Design velocity for steam 3

[MariusChE]

Hi

What is the standard velocity for steam in pipelines?

remove.marius@mailbox.co.za

 

[katmar]

I have Geankoplis on the corner of my desk at the moment and I see he recommends 9 to 23 m/s. I have used considerably higher velocities than these in previous designs and I am aware of many pipelines that have been around for 20+ years at higher velocites.

If your steam is dry and in the 2 to 30 bar range I think you would be very safe at 30-40 m/s. At the higher pressures the pressure drop may become limiting at these high velocities and therefore high mass fluxes.

In the sugar industry what they call "Vapor", which is basically steam below atmospheric pressure, is often sized for velocities around 50 m/s. Again, because there is not much pressure to play with, pressure drop may be more important.

If you know your steam is wet then drop down to 10 to 15 m/s.

I don't have my Crane 410 manual with me at present, but I'm sure it has a good table of typical velocities.

regards
Harvey

 

[davefitz]

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.

 

[friartuck]

Think of steam mains as motorways and side roads. The main roads are higher speeds than the side roads.

For steam mains in 'normal' systems i.e. not superheated etc but say hospital distribution, then 25-30m/sec would be ok. For small branches, drop the speed to around 15m/sec. Noise can occur and higher pressure drops.

CIBSE also work on pressure factors where a reasonable circuit pressure drop is used, but velocity methods yield practical results.

Also be careful how yoy drain the condensate, and make sure the steam main falls in the direction of the pipe run and not against it.

Go to Spirax Sarco for info

spiraxsarco.com or .co.uk i think



Friar Tuck of Sherwood

 

[saxon]

mariusCHe, Steam velocity ranges are dependant on the class of service. Here is a table of recommended velocities that I've used for designing steam lines. From the NAVCO Datalog:

Boiler & Turbine Leads: 9000 to 20000 ft/min
Extraction,Aux.&Exhaust lines: 6000 to 15000 ft/min
Low press, & Saturated Steam: 6000 to 10000 ft/min

Where the flow is steady the higher velocities can be used. If connected to reciprocating steam machinery where the flow is pulsating, lower velocities are required. The higher velocities are allowed with superheated steam, for saturated, lower velocities are required.

Hope this helps.
saxon

 

[rmw]

The site listed below has some recommendations for steam piping velocities for a variety of pressures.

http://www.sugartech.co.za

I will leave searching the site to you to find the link to "fluid flow velocities".

rmw

 

[MJCronin]

Marious,

There is an excellent, well worded FAQ dealing with saturated steam pipe sizing on this forum..

Did you read it ???

MJC

 

[25362]

Curiously enough while most process pipes are designed to avoid a mist flow regime, steam pipelines are so designed that any moisture drops therein are transported as a mist to avoid the use or misuse of steam traps.

 

[MariusChE]

Cronin

I did not read it. Where is it? There are possibly a thousand or more threads on the forum. Maybe a search function would be a good idea? If there is a search function then I do not know where to find it.

Marius

remove.marius@mailbox.co.za

 

[25362]

MariusChE, I think the reference is FAQ378-152. Right ?

 

[katmar]

The FAQs are at the very top of this thread, just below the title. You will see the tabs for Forum, Search, FAQs and Links.

Something that I did not make clear in my earlier post is that in the overwhelming majority of designs I would do my calculations on the basis of pressure drop first, and then check to see if the velocity criteria are met. Very rarely would I start with the velocity - if I were doing a very short pipe on a relief vent I would probably do it this way.

In the early stages of a project when you do not have run lengths you would use the velocity as a basis, but as the layout gets firmed up you should switch to rigorous pressure drop calcs. When we talk of an "economic" diameter it is basically a trade off between capital cost where small sizes are cheaper, and operating cost (ie pressure drop) where small sizes are more expensive. The velocity check is really just to ensure that you have selected a feasible solution to the economic problem.

 

[MariusChE]

Thanks for pointing me in the right direction.
Marius

remove.marius@mailbox.co.za

 

[rmw]

MariusChE,

The search function is at the very top of the page, right under the blue border that has the "eng-tips forum" logo in it. Click on the advanced search link at the far right of the search bar, and set up your search with the options given.

rmw

 

[25362]

The magazine Chemical Engineering Progress of April 1991 -under the section Fluids/Solids Handling- brings a 4-page article by Art Heming (Spirax Sarco, Inc.) titled Prolong the Service Life of Steam Distribution Systems covering the subject in hand.

 

[MariusChE]

Thanks 25362; I've asked our library to get it for us.

Best
M

remove.marius@mailbox.co.za

 

[quark]

http://www.spiraxsarco.com/learn/

Click on the modules link and go to distribution and enjoy.

 

[25362]

There is also an interesting (related) article in the ChE, March 14, 1977 issue by Mikasinovic and Dautovich titled Designing steam transmission lines without steam traps.

 

[onuigbo]

Most of the responses to this thread are reasonable, steam velocity will depend of the pressure, size of pipe and specific volume of the steam. But to be sure, get the "HVAC Data and Rules of Thumb" reference. It is an excellent source of technical information for steam piping designers. I wonder how any steam or HVAC engineer could live without it.

We deliver steam as if your life depends on it.