There are several different criteria to consider, depending on the application .
In the power industry, the velocity is usually based on limiting the pressure drop. Typical values may be to limit the pressure loss in the steam transfer pipes to 2.5% for HP main steam, 2% for hot reheat, 1.5% for cold reheat, etc. For a 200 ft lng pipe with 10 x 90 deg els the design velocity may be 200 fps.
In turbine bypass piping, noise and erosion are limiting factors. The bypass inlet pipe max velocity may be 325 fps ( to limit dynamic forces on bypass valve plug) and outlet velocity of 200 fps ( to limit erosion by wet steam from attemporator).
For simple drains dumping to flash tanks or condensers, an inlet velocity of 30% soundspeed ( mach=0.3) is typical.
For relief valve vent stacks, pressure drop governs to ensure the back pressure on the relief valve does not exceed permitted values.