Hot rolled seamless tube tolerances are not straightforward. Providing industry standards is ASTM A519, which specifies the acceptable degree of dimensional variations (aka the tolerance) for steel tube manufacturing.

But, no matter how good a spec is, misinterpreting it can lead to serious ramifications. It’s important to note the tolerancing of A519 for hot rolled tubing generally only applies to the outer diameter (OD) and the wall thickness—not the inner diameter (ID). With wall tolerances generally being 10%, this means the center of a tube may not be concentric with the OD and can lead to large differences between the nominal and guaranteed finish ID.

Read ahead to learn about tube manufacturing, ASTM A519, and how to get tubing that’s guaranteed to fit your application.

How Steel Manufacturers Make Seamless Tubing

Manufacturing hot rolled seamless tubing involves heating a solid billet to over 2,000 degrees Fahrenheit and then piercing it through the center to make a tube shape. The process happens in seconds, and the associated strain rates are extremely high.

You can see the piercing process in this video by TimkenSteel.

Manufacturers generally follow tolerancing guidelines per ASTM A519 standard specification, which generally governs the tolerancing for seamless tubing.

Compliance with ASTM A519 Tolerances

Within the ASTM A519 standard is a table of tolerances for hot rolled seamless tubing; it lists tubing OD and wall thickness (WT). In general, WT is plus/minus 10 - 12.5%, depending on the OD-to-WT ratio.

ASTM’s tolerancing methodology is consistent with the nature of tube manufacturing. And, like any industrial process, production variations can result in tubing being at the edge of allowable tolerances. This means that given the manufacturing methodology and the allowances in A519, a tube’s ID might be non-concentric with its OD.

Example: Consider a tube with a 10” OD and 2.5” WT (nominal 5.000” ID). In this case, the tube’s ID can vary from 4.45” to 5.55” due to the allowance for OD (±.050”) and wall (±10% or ±0.250”) tolerance. This means a seamless tube might meet ASTM A519 tolerances, but not clean up to your finish size with every production run.

Off-Centered Tubing Cause Challenges

Steel manufacturers generally produce seamless tubing at near-nominal tolerances. However, owing to normal process variation and the nature of seamless tube manufacturing, this cannot be guaranteed.

It’s best to account for the edge-tolerance concentricity issues when ordering—a hot rolled tube that typically cleans up for your application might not work if it’s at the edge of A519 tolerances.

Sullivan Makes it Easy to Get the Steel Tubing You Need

At Sullivan, we want our customers to get seamless tubing that is sure to clean up. We ask for your finish OD, ID, and part length and use those dimensions to recommend a tube size that accounts for stock removal as well as ASTM A519 tolerancing.

Just let us know what you need to get to, and we’ll do the work to figure out how to get you there.

Reach out to the experts at Sullivan Steel today to take the guesswork out of ordering hot rolled seamless tubing.