API 5CT steel grade classification
There are twenty different steel grades and types of oil casing, including H40, J55, K55, Mg65, N80 (n80-1, n80ql80 (l80-1, l80-9cr, l80-13cr), C90 (c90-1, c90-2), T95, C95, P110, q125. In order to distinguish different steel grade strength and thread type, different color codes and symbols are used to represent the steel grade and thread of oil casing.
H. J, K and N represent general strength oil casing,
C. L, m and t represent the oil casing with limited yield strength, which has certain sulfur corrosion resistance.
K55 and J55 are generally normalized with 36m2v and 37Mn5,
L80 quenched and tempered with 25n2q
J55 / K55: 37Mn5, 36Mn2V normalizing heat treatment
L80: 13Cr, 25mn2-q quenching and tempering heat treatment