K55 Oil Casing

K55 Oil Casing is one of the most widely used low strength casings in API standards, with "K55" representing its minimum yield strength of 55ksi (approximately 380MPa). It is known for its economy and practicality, and has a market share of over 30% in shallow oil and gas wells and non high pressure environments.

Performance and Material

K55 casing is mainly made of carbon structural steel (such as J55 steel grade with optimized composition), which is subjected to normalizing heat treatment (880 ℃ normalizing+air cooling), with a yield strength of 380-552MPa, tensile strength ≥ 517MPa, elongation ≥ 20%, and impact energy ≥ 25J. It has excellent plasticity and can withstand certain bending deformation, but has a low upper limit of temperature resistance (≤ 120 ℃), basic corrosion resistance, and is only suitable for neutral medium environments (no H ₂ S, low CO ₂).

Structure and specifications

For seamless steel pipes or straight submerged arc welded pipe structures (large diameter), the end is processed with API standard threads (STC/LTC mainly), and the airtight sealing pressure is ≥ 25MPa. Common specifications: outer diameter 114.3mm-339.7mm, wall thickness 5.21mm-12.14mm, single length 6-12m, connected to a complete set of pipe columns through couplings, with a weight about 15% lighter than the same specification L80.

Production process

Simple and mature process: The tube blank is made into a blank tube through hot rolling perforation (seamless) or steel plate coil welding (straight seam), and after normalizing heat treatment, it is cold-rolled and straightened. The thread processing accuracy meets the API 5B standard, and the surface is coated with anti rust paint. Due to the lack of complex alloy addition and quenching treatment, the production cycle is 20% shorter than L80, and the cost is 30% -40% lower.

Application scenarios

Shallow oil and gas wells with a depth of ≤ 2000 meters (such as coalbed methane wells and shallow oil fields);

Low pressure water injection/production well (wellhead pressure ≤ 10MPa);

Surface casing or technical casing in non corrosive environments, serving as temporary support.