Best pipe material for submerged water service 1

[clyde65]

I am designing a pressurized water system that will be submerged in lake water. It will be 2 to 6 inch steel. I would like to know if I should specify stainless (if so, what type) or carbon steel with some kind of coating (paint or hot dip galv.) Do I need to coat inside and out? The system will supply a network of spray nozzles, so I would like to minimize their plugging with rust, etc. Thanks in advance.

 

[MikeHalloran]

The nozzles spray what fluid into what fluid?

How deep?

How much internal pressure?

What do you do when the lake freezes?






Mike Halloran
Pembroke Pines, FL, USA

 

[clyde65]

Mike,

The nozzles spray lake water onto the back side of submerged wedgewire screens to remove leaves, etc. It's an underwater backwash system. The deepest nozzle is 12 feet down, and I'm supplying 80 psi water. It works great--we've tested it. The system is raised during the winter and mothballed. My client is concerned that the pipe will corrode internally and rust flakes will plug the nozzles, which have 0.14 inch orifices. So I'm looking for alternatives for pipe--stainless, painted CS, hot dipped galv., etc. It can't be plastic. Thanks for the interest.

 

[rconner]

If 4"-6" pipe could be utilized, perhaps cement mortar lined ductile iron piping might be considered (see for example the article "Ductile in Delran" mentioned at

http://www.acipco.com/pipeprogress/indexfw96.shtml).

 

[EdStainless]

Fresh water? If so look for a lean duplex stainless grade.

My guess is though that you will have better luck doing this economically with epoxy coated carbon steel. Get pipe that is shop coated inside and out. cut, fab, weld, and then hand coat the joints. Every fall when you pull it out you can inspect and repair.

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Rust never sleeps
Neither should your protection

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[clyde65]

Ed,
Thanks for the reply. What exactly is a lean duplex stainless grade?

 

[EdStainless]

I am glad that you asked.....
On a microscopic level these alloys are a mixture of austenitic and ferritic stainless steels. They have some properties of each, and some advantages. They have been designed so that the corrosion resistance of the two phases is nearly equal. These alloys are much stronger than 3XX series austenitic alloys, and much better at resisting chloride stress corrosion cracking. They are easier to form and weld than ferritic alloys, and more ductile.

The traditional duplex grade is 2205 (22% Cr, 5% Ni, 3% Mo doesn't get listed).
The lean alloys have lower alloy content and lower cost. Alloys like LDX2101 and AL2003.
The LDX2101 material cost is less than 304 today. It is an easy decision, if you can find the product forms that you need.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Ashereng]

Just curious, when you say it can't be plastic, do you mean no plastic at all? Just curious, why no plastic.

My initial suggestion was "Flexpipe":

http://www.flexpipesystems.com/about.html

It does have "plastic" though. Would something like this be worth investigating for your application?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[rustbuster]

would lean toward fibreglass or plastic's. Lower cost's and no corrosion issues.

 

[EdStainless]

I like the idea of fiberglass for this application. Just be wary about coatings for protection from UV for the above water parts. Also make sure that it doesn't flex too much.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[thewellguy]

If it has to be steel pipe, we have seen that best longevity from standard black pipe that has been sandblasted and epoxy coated. You could also add zinc sleeves it you were very concerned about longevity.

 

[Oceania]

I would suggest FRP Pipe would be an ideal candidate for this application. No corrosion, so long life, no flaking to block nozzles so it can stay in during the winter. UV protection is easily resolved with a pigmented external flow-coat (pic the colour you like here as well).

As for stiffness of the system, by modifying the construction of the pipe in critical areas additional stiffness can be incorporated and this can be checked using an analysis program such as Ceasar. In addition the pipe joints are not necessarily flanged so assmbly time can be as low as a couple of minutes per joint.

Hope this helps.