velocity of sea water in pipes 1

[lomli]

Hi,

what value of velocity for sea water piping i should take for sizing a network to feed 8 heat exchangers all over a plant.

literatures give diffenet values

 

[MJCronin]

lomotil...

For a properly designed piping system, the desired velocity range depends on the piping materials, temperature, coatings, interior roughness etc

Can you tell us more about the piping system and the service....????

Desired velocities for FRP are significantly different than for Titanium

Eight heat exchangers, you say......hmmmmmmmmmmmmmmm?

"All over the plant"........hmmmmmmmmmm..???

-MJC

 

[BigInch]

For initial sizing, try values beteen 4 and 6 fps.

"Less than 1% of the energy moving a car goes towards the driver."
Amory Lovins - The Oil End Game

http://virtualpipeline.spaces.live.com/

 

[lomli]

there is a principal network which feeds heat exchangers by sea water to cool process fluids.

what material is to recomand for a sea water piping, vélocity.

sea water T = 25°C
air T = 45 °C.
T max at the exchangers inlets <= 28.5 °C

thank you

 

[lomli]

thank you "BigInch", my first simulation in hysys i used 1,4 m/s - 2.07 m/s but i the "Total_Company_Process_Eng_Design_Manuall" they say :
D<2" ==> 1.3 m/s
3">D>6" ==> 2.5 m/s
8">D>18" ==> 3.5 m/s
D>20" ==> 4m/s

but this book is very old I want to confirm these values?????
thank you

 

[BigInch]

Really you should determine the optimum pipe size based on energy cost of the head loss you get with each diameter and the cost of providing that head by running some kind of pump plus the cost of providing each pipe diameter.

The book might be considering those aspects using some given acceptable pressure loss for the "average" system.

For sizing a system, I would use a velocity that will not be too sensitive to waterhammer effects from closing valves, getting a relatively conservative diameter and not worrying too much about erosion, which shouldn't be too bad at 4-6 fps anyway, if sea water intake is not picking up too much sand, and if it is, use an interior coating.

You may be able to go to higher velocities, say 10 fps (3m/s) or even higer, if you want to take more chance and possible expense on mitigating water hammer effects and can handle a greater pressure loss in whatever length of pipe you have.

"Less than 1% of the energy moving a car goes towards the driver."
Amory Lovins - The Oil End Game

http://virtualpipeline.spaces.live.com/

 

[lomli]

Thank you " BigInch "

 

[strider6]

Velocity should be limited to avoid corrosion , erosion-corrosion or other forms of damage. Every materials has a proper velocity limits as you can see from this article.

here you can find a table with suggest velocity limits:

http://www.standard.no/pronorm-3/data/f/0/13/26/4_10704_0/P-001e5.pdf

MATERIALS SELECTION FOR HIGH RELIABILITY COPPER ALLOY SEAWATER SYSTEMS

http://www.copper.org/applications/cuni/txt_materials_selection.html

S

Corrosion Prevention & Corrosion Control

 

[Artisi]

Another factor that dictates velocity is pipe diameter which are manufactured to standard sizes, you can therefore have the situation where one pipe maybe be on the upper limit of your design velocity thereas the next size up is low and of course a lot more expensive.
For example 1000 USGPM -
6" ' ' ' = 11 ft/sec
8" ' ' ' = 6.5 ft/sec
10" ' ' ' = 4 ft/sec

For my thinking, selecting on velocity alone is not always the best solution, you need to consider the overall economics factoring in total head loss which reflects in the pumping costs, pump, pipe and valve costs, handling and installation, life of the pipeline(wear) etc.

There is really no problem with velocities at the higher end if the product is clean and friction losses are within manageable limits.

This is what BigInch has already pointed out and is normal practice when selecting pump systems:-

"BigInch (Petroleum) 12 Nov 08 14:12
Really you should determine the optimum pipe size based on energy cost of the head loss you get with each diameter and the cost of providing that head by running some kind of pump plus the cost of providing each pipe diameter."

 

[BigInch]

the OP said he was "sizing", so I figured he asked the wrong question. Erosion limit is something I check just after the system is "sized". You can do other things to increase erosion limits, but you can't beat energy useage over the long run, especially when your pipe is sized wrong.
10 years operating at the wrong BEP and pipe diameter can easily buy you a new pipeline.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic
"Note: Make that 99.99% for pipeline companies" -

http://virtualpipeline.spaces.live.com/