What are the grades of API 5CT

API 5CT is an internationally recognized standard developed by the American Petroleum Institute (API) for casing and tubing used in oil and gas drilling. The latest version is API 5CT Edition 10 (released in 2022).

Its core requirements include:

1. Material Grades: Divided into H40, J55, K55, N80, L80, C90, T95, P110, etc., each grade corresponds to a different yield strength (e.g., J55 is 55-80 ksi, P110 ≥ 110 ksi).

2. Dimensions: Outer diameter ranges from 4.5 inches to 20 inches, wall thickness from 2.5 mm to 25 mm, and must conform to API SPEC 5B thread standards.

3. Testing Items: Must pass hydrostatic testing (pressure value ≥ 80% of the minimum yield strength of the steel pipe), non-destructive testing (ultrasonic or eddy current), chemical composition analysis, etc.

The API 5CT international standard applies to the following four groups of products:

Group 1: All casing and tubing (standard casing and tubing) of H, J, K, and N steel grades

Group 2: All casing and tubing (corrosion resistant) of C, L, M, and T steel grades

Group 3: All casing and tubing (high strength) of P steel grade

Group 4: All casing (high strength) of Q steel grade

API 5CT OCTG

chemical composition

Standard	Grade	C(%)	Si(%)	Mn(%)	P(%)	S(%)	Cr(%)	Ni(%)	Cu(%)	Mo(%)	V(%)	Als(%)
API SPEC 5CT	J55 K55 (37MnVS)	0.34～0.39	0.20～0.35	1.25～1.50	≤0.020	≤0.015	≤0.15	≤0.20	≤0.20	/	/	≤0.020
	N80 (36Mn2V)	0.34～0.38	0.20～0.35	1.45～1.70	≤0.020	≤0.015	/	/	/	/	0.11～0.16	≤0.020
	L80 (13Cr)	0.15～0.22	≤1.00	0.25～1.00	≤0.020	≤0.010	12.0～14.0	≤0.20	≤0.20	/	/	≤0.020
	P110 (30CrMo)	0.26～0.35	0.17～0.37	0.40～0.70	≤0.020	≤0.010	0.80～1.10	≤0.20	≤0.20	/	0.15～0.25	≤0.08

Mechanical properties

Standrd	Grade	Tensile strength (MPa)	Yield strength (MPa)	Hardness
API SPEC 5CT	J55	≥517	379～552	-
	K55	≥517	≥655	-
	N80	≥689	552～758	-
	L80(13Cr)	≥655	552～689	≤241HB
	P110	≥862	758～965	-

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