Steel Grade Classification of Oil Casing Pipe

The American Petroleum Institute API standard specifically targets oil and gas: casing, tubing and line pipe standards used in industry. In the standard, the casing and tubing steel grades are divided into several grades, namely H-40, J-55, K-55, N-80, L-80, C-90, T-95, P-110, Q- 125, each level has a different heat process. In API 5CT, the raw materials were divided into four groups. The first group is H, J, K, N, the second group is C, L, T, the third group is P, and the fourth group is Q. The numbers represent the intensity level, and the codes K, N, L, C, and T represent nothing to explain. The following numbers represent the minimum yield strength of the material. The unit is KSI (thousands per square inch), H, N, K, J is the first group, the yield strength of the material is 200 MPa, L, C, T are two groups, the yield strength of the material is 100 MPa, P110 is the third group, and Q125 is the fourth group.

The API is divided into 4 groups.
The first group represents an ordinary pipe, that is, a low-strength pipe;
The second group represents a tube resistant to sulfur and corrosion;
The third and fourth groups represent high intensity levels;

J is the code name, and the API specification states that the value after the steel grade code is the minimum yield strength in units of 1000 psi (6894.7632 kPa).
For example, J-55, J is a steel grade symbol, and "55" means 55 x 1000 psi, which refers to the minimum yield strength of steel.