Piping cautions for high velocity seawater 2

[AoA]

Hi,

I am going to start piping for a project for which I found following details in process calculation sheet:

seawater intake; pipe size 24"; velocity inside pipe is more than 25 meters per second.
temperature is 30 Celsius. material is going to be super duplex or some other exotic expensive material.

Above is the maximum pipe size so if I know answers for this I would be able to manage others.

Please tell me if because of high velocity I have to apply special techniques in piping or if certain pipe routing practices are to be avoided.
And NPS 24 pipe routing is new to me. What are things to consider.

Your experience and knowledge would be beneficial.

Thanks.

 

[EmmanuelTop]

With 25 m/sec and 24" line you are going to pump out the entire ocean in a matter of days. This velocity is beyond any meaningful range.
Check with Process guys - maybe they just forgot to type a dot between 2 and 5 in the velocity number.

Dejan IVANOVIC
Process Engineer, MSChE

 

[bimr]

The recommended flow range for SS in seawater applications is 4-8 ft/sec.

http://www.stainless-steel-world.net/pdf/11003.pdf

 

[BigInch]

At that velocity water hammer is likely to be your worst problem.

 

[georgeverghese]

At 24inch in superduplex, a lot of fittings and valves may be long lead - another option may be parallel intakes / feeders of smaller size?

 

[AoA]

Thank you all for the technical info.

The project is going to be one of the largest so there is big flow however mentioned velocity has to be checked.

Process Engr. will be available after a week and i will update you guys about his response.

 

[BigInch]

No it doesn't. Don't waste your client's time. It is too high. Simple as that.

 

[MJCronin]

Once again, this noble forum rises up to perform it's primary purpose ......... explaining typos to demanding newbies

MJCronin
Sr. Process Engineer

 

[bimr]

Wonder if the process engineer is able to read a reference from the stainless steel manufacturers and make sense of it. Guess the problem is that the newbies are building the largest whatever.

 

[LittleInch]

If indeed it is twenty five m/sec, this equates to 24,500 m3/hr(!!)

That is some flow rate.

This is far too high a flowrate to be economically feasible or practical.

Even super duplex will suffer erosion and stripping of the corrosion resistant layer at that speed.

will be interesting to see if this becomes more realistic.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Unit pressure drop works out to be 21psi/100ft at 25m/sec - too high.
At 8m/sec, dp = 2.4psi/100ft.
It may well be that the process engineer is trying to maximise on the capabilities inherent with 25Cr superduplex, but unit pressure drop, high momentum stresses on piping supports (rho-v2 = 625e3 >> 200e3 in SI units) and probably water hammer also might get in the way.

 

[rconner]

I am just curious why this is being designed this way to begin with (with this small of pipe?)

 

[DubMac]

At roughly 100K gpm, I'm wondering about the pumps. Even with 4 of them, they would have over 24" discharge, EACH.

Go back and check decimal points.

 

[EdStainless]

The material will not be damaged, I have seen the results of jet impingement tests at 120ft/sec and there is no surface damage in 90 days.
However the hp required to move that much water is another issue. If this line is longer than a few feet the pressure drop would be huge.
And the reaction forces at an elbow or the closing of a valve would be difficult to handle.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[MJCronin]

Agreed, Ed.....

If this system is ever actually built it will be a giant energy waster....

How much longer will it be before we, once again, find out that this is a mistake or typo ?

MJCronin
Sr. Process Engineer

 

[BigInch]

Just a desal plant for a city & population of 330,000
???
Just needs a larger intake diameter.

 

[LittleInch]

Pipe size 240" maybe?? , make that tunnel size....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

It may take some time for the error to be uncovered since the OP seems to log in every 7 months or so on average.

Reviewing of the post shows that this application is a seawater intake. Although, the particular type of seawater intake is not specified.

The typical seawater intake is gravity flow with a velocity of around 0.6 m/s. Multiple pipes are used.

The recommended material for this type of gravity flow system is HDPE, because the low velocity will cause corrosion problems with most metallic piping materials.

A velocity of 25 m/s is probably not realistic for any type of seawater intake.

 

[LittleInch]

Edstainless - good to know that - I wasn't sure what the potential surface stripping was. However if the seawater contains any particles then straightforward erosion at any bend or fitting would be only one of your problems.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1gibson]

If he wants to make a scale model, a fire hydrant and drinking straw would work out pretty well.