Technical Tables and Calculators

Steam Pipe Capacity Table by Pipe Size, with Calculator

Saturated steam capacities of DN15–DN150 steel pipes from 0.1 to 100 bar g at 30 m/s, with the formula, velocity guidance and a pipe sizing calculator.

ORFA Technical TeamUpdated: Oct 30, 20266 min read

The steam pipe capacity of a line is the mass of saturated steam it can carry per hour at a given pressure and velocity. It is the first figure checked when sizing steam mains, branch lines and steam distribution manifolds: an undersized pipe leads to high velocity, noise, erosion and pressure drop, while an oversized one increases installation cost and heat losses.

The table below gives capacities of DN15–DN150 steel pipes at a steam velocity of 30 m/s for pressures from 0.1 to 100 bar g. Use the calculator to find the capacity for another velocity, pressure or bore, or to pick a pipe size for a required steam flow.

How Is Steam Capacity Calculated?

The steam mass flow through a pipe is the product of steam density, velocity and the internal cross-sectional area:

ṁ (kg/h) = 3600 × ρ (kg/m³) × v (m/s) × π × d² / 4

Here d is the inside diameter in metres. Because steam density rises quickly with pressure, the same pipe carries much more steam by mass at higher pressure. A DN100 pipe (bore 107.1 mm) at 30 m/s carries about 1,110 kg/h at 1 bar g but about 5,490 kg/h at 10 bar g.

Which Steam Velocity Should Be Used?

Saturated steam mains: typically 25–40 m/s; the table is based on 30 m/s.
Short branches and equipment connections: lower velocities may be preferred to limit noise and erosion.
Superheated steam lines: higher velocities are acceptable because there is no condensate.

Velocity alone is not enough: on long lines the pressure drop must also be checked to make sure the pressure at the end of the line is still sufficient for the consumers.

Tip: The capacities are for saturated (dry) steam. Base the sizing on the pressure needed at the end of the line; a long main sized at boiler outlet pressure will reach higher velocities downstream, as density falls with pressure.

Steam Pipe Capacity Table (kg/h at 30 m/s)

Steam Pipe Capacity Calculator

Steam pressure (bar g)Steam velocity (m/s)PipeInside diameter (mm)Required flow (kg/h, optional)

ṁ = 3600 × ρ × v × π × d² / 4. Saturated steam density is taken from IAPWS-IF97 and interpolated linearly between table pressures. Inside diameters are for EN 10220 (DIN 2448) standard wall thickness; enter the bore manually for other pipes.

Pressure (bar g)	Density (kg/m³)	DN15	DN20	DN25	DN32	DN40	DN50	DN65	DN80	DN100	DN125	DN150
0.1	0.653	17	28	45	77	103	165	274	377	635	961	1,410
0.3	0.762	19	32	52	89	120	192	319	440	741	1,120	1,640
0.5	0.870	22	37	60	102	137	219	365	502	846	1,280	1,870
1	1.136	29	48	78	133	179	286	476	656	1,110	1,670	2,450
2	1.658	42	70	114	195	261	418	695	957	1,610	2,440	3,570
3	2.169	55	91	149	255	342	546	909	1,250	2,110	3,190	4,670
4	2.675	68	113	184	314	421	674	1,120	1,540	2,600	3,940	5,760
5	3.175	81	134	219	373	500	800	1,330	1,830	3,090	4,670	6,830
6	3.673	93	155	253	431	579	925	1,540	2,120	3,570	5,400	7,910
8	4.660	118	197	321	547	734	1,170	1,950	2,690	4,530	6,860	10,000
10	5.642	143	238	389	662	889	1,420	2,370	3,260	5,490	8,300	12,100
12	6.621	168	279	456	777	1,040	1,670	2,780	3,820	6,440	9,740	14,300
14	7.599	193	321	524	892	1,200	1,910	3,190	4,390	7,390	11,200	16,400
16	8.578	218	362	591	1,010	1,350	2,160	3,600	4,950	8,350	12,600	18,500
18	9.558	243	403	659	1,120	1,510	2,410	4,010	5,520	9,300	14,100	20,600
20	10.540	268	445	726	1,240	1,660	2,660	4,420	6,090	10,300	15,500	22,700
22	11.526	293	486	794	1,350	1,820	2,900	4,830	6,650	11,200	17,000	24,800
25	13.011	330	549	896	1,530	2,050	3,280	5,450	7,510	12,700	19,100	28,000
30	15.509	394	654	1,070	1,820	2,440	3,910	6,500	8,950	15,100	22,800	33,400
35	18.042	458	761	1,240	2,120	2,840	4,550	7,560	10,400	17,600	26,500	38,800
40	20.614	523	870	1,420	2,420	3,250	5,190	8,640	11,900	20,100	30,300	44,400
50	25.895	657	1,090	1,780	3,040	4,080	6,520	10,900	14,900	25,200	38,100	55,700
60	31.385	797	1,320	2,160	3,680	4,950	7,910	13,200	18,100	30,500	46,200	67,600
70	37.116	942	1,570	2,560	4,360	5,850	9,350	15,600	21,400	36,100	54,600	79,900
80	43.126	1,090	1,820	2,970	5,060	6,800	10,900	18,100	24,900	42,000	63,400	92,800
100	56.149	1,430	2,370	3,870	6,590	8,850	14,100	23,500	32,400	54,600	82,600	121,000

Inside diameters used (EN 10220 / DIN 2448, standard wall thickness): DN15 = 17.3 mm, DN20 = 22.3 mm, DN25 = 28.5 mm, DN32 = 37.2 mm, DN40 = 43.1 mm, DN50 = 54.5 mm, DN65 = 70.3 mm, DN80 = 82.5 mm, DN100 = 107.1 mm, DN125 = 131.7 mm, DN150 = 159.3 mm.

Values are calculated for saturated steam at 30 m/s and rounded to three significant figures (kg/h). Pressures are gauge pressures (bar g).

Frequently Asked Questions

Can I size a steam main using this table alone?

The table is suitable for initial sizing by velocity. On long lines the pressure drop should also be calculated and the pressure at the end of the line checked against consumer requirements.

Why does the same pipe carry more steam at higher pressure?

Steam is compressible, so its density increases with pressure. At the same velocity and cross-section, the mass passing per unit time increases in proportion to density.

What about pipes with a different wall thickness?

Enter the actual bore of your pipe in the calculator. Capacity varies with the square of the inside diameter, so even a few millimetres make a noticeable difference.

Conclusion

A correctly sized steam line delivers dry steam in sufficient quantity and at the required pressure to every consumer. With the table and calculator you can quickly check capacity by pressure, velocity and pipe bore. For steam distribution, see our steam distribution and condensate collection manifolds product group.

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