API 5CT Casing and Tubing Size Chart | Complete OCTG Specification Guide

What is API 5CT Casing and Tubing?

API 5CT is an international standard established by the American Petroleum Institute (API) to specify steel pipe products for oil and gas wells, primarily including casing and tubing.

It is part of the OCTG (Oil Country Tubular Goods) system in the oil and gas industry and is one of the most important pipe standards for oil well engineering worldwide.

Difference Between Casing and Tubing

API 5CT Casing Size Chart

Common Casing Sizes

✔ Outer Diameter (OD) Range

• 4 1/2"（114.3 mm）
• 5"（127.0 mm）
• 7"（177.8 mm）
• 9 5/8"（244.5 mm）
• 13 3/8"（339.7 mm）
• 16"（406.4 mm）
• 20"（508.0 mm）

👉 Coverage: 4 1/2“ – 20” (small-diameter to extra-large well sections)

✔ Wall Thickness Range

5.21 mm – 25.4 mm (varies with well depth and pressure)

Typical range: 6 mm – 15 mm

API 5CT Tubing Size Chart

Common Tubing Sizes

✔ Outer Diameter (OD) Range

• 1.05"（26.7 mm）
• 1.315"（33.4 mm）
• 1.66"（42.2 mm）
• 2 3/8"（60.3 mm）
• 2 7/8"（73.0 mm）
• 3 1/2"（88.9 mm）
• 4 1/2"（114.3 mm）

👉 Coverage Range: 1.05“ – 4 1/2”

✔ Wall Thickness Range

• 2.87 mm – 10.54 mm
• Common range: 3.18 mm – 7.72 mm

API 5CT Steel Grades Explained

Common Grades

• J55 / K55 (low strength)
• N80 (medium strength)
• L80 (corrosion-resistant)
• P110 (high strength)

Selection Guide

• shallow wells → J55/K55
• medium depth → N80
• sour service → L80
• deep/high pressure → P110

How API 5CT Size Chart Is Used in Well Design and Casing Programs

In API 5CT applications, the casing and tubing size tables are used for both well design and casing programs to determine the size, sequence, and running depth of casing strings.

In well design, these tables provide the basis for planning the overall casing structure from surface casing to production casing. In the casing program, they are used to assign specific casing and tubing specifications to each well section based on depth and pressure requirements.

How Casing and Tubing Sizes Relate to Well Depth and Pressure

In the API 5CT standard system, different sizes of casing and tubing are not simply assigned to a specific well depth or pressure value, but are determined based on a comprehensive assessment of the well’s design conditions, formation conditions, and steel grade strength.

In engineering practice, the approximate application ranges of different sizes can be quickly understood in the following ways:

Overall, the selection of a size depends on depth, pressure, and mechanical strength requirements rather than a fixed one-to-one correspondence; what truly determines the scope of application is the combined configuration of the entire API 5CT design system.

FAQ – API 5CT Casing and Tubing Size Chart

1. What is the API 5CT casing and tubing size chart used for?

It is used to select casing and tubing sizes, grades, and wall thickness for oil and gas well design.

2. What information does the size chart include?

It includes outer diameter, wall thickness, weight, and steel grades such as J55, K55, N80, and P110.

3. How is casing size selected from the API 5CT chart?

Casing size is selected based on well depth and pressure conditions, with larger sizes used for shallow sections and smaller sizes for deeper zones.