DN100 Pipe Friction Loss and Velocity Table

Velocity and Hazen-Williams friction loss by flow for DN100 pipe. Loss values are in bar per 100 m, calculated on an internal diameter of roughly 102.3 mm.

Typical use: Main risers and supply lines.

Velocity and friction loss table (DN100)

Flow (L/min)	Velocity (m/s)	C=100	C=120	C=140
50	0.10	0.003	0.002	0.001
100	0.20	0.010	0.007	0.005
150	0.30	0.021	0.015	0.011
200	0.41	0.036	0.025	0.019
300	0.61	0.075	0.054	0.040
400	0.81	0.128	0.091	0.069
600	1.22	0.271	0.194	0.146
800	1.62	0.462	0.330	0.248
1200	2.43	0.978	0.698	0.525
1600	3.24	1.664	1.188	0.893
2400	4.87	3.524	2.515	1.891
3200	6.49	6.001	4.283	3.220
4800	9.73	12.704	9.067	6.817

The C factor represents internal pipe roughness. EN 12845 Table 22 gives, regardless of system type, 100 for cast iron, 110 for ductile iron, 120 for mild and galvanized steel, and 140 for stainless steel and copper. NFPA 13 Table 28.2.4.8.1 specifies 120 for black and galvanized steel in wet systems and 100 in dry and preaction systems (120 for dry systems using nitrogen, vacuum or a vapor corrosion inhibitor).

The calculation

Hazen-Williams in metric form: p = 6.05 × 10⁵ × Q^1.85 / (C^1.85 × d^4.87), where p is bar/m, Q is L/min and d is the mean internal diameter in mm (EN 12845 clause 13.2.1; NFPA 13 clause 28.2.4.8.1).

The relation has two consequences:

• Doubling the flow raises the loss by roughly 3.6 times (2^1.85).
• Going up one pipe size cuts the loss sharply; loss falls with the 4.87 power of diameter.

Velocity check

High velocity brings noise, water hammer and long-term erosion. The velocity column lets you see at a glance whether the chosen size stays in a reasonable range. Where the velocity comes out too high, the answer is a larger diameter. EN 12845 clause 13.2.3 limits velocity to 6 m/s through any valve, flow monitoring device or strainer and to 10 m/s at any other point in the system. In this table the velocity exceeds 6 m/s at 3200 L/min and above, so those flows cannot be used in sections containing valves or strainers.

How to use it

1. Determine the flow through this pipe section in the hydraulic calculation.
2. Read the bar per 100 m loss from the table at the appropriate C value.
3. Scale it to the actual length of the section.
4. Add the equivalent lengths of fittings and valves.
5. Add the elevation difference as static pressure.

Frequently Asked Questions

What C factor applies to DN100 pipe?

Use the value the standard gives for the pipe material and system type: 120 for steel pipe in EN 12845 Table 22; in NFPA 13 Table 28.2.4.8.1, 120 for steel in wet systems and 100 in dry and preaction systems. The table has separate columns for C=100, 120 and 140.

What happens to the loss if flow doubles?

It rises by roughly 3.6 times (2^1.85). Flow increases therefore affect loss more than expected.

Is the nominal size the same as the bore?

No. The table assumes an internal diameter of roughly 102.3 mm; a different wall thickness changes the bore and the loss.

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