API N80 Oil Casing

API N80 Oil Casing is a widely used medium strength casing in the API 5CT standard. "N80" represents a minimum yield strength of 80ksi (approximately 552MPa), with performance between J55/K55 and L80. With balanced strength, toughness, and economy, it has become the main casing for conventional oil and gas wells, with a global market share of over 25%.

Performance and Material

The N80 casing is made of low-alloy structural steel (such as 30Mn2) and undergoes quenching and tempering heat treatment (830 ℃ quenching+580 ℃ tempering). The yield strength is 552-758MPa, the tensile strength is ≥ 655MPa, the elongation rate is ≥ 18%, the impact energy is ≥ 30J, and the toughness is better than J55/K55. It can withstand moderate pressure fluctuations. The upper limit of temperature resistance is 120 ℃, and the anti-corrosion performance is basic level. It is suitable for neutral or weakly corrosive environments (CO ₂ concentration ≤ 0.1%), but cannot be used in formations containing H ₂ S.

Structure and specifications

Most of them are seamless steel pipe structures, and large-diameter models can use straight seam submerged arc welded pipes. The ends are processed with API standard threads (STC/LTC/BTC), and the airtight sealing pressure is ≥ 30MPa. Common specifications: outer diameter of 114.3mm-273.1mm, wall thickness of 6.2mm-11.05mm, single length of 6-12m, connected to a complete set of pipe columns through couplings, with a weight about 5% lighter than the same specification L80.

Production process

The tube blank undergoes hot rolling perforation, cold rolling finishing, and quenching and tempering heat treatment to ensure a balance between strength and toughness. The thread processing is carried out using a CNC lathe, with precision in accordance with API 5B standards. The surface is treated with phosphating to enhance rust prevention ability. The production cycle is 10% shorter than L80, and the cost is 10% -15% lower.

Application scenarios

Conventional oil and gas wells with a depth of 2000-3500 meters;

Production casing for onshore oil fields (transporting oil and gas to the surface);

Medium pressure water injection/production system (wellhead pressure 10-20MPa);

Deep well sections in non corrosive environments offer better cost-effectiveness than L80.