Why Is Steel Pipe Manufactured in 21 Foot Lengths?

eHow may earn compensation through affiliate links in this story. Learn more about our affiliate and product review process here.
The standard length for buying steel pipe is 21 feet.

Anyone who works with steel pipe will be aware that it is generally sold in lengths of 21 feet. Although several theories exist as to why this is, the actual reason is most likely due to its manufacturing history.

Advertisement

Misconceptions

Video of the Day

One common misconception is that the standard length of 21 feet is the result of a metric conversion, while another suggests that it is to conform to the average length of a flat-bed truck. Neither of these theories is generally accepted.

Advertisement

Video of the Day

History

For much of its existence, steel pipe was produced using some variation of the bell and tong method, which utilized a heated strip of steel that was pulled through a cone-shaped hole to curve it into a tube. As it turned out, 21 feet was the length at which the steel could both hold a quality weld along the seam, and exhibit the necessary yield for forming the tube.

Advertisement

Other Sizes

Although 21 feet is still the standard, today, steel pipe can also be ordered at lengths of single random (18 to 25 feet), double random (38 to 40 feet) and specific cut lengths.

Advertisement

references & resources