Both under and over sizing of steam mains has adverse impact on distribution. Long saturated steam distribution lines should be sized on pressure drop method.

The design of steam mains and the steam piping distribution network requires critical examination. The safety margins included should be on the basis of engineering inputs rather than speculation.

Over sizing steam main increases the material cost and erection cost (supports, insulation, etc). Importantly oversized steam main provides a larger heat transfer surface thereby increasing radiation losses.


Under sizing steam main leads to pressure drops and could lead to steam starvation in equipment. This impacts the process quality.

For long distribution lines limiting the pressure drop is critical and hence pressure drop method is suited for sizing these lines.


Illustration :

Line size

DN 80

DN 100

Material costs 20%

Heat losses 15%

Insulation costs 25%

Line size
DN 100

DN 80

Velocity 60%

Pressure drop 300%

Steam starvation - process product can get affected