Steam Pipes Maximum Allowable Flow Pressure Drop
Reference data and engineering information about steam pipes maximum allowable flow pressure drop for fluid mechanics applications.
Overview
Steam pipe sizing depends on operating pressure and allowable pressure drop. The following reference data gives maximum steam flow rates—expressed in thousands of pounds per hour (10³ lb/h)—for mains and lateral branches across common pressure classes. Lateral branches permit higher velocities (and thus higher pressure drops per 100 ft) than mains, so their allowable flows are slightly greater at the same nominal pipe size.
Design Table
The original source table contains 14 HTML rows: 3 multi-row header lines, 10 pipe-size data rows, and one trailing width/layout row with empty cells. The migrated table below preserves all 10 engineering data rows for nominal pipe sizes 3 through 20 in, with blank source cells represented by omitted values where the original table had no 600 psi or 175 psi entry. The empty trailing row is documented here and not rendered as engineering data.
Nominal Pipe Size(in) | Mains 600 psi(10³ lb/h) | Mains 175 psi(10³ lb/h) | Mains 30 psi(10³ lb/h) | Laterals 600 psi(10³ lb/h) | Laterals 175 psi(10³ lb/h) | Laterals 30 psi(10³ lb/h) |
|---|---|---|---|---|---|---|
| 3 | 6.2 | 2.7 | 0.9 | 7.5 | 3.6 | 1.2 |
| 4 | 12 | 5.7 | 2.5 | 15 | 7.5 | 3.2 |
| 6 | 33 | 16 | 6.6 | 40 | 21 | 8.5 |
| 8 | 63 | 32 | 14 | 76 | 42 | 18 |
| 10 | 108 | 58 | 25 | 130 | 76 | 32 |
| 12 | 158 | 87 | 39 | 190 | 115 | 50 |
| 14 | 217 | 117 | 54 | 260 | 155 | 70 |
| 16 | 300 | 166 | 78 | 360 | 220 | 100 |
| 18 | — | 227 | 101 | — | 300 | 130 |
| 20 | — | — | 132 | — | — | 170 |
Source: engineeringtoolbox.com
Pressure Drop Basis
The flow limits above assume the following maximum pressure drops per 100 feet of pipe:
Line Type | Operating Pressure(psi) | Max Pressure Drop(psi/100 ft) |
|---|---|---|
| Mains | 600 | 0.7 |
| Mains | 175 | 0.5 |
| Mains | 30 | 0.3 |
| Laterals | 600 | 1 |
| Laterals | 175 | 0.7 |
| Laterals | 30 | 0.5 |
Source: engineeringtoolbox.com
Mains Flow vs Pipe Size
Maximum Mains Flow by Pipe Size
Engineering Notes
Steam Flow and Pressure Drop Converter
- Data scope. The table covers Schedule 40 / standard-weight carbon steel pipe. For Schedule 80 or stainless, consult manufacturer-specific pressure-drop curves.
- Why laterals carry more. Lateral branches tolerate a higher pressure drop per 100 ft (roughly 1.4 × the mains limit) because their shorter runs and intermittent demand produce less total system loss.
- Pipe size interpolation. Intermediate nominal sizes (e.g., 5 in, 7 in) can be estimated by interpolation, but always verify against actual pipe inside diameter and schedule.
- Steam quality. Values assume dry saturated steam. Superheated steam has lower density and may require adjustments. Wet steam (low quality) increases erosion risk and reduces effective flow capacity.
- Velocity limits. A common rule of thumb for saturated steam mains is 6,000–8,000 ft/min. Excessive velocity causes noise, erosion, and water hammer.
- Metric conversion. Multiply 10³ lb/h by 0.126 to obtain kg/s; 1 psi = 6,894.8 Pa; 1 ft = 0.3048 m.
References
- Steam Pipes — Maximum Allowable Flow Pressure Drop — Engineering ToolBox