Steel pipe schedule number (SCH)
- The definition of the steel pipe schedule number (Sch) is the pipe schedule number, code named Sch, which is defined as the ratio of the allowable stress of the steel pipe sub material under the design pressure to the design strength multiplied by 1000 and rounded. It is a code representing the series of steel pipe wall thicknesses.
- The source of the steel pipe schedule number (Sch) was first specified in the American standard ANSI/ASME B36.10 “WELDED AND SEAMLESS WROUGH STEAL PIPES” in 1938 and has been used ever since.
- The corresponding relationship between the steel pipe schedule number (Sch) and the steel pipe wall thickness is as follows: t=PD/1.75S+2.54. In the formula, t is the wall thickness in millimeters (mm), P is the design pressure in megapascals (MPa); D: Outer diameter, in millimeters (mm); S: The allowable stress of the material at the design temperature, in megapascals (MPa); 2.54: Corrosion allowance and thread depth, in millimeters (mm); 1.75:2 × (1-12.5%), 12.5% is the negative deviation of steel pipe wall thickness. Taking Sch=P/S × 1000, the wall thickness value corresponding to Sch number can be approximately obtained from the above equation. For example, the wall thickness corresponding to Sch40 is approximately equal to the calculated value of t=0.040D/1.75+2.54.
- The meaning of the steel pipe schedule number (Sch) is not the specific wall thickness, but the wall thickness series. The actual wall thickness of steel pipes varies depending on their diameter; The wall thickness of different Sch grades varies for the same steel pipe diameter. The steel pipe schedule number (Sch) to some extent reflects the pressure bearing capacity of the steel pipe, but it does not correspond to the accurate pressure bearing value of the specific material wall thickness. The introduction of steel pipe schedule number (Sch) can significantly reduce wall thickness specifications, which is beneficial for mass production, inventory, and procurement. The introduction of the steel pipe schedule number (Sch) simplifies the expression of steel pipe specifications and facilitates engineering design.
