Steam Pipe Velocity 2

[BarmEng]

There is a central plant which supplies me with Saturated Steam @ 125 psig. I would like to add another building at
one end of the loop. Is there a recommend maximum velocity for steam so I can size my lines properly

Thanks in Advance

 

[TBP]

On short runs (100 feet or so), in areas in which noise isn't a problem, you can hit 200 feet per minute for peak loads. On long runs (several hundred feet or more), you'll likely find that the pressure drop will get you before velocity becomes an issue. If you try to hit the 200 feet per second mark for peak useage, you'll find the pressure at the end of the run will be in the order of 75 PSIG on your 125 system. The greatly reduced supply pressure will have the effect of making all of your control valves too small, until the pressure comes back up.

Aim for something like a 10 PSI drop maximum on long runs.

 

[Keef]

TBP is correct as far as the pressure drop concern over longer runs of steam main. The pressure drop you can live with will depend on the pressure you require in the new building - I presume that you will be reducing down at each steam usage point anyway. For shorter runs, you can base your pipe sizing on a line velocity of 25m/s. I would prefer not to see line veolocities of 200ft/sec (61m/s) in a saturated steam line. The potential problems are errosion of the pipework if the steam does not have a high dryness fraction and, if the line is inadequately trapped, water hammer would be more likely. As a general rule, you should be looking at putting in a line trap set every 30m on a steam main and separators before control and reducing valves.

And don't forget about expansion as I have seen some people do in the past!

 

[quark]

Keef is right about velocity. 25m/s is generally used velocity. I prefer expansion bends at for every 50 meters length and steam traps at expansion bends. (this will be a strategic placement if you are taking your bends vertically)

Even if one provides pressure reducing stations, it is not better to drop pressure below 10psi (a good point TBP referred).

Regards,



Repetition is the foundation of technology

 

[TBP]

For the 10 minutes every couple of winters that a given building will see it's peak load, 200 ft/min works just fine. Bear in mind that this is PEAK load, not steady. I've sized many system like this for 20 years, and no problems so far, and that includes a record cold winter.

Given that most people in the chain err on the side of caution - building heat loss, actual heat emitters, the convertor station, etc - by the time the steam supply is sized to meet this, you get a grossly oversized installation in which control valves hunt themselves to death, steam meters usually run far below the bottom of their accurate range, and the whole steam installation costs FAR more than it should have.

I've lost track of how many building steam supplies I've seen that have a 6" supply line that we dropped to 2" inside the building, and then to 1-1/2" for the meter.

 

[LeaderP]

The following is published on page 3-16 of the Crane Technical Paper No. 410 which dates back to 1957 but is still widely used, even by some software programs such as Design Flow Solutions DesigNet.

Saturated Steam 0-25 psig 4,000 to 6,000 fpm
Above 25 psig 6,000 to 10,000 fpm

Superheated Steam 200 psig and up 7,000 to 20,000 fpm