Definition and Function of Pipe Schedule (SCH)
SCH (Schedule) is the wall thickness grade identifier for American standard piping systems, used in conjunction with Nominal Pipe Size (NPS) to standardize pipe wall thickness selection.
Unify the wall thickness representation rules for pipes of different diameters
Guarantee the safety and compatibility of pipelines under specified design pressure and temperature
Relationship Between SCH and Wall Thickness
SCH does not directly refer to the exact wall thickness value. The corresponding wall thickness for a specific pipe size needs to be queried from standard specifications (such as ASME B36.10M).
Early approximate formula (for reference only): SCH≈1000×P/S
P: Design pressure (psi)
S: Allowable stress of pipe material (psi)
Current Valid Standards
| Standard No. | Applicable Materials | Common SCH Grades |
|---|---|---|
| ASME B36.10M | Carbon steel, alloy steel | SCH 10, 20, 40, 80, 160 |
| ASME B36.19M | Stainless steel | SCH 5S, 10S, 40S (the suffix "S" stands for stainless steel exclusive) |
Significance of Standardization
The SCH system solves the mess of inconsistent wall thickness description for pipes of different diameters, and greatly improves the efficiency of pipeline design, manufacturing and maintenance.
SCH Labeling Rules and Practical Applications
Standard Labeling Format
Example: NPS 2" SCH 40
NPS: Nominal Pipe Size (in inches), which is not equal to the actual outer diameter of the pipe (for example, the actual outer diameter of NPS 2" pipe is approx 60.3mm)
SCH: Wall thickness grade, the higher the number, the thicker the pipe wall (e.g. SCH 80 has thicker wall than SCH 40 under the same NPS)
Common SCH Grade Comparison (Take NPS 2" pipe as an example)
| SCH No. | Wall Thickness (mm) | Typical Application Scenarios |
|---|---|---|
| 10 | 2.77 | Low-pressure fluid transmission (e.g. drainage) |
| 40 | 3.91 | Municipal water supply, natural gas transmission |
| 80 | 5.54 | High-pressure pipelines in chemical industry |
Key Notes
For the same SCH number, wall thickness varies with NPS (e.g. wall thickness of NPS 1" SCH 40 is not equal to that of NPS 2" SCH 40)
Selection Recommendations
SCH 20/30/40: Medium wall thickness, suitable for conventional pressure scenarios (water supply, domestic gas)
SCH 60/80: For harsh working conditions such as high-pressure transmission and chemical process pipelines
