API 5CT steel pipes are basically divided according to the numerical range of material properties (steel grade, rolling, and heat treatment, the final result is performance). As for the classification of steel grades in each group, they are also divided according to their properties. It should be said that the steel grade is also determined based on the on-site oil casing string and well depth calculations to determine its pressure resistance requirements, thread sealing requirements, thread pull-off requirements, collapse resistance, crush resistance, etc.
H40J55, K55M65N80 (N80-1N80Q) L80 (L80-1 L80-9Cr L80-13Cr), C90 (C90-1C90-29551125 and other twenty different steel grades and types of oil casing, in order to distinguish the strength of different steel grades, The thread type uses different color codes and symbols to represent the steel grade and thread of the oil and casing respectively. The two or three numbers after the color code and English letters represent the minimum yield strength of the steel grade of the oil and casing, such as J55. Its minimum yield strength is 55,000 lb/in2 (379Mpa) and its maximum is 80,000 lb/in2 (552Mpa). P110 has a minimum yield strength of 110,000 lb/in2 (758Mpa) and its maximum yield strength is 140,000 lb/in2 (965Mpa). HJIK, N stands for general strength oil casing, and CLIMT stands for limited yield strength.
- Oil casing has certain resistance to sulfur corrosion.
K55J55 is generally made of 36Mn2V, 37Mn5 normalized, L80 is tempered with 25Mn2-Q
- P110:30CrMo
- J55/k55: 37Mn5, 36Mn2V normalizing heat treatment
- N80:36Mn2V
- L80:13Cr, 25Mn2-Q quenching and tempering heat treatment
