An article takes you to know what is pipe schedule (Sch)?
1.Definition of Pipe Schedule (Sch)
The pipe schedule number, abbreviated as Sch, is a numerical designation that represents the wall thickness series of pipes. It is defined as the ratio of the design pressure to the allowable stress of the pipe material under design conditions, multiplied by 1000 and rounded to the nearest whole number. Essentially, it is a code that helps in identifying the wall thickness of pipes used in various applications.
2.Origin of Pipe Schedule (Sch)
The concept of pipe schedule was first introduced in 1938 in the American standard ANSI/ASME B36.10, titled “Welded and Seamless Wrought Steel Pipe.” Since then, it has been widely adopted and continues to be used in the industry to this day.
ASME B16.9 Sch160 90 degree elbows
3.Relationship Between Pipe Schedule (Sch) and Pipe Wall Thickness
The wall thickness of steel pipes can be calculated using the following formula:
t=PD1.75S+2.54t = \frac{PD}{1.75S} + 2.54t=1.75SPD+2.54
Where:
ttt: Wall thickness, in millimeters (mm)
PPP: Design pressure, in megapascals (MPa)
DDD: Outer diameter, in millimeters (mm)
SSS: Allowable stress of the material at the design temperature, in megapascals (MPa)
2.54: Corrosion allowance and thread depth, in millimeters (mm)
1.75: A factor derived from 2×(1−12.5%)2 \times (1 – 12.5\%)2×(1−12.5%), where 12.5% is the negative deviation of the pipe wall thickness
Using the pipe schedule formula:
Sch=PS×1000\text{Sch} = \frac{P}{S} \times 1000Sch=SP×1000
The wall thickness value corresponding to a specific Sch number can be approximately obtained using the formula above. For example, the wall thickness for Sch 40 is approximately:
t=0.040D1.75+2.54t = \frac{0.040D}{1.75} + 2.54t=1.750.040D+2.54
SS316 SCH80 Pipe Nipples
4.Significance of Pipe Schedule (Sch)
The pipe schedule (Sch) does not indicate a specific wall thickness but rather a series of wall thicknesses. The actual wall thickness of a pipe varies with the diameter of the pipe; for the same diameter, different Sch numbers represent different wall thicknesses. While the Sch number provides an indication of the pipe’s pressure handling capacity, it does not correspond to the exact pressure capacity of a specific material’s wall thickness.
The introduction of the pipe schedule system has several benefits:
It significantly reduces the number of wall thickness specifications, facilitating mass production, inventory management, and procurement.
It simplifies the expression of pipe specifications, making it easier for engineers to design and specify the pipes needed for various projects.
In conclusion, the pipe schedule (Sch) is a vital coding system in the piping industry that standardizes the wall thickness of pipes, aiding in design, production, and application in various fields, including industrial and engineering projects.