API 5CT C90 is a high-strength OCTG (Oil Country Tubular Goods) steel grade used in oil and gas wells, primarily for casing and tubing. It is the Sour Service (hydrogen sulfide corrosion-resistant) steel grade specified in the
API 5CT standard, designed specifically for deep wells, high-pressure wells, H₂S-containing acidic environments, and highly corrosive conditions.
API 5CT C90 Casing and Tubing Specifications
O.D.:
Casing
4 1/2″ – 20″ (114.3 mm – 508 mm)
Tubing
2 3/8″ – 4 1/2″ (60.33 mm – 114.30 mm)
W.T.:
Casing
5.21 mm – 16.13 mm (common)
Tubing
2.87 mm – 12.65 mm (common)
Length:
R1 (4.88 – 7.62 m)
R2 (7.62 – 10.36 m)
R3 (10.36 – 14.63 m)
Thread Types:
STC（Short Thread Casing）
LTC（Long Thread Casing）
BTC（Buttress Thread）
Premium Connection
Heat Treatment:
Quenched and Tempered（Q&T）
Standard:
API 5CT
Surface Treatment:
Black Painting/ Clear Varnish/ Anti-Rust Oil/ 3PE / FBE
Color Code:
Purple Band
Why Choose ALLLAND Steel Pipe for API 5CT C90
Specializing in the manufacture of high-specification oil country tubular goods (OCTG): API 5CT casing and tubing, sulfur-corrosion-resistant OCTG, and high-strength oilfield tubing.
Comprehensive API 5CT certification system: ALLLAND holds certifications including API, ISO, CE, and CNAS,etc.
Strict quality control: Focusing on heat treatment and chemical composition to ensure strength and sulfur-corrosion resistance.
Extensive export experience: Serving international markets including the Middle East, Russia and CIS countries, Southeast Asia, and South America,etc.
Full range of product sizes available.
API 5CT C90 Dimensional Tolerances
OD Tolerance
Tubing Outer Diameter Tolerance: Typically: ±0.79 mm (±1/32″)
Casing Outer Diameter Tolerance:
OD ＜ 114.3 mm, ±0.79 mm
OD ≥ 114.3 mm, ±1% OD
Wall Thickness Tolerance: WT Tolerance = -12.5%
The API 5CT standard specifies a minimum wall thickness: not less than 87.5% of the nominal wall thickness.
Weight Tolerance: Permitted deviation in weight per piece: -3.5% to +6.5%
The average weight of the entire batch must not be lower than the theoretical weight.
Length Tolerance: R1 / R2 / R3
R1: 4.88 – 7.62 m
R2 (most common): 7.62 – 10.36 m
R3: 10.36 – 14.63 m
Thread Tolerance
API thread specifications require that STC, LTC, and BTC meet precision requirements for pitch, taper, thread height, and roundness. In deep well conditions, even the slightest deviation can lead to leaks or thread breakage.
API 5CT C90 Mechanical Properties
| Property |
Value |
| Yield Strength |
621–724 MPa |
| Tensile Strength |
≥ 689 MPa |
| Hardness |
≤ 25.4 HRC |
| Elongation |
≥ 15% (Reference) |
In the API 5CT standard, the strength grades are L80 → C90 → T95 → P110.
C90 offers higher strength than L80 while still providing a certain level of sulfur resistance, making it suitable for deeper well depths, higher well pressures, and greater axial loads.
API 5CT C90 also employs Quenched and Tempered (Q&T) treatment, a precise heat treatment process designed to achieve a balance between strength, toughness, and hardness.
Chemical Properties of API 5CT C90 Casing & Tubing
| Element |
Content |
| C |
0.30–0.37% |
| Mn |
1.00–1.35% |
| Cr |
0.80–1.10% |
| Mo |
0.20–0.30% |
| Ni |
0.25–0.65% |
| P |
≤ 0.020% |
| S |
≤ 0.01 |
Sour Service steels generally require extremely low sulfur (S) and phosphorus (P) content.
C90 offers higher strength than L80 and better resistance to SSC than P110, making it particularly suitable for deep-well acidic environments. Sulfide stress cracking is a sudden failure mode that poses a significant risk in oil wells. Although P110 has higher strength, it is more susceptible to hydrogen embrittlement.
Main Applications of API 5CT C90 Casing and Tubing
Deep Wells: Higher strength, capable of withstanding greater suspension loads
High-Pressure Wells: Suitable for high formation pressure, high blowout pressure, and high collapse pressure.
Sour Gas Wells: H₂S corrosive environments and acidic natural gas wells.
Offshore Oilfields: Offshore platforms face complex operating conditions and severe corrosion; high-grade steel pipes such as C90 are generally the preferred choice.
API 5CT C90 vs Other Steel Grades
C90 vs L80
| Item |
L80 |
C90 |
| Strength |
80 ksi |
90 ksi |
| Cost |
Lower |
Medium to High |
| Sour Service Resistance |
Excellent |
Excellent |
| Deep Well Capability |
Standard |
Stronger |
C90 vs T95
| Item |
C90 |
T95 |
| Yield Strength |
90 ksi |
95 ksi |
| SSC Risk |
Lower |
Higher |
| Cost |
Lower |
Higher |
| Applications |
Deep Sour Wells |
More Severe Sour Service Wells |
C90 vs P110
| Item |
C90 |
P110 |
| Sour Service Resistance |
Strong |
Weaker |
| Strength |
Medium to High |
Very High |
| H₂S Service Suitability |
Suitable |
Generally Not Recommended |
| Deep Well Capability |
Strong |
Extremely Strong |
FAQ
