# ASTM A500 Grade C tubing

Cold-formed structural tubing: edition-specific strength, nominal versus design wall thickness, procurement and fabrication boundaries.

Reviewed: 2026-11-01

Tags: materials, steel, structural-tubing, hss

## What the designation establishes

The **2021 A500 revision** raised round Grade C tubing from **46 to 50 ksi minimum yield**, aligning it with square and rectangular tubing. The **62 ksi minimum tensile strength** stayed the same. Use the ordered edition and mill records for existing structures or old stock. [AISC June 2022 guidance](https://www.aisc.org/globalassets/modern-steel/archives/2022/june2022.pdf), [Steel Tube Institute A500 table](https://steeltubeinstitute.org/resources/astm-a500/)

ASTM A500/A500M covers cold-formed welded or seamless carbon-steel structural tubing, including round, square, rectangular and special shapes. Its applications include general structural construction. The publisher lists **A500/A500M-23** as active, updated November 21, 2023. Its scope limits periphery to 88 in. [2235 mm] and specified wall to 1.000 in. [25.4 mm]. These are specification boundaries, not a promise that every combination is manufactured or stocked. [ASTM A500/A500M-23, public scope](https://store.astm.org/a0500_a0500m-23.html)

“Grade C” identifies a grade within that product specification. It does not specify a complete member: the order still needs shape, outside dimensions, nominal wall, length, edition, units, finish and certification requirements. For welded A500 tubing, the longitudinal seam is produced by electric-resistance welding from flat-rolled steel. [Steel Tube Institute, ASTM A500](https://steeltubeinstitute.org/resources/astm-a500/)

Do not treat an HSS designation as a pressure-pipe approval or a precision mechanical-tube tolerance specification. A structural drawing, a telescoping assembly and a pressure system ask different questions. Select the product specification for the application, then check the actual dimensional and certification requirements rather than relying on a supplier's broad “steel tube” category.

## Strength: distinguish current and historical rounds

The 2021 A500 revision aligned Grade C round tubing with shaped tubing:

| Grade C product | Minimum yield strength | Minimum tensile strength |
|---|---:|---:|
| Round, square and rectangular HSS under the revised requirements | 50 ksi | 62 ksi |
| Historical round Grade C requirement before the 2021 change | 46 ksi | 62 ksi |

AISC's June 2022 guidance explicitly identifies the change in round yield strength; STI's A500 summary reflects the 2021 requirements for all HSS shapes. These are specified minima, not typical mill-test results or allowable stresses. [AISC, Modern Steel Construction, June 2022, “Are You Properly Specifying Materials?”](https://www.aisc.org/globalassets/modern-steel/archives/2022/june2022.pdf); [STI, ASTM A500](https://steeltubeinstitute.org/resources/astm-a500/)

STI's August 2022 webinar reproduces the revised table, including SI entries of 345 MPa yield and 425 MPa tensile. ASTM treats SI and inch-pound systems independently; those table entries are not an instruction to replace specified values with freshly rounded unit conversions. Elongation entries also have footnotes: do not quote a headline percentage without its specimen, thickness and testing qualifications. [STI webinar, slide 13](https://steeltubeinstitute.org/wp-content/uploads/2022/08/STI_Webinar_Dos_and_Donts_HSS_1Slide.pdf); [ASTM, scope §1.3](https://store.astm.org/a0500_a0500m-23.html)

## Nominal, permitted and design wall thickness

STI explains the AISC treatment of A500 wall thickness: use **0.93 times nominal wall** in the referenced design calculations. This is a design convention associated with the product's wall tolerance, not a statement that each delivered tube measures exactly 93% of nominal. AISC Manual tabulated A500 section properties already incorporate the reduction; applying it again to those properties would double-count it. Connection calculations must also use the appropriate design thickness. [STI, December 2019 Chapter K questions and answers](https://steeltubeinstitute.org/resources/questions-answered-aisc-360-16-chapter-k-hss-connections/); [STI webinar, slide 15](https://steeltubeinstitute.org/wp-content/uploads/2022/08/STI_Webinar_Dos_and_Donts_HSS_1Slide.pdf)

Keep three questions separate: does delivered stock meet its dimensional tolerances, what thickness does the adopted design standard require, and what measured geometry is needed for fabrication? A design-thickness factor does not replace incoming inspection. Nor should nominal shipping weight be treated as proof of an individual member's wall thickness. Atlas's round-HSS tables explicitly separate nominal wall, design wall, nominal weight and area. [Atlas Tube, round A500 section properties](https://www.atlastube.com/wp-content/uploads/2018/04/A500-Round-Current.pdf)

**Illustrative arithmetic, not a member capacity:** assume a circular tube with outside diameter 4.000 in. and nominal wall 0.250 in. Using the cited 0.93 convention gives `td = 0.2325 in.`. An ideal annulus then has:

- `A = π × td × (D − td) = 2.752 in²`.
- Using nominal wall instead gives `2.945 in²`, about 7.0% larger than the design-thickness result.
- `50 ksi × 2.752 in² = 137.6 kip` is only the gross-section yield-force calculation.

It is not an allowable load or compression resistance. It includes no resistance/safety factors, buckling, effective length, net-section effects or connection checks. For a real member, use the adopted specification and applicable tabulated properties. For square and rectangular HSS, an ideal sharp-corner rectangle also misses the rounded-corner geometry.

## Fabrication, exposure and service qualification

A500's scope cautions that low-temperature notch toughness may matter in dynamically loaded welded structures and points to other specifications with Charpy requirements. Grade C yield strength alone therefore cannot establish suitability for a cold-service fatigue detail. Define the service temperature, loading and required toughness evidence before purchasing. [ASTM A500/A500M-23, scope note 1](https://store.astm.org/a0500_a0500m-23.html)

Connections deserve their own design checks; sizing a member does not qualify a welded branch or attachment. STI emphasizes that connection geometry and material applicability limits affect whether HSS connection equations can be used. Establish the load path and connection detail alongside member selection. [STI, HSS limits of applicability](https://steeltubeinstitute.org/resources/hss-limits-of-applicability/)

For hot-dip galvanizing, coordinate the complete fabrication with the galvanizer. STI warns that sealed HSS can burst during dipping and discusses cold-formed corner cracking. Venting, drainage and post-process inspection must suit the actual assembly; a generic hole size or an acceptable bare tube is insufficient approval of the galvanized fabrication. [STI, Galvanizing HSS](https://steeltubeinstitute.org/resources/galvanizing-hss/)

## Procurement and source versions

Retain the specification edition and mill certification with the member identification. Confirm actual producer capability for the size and grade; STI's capability tool locates manufacturing capability rather than guaranteeing local inventory. Record any additional toughness, coating, weld-location or fabrication requirements explicitly. [STI production capability tool](https://steeltubeinstitute.org/hollow-structural-sections/capability-tool/)

Sources include the **2023** ASTM listing and AISC’s **June 2022** article. The STI sources are its **©2022** webinar and its **December 2019** design explanation. The linked Atlas table does not supply an explicit edition date; its upload path is not treated as one. Confirm the project's adopted design code independently of these explanatory sources.

See also [grades, tempers and conditions](../grades-tempers-and-conditions.md).