The right steel tubing is the one that matches five things: what the part has to do, its shape, the specification it is made to, its size and wall, and its finish. Settle them in that order and the choice usually narrows to one or two options.
Curtis Steel & Aluminum Co has supplied metal in Las Vegas since 1970. The questions below are the ones to answer before you ask for a quote.
1. What does the part have to do?
Steel tubing falls into two working groups. Structural tubing holds things up: columns, frames, racks, gates, trailers, and equipment stands. Mechanical tubing becomes a part: rollers, bushings, axles, handles, and furniture, where dimensions and surface matter more than load.
If the job is carrying water, gas, or air under pressure, you need pipe and not tube. The two are sized and tested differently, which our post on steel pipe vs steel tubing explains.
2. Which shape fits the load?
- Round tube resists twisting and takes load evenly from any direction. It suits handrails, roll cages, and rotating parts.
- Square tube is easy to cut, fit, and weld at right angles. It suits gates, fences, frames, and posts.
- Rectangular tube is stiffer in its tall direction than a square tube of similar weight. It suits beams, shelving, workbenches, and trailer frames.
Flat faces also make drilling and bolting simpler. If other parts have to mount to the tube, square or rectangular sections save time in the shop.
3. Which specification should the tube meet?
Two ASTM standards cover most carbon steel tubing, and they are written for different jobs.
ASTM A500 for structural work
A500 covers carbon steel structural tubing in round, square, and rectangular shapes. It is the usual choice for buildings and welded or bolted frames. Grade B is commonly listed with a minimum yield strength of 46,000 psi and Grade C with 50,000 psi. Round sections carry slightly lower minimums, so check the figures for the shape you are buying.
ASTM A513 for mechanical work
A513 covers electric-resistance-welded mechanical tubing. It can be held to tighter dimensional tolerances than structural tube, which is why it is used for parts that have to fit. The common types are hot-rolled electric-welded (HREW), cold-rolled electric-welded (CREW), and drawn-over-mandrel (DOM). DOM has the most consistent wall and the smoothest inside surface of the three.
Surface is part of the choice. Tube made from hot-rolled strip has a darker, scaled surface, while cold-rolled tube is smoother and takes paint with less preparation. The same trade-off is covered in our post on hot rolled and cold rolled steel.
Ask which specification the tubing you are buying is made to, and ask for the mill test report if the project is engineered or inspected.
4. What size and wall thickness?
A tube is ordered by its actual outside dimensions and its wall thickness. A 2-inch square tube measures 2 inches across the outside. The wall is given in inches, such as 1/8, 3/16, or 1/4, or as a gauge number on lighter tube.
- 16 gauge: 0.065 inch
- 14 gauge: 0.083 inch
- 11 gauge: 0.120 inch
Size does more for stiffness than wall does. A larger tube with a thinner wall is often stiffer and lighter than a smaller tube with a thick wall. Thicker wall earns its place where the tube is welded heavily, bolted through, or likely to be dented.
Square and rectangular tubes have rounded corners, and the radius grows with the wall. Allow for that when a tube has to sit flush against a plate or take a snug end cap.
For anything that carries people, vehicles, or overhead loads, have an engineer size the member. For lighter work, our guide to how thick steel needs to be gives starting points.
5. What finish does the job need?
Bare carbon steel tube arrives with mill scale or a light oil coating, and it will rust outdoors unless it is painted, powder coated, or galvanized. Galvanized tube has a zinc coating for corrosion resistance and suits fences, rails, and outdoor frames.
Two fabrication notes apply to galvanized tube. Grind the zinc back from the joint before welding, and weld with good ventilation, because zinc fumes are hazardous. Touch up the weld area afterward, since the coating is gone there.
Where low weight or rust resistance matters most, aluminum tubing is worth comparing. Stainless is the choice for food, chemical, and coastal conditions.
6. How will it be cut and joined?
Stock lengths are long, and most projects use short pieces. Cut lengths save handling and waste. Our saw cutting service makes straight and 45-degree cuts, so frame corners can arrive ready to weld.
Welded tube has a seam, and the weld leaves a small ridge on the inside. That does not matter for a frame. It does matter if one tube has to slide inside another, so mention telescoping fits when you order.
Two examples of the method
A driveway gate has to carry its own weight, sit outdoors, and look square. That points to square structural tube, a light wall, galvanized or painted finish, and mitered corners cut before delivery.
A conveyor roller has to spin true on a shaft. That points to round mechanical tube, DOM if the fit is close, with the wall chosen from the bearing and the load. Both examples run through the same questions and arrive at different tubes.
What to tell the supplier
- Shape: round, square, or rectangular
- Outside dimensions and wall thickness
- Specification or grade, if the drawings call for one
- Finish: bare or galvanized
- Total length and the cut list
- Whether any pieces need mitered ends or holes
With that list, a quote takes one call. Our carbon steel tubing comes in round, square, and rectangular sections, and no order is too small.
Material can be picked up in Las Vegas or drop-shipped. Customers looking for steel distributors in Phoenix can order the same way.
Frequently asked questions
1) Is square tubing stronger than round tubing?
It depends on the load. Round tube handles twisting and loads from every direction evenly. Square and rectangular tube are easier to join and are efficient in bending when the load comes from a known direction.
2) What is the difference between A500 and A513 tubing?
A500 is a structural specification for frames and buildings. A513 is a mechanical specification with tighter dimensional tolerances for parts that must fit. Use the one your drawings call for.
3) What is DOM tubing?
DOM stands for drawn over mandrel. Welded tube is drawn through a die and over a mandrel, which gives a consistent wall and a smooth bore. It is used for cylinders, axles, and roll cage parts.
4) Can I weld galvanized steel tubing?
Yes, with preparation. Remove the zinc around the joint, weld in a well-ventilated area or with fume extraction, and recoat the weld afterward.
5) Can I buy a short piece of tubing?
Yes. We sell to individuals as well as contractors, and tubing can be saw cut to the lengths you need.
Conclusion
Work through use, shape, specification, size, and finish, and write the answers down before you call. A complete list gets you the right tube the first time.
When the list is ready, request a quote or call Curtis Steel & Aluminum Co at 702.952.3000.