Quick Answer
Quick Answer
ASTM A500 covers cold-formed welded and seamless carbon steel structural tubing in round and shaped (square, rectangular, and special) cross-sections. Four grades — A, B, C, and D — are defined by minimum yield and tensile strength. Grade B is the most commonly specified for hollow structural sections (HSS), with a minimum yield of 317 MPa (46 ksi) for round and 317 MPa for shaped sections. Grade C offers higher strength at 345 MPa minimum yield.
ASTM A500/A500M is published by ASTM International and is the primary North American specification for cold-formed structural hollow sections (HSS). It covers tubing produced by cold-forming flat-rolled steel coil into a round shape, welding the seam, and then (for shaped sections) reforming the round into square, rectangular, or special cross-sectional profiles. A500 tubing is widely used in building construction, sign structures, vehicle frames, transmission towers, and light-duty industrial equipment.
Scope and Applicability
A500 applies to:
- Cold-formed welded and seamless carbon-steel tubing
- Round, square, rectangular, and special cross-sections
- Structural applications (building frames, trusses, columns, braces)
- Outside diameter range: 12.7 mm to 406 mm (round); custom dimensions for shaped
The standard does not cover:
- Hot-formed structural hollow sections (those are covered by ASTM A501)
- Mechanical tubing (ASTM A513)
- Pressure-service tubing
Grade Coverage
A500 defines four grades, each available in both round and shaped cross-sections. The mechanical requirements differ between round and shaped forms within each grade.
| Grade | Primary Use | Relative Strength |
|---|---|---|
| A | General purpose; rarely specified | Lowest strength |
| B | Most common; standard structural HSS | Medium-high |
| C | Higher-strength applications; weight-optimized designs | High |
| D | Special applications; normalized condition | High (tighter chemistry) |
Chemical Composition Requirements
ASTM A500 — Chemical Composition (wt%, ladle analysis, all grades)
| Element | Grade A | Grade B | Grade C | Grade D |
|---|---|---|---|---|
| C max | 0.26 | 0.26 | 0.23 | 0.23 |
| Mn max | 1.35 | 1.35 | 1.35 | 1.35 |
| P max | 0.035 | 0.035 | 0.035 | 0.035 |
| S max | 0.035 | 0.035 | 0.035 | 0.035 |
| Cu min (when copper-bearing steel is specified) | 0.20 | 0.20 | 0.20 | 0.20 |
Notes:
- Grade C and D have a lower maximum carbon (0.23%) compared to A and B (0.26%), improving weldability.
- Grade D is typically produced from killed steel with fine grain practice; the standard does not restrict the use of microalloying additions (Nb, V, Ti) in any grade, provided mechanical requirements are met.
- No Si limit is specified in A500; silicon is controlled by the steelmaker to meet mechanical properties.
Mechanical Properties
Round (Circular) Sections
| Grade | Min Yield Strength MPa (ksi) | Min Tensile Strength MPa (ksi) | Min Elongation in 50 mm % |
|---|---|---|---|
| A | 228 (33) | 310 (45) | 25 |
| B | 317 (46) | 400 (58) | 23 |
| C | 345 (50) | 427 (62) | 21 |
| D | 317 (46) | 400 (58) | 23 |
Shaped (Square, Rectangular, and Special) Sections
| Grade | Min Yield Strength MPa (ksi) | Min Tensile Strength MPa (ksi) | Min Elongation in 50 mm % |
|---|---|---|---|
| A | 269 (39) | 310 (45) | 25 |
| B | 317 (46) | 400 (58) | 23 |
| C | 345 (50) | 427 (62) | 21 |
| D | 317 (46) | 400 (58) | 23 |
Key observation: For Grade A, shaped sections have a higher minimum yield (269 MPa) than round sections (228 MPa). This results from the cold-work strengthening that occurs during the forming of corners in shaped sections. Grades B, C, and D have identical YS requirements for round and shaped because their specified YS is already higher than the as-rolled base material, accounting for this effect in design.
Wall Thickness and Size Tolerances
Outside Diameter Tolerances (Round)
| OD Range | Tolerance |
|---|---|
| OD ≤ 48.3 mm | ± 0.40 mm |
| OD > 48.3 mm to ≤ 101.6 mm | ± 0.79 mm |
| OD > 101.6 mm to ≤ 203.2 mm | ± 1.59 mm |
| OD > 203.2 mm | ± 0.75% of OD |
Width and Height Tolerances (Shaped — Square/Rectangular)
| Dimension Range | Tolerance |
|---|---|
| ≤ 63.5 mm | +0.76 mm / −0.38 mm |
| > 63.5 mm to ≤ 127 mm | +1.52 mm / −0.76 mm |
| > 127 mm to ≤ 254 mm | +2.29 mm / −1.14 mm |
| > 254 mm | +3.18 mm / −1.59 mm |
Wall Thickness Tolerance
| Wall Thickness | Tolerance |
|---|---|
| All thicknesses | −10% of specified wall, no positive limit (mass-based acceptance) |
Note: Wall thickness tolerance is a minimum-only specification (no positive limit). The actual average wall must be consistent with the ordered mass (weight per foot), which is the controlling dimension for structural design purposes.
Corner Radius (Shaped Sections)
Outside corner radius for shaped sections: 3t max (where t = specified wall thickness). This is relevant for calculating effective section properties in structural analysis.
Heat Treatment Condition
A500 Grades A, B, and C are produced in the as-cold-formed (as-welded) condition. Grade D may be produced in the normalized condition, but normalization is not mandatory unless specified on the purchase order.
When normalized (Grade D):
- Normalizing temperature: typically 870–955 °C, air-cooled
- Normalizing improves uniformity of properties and toughness
- The MTC should state the heat treatment condition
Additional Tests and Requirements
- Bend test: Not required for A500.
- Flattening test: Required for round tubing — a section is flattened until the distance between platens equals 60% of the OD (for Grades A and B) or 50% (for Grades C and D), with no cracking in the weld area.
- Hydrostatic or nondestructive electric test: Each length must pass either a hydrostatic test or NDET (nondestructive electric test). The NDET is standard for structural tubing.
- Weld seam: The weld seam in electric-resistance-welded (ERW) tubing must be properly processed (weld flash removed from the interior on tubing where required).
ASME Equivalent
There is no direct ASME Boiler and Pressure Vessel Code equivalent for A500, as A500 is a structural specification and is not listed in ASME Section II. For structural hollow sections used in pressure equipment support structures, the engineer of record specifies A500 directly by its ASTM designation. When structural tubing is used as a pressure-retaining component, ASTM A618 (hot-formed HSLA) or A501 (hot-formed carbon steel) may be more appropriate.
Cross-Standard Equivalents
By Grade Strength Level
| A500 Grade | EN 10219-1 | EN Description | IS 1161 | JIS G3466 | Notes |
|---|---|---|---|---|---|
| Gr A (round) | S235NH | Cold-formed welded HSS, 235 MPa | YSt 210 | STKR400 (approx) | Close match; EN Si and Mn differ |
| Gr A (shaped) | S275NH | — | YSt 240 | — | A (shaped) YS closer to S275 |
| Gr B | S355NH | Cold-formed welded HSS, 355 MPa | YSt 310 | STKR490 | Most common EN equivalent |
| Gr C | S355NH / S420NH | S420NH for higher-strength designs | YSt 355 | — | S355NH is minimum; S420 for Gr C |
| Gr D | S355NH (normalized) | Normalized cold-formed HSS | YSt 310 | — | Equivalent heat treatment condition |
EN 10219 Grade Designation Suffix:
- NH = normalized or thermomechanically rolled (cold-formed, direct-cooled)
- NLH = normalized, low-temperature toughness version
For procurement equivalence, A500 Grade B is most commonly matched to EN 10219 S355J2H (355 MPa YS, Charpy tested at −20 °C) in international projects.
IS 1161 Equivalents (Indian Standard)
| A500 Grade | IS 1161 Grade | YS min MPa |
|---|---|---|
| Gr A | YSt 210 | 210 |
| Gr B | YSt 310 | 310 |
| Gr C | YSt 355 | 355 |
MTC Verification Checklist
When verifying a mill test certificate for A500 tubing, confirm:
- Standard designation, grade, and section type (round or shaped) match the purchase order
- Heat number is traceable to physical markings on the tube
- Carbon complies with grade-specific limit (0.26% for A/B, 0.23% for C/D)
- Mn, P, S are within limits for all grades
- Yield strength meets the grade minimum for the applicable section type (round vs shaped)
- Tensile strength meets the grade minimum
- Elongation meets the 50 mm gauge-length minimum
- Flattening test result (pass/fail) reported
- NDET or hydrostatic test result reported
- Dimensions: OD (round) or width/height (shaped) are within A500 tolerance
- Wall thickness: nominal wall is stated and within −10% tolerance
Frequently Asked Questions
What is the most commonly specified ASTM A500 grade for structural hollow sections (HSS)?
Grade B is by far the most commonly specified grade for structural HSS in North American building and bridge construction. It has a minimum yield strength of 317 MPa (46 ksi) and minimum UTS of 400 MPa (58 ksi) for both round and shaped sections. Grade C (345 MPa YS) is used when higher strength is required to reduce wall thickness or weight.
Why does ASTM A500 Grade A have different yield strengths for round and shaped sections?
Cold-forming a round tube into a square or rectangular shape induces additional work-hardening at the corners and along the flat faces. This increases the yield strength of shaped sections above what the material has in round form. A500 reflects this by specifying a higher minimum yield (269 MPa vs 228 MPa) for Grade A shaped sections. Higher grades already have elevated base-material strength, so the cold-forming increment is relatively less significant.
What is the EN 10219 equivalent of ASTM A500 Grade B?
EN 10219 S355J2H is the most commonly cited equivalent. Both specify a minimum yield strength of approximately 317–355 MPa for cold-formed structural hollow sections. The key difference is that EN 10219 S355J2H requires Charpy V-notch impact testing at −20 °C (27 J minimum), while A500 Grade B does not require Charpy testing unless specified as a supplementary requirement.
Is ASTM A500 tubing suitable for pressure vessel applications?
No. A500 is a structural specification and is not listed in ASME Boiler and Pressure Vessel Code Section II. It is not approved for pressure-retaining components. For pressure service tubing in square or rectangular cross-section (rare), ASTM A500 would need an engineering deviation. Standard pressure tubing for round cross-sections uses A106 (seamless), A53 (welded/seamless), or API 5L depending on the service.
What corner radius should be assumed for ASTM A500 shaped sections in structural calculations?
ASTM A500 specifies a maximum outside corner radius of 3t (three times the wall thickness) for shaped sections. For section property calculations (moment of inertia, section modulus), designers typically use the AISC Steel Construction Manual tabulated values for HSS, which assume a specific corner radius and wall thickness measured at the flat face. The actual corner radius from the producer may be less than 3t.
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