Mittel offers A500 structural steel tubing in a range of sizes and shapes. The ASTM A500 specification covers cold-formed welded and seamless carbon steel tubing in round, square, rectangular, and “special” shapes for welded, riveted, or bolted construction applications, as well as for general structural purposes.
The aspects of the ASTM A500 specification that are most important for our purposes include:
Manufacture
ASTM A500 spec states that welded tubing shall be made from flat-rolled steel using electric-resistance welding. Longitudinal butt joints of welded tubing shall be welded across its thickness in such a manner as to assure the structural design strength of the tubing section. Welded structural steel tubing is normally furnished without the removal of inside flash.
Chemical Requirements
| Composition, % |
| Element | Grades A, B and D | Grace C |
| | Heat
Analysis | Product
Analysis | Heat
Analysis | Product
Analysis |
| Carbon, max | 0.26 | 0.30 | 0.23 | 0.27 |
| Manganese, max | ... | ... | 1.35 | 1.40 |
| Phosphorus, max | 0.035 | 0.045 | 0.035 | 0.045 |
| Sulfur, max | 0.035 | 0.045 | 0.035 | 0.045 |
Copper, when copper steel
is specified, min | 0.20 | 0.18 | 0.20 | 0.18 |
Tensile Requirements
| Round Structural Tubing |
| | Grade A | Grade B | Grade C | Grade D |
| Tensile strength, mn, ps (MPa) | 45 000
(310) | 58 000
(400) | 62 00
(427) | 58 000
(400) |
| Yield strength, mn, psi (MPa) | 33 000
(228) | 42 000
(290) | 46 000
(317) | 36 000
(250) |
| Elongation in 2 in. (50.8 mm), min, %A | 25B | 23C | 21D | 23C |
| Shaped Structural Tubing |
| | Grade A | Grade B | Grade C | Grade D |
| Tensile strength, mn, ps (MPa) | 45 000
(310) | 58 000
(400) | 62 00
(427) | 58 000
(400) |
| Yield strength, mn, psi (MPa) | 39 000
(269) | 46 000
(317) | 50 000
(345) | 36 000
(250) |
| Elongation in 2 in. (50.8 mm), min, %A | 25B | 23C | 21D | 23C |
Permissible Dimensional Variations
OUTSIDE DIMENSIONS
Outside diameter measurements must be made at positions at least 2” (50.8mm) from either end of the tubing.
For round structural tubing with nominal OD of 1.900” (48.26mm) and smaller, the outside diameter may not vary more than ±0.5%, rounded to the nearest 0.005” (0.13mm), of the specified size. For nominal ODs of 2” (50.8mm) and larger, outside diameter may not vary more than ±0.75%, rounded to the nearest 0.005”.
Square structural tubing and rectangular structural tubing must be measured across the flats and include an allowance for convexity or concavity. Specified dimensions shall not exceed the plus/minus allowances shown in the table below.
Outside Dimension Tolerances For Square and Rectangular Structural Tubing
| Outside Large Flat Dimension, in. (mm) | Large Flat Dimension Tolerance, A plus and minus, in. (mm) |
| 2½ (63.5) or under | 0.020 (0.51) |
| Over 2½ to 3½ (63.5 to 88.9), incl | 0.025 (0.64) |
| Over 3½ to 5½, inc | 0.030 (0.76) |
| Over 5½ (139.7) | 0.01 times large flat dimension |
WALL THICKNESS
Minimum wall thickness at any point of measurement shall not be less than 90% of specified nominal wall thickness. Maximum wall thickness, excluding weld seams, shall not be more than 110% of specified nominal wall thickness. Wall thickness of square structural tubing and rectangular structural tubing must be measured at the center of the flat.
STRAIGHTNESS
Permissible variation in straightness for structural tubing is 1/8” times the total length in feet (or 10.4mm times the number of meters) divided by five.
SIDE SQUARENESS
For square structural tubing and rectangular structural tubing, adjacent sides may deviate from 90° by no more than ±2°.
CORNER RADII
For square structural tubing and rectangular structural tubing, the radius of any one outside corner may not exceed three times (3x) the specified wall thickness.
TWIST
For square structural tubing and rectangular structural tubing, the tolerances for twist (variation with respect to axial alignment) are shown in the table below.
Twist Tolerances for Square and Rectangular Structural Tubing
| Specified Dimension of Longest Side, in. (mm) | Maximum Twist in the First 3 ft (1 m) and in each additional 3 ft |
| | in. | mm |
| 1½ (38.1) and under | 0.050 | 1.39 |
| Over 1½ to 2½ (38.1 to 63.5),incl | 0.062 | 1.72 |
| Over 2½ to 4 (63.5 to 101.6), incl | 0.075 | 2.09 |
| Over 4 to 6 (101.6 to 152.4), incl | 0.087 | 2.42 |
| Over 6 to 8 (152.4 to 203.2), incl | 0.100 | 2.78 |
| Over 8 (203) | 0.112 | 3.11 |
Twist is measured in one of two ways: 1) By holding down one end of a square/rectangular tube on a flat surface, with the bottom side of the tube parallel to the surface plate of the two corners at the opposite end of the bottom side of the tube; or, 2) By measuring this difference on the heavier sections by a suitable measuring device. Difference in the height of the corners must not exceed the values in the table above.
