How to space pipe supports to MSS SP-58 and SP-69
Horizontal pipe sags under its own weight plus whatever it carries, and too much sag concentrates stress and traps condensate where the line should drain. Allowable spacing shrinks as the pipe gets larger and as the contents get heavier. This calculator uses the suggested support spacing published in MSS SP-58 and SP-69, the tables most US mechanical specifications point to.
| Size | Steel, water | Steel, steam or gas |
|---|---|---|
| NPS 1 | 7 ft | 9 ft |
| NPS 2 | 10 ft | 13 ft |
| NPS 4 | 14 ft | 17 ft |
| NPS 8 | 19 ft | 24 ft |
| NPS 12 | 23 ft | 30 ft |
These are upper limits for straight runs under uniform load. Valves, flanges, strainers and any other concentrated weight need a support close by regardless of the table, and so do changes of direction and both ends of an expansion joint. Copper is less stiff than steel and spans less, while thermoplastics such as PVC and CPVC lose allowable span quickly as temperature rises, so always use the manufacturer's table for those. Seismic bracing, vibrating service and high-temperature lines call for a separate stress analysis, so have a mechanical engineer or the authority having jurisdiction confirm the final layout.
Frequently Asked Questions
The same pipe filled with water is far heavier and deflects more. Steam and gas add almost no weight, so the same size can span farther between hangers.
No. A riser is carried rather than kept from sagging, so it is normally supported with riser clamps at each floor level or at each floor penetration under a separate rule.