API 5CT C90 is a high-strength, low-alloy steel casing pipe belonging to Group 2 of the API 5CT standard. It is specifically engineered for Sour Service environments, where Hydrogen Sulfide ( H2S ) is present. The most critical characteristic of C90 is its excellent resistance to Sulfide Stress Cracking (SSC).
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API 5CT C90 Specification Table
| Item | Details |
| Standard | API Spec 5CT / ISO 11960 |
| Grade | C90 |
| Group | Group 2 (Controlled Yield Strength) |
| Product Specification Level | PSL1, PSL2, PSL3 |
| OD Range | 4-1/2" – 20" (114.3mm – 508mm) |
| Delivery Condition | Quenched & Tempered (Q&T) |
| Service Environment | Sour Service ( H2S Environment) |
API 5CT Grade C90 Casing Color Code
The color coding for C90 is unique to distinguish it from other sour service grades like L80 or T95.
| Grade | Band on Pipe Body | Coupling Color |
| C90 | One Purple Band + One Yellow Band | Entire Coupling Purple |
Note: In some manufacturing standards, it may be identified by a single purple band, but the purple + yellow combination is the standard API identifier.
Chemical Composition Table (%)
C90 has very strict chemical requirements, particularly limiting impurities to improve its resistance to cracking.
| Element | C (max) | Mn (max) | P (max) | S (max) | Si (max) | Cr (max) | Mo (max) |
| C90 | 0.35 | 1.20 | 0.020 | 0.010 | 0.45 | 1.50 | 0.85 |
Mechanical Properties Table
The most critical factor for C90 is the Hardness Ceiling, which prevents the material from becoming brittle in sour environments.
| Property | Metric Units (SI) | Imperial Units (USC) |
| Yield Strength | 621 - 724 MPa | 90,000 - 105,000 psi |
| Tensile Strength | ≥ 689 MPa | ≥ 100,000 psi |
| Max Hardness | ≤ 25.4 HRC | ≤ 25.4 HRC |
| Hardness Variation | ≤ 3.0 HRC (across section) | ≤ 3.0 HRC |
API 5CT C90 Casing Pipe Dimensions Table
| Outer Diameter (OD) | Nominal Weight | Wall Thickness (WT) | Inner Diameter (ID) | Drift Diameter |
| inch (mm) | lb/ft ( kg/m ) | inch (mm) | inch (mm) | inch (mm) |
| 4-1/2" (114.30) | 11.60 (17.26) | 0.250 (6.35) | 4.000 (101.60) | 3.875 (98.43) |
| 13.50 (20.09) | 0.290 (7.37) | 3.920 (99.57) | 3.795 (96.39) | |
| 15.10 (22.47) | 0.337 (8.56) | 3.826 (97.18) | 3.701 (94.01) | |
| 5" (127.00) | 15.00 (22.32) | 0.296 (7.52) | 4.408 (111.96) | 4.283 (108.79) |
| 18.00 (26.79) | 0.362 (9.19) | 4.276 (108.61) | 4.151 (105.44) | |
| 5-1/2" (139.70) | 17.00 (25.30) | 0.304 (7.72) | 4.892 (124.26) | 4.767 (121.08) |
| 20.00 (29.76) | 0.361 (9.17) | 4.778 (121.36) | 4.653 (118.19) | |
| 23.00 (34.23) | 0.415 (10.54) | 4.670 (118.62) | 4.545 (115.44) | |
| 6-5/8" (168.28) | 24.00 (35.72) | 0.352 (8.94) | 5.921 (150.39) | 5.796 (147.22) |
| 28.00 (41.67) | 0.417 (10.59) | 5.791 (147.09) | 5.666 (143.92) | |
| 7" (177.80) | 26.00 (38.69) | 0.362 (9.19) | 6.276 (159.41) | 6.151 (156.24) |
| 29.00 (43.16) | 0.408 (10.36) | 6.184 (157.07) | 6.059 (153.90) | |
| 32.00 (47.62) | 0.453 (11.51) | 6.094 (154.79) | 5.969 (151.61) | |
| 35.00 (52.09) | 0.498 (12.65) | 6.004 (152.50) | 5.879 (149.33) | |
| 7-5/8" (193.68) | 33.70 (50.15) | 0.430 (10.92) | 6.765 (171.83) | 6.640 (168.66) |
| 39.00 (58.04) | 0.500 (12.70) | 6.625 (168.28) | 6.500 (165.10) | |
| 9-5/8" (244.48) | 40.00 (59.53) | 0.395 (10.03) | 8.835 (224.41) | 8.679 (220.45) |
| 43.50 (64.73) | 0.435 (11.05) | 8.755 (222.38) | 8.599 (218.41) | |
| 47.00 (69.94) | 0.472 (11.99) | 8.681 (220.50) | 8.525 (216.54) | |
| 53.50 (79.62) | 0.545 (13.84) | 8.535 (216.79) | 8.379 (212.83) | |
| 10-3/4" (273.05) | 51.00 (75.90) | 0.450 (11.43) | 9.850 (250.19) | 9.694 (246.23) |
| 55.50 (82.59) | 0.495 (12.57) | 9.760 (247.90) | 9.604 (243.94) | |
| 13-3/8" (339.72) | 68.00 (101.19) | 0.480 (12.19) | 12.415 (315.34) | 12.259 (311.38) |
| 72.00 (107.15) | 0.514 (13.06) | 12.347 (313.61) | 12.191 (309.65) |
Connections of API 5CT Grade C90 Casing
Since C90 is used in high-pressure gas wells with H2S , the choice of connection is vital for safety:
BTC (Buttress Thread): Common trapezoidal thread with high tensile load capacity.
Premium Connections: Brands like VAM, TenarisXP, or Hunting. For C90, Metal-to-Metal Seals are highly recommended to ensure 100% gas-tightness in corrosive high-pressure environments.
LTC (Long Round Thread): Occasionally used in medium-pressure applications.
Manufacturing Process of API 5CT Grade C90
C90 is a "Restricted Grade," meaning the manufacturing process is tightly controlled:
Pipe Body: Must be Seamless (SMLS). API 5CT does not allow welded (ERW) C90.
Heat Treatment: Full-length Quenching and Tempering (Q&T) is mandatory.
Grain Refinement: Fine grain size (typically 7 or finer) is required to ensure toughness.
Straightening: Must be performed at temperatures above the final tempering temperature or controlled to minimize residual stress.
Testing Requirements of API 5CT Grade C90
Testing for C90 is significantly more rigorous than for standard J55/K55 grades:
| Test Item | Purpose / Requirement |
| SSC Test | Core requirement. Conducted per NACE TM0177 to ensure resistance to Sulfide Stress Cracking. |
| Hardness Test | Mandatory full-length scanning to ensure hardness never exceeds 25.4 HRC. |
| Tensile Test | Verifies yield strength stays within the strict 90,000–105,000 psi window. |
| Hydrostatic Test | Verifies the pipe body's integrity and sealing under high pressure. |
| NDT (Non-Destructive) | Mandatory full-body inspection (Ultrasonic or Magnetic Particle) for all C90 pipes. |
| Metallographic Exam | Checks for uniform microstructure and ensures no untempered martensite exists. |
API 5CT C90 Casing pipe factory
API 5CT C90 Oil Well casing pipe certificate
FAQ
What is a 5CT pipe?
An API 5CT pipe is a specialized steel pipe used in the oil and gas industry for lining and operating wells.
The "5CT" refers to the specific American Petroleum Institute (API) standard that covers two main types of downhole pipes:
Casing: Large-diameter pipes used to line the wellbore, providing structural support and preventing the well from collapsing.
Tubing: Smaller-diameter pipes placed inside the casing to transport oil or gas from the reservoir to the surface.
What is the tolerance for API 5CT casing?
The tolerances for API 5CT casing are strictly defined to ensure safety and compatibility at the well site. Here are the primary tolerances:
1. Outside Diameter (OD)
Pipes < 4-1/2": ± 0.79 mm (± 0.031 in).
Pipes ≥ 4-1/2": +1.00% / -0.75% of the nominal diameter.
2. Wall Thickness (WT)
The minimum wall thickness must not be less than -12.5% of the nominal thickness. (There is no specific maximum limit, as it is controlled by the weight tolerance).
3. Weight
Single Joint: -3.5% to +6.5% of the nominal weight.
Carload (Batch): -1.75% of the total nominal weight.
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