Pipe Support Spacing: Suggested Maximum Spans

TECH NOTE 05 — PIPEANCHOR SUPPLY ENGINEERING · JULY 2026

How far apart can pipe supports be? For preliminary layout and BOQ estimating, industry practice starts from the suggested spans published in ASME B31.1 (Table 121.5) — the values reproduced below. They answer the estimator's question "roughly how many supports does this run need?" before any stress analysis exists.

Scope of this table: straight horizontal runs of standard weight carbon steel pipe, no concentrated loads between supports, water service or steam/gas service as tabulated. It is a layout aid, not a design verdict — hot lines, alloy materials and anything with valves in the span need engineering (more below).

Suggested maximum span table

SUGGESTED MAXIMUM SPANS PER ASME B31.1 TABLE 121.5 PRACTICE — STANDARD WEIGHT CS PIPE. VERIFY AGAINST YOUR PROJECT EDITION AND SPEC.
Pipe size NPS (DN)	Water service	Steam / gas / air
1" (DN25)	7 ft ≈ 2.1 m	9 ft ≈ 2.7 m
2" (DN50)	10 ft ≈ 3.0 m	13 ft ≈ 4.0 m
3" (DN80)	12 ft ≈ 3.7 m	15 ft ≈ 4.6 m
4" (DN100)	14 ft ≈ 4.3 m	17 ft ≈ 5.2 m
6" (DN150)	17 ft ≈ 5.2 m	21 ft ≈ 6.4 m
8" (DN200)	19 ft ≈ 5.8 m	24 ft ≈ 7.3 m
12" (DN300)	23 ft ≈ 7.0 m	30 ft ≈ 9.1 m
16" (DN400)	27 ft ≈ 8.2 m	35 ft ≈ 10.7 m
20" (DN500)	30 ft ≈ 9.1 m	39 ft ≈ 11.9 m
24" (DN600)	32 ft ≈ 9.8 m	42 ft ≈ 12.8 m

The two service columns exist because a water-filled line weighs far more per meter than the same pipe carrying steam or gas — spans shorten accordingly. If a gas line will ever be hydrotested in position, check the span for the water-filled condition too.

What shortens these spans

Concentrated loads. Valves, flange pairs, strainers and inline instruments need a support adjacent to the load — the table assumes bare straight pipe.
Insulation and lining. The tabulated values reflect the pipe and its contents; heavy insulation, refractory or internal lining adds weight the span must carry.
Thin-wall and non-CS materials. Schedule 10S stainless, alloy and non-metallic pipe deflect more — spans come down, sometimes sharply.
Direction changes. Place a support close to elbows and tees; a span across a corner behaves worse than a straight one.
Risers. Vertical pipe is supported by riser clamps at floors, not by span rules — a different design question.
Seismic and dynamic loads. Gravity spacing is only the start where seismic bracing applies — bracing spacing follows the project's seismic design, layered on top of the supports counted here. See our strut & seismic bracing range.

When the table is not enough

Hot lines change the question entirely: thermal movement decides what kind of support goes at each location, not just how many. That is where variable spring hangers, constant supports and sliding shoes and guides enter, selected from the stress analysis — the span table only positions the candidates. For that workflow, see the spring hanger selection guide.

Typical hanger rod sizes

Once support positions are set, rod-hung supports need rods sized to the load. Common minimum rod diameters used with MSS SP-58 practice hardware:

TYPICAL MINIMUM ROD DIAMETERS — CONFIRM PER PROJECT SPEC AND ACTUAL LOAD
Pipe size NPS	Typical rod diameter
Up to 2"	3/8" (M10)
2½" – 3½"	1/2" (M12)
4" – 5"	5/8" (M16)
6"	3/4" (M20)
8" – 12"	7/8" (M22)

Our threaded rods and hardware ship in metric and imperial threads, HDG, zinc plated or stainless, cut to length or in stock lengths.

Estimating a rack or a whole unit? Send the piping layout or line list to sales@pipeanchorsupply.com — we return a support count, bill of materials and quotation within 24 hours on working days.

Pipe Support Spacing: Suggested Maximum Spans

Suggested maximum span table

What shortens these spans

When the table is not enough

Typical hanger rod sizes

From span count to shipped supports