API, shorted for American Petroleum Institute, is considered as the most authoritative and comprehensive principles for oil and gas industry. API 5B and API 5CT are mainly used for tubing and casing, which standard the chemical properties, steel grades, manufacturing methods, color coding, heat treatment, inspection and other information.
The API steel grade is also used in the floating equipment production, such as the K-55 steel grade floating shoes.
Here we will introduce the classification and properties of different steel grade in API standard.
Steel grade refers to the yield strength of the products. It can be divided into nine categories of steel grade: H-40, J-55, K-55, N-80, L-80, C-90, T-95, P-110, Q-125.
In it, the letters are stand for the steel grade, which has no relation with the properties and the number refers to the minimum yield strength. The bigger the number is, the higher yield strength will be.
Besides, the API standard divide the nine categories into four groups, H, J, K, N in the first ground, L, C, T in the second ground, P in the third group and Q in the fourth group.
Group | Grade | Type | C | Mn | Mo | Cr | Ni | Cu | P | S | Si | ||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
min. | max. | min. | max. | min. | max. | min. | max. | max. | max. | max. | max. | max. | |||
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 |
1 | H40 | — | — | — | — | — | — | — | — | — | — | — | 0.030 | 0.030 | — |
J55 | — | — | — | — | — | — | — | — | — | — | — | 0.030 | 0.030 | — | |
K55 | — | — | — | — | — | — | — | — | — | — | — | 0.030 | 0.030 | — | |
N80 | 1 | — | — | — | — | — | — | — | — | — | — | 0.030 | 0.030 | — | |
N80 | Q | — | — | — | — | — | — | — | — | — | — | 0.030 | 0.030 | — | |
2 | M65 | — | — | — | — | — | — | — | — | — | — | 0.030 | 0.030 | — | |
L80 | 1 | — | 0.43 a | 1.90 | — | — | — | — | 0.25 | 0.35 | 0.030 | 0.030 | 0.45 | ||
L80 | 9Cr | — | 0.15 | 0.30 | 0.60 | 0.90 | 1.10 | 8.00 | 10.0 | 0.50 | 0.25 | 0.020 | 0.010 | 1.00 | |
L80 | 13Cr | 0.15 | 0.22 | 0.25 | 1.00 | — | — | 12.0 | 14.0 | 0.50 | 0.25 | 0.020 | 0.010 | 1.00 | |
C90 | 1 | — | 0.35 | — | 1.20 | 0.25 b | 0.85 | — | 1.50 | 0.99 | 0.020 | 0.010 | — | ||
C90 | 2 | — | 0.50 | — | 1.90 | — | NL | — | NL | 0.99 | — | 0.030 | 0.010 | — | |
C95 | — | — | 0.45 c | — | 1.90 | — | — | — | — | — | — | 0.030 | 0.030 | 0.45 | |
T95 | 1 | — | 0.35 | — | 1.20 | 025 d | 0.85 | 0.40 | 1.50 | 0.99 | 0.020 | 0.010 | — | ||
T95 | 2 | — | 0.50 | — | 1.90 | — | — | — | — | 0.99 | — | 0.030 | 0.010 | — | |
3 | P110 | e | — | — | — | — | — | — | — | — | — | — | 0.030 e | 0.030 e | — |
4 | Q125 | 1 | — | 0.35 | 1.35 | — | 0.85 | — | 1.50 | 0.99 | — | 0.020 | 0.010 | — | |
Q125 | 2 | — | 0.35 | — | 1.00 | ― | NL | — | NL | 0.99 | — | 0.020 | 0,020 | — | |
Q125 | 3 | — | 0.50 | — | 1.90 | — | NL | — | NL | 0.99 | — | 0.030 | 0.010 | ||
Q125 | 4 | — | 0.50 | — | 1.90 | — | NL | — | NL | 0.99 | — | 0.030 | 0.020 | — | |
a The carton content for L80 may be increased up to 0.50% maximum if me product is oil-quenched. b The molybdenum content for Grade C90 Type 1 has no minimum tolerance if the wall thickness it less than 17.78 mm c The carton content for C95 may be increased up to 0.55% maximum if the product is oil-quenched. d The molybdenum content for T95 Type 1 may be decreased to 0.15% minimum if the wall thickness is less than 17.78 mm e For EW Grade P110, the phosphorus content shall be 0.020% maximum and the sulfur content 0.010% maximum NL = No limit elements shown shall be reported in product analysis. |
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