (e.g., NACE TM0177). Some products require customer-specific approvals from operators such as CNPC or Sinopec.
Line Pipe: Primarily produced under API 5L or GB/T 9711 standards. Quality control emphasizes chemical composition, tensile strength, impact toughness, weldability, and external coating performance. Certifications are based mainly on standard compliance.
In short, OCTG Pipe serves as the foundation of oil and gas wells, built for extreme downhole challenges, while Line Pipe forms the arteries of energy transport networks, optimized for long-distance, stable delivery.
