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

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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.My role in this is as responsible of this piece of rolling equipment, to have a welding firm fabricate us a tank according to certain specs. We don't have a dedicated stainless steel workshop, and probably we lack the skills to pull this of inside of our own firm.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 steel tank.Will austenitic stainless (304 or 316) cause problems with this environment?Alternative is a duplex, but that limits the choice of subcontractors to do the welding part.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 tankI 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" heightMaterial: probably either 304 or 316, depending on your reactions perhaps something else.thanks in advance for your remarks...
Reply:Kingnero,A quick search of the internet suggests that Urea solutions can be extremely corrosive to austenitic(3XX series) stainless steels.  The corrosion rate is influenced by temperature(higher is faster corrosion) and the absence of oxygen(which serves to renew the passive oxide surface layer on the stainless steel).  The fact that the tank is at low temperature is going to help; but I don't think it will eliminate your problem.  I found some industrial reports on corrosion in Urea reactors(manufacuturing Urea from Ammonia and CO2) that mentioned corrosion rates of 1mm/year at room temp to 50mm/year at 400F.Since this is a tank, and you mentioned baffles in th design, I'm assuming the tank is thin walled and/or on something that moves.  Even 1mm/year could cause leaks or outright failures in a short timeframe.Duplex stainless steels will perform far better than austentic stainless steels.  I would look again at using a duplex stainless steel unless you prefer to replace the tank on a regular basis.If the Urea solution is oxygenated(which is should be with your aeration system), I would not worry about crevice corrosion.  General pitting corrosion is likely to be a much larger factor.Have you explored having the the interior of the tank coated with a polymer or epoxy resin?  This might solve your problems and enable you to use 304L stainless for the tank structure or even mild steel if you coat the inside and paint or coat the outside.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Thanks for your reply.coating the inside is probably a bad idea because the tank will regularly need to be cleaned (the stuff cristallises with cold temps, and it leaves a sticky, gooey, hard deposit). Will probably be scraped from the inside.The aeration system only serves to add air when the fluid is pumped to another (primary) tank. Does this matter when we're talking crevices (not fully welded baffles) that are submerged?In the meanwhile, I've asked our supplier whether or not there is any chlorine/chloride in the solution. But it seems it's probably the best idea to go straight to a lean duplex stainless steel.
Reply:Originally Posted by kingneroThanks for your reply.coating the inside is probably a bad idea because the tank will regularly need to be cleaned (the stuff cristallises with cold temps, and it leaves a sticky, gooey, hard deposit). Will probably be scraped from the inside.The aeration system only serves to add air when the fluid is pumped to another (primary) tank. Does this matter when we're talking crevices (not fully welded baffles) that are submerged?In the meanwhile, I've asked our supplier whether or not there is any chlorine/chloride in the solution. But it seems it's probably the best idea to go straight to a lean duplex stainless steel.
Reply:Originally Posted by kingneroI 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.My role in this is as responsible of this piece of rolling equipment, to have a welding firm fabricate us a tank according to certain specs. We don't have a dedicated stainless steel workshop, and probably we lack the skills to pull this of inside of our own firm.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 steel tank.Will austenitic stainless (304 or 316) cause problems with this environment?Alternative is a duplex, but that limits the choice of subcontractors to do the welding part.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 tankI 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" heightMaterial: probably either 304 or 316, depending on your reactions perhaps something else.thanks in advance for your remarks...
Reply:Thx,  I guess shipping to Europe will kill the price.But I will check it before jumping to conclusions...
Reply:I have some experience with urea.  I hate the stuff, but it is the only way to get air quality permits for generators in many states these days.  We mostly use a 40% solution to reduce consumption rates. If you look up the MSDS for urea it has plenty of recommended handling materials.  316 and 304 are both listed.  Additionally titanium and Hasteloy are on the list.  We use large amounts of 316 in our pumping and dosing systems. No issues with it in the 7 years I have been dealing with it and 40% is more corrosive. The tanks we use are always fiberglass though.  Last job i built a pumpset for had 2 x 12k gallon tanks.  All 316 for pumps fittings and piping. Anything copper will be gone in a matter of weeks typically so be sure you avoid that when you pipe it out. Nickel plating doesnt help.Multimatic 200Ellis 1800Haberle S225 9" cold sawMM 300;  Spoolmate 30A w/ WC-24TB 302GDynasty 280 DX Tigrunner
Reply:Thx for the information.I'm mostly worried about crevice corrosion in the inside, here the baffles will be welded, and about strength as it's being used on rolling equipment, so vibrations will be always present.I doubt a Ti or Hastelloy tank will be in our budget.
Reply:Originally Posted by kingneroThx,  I guess shipping to Europe will kill the price.But I will check it before jumping to conclusions...
Reply:why not a fiberglass tank with some hard guarding?Vantage 500's LN-25's, VI-400's, cobramatics, Miller migs, synch 350 LX, Powcon inverters, XMT's, 250 Ton Acurrpress 12' brake, 1/4" 10' Atlantic shear,Koikie plasma table W/ esab plasmas. marvel & hyd-mech saws, pirrana & metal muncher punches.