Maximum Steam Velocities 1

[gjb1]

I have come across a statement saying that the velocity of steam should not exceed a certain % of the "Threshold Steam Speed".

Has anyone come across this term ? And if so what value is it referring to.

My normal "ruler of thumb" is that the maximum velocity of steam should not exceed 200ft/s or 60m/s. Is this assumption correct and what are the negatives associated with going over this value.

Thanks in Advance

 

[TD2K]

I'm not familar with the 'threshold steam speed' term.

If the steam is wet, then I've seen potential erosion problems listed at higher velocities (superheated steam typically has a higher allowable velocity in many company specs than saturated steam). 200 ft/sec is not an uncommon velocity limit for steam in my experience.

The only other problem I see with going with higher velocities is additional pressure drop. If that isn't a problem, such as doing into a pressure let-down valve, I'd be willing to look at dropping a line size and seeing what the resulting velocity is.

 

[SHARQ]

There Are No recognized velocity limits for dry vapor, on some liquid lines, velocity limitations override economic pressure drop criteria or the allowable pressure drop, This is true where excessive vibration or erotion would otherwise result. Erotion of metal is rare in carbon steel or stainless steel except at the extreme velocities encountered in reducing valves. However, erosion can occur in the following lines

1- Corrosive service
2- soft metal (copper alloys or lead)
3- Presence of abrassive solids in the process fluid.

For Steam , industerial practice of Max. vel. = 350 ft/sec

However, the velocity to determine the economic pipe size depends on Line pressure which range from 50-350 ft/sec.

Regards