Velocity of Fuel Gas/Oil Line for Power Plant

A usually conservative rule of thumb is 1 m/s for liquids, 3 m/s for gases. But for extremes of density, viscosity, or pipeline length, you might want to check more closely with some pressure drop formula(s).

Another rule-of-thumb is that if a liquid velocity exceeds 3m/s, the line is undersized.

Another rule-of-tumb is that the velocity of non-polar highly-flammable liquids needs to be kept below 1m/s to avoid problems with static electrical charge build-up and risks of dissipation. Fuel oil falls outside this requirement.

My earlier rule of thumb was a bit off; try 3 m/s for liquids and 10 m/s for gases. Again this is only rough, and specific circumstances may vary.

[I don't want to vote myself 5 OT points, but maybe a 1-point OT vote or two would make sense.]

You are right. It is 1 m/s to 3 m/s for fluid and 6 m/s to 10 m/s for gas. I stay good with 1.5 m/s with liquid and 7 m/s with gas.