The basic size of steel refers to its length, width, height, diameter, radius, inner diameter, outer diameter and wall thickness. The legal units of measurement for steel length are meter (m), centimeter (cm) and millimeter (mm). Although inches (“) are commonly used in practice, they are not considered a legal unit of measurement.
1. Steel Size Range
Specifying the steel size range is an effective way to conserve materials. Range scale refers to the minimum length size or length multiplied by width, or the range of length and width sizes that can be delivered. The production unit can produce and supply steel as per specified size requirements.
2. Random length (normal length)
A product size (length or width) that is within the standard range but does not have a fixed size is called undefined. Random length, also known as normal length, refers to metal materials that can be delivered within a specified length range. For example, common round steel with a length of no more than 25 mm, typically ranging from 4 to 10 meters, can be delivered within this range.
3. Fixed length
Fixed length refers to cutting the metal materials into a specific size according to the order requirements. When delivering fixed-length materials, the length specified in the order contract must be met. For example, if the contract specifies a fixed length of 5 meters, the materials delivered must be 5 meters long, and materials shorter or longer than 5 meters will be considered non-conforming. In reality, it may not be possible to deliver materials that are exactly 5 meters long, so a positive deviation is allowed, but a negative deviation is not.
4. Double length
Double length refers to cutting metal materials into whole multiples of a specified size according to order requirements. When delivering materials in double length, the length of the materials delivered must be an integer multiple of the length specified in the order contract (known as single length) plus a saw bite.
For example, if the single length specified in the contract is 2 meters, the length would be 4 meters when cut into double lengths, 6 meters when cut into three lengths, with one or two saws added respectively. The amount of saw bite is specified by the standard. Only positive deviations are allowed and negative deviations are not allowed when delivering double length materials.
5. Short feet
Short length refers to materials that are shorter than the lower limit of the random length specified in the standard, but not shorter than the shortest length allowed. For example, the standard for steel pipes for water and gas transmission allows 10% of 2 to 4 meter steel pipes to be shorter in each batch. 4 meters is the lower limit of random length, while the minimum length allowed is 2 meters.
6. Strict rule
A narrow rule refers to a material whose width is less than the lower limit of the width specified in the standard, but not less than the narrowest width allowed. When delivering materials in narrow sizes, care must be taken to respect the proportion of narrow sizes and the narrowest size specified in the relevant standards. The diagram shows the steel production process.
7. Steel length measurement examples
7.1 Length dimension of steel section
- There are two standard lengths for railway tracks: 12.5 meters and 25 meters.
- The dimensions of round steel, wire rod and steel wire are calibrated in millimeters (mm) in diameter (D).
- The dimensions of square steel are calibrated in millimeters (mm) of side length (a).
- The dimensions of hexagonal and octagonal steel are calibrated in millimeters (mm) of the distance(s) from the opposite side.
- The dimensions of flat steel are calibrated in millimeters (mm) of width (b) and thickness (d).
- The dimensions of the I-beam and steel channel are calibrated in millimeters (mm) of waist height (h), leg width (b) and waist thickness (d).
- The dimensions of the equilateral angle are calibrated in millimeters (mm) of equal lateral width (b) and lateral thickness (d). The size of the uneven angle is calibrated in millimeters (mm) of side width (b, B) and side thickness (D).
- H beam dimensions are calibrated in millimeters (mm) of web height (h), flange width (b), web thickness (t1) and flange thickness (t2).
7.2 Measuring the length of steel sheets and strips
- The thickness (d) of a steel plate is normally calibrated in millimeters (mm). The width (b) and thickness (d) of a steel strip are also calibrated in millimeters (mm).
- There are several sizes for individual steel sheets, such as hot-rolled steel sheets: 1 millimeter thick with a width of 600 millimeters and a length of 2,000 millimeters; 650 x 2,000 millimeters; 700 x 1420 mm; 750 x 1500 mm; 900 x 1800 mm; 1000 x 2000 mm, etc.
7.3 Steel pipe length measurement
- The diameter (D), inner diameter and wall thickness(s) of a steel pipe are typically calibrated in millimeters (mm).
- Different types of steel pipes have various sizes. For example, seamless steel tubes have an outer diameter of 50 millimeters and a wall thickness of 2.5 to 10 millimeters. There are 29 different types with a wall thickness of 5 millimeters and an outer diameter of 32-195 millimeters. Another example is a welded steel pipe with a nominal diameter of 25 millimeters, including 3.25 millimeters ordinary steel pipe and 4 millimeters thick steel pipe.
