SS material grade selection for Deionized water tank 2

[qualitypro]

We need to design and construct a stainless steel water tank for our customer of 125,000 gallons capacity.

a) What grade is normally used for SS tank construction?
b) Is using the stabilized grades such as 304L or 316L preferred than 304 or 316?
c) What is the advantage in using 316L over 304L and will there be a huge price impact?

 

[CastMetal]

Use 316L that is electropolished and passivated for least effect from DI corrosive properties. This would not prevent ions leaching from SS and heat makes things worse. depending on the quality of the deionized water many piping systems actually use aluminum.

With stainless you need to take the quality of the DI into account because lower grade stainless will leach far worse in high quality DI. Also consider Teflon coating for high purity applications.

 

[Metalguy]

The "L" grades are NOT stabilized; those are 321 and 347. The L's are lower in carbon which CAN do the same job in thin sections (preventing sensitization in HAZs).

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[EdStainless]

The trend today is to use lean duplex (2003, 2404, 2304) ss grades. When you electroploish them they don't look as shiny, but they do a better job than 316. The welds are very similar to the base metal in corrosion resistance, in 316 the welds are noticeably inferior.
The cleaner the water the better the alloy that you need. A small amount of air and CO2 in high purity water will attack many alloys.

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Plymouth Tube

 

[qualitypro]

Thanks Castmetal, Metalguy and EdStainless for your inputs.
For this DI tank when we approached tank fabricators we are told that Grade 304L will be good enough. I do not agree totally with the tankie as it may be OK from a cost perspective. Any thoughts??

 

[Metalguy]

It all depends on how pure your DI water is--and must stay. There are a LOT of 304L tanks around that work fine. Because you shouldn't have chlorides around, there is no need for 316L--assuming the tank doesn't sit on wet ground.

It comes down to price, for the SS and for the fab. 304L is pretty weak, especially low yield strength which is of major importance. You could probably use thinner gauge with a newer alloy--it all has to be priced out.

Watch for MIC after you first fill the tank, esp. if DI water isn't used vfor a hydrotest. Do not let non-DI water remain in the tank for more than a very few days.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[stanweld]

304/304L is commonly used for demin tanks. It is normally the responsibility of the Engineer/Owner to select the alloy - not the tank fabricator. If you are the Engineer/Owner, consider the excellent advise provided above in your selection process. Also consider outside environmental exposures; e.g., marine, tropical, desert marine, heavy industrial, etc.

 

[EdStainless]

So roughly 24" diam x 24' tall.
I presume that the system is designed to exclude air, and sealed against microbiological contamination.
I also presume that you have a good cleaning and passivation practice to follow.

Seriously look at LDX2101. The tanks that I worked with were large than this but the weight of metal was reduced by 45% over 304L/316L. Lighter material welds faster and uses less filler. The material is slightly more difficult to form because of its strength but the total fab cost didn't go up and the metal cost went down a lot.

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Plymouth Tube

 

[EdStainless]

OK, 28ft

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Plymouth Tube