What is the difference between dom and regular tubing?

Drawn Over Mandrel (DOM) tubing and regular tubing (commonly Electric Resistance Welded, ERW, or seamless) differ mainly in how they’re made, their dimensional accuracy, surface finish, and mechanical properties. DOM tubing starts as ERW tube but is then cold–drawn over a mandrel to remove weld flash and refine wall thickness, yielding tighter tolerances, better concentricity, and a smoother finish. Regular ERW tubing is formed and welded without this cold–drawing step, making it more economical but with looser tolerances and a rougher interior. Seamless tubing, produced by piercing or extrusion of a solid billet, has no seam at all but may not achieve the same precision as DOM unless further cold–drawn.

Manufacturing Processes

DOM Tubing

1. ERW Base Tube: Steel coil strip is formed into a tube and the edges welded.

2. Flash Removal & Annealing: Flash from the weld is removed, and the tube is heat-treated to relieve stresses.

3. Cold Drawing Over Mandrel: The tube is drawn through dies over a mandrel, smoothing the interior, refining wall thickness, and tightening both outer and inner diameter tolerances.

Regular ERW Tubing

1. Forming & Welding: Steel strip edges are formed and butt-welded electrically.

2. Sizing & Cutting: The welded tube is sized by rolls and then cut to length without additional cold drawing.

Seamless Tubing

1. Billet Piercing: A heated solid billet is pierced to create a hollow shell.

2. Rolling & Finishing: The shell is rolled or extruded. It can be hot-finished (HFS) or cold-drawn (CDS) to improve properties, though CDS still generally yields looser tolerances than DOM.

Dimensional Tolerances & Surface Quality

• DOM Tubing

  • OD/ID tolerances as tight as ±0.005″ on smaller sizes

  • Excellent concentricity minimizes need for machining

  • Smooth ID and OD surface finish ideal for hydraulic and precision assemblies

• ERW Tubing

  • Typical OD tolerances of ±0.015″ to ±0.030″

  • Interior weld flash may remain if not removed, often requiring further processing

• Seamless Tubing

  • Cold-drawn seamless can achieve tolerances around ±0.010″ to ±0.020″

  • Hot-finished seamless has coarser OD finish and wider tolerances but is cost-effective for large diameters

Mechanical Properties

• DOM vs. ERW

  • Cold drawing work-hardens the steel, increasing yield and tensile strengths over standard ERW

  • Weld seam in DOM is compacted and flash-free, offering higher seam strength than basic ERW

• Seamless vs. DOM

  • Seamless has uniform properties around the circumference with no seam

  • Cold-drawn seamless approaches DOM strength, but DOM often offers the best combination of precision and strength for most applications

Typical Applications

• DOM Tubing: Hydraulic cylinders, axle shafts, firearm barrels, automotive frames, and other precision mechanical parts requiring tight tolerances and high strength

• ERW Tubing: Structural framing, fencing, furniture, and general mechanical uses where ultra-tight tolerances aren’t critical

• Seamless Tubing: High-pressure piping, heat exchangers, and critical fluid or gas transport where the absence of a seam is paramount