Steel Casing Pipe Size Chart

Steel casing pipe sizes are typically specified by outside diameter, wall thickness, weight per foot, and internal dimensions. These parameters determine the strength, collapse resistance, and installation requirements of the casing string.

The size chart below summarizes common steel casing pipe dimensions used in drilling and well construction projects. In addition to outside diameter and nominal weight, engineers often reference wall thickness, inside diameter, and drift diameter when selecting casing and tubing for a specific application. 

1. Steel Casing Pipe Size Chart

The chart covers common API casing sizes together with their corresponding wall thickness, inside diameter, drift diameter, and nominal weight values.

Drift diameter is the inside diameter less 1/8 in for sizes through 8 5/8 in, 5/32 in for 9 5/8 in through 13 3/8 in, and 3/16 in for 16 in and larger. The last four columns give the mass gain or loss due to end finishing for STC, LTC, BTC-RC and BTC-SCC connections.

2. How to Read a Steel Casing Pipe Size Chart

When selecting steel casing pipe, engineers typically evaluate several key dimensions. Understanding these parameters helps ensure the casing can meet installation, load, and operational requirements.

2.1 Outside Diameter (OD)

Outside diameter refers to the overall external diameter of the casing pipe. Casing sizes such as 4-1/2", 7", and 9-5/8" are identified by their OD.

2.2 Nominal Weight (lb/ft)

Nominal weight indicates the theoretical pipe weight per foot. A higher weight generally corresponds to a thicker wall and greater collapse resistance.

2.3 Wall Thickness

Wall thickness is the distance between the outside and inside surfaces of the pipe. Different wall thicknesses may be available for the same casing size.

2.4 Inside Diameter (ID)

Inside diameter represents the available internal flow area of the casing. It decreases as wall thickness increases.

2.5 Drift Diameter

Drift diameter is the minimum internal diameter through which a standard drift mandrel can pass. It is commonly used to verify casing clearance before running downhole equipment.

3. Steel Casing Pipe Dimensions by Application

3.1 Water Well Casing

For water well projects, casing sizes between 4" and 12" are commonly used. Residential wells often use 4" to 6" casing, while larger municipal and irrigation wells may require 8" to 12" diameters to accommodate higher pumping capacities.

3.2 Oil and Gas Well Casing

Oil and gas wells normally use several casing strings of progressively smaller diameters from the surface to the production zone.

Common examples include 13-3/8" surface casing, 9-5/8" intermediate casing, and 4-1/2" or 5-1/2" production casing.

3.3 Borehole Casing

Borehole casing is commonly used in groundwater investigation, monitoring wells, environmental sampling, and geotechnical drilling projects.Depending on the borehole design, casing sizes typically range from 4" to 10", with larger diameters often selected when additional instrumentation or higher water flow capacity is required.

3.4 Conductor Casing

Conductor casing is the first casing string installed during drilling operations. Large diameters such as 16", 18-5/8", and 20" are commonly used to support shallow formations, prevent surface collapse, and provide a stable foundation for subsequent casing strings.

4. Common Steel Casing Pipe Sizes

Although API casing is available in a wide range of diameters, several sizes are used more frequently in drilling and well construction projects. The table below summarizes common casing sizes and their typical applications.

In most drilling projects, multiple casing sizes are installed sequentially to provide structural support, isolate formations, and maintain wellbore integrity throughout drilling and production operations.

5. FAQs

Q1. How is casing pipe size measured?

Casing size is generally identified by its outside diameter (OD). Additional dimensions such as wall thickness, inside diameter (ID), and drift diameter are used to define the complete casing specification.

Q2. What is the difference between casing size and inside diameter?

Casing size refers to the nominal outside diameter of the pipe, while inside diameter represents the usable internal opening. For the same casing size, the ID changes as wall thickness increases or decreases.

Q3. Why does the inside diameter change while the outside diameter remains the same?

API casing is classified by outside diameter. Different weight options are available for the same OD, resulting in different wall thicknesses and therefore different inside diameters.

Q4. What is drift diameter in steel casing pipe?

Drift diameter is the minimum internal diameter through which a standard drift mandrel can pass. It is used to verify that downhole tools and equipment can move through the casing without obstruction.

Q5. Can the same casing size have different weights?

Yes. A single casing size may be produced with multiple wall thicknesses and nominal weights. For example, 7" casing is available in several weight grades, each providing different strength and internal dimensions.

Q6. What casing sizes are commonly used for water wells?

Water well casing typically ranges from 4 inches to 12 inches in diameter. The selected size depends on well depth, pump capacity, and required water production.

Q7. What are the standard steel casing pipe sizes?

Standard API casing sizes range from 4-1/2" to 20" OD. Common sizes include 4-1/2", 5-1/2", 7", 9-5/8", 13-3/8", and 20", depending on the well design and application requirements.

Related Steel Casing Pipe Resources

For additional sizing and specification information, refer to the following resources:

Steel Casing Pipe Weight Chart

Steel Casing Pipe Wall Thickness

Steel Casing Pipe Length

Applications of Steel Casing Pipe

How To Choose The Size of Steel Casing Pipe?