The Global Standard for Downhole Tubulars in Drilling and Production
Published by: American Petroleum Institute (API)
Current Edition: 10th (2022), Equivalent to ISO 11960:2022
Overview
API 5CT (Specification for Casing, Tubing, and Drill Pipe) is the internationally recognized standard that defines the technical requirements for steel tubulars used in oil and gas well drilling, completion, and production operations.
These tubulars - including casing, production tubing, and drill pipe - are critical components in well construction, providing structural integrity, zonal isolation, and a conduit for hydrocarbons from the reservoir to the surface.
API 5CT ensures that these downhole components meet rigorous performance, safety, and quality standards under extreme conditions such as high pressure, high temperature, corrosive environments (e.g., H₂S and CO₂), and mechanical loading.
✅ API 5CT is not just a material standard - it's a performance specification for one of the most critical systems in oilfield operations.
Scope
API 5CT covers the following types of steel tubulars:
|
Product |
Function |
|
Casing |
Structural lining of the wellbore; provides wellbore stability and zonal isolation |
|
Production Tubing |
Conduit for transporting oil/gas from the reservoir to the surface |
|
Drill Pipe |
Used during drilling to transmit drilling fluid and torque to the drill bit |
It applies to both:
● Seamless pipes (most common)
● Welded pipes (limited applications, subject to additional requirements)
The standard specifies requirements for:
● Dimensions, weights, and tolerances
● Steel grades (product forms)
● Mechanical properties
● Manufacturing processes
● Testing and inspection
● Marking and packaging
● Quality control and traceability
Product Forms and Grades (Groups and Types)
API 5CT classifies tubulars into three main groups, each with specific types based on chemical composition, heat treatment, and performance capabilities:
Group 1: Carbon and Low-Alloy Steels (Non-Corrosion Resistant)
|
Grade |
Yield Strength (min) |
Tensile Strength (min) |
Heat Treatment |
Key Features |
|
H40 |
40 ksi (276 MPa) |
60 ksi (414 MPa) |
As-rolled or normalized |
General purpose, shallow wells |
|
J55 |
55 ksi (379 MPa) |
75 ksi (517 MPa) |
As-rolled or normalized |
Most common casing grade |
|
K55 |
55 ksi (379 MPa) |
95 ksi (655 MPa) |
Normalized |
Higher strength than J55 |
|
N80 |
80 ksi (552 MPa) |
95 ksi (655 MPa) |
Quenched & Tempered (Q&T) or Normalized |
Medium-depth, higher pressure |
|
L80 |
80 ksi (552 MPa) |
95 ksi (655 MPa) |
Q&T or Normalized |
Corrosion-resistant variants available (see below) |
|
M65 |
65 ksi (448 MPa) |
80 ksi (552 MPa) |
As-rolled or normalized |
Lower-strength alternative to N80 |
Note: "80" in N80/L80 refers to 80,000 psi minimum yield strength, not tensile.
Group 2: Corrosion-Resistant Alloys (CRA) – Sour Service Grades
These grades are designed for H₂S (sour) environments and must meet strict hardness and chemical composition limits per NACE MR0175 / ISO 15156.
|
Grade |
Type |
Key Features |
|
L80 9Cr |
9% Chromium steel |
Good resistance to CO₂ corrosion and mild H₂S |
|
L80 13Cr |
13% Chromium steel (Martensitic stainless) |
Excellent resistance to CO₂ and moderate H₂S; used in tubing |
|
C90 |
≥90 ksi yield |
High-strength, sour service capable |
|
T95 |
≥95 ksi yield |
Higher strength than C90, sour service |
|
C90, C110, T95, T110 |
High-strength CRAs |
Used in deep, sour, or HPHT (High Pressure High Temperature) wells |
Cxx / Txx: "C" for Casing, "T" for Tubing; e.g., C90 = casing with 90 ksi min yield.
Group 3: High-Strength Non-Corrosion Resistant Steels
|
Grade |
Yield Strength |
Application |
|
P110 |
110 ksi (758 MPa) |
High-strength casing for deep wells |
|
Q125 |
125 ksi (862 MPa) |
Ultra-deep wells; limited ductility, requires careful handling |
Key Technical Requirements
|
Parameter |
Requirement |
|
Manufacturing |
Seamless (common), welded (limited use with full NDT) |
|
Heat Treatment |
Mandatory: As-rolled, normalized, or quenched & tempered depending on grade |
|
Hardness Control |
Max 22 HRC for sour service grades (e.g., L80, C90); verified per API 5CT Annex B |
|
Chemical Composition |
Controlled carbon equivalent (CE) to ensure weldability and toughness |
|
Tensile Testing |
Required for every heat (heat batch) |
|
Hardness Testing |
On body, weld (if applicable), and ends |
|
Non-Destructive Testing (NDT) |
100% Ultrasonic Testing (UT) or Electromagnetic Testing (ET) of entire body |
|
Hydrostatic Testing |
100% performed at specified pressure (varies by size and grade) |
|
Thread Inspection |
For threaded products: API Round Thread (e.g., BTC, LTC) or Premium Connections |
|
Dimensions & Tolerances |
Strict limits on OD, wall thickness, length, ovality, and straightness |
Threaded and Plain-End Options
API 5CT tubulars are supplied in various end configurations:
Plain End (PE) – For welding or coupling in field
Threaded and Coupled (T&C) – With API standard threads:
API Thread Types: Round Thread (BTC, LTC, STC), Buttress Thread (BC)
Premium Connections – Non-API proprietary connections with enhanced sealing and strength (e.g., Tenaris TF, Weatherford W-Hy, VAM Top)
Premium connections require type approval testing and are often used in HPHT or sour service.
Special Service Requirements (Optional)
Sour Service Compliance: Must meet NACE MR0175 / ISO 15156 for H₂S environments
Hardness Testing: Required for CRA and high-strength grades
Impact Testing: Optional for low-temperature service
Through-Wall Ultrasonic Testing: For thick-walled casings
Drift Testing: To verify internal clearance
Traceability: Full heat trace from billet to finished product
Applications
Surface, Intermediate, and Production Casing – Structural support and zonal isolation
Production Tubing – Hydrocarbon production conduit
Liner Tubulars – Used in open-hole completions
Gas Lift Strings – For artificial lift systems
Injection Wells – Water, gas, or steam injection
HPHT and Deepwater Wells – Using high-grade materials like P110, Q125, C90, T95
API Monogram & Certification
Manufacturers must be licensed by API and comply with API Q1 Quality Management System
Products bearing the API Monogram are independently verified for compliance
Buyers should verify manufacturer status on the API ICP (Individual Certification Programs) website: https://icp.api.org
Summary Table
|
Feature |
Description |
|
Standard |
API 5CT (10th Ed., 2022) / ISO 11960:2022 |
|
Products |
Casing, Tubing, Drill Pipe |
|
Manufacturing |
Seamless (primary), welded (limited) |
|
Key Grades |
J55, K55, N80, L80, C90, T95, P110, Q125, L80 13Cr |
|
Heat Treatment |
As-rolled, Normalized, Quenched & Tempered |
|
Testing |
100% UT/ET, hydrotest, tensile, hardness |
|
Special Options |
Sour service, premium connections, HRC control |
|
Global Use |
Universal in oil & gas drilling and production |
