API Steel Grade – K55, N80, L80, C90, T95, P110, Q125

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.

• The first group steel grade has relatively low strength
  • H-40 is generally not used in tubing sizes becsuse the yield strength is relatively low and the cost saving over J-55 is minimal.
  • The J-55 are used for most wells when it meets the design criteria. J-55 has been the standard grade for tubing in most relatively shallow (< 9,000 ft) and low pressure (< 4,000 psi) wells on land.
  • Grade K-55 is similar to the J-55 except that the minimum tensile strength of K-55 is higher.
  • Grade N-80 is a relatively old grade with essentially open chemical requirements. It is acceptable for sweet oil and gas wells when it meets design condition. is further divided into two types: N-80-1 and N-80-Q. Both types share the same tensile strength but differentiate in delivery conditions.
    • Grade N80-1 can be either normalized or hot rolling.
    • Grade N80-Q must be through quenching-and-tempering heat treatment before delivery.
• Grade L, C, T represent restricted-yield casing and tubing which has normally anti-sulfur and an-corrosive performance
  • L-80 is a restricted yield-tubing grade which is divided into three types. L80-1, L80-9CR abd L80-13Cr.
    • L80-1 is less expensive but more subject to weight-loss corrosion. It is used commonly in many oil and gas fields because of higher strength than J-55.
    • L80-9CR and L80-13Cr is expensive and difficult to manufacture but they have strong corrosion resistance abilities. These two types are recommended to be used in heavily corrosive wells.
  • C-90 is a relatively new API grade, which is divided into two types: C90-1 and C90-2. only C90-1 is suggested being used in sour conditions. Typical, this grade must be special ordered and its use has been gradually replaced by T-95.
  • T-95 has relatively high strength and is SSC resisant but not weight-loss resistant. It is also have two types: T95-1 and T95-2.
• P-110 in the third ground is a high strength steel grade, which allows quenching-and-tempering heat treatment. It can be adopted in high pressure deep wells
• Grade Q-125 is high strength. If you need tubing or casing to bear quite high pressure, Q-125 is a good choice

Chemical Composition of API Steel Grade for Casing and Tubing, Mass Fraction (%) 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.