What Is ASTM A500 Steel Pipe?
ASTM A500, formally designated A500/A500M, is the standard specification for cold-formed welded and seamless carbon steel structural tubing in round, square and rectangular shapes. It is one of the most commonly specified products for steel construction in North America and is widely used worldwide for columns, trusses, bracing and framing members where predictable strength and stiffness are required.
The tubing is produced from hot-rolled or cold-rolled sheet and strip by cold forming and high-frequency electric resistance welding, or as seamless product. Square and rectangular sections are defined by their outside dimensions and wall thickness, while round sections are defined by outside diameter and wall thickness. Because the product is cold formed, the corner regions of shaped tubing are strengthened by the forming process, and the standard accounts for this in the minimum yield and tensile requirements.
Grades and Mechanical Properties
ASTM A500 defines four grades, A, B, C and D, with different minimum strength levels. Grade B is the most widely specified for general structural work, Grade C offers higher yield strength for more efficient sections, and Grade D provides a good balance of strength and ductility with improved weldability characteristics.
| Grade | Shape | Yield strength, min | Tensile strength, min |
|---|---|---|---|
| Grade A | Round | 33 ksi, 228 MPa | 45 ksi, 310 MPa |
| Grade A | Shaped | 39 ksi, 269 MPa | 45 ksi, 310 MPa |
| Grade B | Round | 42 ksi, 290 MPa | 58 ksi, 400 MPa |
| Grade B | Shaped | 46 ksi, 317 MPa | 58 ksi, 400 MPa |
| Grade C | Round | 46 ksi, 317 MPa | 62 ksi, 427 MPa |
| Grade C | Shaped | 50 ksi, 345 MPa | 62 ksi, 427 MPa |
| Grade D | Round | 36 ksi, 250 MPa | 58 ksi, 400 MPa |
Shaped sections show higher minimum yield values than rounds of the same grade because the corner work-hardening of cold-formed square and rectangular tubing increases its yield response. The carbon content is limited to support weldability, and the standard also covers tolerances for outside dimensions, wall thickness, straightness, length, squareness of sides and corner configuration.
Size Ranges and Tolerances
The standard covers a wide spectrum of sizes, from small mechanical tubing of roughly 1/2 inch up to large structural sections of 20 inches or more for rounds, with square and rectangular sections available in a correspondingly broad range. Wall thickness is selected from standard values and the minimum wall is controlled at the flat faces for shaped tubing. Key tolerances include outside dimension, out-of-roundness, wall thickness variation, twist for shaped sections, and sweep or straightness, all of which matter for fit-up in welded connections and for architectural applications.
Typical Applications
Building construction: columns, roof trusses, space frames, bracing and moment frames.
Infrastructure: highway sign structures, light poles, pedestrian bridges and barrier systems.
Equipment and machinery: agricultural implements, truck and trailer frames, racking, conveyor supports and material handling structures.
Architectural and recreational: handrails, guardrails, playground equipment, bleachers and exhibition structures.
Selection and Fabrication Points
Choose the grade based on the governing load combination: Grade B is the default for most structural applications, Grade C reduces member weight where strength governs, and Grade D is a good option where enhanced weldability and ductility are priorities.
For welding, match filler metal to the strength level of the tube and follow the requirements of the applicable structural welding code. For hot-dip galvanizing, discuss venting and draining hole requirements with the galvanizer so that shaped sections can be processed safely.
Verify that the specified wall thickness and corner radius are commercially available in the required size, since very heavy walls in small sections can be difficult to cold form.
Frequently Asked Questions
What is the difference between A500 pipe and A53 pipe?
A500 is a structural tubing specification with minimum yield and tensile requirements and cold-formed shapes, while A53 is a pressure and mechanical pipe specification that also allows hot-rolled and welded product. They are not interchangeable unless the design explicitly permits either.
Which A500 grade is most common?
Grade B is the most commonly specified because it offers a good combination of strength, weldability and availability. Grade C is selected when higher yield strength reduces material weight.
Is A500 square tubing weldable?
Yes, A500 tubing is designed for welding. Preheating is generally not required for ordinary structural thicknesses, and standard structural welding procedures apply.
Can A500 tubing be galvanized?
Yes, A500 tubing is frequently hot-dip galvanized. Shaped sections must have suitable vent and drain holes so that molten zinc can flow through the interior, and the galvanizer should confirm the hole layout before processing.
Does A500 include seamless tubing?
Yes, the standard covers both welded and seamless cold-formed carbon steel structural tubing, although welded product represents the overwhelming majority of supply.
What do the letters in the grade designation mean?
The letters simply identify the strength levels defined in the standard. They do not indicate chemical composition differences beyond the general limits, and the governing requirement is the mechanical property table plus the tolerances and supplementary requirements of A500.