Oil well casing lines boreholes for oil extraction. Like drill pipes, it bears axial tension and is made of high-strength steel. As a large-diameter OCTG pipe fixed by cement, it stabilizes boreholes and prevents collapse, serving the whole service life of oil wells, with diameters from 4.5″ to 36″.
It is classified into five types:
Conductor Casing: The first underground barrier, for collapse prevention, groundwater isolation and structural support, sized 18″–36″.
Surface Casing:: Focuses on environmental protection and well safety, protects freshwater layers and wellhead devices, commonly 13 3/8”.
Intermediate Casing: Optional, installed between surface and production casing, 13 3/8”–16”.
Production Casing:Maintains structural stability and pressure control in oil production zones.
Production Liner: : Hung on upper casings, cuts costs without full-depth installation, and can be pre-perforated.

Standard

API Spec 5CT (8th Ed.) / ISO 11960

Chemical Composition, Mass Fraction(%)

Note: If the wall thickness is less than 17.78mm, the molybdenum content of the C90-1 steel grade has no lower limit.

Mechanical properties of casing pipe