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ASTM A500/A500m Cold-Formed Welded and Seamless Carbon Steel Structural Tubing
1. Scope and Application:
This specification covers cold-formed welded and seamless carbon steel structural tubing in round (circular), square, rectangular, and "special" shapes (e.g., polygons).
Its primary application is for structural purposes in construction and engineering, such as:
Building frames and columns
Bridges
Support structures (e.g., sign posts, light poles, space frames)
It is not intended for pressure vessel applications or use as cylindrical tubing for boilers.
2. Manufacturing Process:
Tubing can be produced by two main methods:
Welded (Cold-Formed): The most common type. Formed from sheet or strip steel (skelp) and welded along the seam using electric-resistance welding (ERW) or electric-induction welding (EIW). The cold-forming process increases strength and improves surface finish.
Seamless: Produced without a weld seam by piercing a solid billet. Less common for structural shapes, often specified for applications requiring uniform strength in all directions.
3. Grades and Classification:
The standard defines several grades (A, B, C, D) with increasing minimum yield strengths. This allows engineers to select the optimal combination of strength and formability for a design.
Grades are differentiated primarily by their mechanical properties (yield and tensile strength) rather than their chemistry.
4. Chemical Composition Requirements:
The chemical composition (ladle analysis) is specified to ensure weldability, strength, and ductility. Maximum percentages vary by grade.
Key elements and their typical limits (e.g., for Grade B):
Carbon (C): 0.26% max
Manganese (Mn): 1.35% max
Phosphorus (P): 0.035% max
Sulfur (S): 0.035% max
Copper (Cu): 0.20% min (when copper steel is specified for enhanced atmospheric corrosion resistance)
5. Mechanical Properties Requirements:
Mechanical properties are the primary classification method and are tested on a full-section specimen of the tubing.
Key requirements include (values vary by grade and shape):
Tensile Strength: Minimum value required for each grade.
Yield Strength: Minimum value required for each grade. Higher grades have higher yield strengths.
Elongation: A minimum percentage to ensure sufficient ductility and the ability to withstand deformation without fracturing.
Example Mechanical Properties for Rectangular & Square Tubing:
Grade A: Yield Strength = 39 ksi (270 MPa), Tensile Strength = 45 ksi (310 MPa)
Grade B: Yield Strength = 46 ksi (320 MPa), Tensile Strength = 58 ksi (400 MPa)
Grade C: Yield Strength = 50 ksi (345 MPa), Tensile Strength = 62 ksi (425 MPa)
Grade D: Yield Strength = 36 ksi (250 MPa), Tensile Strength = 58 ksi (400 MPa) [Note: Grade D has a unique combination of lower yield but high tensile strength for specific forming applications].
6. Testing and Inspection:
Flattening Test: A sample of welded tubing is flattened to a specified distance to demonstrate the soundness of the weld and the ductility of the base metal without cracking.
Bend Test: For shapes other than round, a bend test may be required to demonstrate ductility.
Electrical Test (for Welds): A nondestructive test (e.g., eddy current or ultrasonic) is required on the weld seam of each finished welded tube to ensure its integrity and detect imperfections.
Tensile Test: Conducted to verify the mechanical properties of the material.
7. Dimensions and Tolerances:
The standard provides detailed tables for outside dimensions (O.D.), wall thickness, and length for all shapes.
It specifies strict tolerances for:
Outside Dimensions (e.g., for square tubes, the tolerance on width and depth)
Wall Thickness
Straightness (or camber)
Twist (for rectangular and square tubes)
Squareness of ends
Mass (Weight)
8. Certification and Marking:
The manufacturer must provide a Test Report (Mill Test Certificate - MTC) certifying that the product conforms to all requirements of the A500/A500M specification.
This report includes results for chemical analysis, mechanical tests, and details of the NDT performed.
Bundles are typically marked with the standard number, grade, heat number, size, and manufacturer's name.
9. Dual Designation (A500 / A500M):
The "M" designation in "A500M" indicates that the standard supports metric units (SI units).
"A500" (without the M) indicates the use of U.S. customary (inch-pound) units.
The choice of units must be specified in the order, and dimensions must not be mixed.
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