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DEF Storage and Handling

DEF Storage and Handling

Ignore the haters. Diesel is awesome, and diesel exhaust fluid makes it nearly perfect. Knowing how to store and handle DEF will ensure you get most perfect miles out of your diesel vehicle or fleet.

Diesel’s biggest downside is downstream of the final stroke: the exhaust or, the industry’s favorite term, the emissions. Diesel’s particulate emissions – the ones that make some pickup trucks look like six-wheeled early 20th century coal plants - are easily removed by a filter in the exhaust line. But filters can’t remove exhaust gases that are dangerous at the molecular level. Nitrogen oxides – which you’ll often see as NOx (NOx, noxious, right?) - are the major emissions of concern. NOx are carcinogenic, and are a major contributor to smog.

Diesel exhaust fluid breaks down NOx, leaving nitrogen, water and carbon dioxide as the output of your exhaust pipe.

What is DEF, and what does that tell us about storage and handling requirements?

DEF is a pure form of urea at a 32.5% concentration in deionized water. Urea is a relatively simple, naturally occurring chemical that has many natural and commercial uses, particularly as an agricultural fertilizer.

Even though DEF only has two components, they both set constraints on storage conditions.

DEF freezes at 12°F (-11°C), and while freeze-thaw cycles do not degrade DEF, it should be maintained as a liquid. The upper temperature limit is both more flexible and more impactful. As storage temperature rises above 50°F, its shelf life starts to decrease. Keeping below 65°F maintains a shelf life of about two years, with the shelf life dropping to about a year when the storage temperature rises to 77°F. Minimizing temperature fluctuations will maximize the lifespan and quality.

Deioinized water attracts and absorbs minerals, salts and gases from anything it contacts, including the air and even some metals. Consequently, deioinized water will become “unpure” relatively quickly when exposed to the open air; and can cause some metal corrosion, notably on carbon steel.

DEF storage and equipment best practices

Maintaining the purity of DEF is a primary consideration in storage, transport and transfer. DEF systems should be closed systems to prevent contamination from the air, and should be dedicated to the product to prevent contamination from other fluids.

Many DEF filling systems have built-in interlocks to ensure that only DEF passes from one part of the system to another, and ensure that only components used in DEF handling are introduced into the system. For example, a DEF tank and filling nozzle will have a complementary size and shape, and a magnetic interlock to ensure the fill valve and nozzle “recognize” each other as DEF system components. This prevents a distracted user, for example, from accidentally putting something other than DEF into the DEF storage tanks; and prevents a user from using a funnel from a different application, which could introduce contaminants from whatever that funnel had previously been exposed to.

Along the same lines, at the level of the end user, the DEF tank on a vehicle is designed to look nothing like the fuel tank; and frequently the filling spout is not located near the fuel tank’s to ensure that a distracted user never puts DEF into a diesel tank, or vice versa. The urea in it would seriously corrode the fuel lines. An immediate system flush would just be the start of lengthy and extended maintenance, inspections and rebuilding. Putting diesel into a vehicle’s DEF tank wouldn’t be as catastrophic on the DEF system, but it definitely would not be good for anything in that system. And, wow, what a waste of diesel at a time when we can’t be doing that.

Also helping users distinguish DEF from other common fluids is a blue dye that is often added to it. This doesn’t change the underlying chemistry at all nor affect performance in any way. It’s just a helpful measure of backup reminding you “This is DEF. This is what you want to be working with right now, right?”

Temperature control is the secondary consideration for storage and handling. Depending on your throughput of DEF, it may not be much of a concern at all: the potentially degrading effects of high temperatures only kick in after some passage of time. If a given quantity of DEF is only stored for a short time before going into a vehicle, then keeping the temperature below 70 or 80°F will not be a big deal.

If, though, you expect to store a batch for more than a few months, there are various passive and active temperature controllers (e.g., insulated tank wrappings) to keep DEF in the “max shelf life” part of the temperature range. Obviously, your geographic location will shape your needs significantly.

The full details for diesel exhaust fluid storage and handling requirements, including the material recommendations for tanks, piping, tubing and nozzles, are in ISO 22241-3:2017. If you have any questions about diesel exhaust fluid in the southeast, Whatley Oil is standing by to answer them and help you find the right products and solutions.

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