What Channel Steel Is
Channel steel is a hot-rolled long product with a U-shaped cross-section, formed by a vertical web and two horizontal flanges that are turned in the same direction. The shape puts material where bending demands it, which gives a high strength-to-weight ratio for purlins, bracing, lintels, machine frames and vehicle chassis. Compared with an I beam of the same depth, a channel accepts bolted connections easily on the flat web and flanges, and it is stiff about the axis parallel to the web.
Designation and Dimensional Standards
Sizes are quoted in millimetres as web height (h) x flange width (b) x web thickness (d). A 100 x 48 x 5.3 channel is therefore 100 mm high, 48 mm wide over the flanges and 5.3 mm thick at the web; the same section is known in the trade as a 10# channel. Hot-rolled dimensions, mass and permissible deviations are controlled by GB/T 706 for the Chinese series, by EN 10279 for hot-rolled channels under European practice, and by ASTM A6/A6M for inch-series channels. Material grades are selected from GB/T 700 for carbon structural steel, GB/T 1591 for high-strength structural steel, EN 10025-2 for European grades and ASTM A36 or ASTM A572 for inch-series work.
Common Sizes and Mass per Metre
| Designation | h x b x d, mm | Theoretical mass, kg/m |
|---|---|---|
| 10# | 100 x 48 x 5.3 | 10.007 |
| 12# | 120 x 53 x 5.5 | 12.059 |
| 14a# | 140 x 58 x 6.0 | 14.535 |
| 16a# | 160 x 63 x 6.5 | 17.240 |
| 20a# | 200 x 73 x 7.0 | 22.637 |
Ordinary hot-rolled channels are normally stocked from 5# to 40#, and light channels are supplied against agreement between buyer and mill. Theoretical mass is calculated from nominal dimensions and is the basis for invoicing; the permitted deviation between theoretical and actual mass is fixed by the applicable dimensional standard, so a weighing clause should be agreed before shipment where mass is critical.
Grades and Delivery Condition
Channels for general structures are usually supplied in Q235B or S235JR, while loaded frames, crane supports and transport equipment move to Q355B, S275JR or S355JR and, for low-temperature service, to S355J0 or S355J2. ASTM A572 Grade 50 channels are ordered where a higher yield point is needed in an inch-series section. Sections are delivered hot rolled, and where a finer grain or a specified impact energy is required they are supplied normalised or in a controlled-rolling condition. Welding, riveting and cold working characteristics are part of the specification for these grades, and the carbon and sulfur limits that control them are stated in GB/T 700 and GB/T 1591.
Applications and Fabrication Practice
Building structures, curtain wall framing, equipment skids, conveyor galleries, ship and trailer frames all consume channel in quantity, often paired back to back or boxed with a second channel to build a closed section of much greater torsional stiffness. Fabricators should allow for the taper of the inside flange face when a nut or bolt head must sit flat, and should keep holes away from the flange toe where the section is thinnest. Straightness, out-of-square and flange taper are limited by the dimensional standard and should be quoted in the purchase order, together with the length tolerance and the required surface treatment such as black, shot blasted or primed.
Frequently Asked Questions
Q: What does 10# channel steel mean?
A: It is the trade designation for a channel with a 100 mm web height, commonly rolled as 100 x 48 x 5.3 mm with a theoretical mass of 10.007 kg/m.
Q: What is the difference between ordinary and light channel steel?
A: Light channel has thinner webs and flanges at the same web height, so it is lighter but carries less load; the dimensional ranges and the permitted deviations are agreed between buyer and supplier.
Q: Which standards cover the dimensions of channel steel?
A: GB/T 706 for the Chinese hot-rolled series, EN 10279 for hot-rolled European channels, and ASTM A6/A6M for inch-series channels.
Q: Can channel steel be welded directly to an I beam?
A: Yes, provided the welding procedure is qualified for the grade and thickness involved; grades such as Q235B and S235JR weld readily, and the higher-strength grades are welded with preheat based on the carbon equivalent on the mill certificate.
Q: How is channel steel invoiced?
A: Normally on theoretical mass calculated from nominal dimensions, with the permitted deviation between theoretical and actual mass set by the dimensional standard.
Q: What lengths are available?
A: Standard mill lengths are generally 6 m to 12 m, and cut-to-length supply is arranged to the tolerance stated in the order.