Round Pipe vs. Round Tube—They are NOT the Same and It Is Important To Know Why!

The confusion and misunderstanding around round pipe and round tube is incredibly common—even in metal shops. There are many who do not understand the differences between the two, which leads to a shocking number of quality issues, missed callouts, inaccurate specifications, and ultimately, too many mistakes.

Pipe was originally designed for plumbing applications. Baked clay and straw were used as far back as 4000 B.C. in Babylonia. Egyptians used copper piping in 3000 A.D. and some records suggest that China used rudimentary forms of piping to transport natural gas as early as 2500 B.C.

Pipe started in the early 1600s in Boston, well before flushable toilets, and was often manufactured from wood. Wooden pipes, started from logs, of course, were hollowed out and then joined together.

A few centuries later, other materials started making their way to the market—Orangeburg pipe was popular as late as 1970 but was soon replaced by cast iron which had a much longer life expectancy. Cast iron was then replaced by materials we are more familiar with today: steel, stainless steel and copper.

Tubing came onto the scene with a similar historical background, but began to transition into more of a structural component. Where pipe was designed to move fluid, tube began to take on life as structural support. A popular axiom we use at All Metals Fabrication: “Pipe is for plumbing and tube is for tumbling.”

Unlike pipe, tubing is used in building structures, bridges, automative frames and support skeletons—anything basically driven by structural integrity. Because tubing is so key in developing support and structural integrity, manufacturing standards are usually much more stringent, which leads to higher priced goods; which is, in fact, where the crossover and misunderstandings begin to materialize.

Generally speaking, round pipe can be safely substituted for round tube on smaller-sized structural applications. Because pipe is usually cheaper than tube, manufacturers started making substitutions or even specifying substitutions to, of course, save money.

Guardrail is a good example. Most of the common-budget guardrail is manufactured from pipe. This product is extremely common and something that you see nearly every day. In this type of product, structural integrity from pipe is sufficiently able to ensure the railing does its job—keep people from falling, in this example, off the concrete platform and stairs.

But here is the confusion: pipe railing is manufactured from two pipe sizes. The larger pipe is 1.25″ Schedule 40 pipe and the smaller pickets are fabricated from .75″ Schedule 40 pipe. Most architects are unaware of the difference between pipe and tube, so they likely use specifications that are inaccurate, including some of the following examples which are incorrectly stated:

• 1–½” Pipe-Tube – there is no such thing as 1–½” Pipe-Tube (although we have seen it called out many times)
• 1–½” Pipe – This pipe is actually 1.625″ Outside Diameter, but we are unclear about how thick the pipe wall should be
• 1–½” Tube – This tube is 1.50″ Outside Diameter, but, again, we have no idea how thick the wall of the tube should be

Here are some general rules to remember the differences:

1. Round tubing is called out by Outside Diameter and then wall thickness. For example:
   • 00″ OD x 16 GA t (wall thickness)
   • 00″ OD x .125 GA t (wall thickness)
   • 00″ OD x .250 GA t (wall thickness)
2. Pipe is defined by the nominal size of the ID (inside dimension). We are trying to figure out how much fluid can move through the inside of the pipe, if that makes sense.
   • Wall thickness is defined by a term called, Schedule.
   • This is confusing because Scheduled thickness changes based on pipe size. For example, 1.00″ Schedule 40 pipe has a thinner wall than 2.00″ Schedule 40 pipe.
   • There is no easy way to remember all the sizes and schedules. We recommend using a chart to track pipe sizes and schedules.

3. Pipe and tube do not engineer or calculate the same! That is important to remember. Another way of saying this is 1–½” Schedule 40 Pipe and 1–½” x .125 Wall Tube do not engineer equivalently.
   This becomes more important if you are designing and fabricating items with larger-size diameters or where the structural integrity is paramount. Railing, for example, is a completely different animal than rail cars. Having said that, we have definitely seen pipe specifications that do not actually meet code, but fabricators and designers alike are incorrectly informed and/or simply ignorant to the difference.

A few other informational items that may be obvious, but just to make sure everyone has a better understanding of the difference between pipe and tube, we include the following:

1. Pipe is only manufactured as round. Tube, on the other hand, can be purchased as round, square, rectangular and obround.
2. Companies do manufacture custom extrusions, particularly common in aluminum, that could be nearly any shape or size. These are not considered pipe or tube components; these are called extruded components.
3. Tubing, unlike pipe, can be extremely small as well—like items found in medical devices.
4. Pipe, unlike tubing, can be extremely large—as found underground for gas and oil.

However, in terms of fabrication, pipe and tube are relatively similar. Both pipe and tube can be laser cut, saw cut, formed, rolled, welded, painted, etc. Good fabrication companies pay attention, however, to the differences, because interchanging the two leads to quality errors and reworks. For example, the dies used to form 1–½” Schedule 40 pipe are different that the dies used to form 1–½” x .125 wall tube.

All Metals Fabrication has a dedicated 60-foot tube laser designed to cut and tap pipe and tube hyper-efficiently and incredibly accurately. Dedicated tube lasers are rare in the fabrication industry because they are big and expensive. However, tube lasers are extremely useful when accuracy and speed are demanded. In addition, tube lasers make downstream work—particularly welding—much, much faster because the fit-up is so amazingly accurate. Once welders are spoiled with tube laser work, it is nearly impossible to get them back to saw-cut parts.

All Metals Fabrication specializes in both architectural and light industrial fabrication. We are ISO 9001 certified and always excited to be part of our customer’s special projects.

Learn more on our website, https://www.allmetalsfab.com/. Tube laser information can be found at https://www.allmetalsfab.com/tube-laser-cutting/.

About the Author

Rich Marker

All Metals Fabrication Owner and CEO

Rich Marker is an 18 year, skilled professional in metal fabrication and manufacturing. Co-founder, owner and principal of All Metals Fabrication, Rich has helped to sustain the company’s success over a variety of economic conditions. He has extensive background in continuous improvement, training and process improvement, and emotional intelligence—among other specialized proficiencies. He loves to learn, fly fish, watch college football and devour NY style pizza! He has the best family on earth, loves a good plan, great teaching and the opportunity to get better.

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