A500 vs A36 Steel: Standards, Strength, and Applications

The main difference in A500 vs A36 steel is the product covered by each ASTM standard. ASTM A500 applies to cold-formed structural tubing, while ASTM A36 applies to structural shapes, plates, and bars. This distinction affects dimensions, strength values, certification, fabrication, and material substitution.

Engineers and buyers should therefore specify the complete standard, edition, grade, product form, and dimensions rather than treating A500 and A36 as interchangeable carbon steels.

What Is the Difference Between A500 and A36?

Their different product scopes lead to separate requirements for manufacturing, chemistry, mechanical properties, dimensions, testing, and identification.

Scope and Product Forms

ASTM A500/A500M-23 covers cold-formed welded and seamless carbon steel structural tubing in round, square, rectangular, and special shapes. Welded A500 tubing must be manufactured from flat-rolled steel by the electric-resistance-welding process.

The standard covers tubing with a maximum periphery of 88 in. [2,235 mm] and a maximum specified wall thickness of 1.000 in. [25.4 mm]. A500 products are normally ordered by actual outside dimensions and specified wall thickness rather than Nominal Pipe Size and Schedule.

ASTM A36/A36M-19 covers structural shapes, plates, and bars. Typical products include base plates, gussets, connection plates, angles, channels, and bars. A box member fabricated from A36 plate remains a built-up plate assembly; it is not automatically ASTM A500 tubing.

Buyers requiring hollow sections can review BAOLAI’s square and rectangular structural tubes. The order should identify whether ASTM A500, EN 10219, EN 10210, or another standard governs the finished section.

Chemical Composition

Both standards control elements such as carbon, manganese, phosphorus, sulfur, and copper, but their limits differ.

Under ASTM A500/A500M-23, Grades B and D have a maximum carbon content of 0.26% by heat analysis, while Grade C has a maximum of 0.23%. The base maximum manganese content is 1.35%, while phosphorus and sulfur are each limited to 0.035% by heat analysis. However, when carbon is below its specified maximum, the standard permits a corresponding increase in manganese, subject to a maximum of 1.50% by heat analysis. Product-analysis limits differ from the heat-analysis limits. The minimum copper requirement applies only when copper-containing steel is specified.

A36 limits depend on product form and thickness. Structural shapes have a maximum carbon content of 0.26%, while the requirements for plates and bars vary across thickness and width ranges.

The limits in either standard do not represent the exact composition of every heat. Welding and preheat decisions should use the chemical analysis reported on the material test report where a chemistry-based weldability assessment is required.

Grades and Mechanical Properties

The current ASTM A500/A500M-23 edition lists Grades B, C, and D. Grade A values found in older references should not be applied to an order governed by the 2023 edition.

* For A36/A36M plate over 8 in. [200 mm] thick, the minimum yield point is 32 ksi under A36 or 220 MPa under A36M. For wide-flange shapes with flange thickness over 3 in. [75 mm], the 80 ksi or 550 MPa maximum tensile-strength limit does not apply.

Inch-pound and SI values are separately standardized requirements. Each system must be used independently when determining compliance; values from the two systems should not be combined. Under A500/A500M, the inch-pound requirements apply unless the “M” designation is specified in the order.

A500 Grade D must be heat treated at a temperature of at least 1,100°F [590°C] for one hour per inch [25 mm] of thickness. Grades B and C may be stress relieved or annealed, but the standard does not impose grade-specific mandatory heat treatment on them.

A500 Grade C has a higher minimum yield strength than A36 under their general requirements, but this alone does not make every A500 member stronger. Capacity also depends on wall thickness, section properties, unsupported length, local buckling, loading, and connection design.

Where Are A500 and A36 Used?

A500 is commonly selected for hollow load-bearing members, while A36 is used for plates, bars, and covered structural shapes. Many assemblies use both materials because each performs a different function.

An assembly may therefore use an A500 column welded to an A36 base plate and connected through A36 gussets. The grade and dimensions of each component must follow the structural calculations and project drawings.

International projects may instead specify EN 10219, EN 10210, EN 10025, or local standards. These specifications can serve broadly corresponding functions, but their grades, tolerances, delivery conditions, toughness requirements, and design rules are not identical to ASTM requirements.

Can A500 and A36 Be Substituted or Welded Together?

A500 and A36 can generally be welded together under a suitable welding procedure. Substitution is a separate decision and requires engineering approval because changing the standard may affect the product form, geometry, tolerances, design resistance, and certification.

Material Substitution Requirements

A proposed substitution should be assessed against four areas:

• Product scope: The replacement must be a product covered by the proposed standard.
• Structural performance: Strength, section properties, stability, fatigue, and any required toughness provisions must remain acceptable.
• Fabrication: Dimensions, tolerances, connection details, welding, and coating must suit the assembly.
• Documentation: Material reports, markings, inspection records, and written approval must satisfy the contract.

A500 Grade C should not automatically replace A36 because its minimum yield strength is higher. It cannot compensate for an unsuitable section, inadequate connection, or missing project documentation. A36 plate likewise cannot replace specified A500 tubing without a revised design assessment.

Drawing Specifications and Material Certification

Drawings should assign the correct specification to each component. For example, a hollow member may be identified as ASTM A500/A500M Grade C, while its base plate is specified as ASTM A36/A36M.

An A500 description should include the edition, grade, shape, outside dimensions, wall thickness, length, and surface condition. An A36 description should include the edition, product form, section size or plate thickness, dimensions, and applicable supplementary requirements.

Material test reports and traceability records should identify the applicable heat or lot and be correlated with the delivered material. Product-marking requirements differ by standard: ASTM A500 does not generally require the heat number to be marked on every individual tube, and qualifying smaller sizes may be identified through a securely attached bundle tag.

If the contract requires a particular inspection document, such as an EN 10204 Type 3.1 inspection certificate, it must be stated separately rather than assumed from the ASTM designation.

Welding Compatibility

A500 tubing is commonly welded to A36 plates or shapes in structural frames. Suitability depends on the joint design, actual material chemistry, thickness, loading, and applicable welding code.

AWS D1.1 may govern projects using American structural welding requirements. Other markets may apply ISO-qualified welding procedures, EN execution requirements, or local codes. The project specification determines which rules apply to procedure qualification, welder approval, fabrication, inspection, and acceptance.

Filler metal must suit the welding process, required joint strength, base-metal combination, and service conditions. Its classification should be stated in the approved welding procedure.

Welding Procedure Variables

A welding procedure specification, or WPS, defines the conditions used to make the joint. It should identify both base materials and the permitted thickness range.

Important variables include:

• Welding process and filler-metal classification
• Joint type, backing, welding position, and fit-up
• Preheat and interpass temperature
• Current, voltage, travel speed, and heat input
• Shielding gas and post-weld heat treatment

Inspection methods and acceptance criteria should be specified separately under the governing code and project requirements; they are not WPS welding variables.

For a qualified WPS, Changes to essential variables require WPS requalification when specified by the governing code. Hollow-section joints also need suitable access, corner clearance, weld-seam positioning, and checks for local wall failure.

Additional Controls for Galvanized Material

Controls for welding galvanized material extend beyond the WPS variables. The fabrication plan should address removal of the zinc coating around the joint where required, suitable fume-control and worker-protection measures, and repair of the damaged coating under the applicable galvanizing or coating-repair specification.

How to Choose Between A500 and A36 for Engineers and Fabricators

Selection should begin with the component shown on the drawing. Strength is assessed only after the required product form and governing design rules have been established.

Further guidance on distinguishing hollow structural members from fluid-carrying pipe is available in BAOLAI’s explanation of structural pipe standards and selection.

For specification review or quotation, project teams can contact BAOLAI with the required material, dimensions, fabrication scope, quantity, surface treatment, and documentation requirements. These details support a review of production feasibility and quotation conditions.

Frequently Asked Questions

Can Square Tubing Be Certified to ASTM A36?

ASTM A36 is not a finished structural-tubing specification. Square tubing should normally be certified to ASTM A500 or another applicable hollow-section standard. A box fabricated from certified A36 plate should be described as a built-up A36 member, not A36 tubing.

Can ASTM A500 and ASTM A36 Steel Be Hot-Dip Galvanized?

Yes, both materials can generally be hot-dip galvanized when their chemistry, geometry, and fabrication are suitable. The applicable coating standard depends on the product form and galvanizing process. Enclosed hollow sections also require properly positioned vent and drain openings.

Does ASTM A500 Cover Pressure Pipe?

No. ASTM A500 is a structural-tubing standard and does not establish pressure ratings or pressure-service testing. Fluid, gas, fire-protection, and process systems require a pipe specification accepted by the governing piping code.

When Is Impact-Toughness Testing Required?

Impact testing is required when specified by the contract, design code, service standard, or material specification. Neither the basic A500 nor A36 designation provides a universal Charpy V-notch guarantee.

For low-temperature or fracture-sensitive service, the engineer must determine whether another material specification with established toughness requirements or project-specific testing is appropriate. Fatigue performance must be evaluated separately under the governing structural design code.

Is ASTM A500 Grade C Equivalent to ASTM A36?

No. The standards cover different product forms and requirements. Any proposed substitution requires engineering approval based on geometry, structural design, fabrication, service conditions, and documentation—not yield strength alone.

External Sources

• ASTM A500/A500M-23 Standard Specification for Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes
• ASTM A36/A36M-19 Standard Specification for Carbon Structural Steel
• AWS D1.1/D1.1M Structural Welding Code—Steel