Diesel Exhaust Fluid (urea) and stainless tank - what to look out for? 3

[kingnero]

I need to adapt an existing machine, adding a 700 litre (= 185 US gallon) tank to this machine.
This tank will contain Diesel Exhaust Fluid (DEF), also known as AdBlue, this is an aqueous urea solution made with 32.5% high-purity urea (AUS 32) and 67.5% deionized water.

I've talked to HDPE tank builders, and due to the specific form, they can make a mold but I would need to buy the equivalent of 500-1000 pcs.
As I only need 1, I've been looking for a custom made Stainless tank.

Will austenitic stainless (304 or 316) cause problems? with this environment?
Will the internal baffle plates need to be fully welded, in order to avoid crevice corrosion?

Any other things to watch out for?

So far, I've got this:
I need flanges to have filler pipes, aeration, a pump, a looking glass (to see the level of the fluid), to add resistance heating elements, to clean out the tank
I will double check the stability of the tank once all the unknowns are known (sizes of the flanges, places of the heating, ... but I got a general design with two internal baffle plates (1.5" open at the bottom, a bit more at the top)
Size will be roughly 100" long x 20" wide x 20" height
Material: probably either 304 or 316, depending on your reactions perhaps something else.

thanks in advance for your remarks...

 

[EdStainless]

You need to find long term exposure data, I would want to see 3 months at 120F minimum using welded coupons.
There is urea data, but that is not quite the full story as there are other additives in DEF.
Based on urea data either alloy will work.
What will the outside be exposed to?
If this is on a vehicle then 304 is probably not suitable because of exterior exposure.
Fabrication quality will be the bigger deal, make sure that the work is done by a shop that dose nearly all stainless work. You need good shielding on welds, pickle and passivate after fabrication, no crevices or places to trap liquid (inside of out), and no contact with steel or tools that have been used on steel.
Doing this in 316L should work if you design and execute properly.

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

 

[metengr]

http://www.smt.sandvik.com/en/mater...be-and-pipe-seamless/sandvik-3r60-urea-grade/

 

[EdStainless]

The more that I think about this the more that I feel that I should add that you would be better off making this tank from a lean duplex stainless (2101 or 2202).
It will be much stronger, have better corrosion resistance, and much better chloride cracking resistance. An it should cost the same or a little less.
(ps, you weld these alloys with 2209 filler)

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

 

[kingnero]

Thanks for both your responses.

If we could stay with 304 or 316, we have no problem looking for a contractor to do the fabricating work.
Going to a duplex, there's very few in our area, and I doubt they will accept such a "small" order.
I'll contact them first before requesting a quote.

Cost is a smaller factor in this.

I'll see if the Sandvik 316 grade is available here.

Ed, regarding your remark about 304 and outside conditions, this tank will be placed inside a custom made piece of rolling equipment, and will not directly be exposed to outside conditions nor rain. You do have a valid point though, 316 is without doubt the better choice of those two. If we go the classic austenitic stainless steel route, it'll be 316 and not 304.


Still open for any other additional remarks!

 

[kingnero]

Additional question:
If the tank will be built from either the sandvik steel or a duplex, do standard flanges exist in either material? Duplex has a better chance for this, if I were to hazard a guess.

 

[EdStainless]

You can get flanges in any of the 300 grades and in many of the duplex grades.
If you go the duplex route don't worry about matching alloys, you can freely mix them without problems.
The thing that concerns me long term about 316 is the risk of chloride stress cracking, that is why I favor a duplex.

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

 

[kingnero]

Ed,

appreciate your responses.

Question: I'm no chemist by all means, so I'm probably way off my field of expertise:
when you worry about chloride stress cracking, that would mean that there needs to be Cl (in any form) present, right?

http://en.wikipedia.org/wiki/Diesel_exhaust_fluid

Don't see any Cl there. This does not mean that there is none, I am aware of that. Are you sure that there is any?
I'll contact our supplier to verify this in the meanwhile.

 

[EdStainless]

I am worried about external Cl exposure, perhaps the tank or machine being washed with hot water that is less than potable quality. It doesn't take much with 300 alloys to crack them.

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

 

[kingnero]

Thanks for correcting me. Didn't even think of that.
Mail is sent anyway, if DEF contains any Cl, 316 is out of the question anyway.