International standard for petroleum casing and tubing: API Spec 5CT
Common steel grades for casing: J55 K55 N80 L80 C90 T95 P110 Q125 V150
Common steel grades for tubing: J55 N80 L80 C90 P110
In addition, there are special steel grades such as M65, HCN80, HCP110 and TP110SS.
L80 is divided into L80-1, L80Cr9 and L80Cr13
For oil casing pipes
of different steel grades, different color rings or ribbons are used to mark the coupling (for example, green is J55 or K55, orange is N80 or L80, and white is P110).
During the production process of the tubing body, proper heat treatment, non-destructive testing (NDT), hydrostatic pressure test, thread testing, etc. must be performed.
The tubing is divided into flat end tubing (NU) and outer thickened tubing (EUE) according to the end form.
There must be no folds, hair lines, delamination, cracks, folds and scars on the inner and outer surfaces of the oil casing. These defects shall be completely removed, and the removal depth shall not exceed 12.5% of the nominal wall thickness.
The outer surface of the coupling must be free from defects such as folds, hair lines, delamination, cracks, folds, and scarring. The thread surface of the casing and coupling should be smooth, and no burrs, tears or other defects sufficient to interrupt the thread and affect the strength and tight connection are allowed.
The chemical composition and physical properties should comply with the latest edition of the American Petroleum Institute API SPEC 5CT. For chemical analysis, prepare samples according to the latest version of ASTME59, and perform chemical analysis according to the latest version of ASTME350. Physical properties should be hydrostatic pressure test, flattening test, sulfide stress corrosion cracking test, hardness test (as specified in the latest version of ASTM E18 or E10), tensile test, transverse impact test (as specified in the latest version of ASTM A370, ASTM E23 and related standards) ), grain size determination (ASTME1 12 latest version or other methods).