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Steam Piping

How do I size pipe for Saturated Steam ? by MJCronin
Posted: 14 Nov 01 (Edited 15 Feb 03)

Time after time, the question seems to come up.... How does someone select pipe sizes for delivery of saturated steam ?

Well, the most widely used method is that contained in the Crane Technical Paper No. 410; "Flow of Fluids through Valves, Fittings and Pipe"

Under the section titled "Velocity of Compressible Fluids in Pipe" (page 3-14) There is a criteria for reasonable superheated and saturated steam velocities in piping.

These are:

     Saturated Steam  0 - 25 psig......4000-6000 fpm
     Saturated steam  25 psig and up...6000-10000 fpm
     Superheated Steam  200 psig and up..7000-20000 fpm

The equation used to determine velocity is:

     V = (3.06)W(sp. vol)/ ID^2

where V is velocity in fpm
      W is massflow in lbs/hr
      sp. vol is the specific volume of the steam
      ID is the internal diameter of the pipe

Crane also give a couple of nomographs that allow the novice to "graph his way" to a solution. (I have always hated nomographs.... They are an instrument of the devil)

Example:

What size pipe do I need for 20,000 lbs/hr of 100 psig saturated steam ?

Using a sp. vol of 3.875 and trying various pipe sizes we find out that a 6 inch, sch 40 pipe (ID=6.065) gives us a velocity of aprox 6457 fpm and is the appropriate size for this service.

(It should be also pointed out, that selected steam piping systems may require sizing by another criteria. The systems that typically requires a close evaluation are the "Main Steam" and "Hot Reheat Steam" to and from steam turbines.)

(These systems typically transport superheated steam and are sized based on the economic value of the pressure drop. Other criteria imposed on the design of the system is 2-5% maximum pressure drop between the boier steam drum and the turbine inlet valve.)

The superb Crane manual can be purchased for about $US30 bucks.... Any engineering book in a twenty sixth printing is wise investment

Call 630.226.4900 or see www.cranevalve.com

Good Luck


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