In the design of industrial piping and pressure vessels, understanding pipe Schedule (Sch) ratings and flange Class classifications is critical for ensuring safety and cost-effectiveness. This article provides a concise explanation of these key parameters to support engineers in selection and application.

1. Pipe Sch Rating: Definition and Application

Sch (Schedule) represents the ratio of design pressure to the allowable stress of the material at design temperature, multiplied by 1000 and rounded.

For example, if design pressure is 1MPa and allowable stress is 100MPa, Sch = (1/100)×1000 = 10, requiring a pipe of at least Sch.10

.As a rule of thumb, for materials with an allowable stress of approximately 100MPa, Sch.80 pipes can withstand 8MPa, while Sch.160 pipes resist 16MPa. This offers a quick reference for preliminary selection.

2. B16 Flange Class Ratings and Bolt Design

B16 flange Class ratings are based on the allowable stress of A105/WCB material at 454°C (60.3MPa or 8750PSI). The pressure rating is calculated as:

P₁ = (10S/8750) × Pr ≤ Pc

where S is the allowable stress of the flange material (MPa), and Pr is the Class value. For a Class 150 flange with S=100MPa, the allowable working pressure is approximately (10×100/8750)×150 = 17Bar (1.7MPa), equivalent to 1.7% of the material’s allowable stress.

Bolt areas for flange connections must satisfy:

Ab × 120MPa ≥ Ag × Pc,

where Ab is the bolt cross-sectional area and Ag is the sealing area within the gasket.

B16.5 standard flanges typically include generous bolt safety margins (e.g., A193-B7 bolts with a safety factor ≥6), eliminating the need for additional calculations when standards are followed.

Conclusion

A clear grasp of Sch and Class principles enhances accuracy and efficiency in selecting piping and flange components. Always verify designs against specific material properties and code requirements.