Minimum Wall Thickness for Standard-Weight Piping

ANSI Schedules

• The ANSI used to divide pipes into three categories: standard, extra strong and "double extra strong." However, ever-increasing complexities in pipe manufacturing and plumbing systems led to the creation of "schedules." These so-called schedules provide minimum pipe weight and thickness requirements based on the pressure of water running through the pipe system and the diameter of the pipe. Standard-weight piping follows the same minimum wall thickness requirements as ANSI Schedule 40 in this new measurement model, up to 10-inch-diameter pipes.

Thickness Range

• As per ANSI Schedule 40, minimum wall thickness for steel pipes ranges from .068 inches for a pipe measuring 1/8 inch in diameter to .322 inches for a pipe measuring 8 inches in diameter. All standard-weight pipes measuring 10 inches or more in diameter require a minimum wall thickness of 3/8 inch. Some sources list the nominal minimum thickness of pipes, rounding off decimals to the nearest 10th place. On such charts, thicknesses range from .07 for a 1/8-inch-diameter pipe to .32 for an 8-inch-diameter pipe.

Barlow's Formula

• Barlow's Formula is a mathematical equation developed by mathematician Peter Barlow that describes the relationship between internal pressure, allowable stress, wall thickness and diameter in pipes. You can use Barlow’s Formula to determine the minimum thickness requirements for piping in a plumbing system, regardless of the type of pipe used. This formula reads PD/2S, or P multiplied by D, divided by S multiplied by 2. In this formula, P equals the water pressure in a piping system as measured in pound-force per square inch. D stands for the length of the pipe, and S stands for the pressure rating of a pipe in pounds per square inch.

Local Plumbing Codes

• You can obtain charts of American National Standards Institute pipe requirements from various websites, such as Engineering ToolBox. Always check with your local plumbing code for more specific information about building in your area. Local governments develop building and plumbing codes by considering the specific conditions and requirements of an area. For plumbing, this includes things like standard water pressure and problems like extreme cold, which may cause freezing in pipe systems.