Colors that identify the various grades of structural steel used to be established in ASTM A6/A6M.The requirement for color coding has been eliminated and is no longer required. ASTM A6/A6M Section 18 provides requirements for identification of structural products. Plates are marked with the ASTM standard, grade, heat, size, and brand. Shapes are marked with the heat, size, length and mill. Shapes with a cross section dimension exceeding 6 inches have the manufacturer’s name, brand or trademark in raised letters at intervals along the length. The ASTM standard designation and grade are indicated on the piece or if the pieces are bundled on a tag attached to the bundle.

Chemistry limitations and requirements are specified in certain ASTM specifications for structural steels, such as ASTM A36/A36M, A572/A572M, A588/A588M, A992/A992M, etc. Steel producers are required to report steel chemistry for each heat of steel produced on an MTR (see FAQ 1.3.1).

The most likely are differences between plate and bar (and sheet and strip). They are made using different rolls and different rolling practices. But the AISC Specification uses mechanical properties and treats these product forms as if they are the same. For structural steel building design and fabrication, this practice is safe and effective. Furthermore, plate is becoming a universally applied term. However, the historical classification system for such structural material would suggest the following physical difference: All four sides of a ½ × 4 bar would be rolled edges—i.e., the mill rolled it to that thickness and width. A ½ × 4 plate will have been cut from a ½-in. plate of greater width either by shearing or flame cutting.

Common mill lengths range from 30 ft to 65 ft in 5-ft increments. However, because individual mill practices and standards vary, it is best to consult with individual mills directly. When steel is purchased from a service center, the selection of available lengths may be further limited. Additionally, the method of shipment may also limit the available length.

Per Section 12.3.1 of ASTM A6/A6M, fillet radii are an unspecified dimension. As such, they are manufacturer-specific. Contact an individual manufacturer directly for additional information. AISC performs a periodic survey of producers’ practices to determine the minimum and maximum fillets used in shape production. The results of that survey are used to establish values in the AISC Manual, such as T, kdes, kdet and k1, which are detailing values. T, kdet and k1 are based upon the largest reported fillet radius, which ensures that potentially large fillet radii will not lead to fit-up problems. kdes is a design value based upon the smallest reported fillet, which ensures that the strength will not be overestimated in a design calculation no matter what the fillet size.

Round HSS are intended to be used as structural members. Pipe, though sometimes used as structural members, is intended to be used for mechanical and pressure applications. As used in the AISC Steel Construction Manual, steel pipe and round HSS are manufactured to meet different ASTM standards. Steel pipe is made to requirements in ASTM A53/A53M Grade B (Fy= 35 ksi).

Pipes up to and including NPS 12 are designated by the term Pipe, nominal diameter (in.) and weight class (Std., xStrong, xx-Strong). NPS stands for nominal pipe size. For example, Pipe 5 Std. denotes a pipe with a 5.563-in. outside diameter and a 0.258-in. wall thickness, which corresponds to the standard weight series. Pipes with wall thicknesses that do not correspond to the foregoing weight classes are designated by the term Pipe, outside diameter (in.) and wall thickness (in.), with both expressed to three decimal places. For example, Pipe 14.000·0.375 and Pipe 5.563·0.500 are proper designations.

Round HSS are usually ASTM A500/A500M Grade C (Fy= 50 ksi). They are available in cross sections matching each of the cross sections for ASTM A53/A53M Grade B steel pipe. For example, an HSS 6.625×0.280 has the same dimensional properties as a Pipe 6 Std. Additionally, ASTM A500/A500M HSS can be obtained in many more sizes with periphery not exceeding 88 in. and wall thickness not exceeding 1 in.

The tolerances on ASTM A500/A500M HSS also tend to be tighter than those on A53. For example, ASTM A53/A53M requires only that the pipe be reasonably straight, where ASTM A500/A500M places a specific tolerance on straightness. Also, ASTM A53/A53M specifically allows dents with depths up to the lesser of 10% of the pipe diameter or ¼ in.

Rectangular HSS are designated by the mark “HSS,” overall outside dimensions (in.) and wall thickness (in.), with all dimensions expressed as fractional numbers. For example, a square HSS should be designated as HSS8×8×3⁄8. A rectangular HSS should be designated as HSS5×3×3⁄8. Round HSS are designated by the term “HSS,” nominal outside diameter (in.) and wall thickness (in.) with both dimensions expressed to three decimal places. For example, a round HSS should be designated as HSS5.563×0.258.

Note that ASTM A53/A53M steel pipe designations (e.g., Pipe 5 Std., Pipe 5 x-strong, etc.) are designated differently than round ASTM A500/A500M HSS.