Taking the Confusion out of Pipe and Tube Buying

At first glance, buying pipe may appear to be confusing, but once you understand the basics, it becomes much easier. Determining the grade of steel is the first step in the process. This provides a basis for additional questions to narrow down the best possible product. 

Many first time buyers also struggle when figuring out the size of pipe and or tube they need.  Pipe and tube are not at all the same thing and have different applications, shapes, and measurement techniques. In general pipe is used to move gas, air, or water while tube is generally for structural use.  Pipe is round, but tube can be round, square, or rectangular.

Tube measurement will be covered in a different blog article, but pipe is measured by the length, nominal inner diameter (ID) and pipe “schedule” (wall thickness). It’s important to note that pipe sizes follow an industry standard, so the sizing is the same regardless of grade. March 1927 the American Standards Association formally standardized what is now referred to as the U.S. Standard Pipe Chart sizing for pipe of all materials. While the sizing can seem random, there is a method to the madness particularly in the case of standardization. A 1 inch pipe would be as follows:

1" SCH 40 x 20' 

With a  measured size of 1.315"OD x .133"WT x 20'

This is where the nominal inner diameter (ID) comes in.  In this case the ID 1.049" will be the inner diameter measurement.   The OD size is different for each Size ID; For example 3-1/2" Pipe will have a 4" Diameter. This is another aspect of pipe buying that most novices find confusing.

To add to the non-intuitiveness, once the pipe size is higher than 14," the size called out is actually the outer diameter (OD), instead of the inner diameter, as described above. This remains the OD size from then on, even to the largest made pipes.

There are however exceptions even to this. For the wall thickness, Sch 40 and Sch STD (Standard) is the same up until the 12" Pipe.  For pipes larger than that, the schedule switches to Sch 40S (STD) or what is referred to as “True Sch 40.” Makes sense right?

For example in the case of 12" Pipe sizes would be as follows:

STD or Sch 40s

12" SCH 40s = 12.750"OD x .375"WT

or

Sch 40 (True Schedule 40)

12" SCH 40 = 12.750"OD x .405"WT

This also applies to Sch 80 and Sch 80S.

Please request our pipe chart for specific details and dimensions.

Next on the list is to determine whether seamless or welded tubing is required.  Grades will commonly be available for both types, so it depends on the specific job.  Send the size and grade along with total footage of pipe that you require.

Here’s a review of what we will need to quote the best pipe for your specific project:

1. Grade of steel

2. Size of pipe or tube

3. Seamless or welded

4. Any restrictions on mill or country of origin or DFARS

5. Quantity- footage

Should you need a pipe that does not fall on the industry standard pipe list.  We can have custom sizes fabricated. Custom fabrication is no problem for the U.S. Tube Supply team.