Sea Water Service Pipeline, 316L? 1

[mufasa1]

I am a mechanical engineer at a large petrocehemical complex in Turkey. We are located on the seaside and we have decided to feed our fire water pipeline with sea water during an emergency such as lack of fresh water or very low fresh water pressure. In the project the suction line from sea to the main collector (serving three centrifugal pumps) is about 50m long. What kind of material is appropriate for the suction line? It will be full of sea water at all times. Is 316L OK? We do not want to have corrosion problem in the near future.

 

[MorelG]

90-10 CuNi

 

[MJCronin]

mufasa,

I am surpised that you got ths far with that question....

The "is 304/316L stainless steel OK for seawater" question has been asked many, many times....

The answer is no........chloride corrosion, in the form of pitting will eventually eat through the pipe. 316L stainless can, sometimes be used in marine service where there is (1) occasional exposure or(2) continuous flowing seawater. You can meet neither requirement with the system as you describe.

The specialty steel have extended the "stainless steel family" to include metals specifically for this kind of service...... Look up information on Allegney Ludlums "AL6XN". Coated carbon steels have also been used

The use of 90/10 copper nickel is also acceptable, but it is expensive and very difficult to weld. Thin walled titanium piping has also been used in brackish/seawater duty.

Try this web link:

http://marine.copper.org/2-table7.html

Also see eng-tips "Marine/Ocean" discussion

Good luck.....

Out of respect to fellow engineers, .................would you please report back on your ultimate material choice and why that you made it.

MJC

 

[mcguire]

For the suction line you needn't go to the expense of AL6XN. This grade would avoid all corrosion, but you can have a very functional suction line with 2205 ( specify 0.15%nitrogen minimum ). This grade is commonly available in Europe especially as tubing. This is easily the most important new grade of stainless. It is a duplex ( half austenite, half ferrite ). You can weld it. It doesn't stress corrosion crack. And it's super strong, 50% more than 316. It has a much more reasonable price than AL6XN or copper/nickel base alloys.

 

[MJCronin]

mufasa,

Mcguire is correct about his suggestion for a 2205 duplex- stainless steel, however.....

Consider a thin walled run of piping (Schedule 10S ?)for this short run of piping.

Will the piping be supported by the soil or will it be immersed in sea water ? How will it be supported ?

Check the following link for copper-nickel applications in sea water:

http://www.cda.org.uk

Good Luck

Let us know about the final design....

MJC

 

[mufasa1]

Sorry, for the late response. I appreciated your valuable comments on the subject. I have visited the marine.copper.org website and reviewed the following paper. "Materials Selection for High Reliability Seawater Systems", Brian Todd. I have started the same thread also at the following forums. You can see different views for the same question.

Mechanical Engineers Area - Piping & Fluid Mechanics and Engineering Forum, ( posted 2/27 )

Materials Engineers Area - Corrosion Engineering Forum, ( posted 2/27 )

After considering suitable materials ( 90-10 CuNi, 316L, AL6XN, 254SMO, Carbon Steel w/coating, Ductile Iron w/coating, plastic lined pipe, thermoplastic pipe, and FRP pipe ), we have decided to stick with Ductile Iron Pipe w/cement-mortar lining, and epoxy-resin coating. Because,
- High local cost of very reliable seawater materials such as super austenitic stainless steels
- Material availability locally
- Fire Safety ( This line will be for emergency fire water service from seaside, therefore we skipped thermoplastic, and plastic lined pipes. )

Regards,

Mustafa