3D TRASARTM Technology Optimizes
UAN Corrosion Management Program
CASE STUDY – CHEMICALS
CH-1198
BACKGROUND
Urea Ammonium Nitrate (UAN) is a
water-based nitrogen fertilizer. UAN
has several advantages to farmers. As
a liquid, it is easy to spray with
controlled application rates. UAN can
be mixed with other liquid fertilizers,
herbicides, pesticides, or
micronutrients. This saves the farmer
precious time and money by providing
one pass application.
The downside to UAN is that it is corrosive to most metal surfaces. If not
properly managed, UAN corrosion can damage storage tanks, pipes, rail cars,
and agricultural equipment. The impact of UAN corrosion can cost
manufacturers, distributors and users in many ways, including:
Ÿ Unscheduled plant shutdowns
Ÿ Asset replacement
Ÿ Equipment repair
Ÿ Off-quality product
Ÿ Cost of cleaning, removing, and disposing of UAN corrosion sludge
Ÿ Environmental damage (tank failure)
THE FUNDAMENTALS OF UAN CORROSION MANAGEMENT
The corrosive nature of UAN solutions can be managed by using an integrated
approach that combines an effective chemical corrosion inhibitor with a
disciplined program that identifies and mitigates key corrosion parameters.
UAN is comprised of the following components: urea, ammonium nitrate, water,
and a small amount of ammonia. Ammonium Nitrate (AN) is the more
corrosive component. For 32% UAN, the target ratio of AN/Urea is 1.2 to 1.4.
The corrosive effect of AN is buffered by the small amount of “excess”
ammonia in the solution. Excess ammonia should be no less than 0.01% by
weight (100 ppm), and preferably should be at least 0.02 to 0.05% by weight
(200-500 ppm).
By itself, ammonia is not a corrosion inhibitor. But without
this small amount of excess ammonia, UAN becomes
extremely acidic and overwhelms protection from applied
inhibitors. Measurement of pH is a good indication of how
much excess ammonia is contained in the UAN. Most
producers target a pH range of 6.5 to 8.0. A pH as low as
6.5 is acceptable, but much below that there is a risk of
stressing all the corrosion management systems.
An effective corrosion inhibitor should be added at the
target treatment rate at all times. Corrosion inhibitors are
inexpensive compared to the cost of UAN and are integral
to the overall success of the corrosion management
program. Inhibitor treatment rates should be checked at
least once per shift and by mass balance calculations
every week.
There are also mechanical and operational parameters
that should be followed.
1.
Storage tanks should be drained and cleaned at least
every two years. This will remove the surface
corrosion sludge that leads to the more damaging
“under deposit” or pitting corrosion.
2. Never leave small puddles or “heels” of UAN in
storage tanks for long periods of time. The UAN
solution can easily be stripped of the excess ammonia
resulting in acidic conditions and severe corrosion.
3.
Corrosion coupons should be installed in the storage
tank at mid-level and at the tank bottom in sets of
two; one for short term checks (quarterly) and the
other set for annual corrosion measurements.
4. Install a recirculation header in storage tanks.
Deposition of corrosion sludge at the bottom of the
tank builds up of pockets of corrosion cells. Many
UAN producers now have adopted a best practice of
installing an inlet recirculation pipe across the entire
diameter of their tank bottom. This header pipe has
several outlet spouts that point toward the floor at a
45° angle. Recirculation of the UAN allows tank
sludge to keep moving across the tank bottom. This
helps to greatly reduce pitting corrosion.
5. Maintain storage tanks temperature between 10-47°C
(50-110°F). Elevated temperatures speed chemical
reactions, including corrosion rates.
3D TRASAR TECHNOLOGY FOR UAN
CORROSION MANAGEM,ENT
The aforementioned guidelines should be considered the
bare minimum in mitigating UAN corrosion problems.
Monitoring parameters like inhibitor levels, corrosion
rates, pH, and temperature on a periodic basis may not
detect deviations that can significantly impact corrosion
rates. To address this shortcoming, NALCO Water
developed 3D TRASAR Technology for UAN corrosion
management. It incorporates advanced software and
specially designed monitoring devices to provide
instantaneous identification of parameters that are
outside established limits for minimal corrosion rates and
communicates with system users via cell phone, pagers,
and the web. As shown in Figure 1, the UAN Corrosion
Management Dashboard has gauges with a red, yellow
and green color scheme providing users with a quick
interpretation of performance.
The result is a proactive approach to identifying and
correcting upstream problems that could compromise
asset protection and UAN product quality.
NALCO Water’s UAN corrosion inhibitors contain TRASAR,
an inert fluorescent compound. A slip stream of UAN
solution is illuminated by a special LED light source and a
photodiode measures the amount of fluorescence. The
amount of emitted light is proportional to the inhibitor
Figure 1 – 3D TRASAR Technology – UAN Corrosion Management Dashboard
concentration, thus providing 24/7 verification of
treatment levels.
3D TRASAR Technology provides new insight into UAN
process dynamics and their effect on corrosion rates. As
an example, two pH excursions with corresponding high
corrosion rates were identified (as shown in Figure 2). In
the first excursion, after receiving the alarm, operators
found a faulty nitric acid valve resulting in slugs of acidic
UAN. In this instance, the valve was repaired and the pH
swings in mix tank were ultimately buffered in the bulk
storage tank. The second excursion happened as the plant
was going into shutdown. Until 24/7 monitoring with 3D
TRASAR Technology, the plant did not know the adverse
effect of shutdown procedures and quickly amended
future practices to minimize corrosion upsets.
Figure 2 – UAN Process Dynamics and pH Excursions
If not identified in real time and quickly resolved, these
acidic events could have significantly increased corrosion
in storage tanks and rail cars. One major stress event can
result in major corrosion damage. To illustrate, for UAN
solutions the mild steel corrosion rate at a pH of 7.0 is
around 1 to 2 mpy. However, at a pH of 2.0, the corrosion
rate is 60 mpy or higher; even worse still if localized
pitting occurs.
3D TRASAR Technology provides a step change in UAN
corrosion management by monitoring your system 24
hours a day, 7 days a week, 365 days a year, and,
detecting variability that impacts product quality, asset
protection, and profits.
NALCO Water, an Ecolab Company
North America: 1601 West Diehl Road • Naperville, Illinois 60563 • USA
Europe: Richtistrasse 7 • 8304 Wallisellen • Switzerland
Asia Pacific: 2 International Business Park • #02-20 The Strategy Tower 2 • Singapore 609930
Latin America: Av. das Nações Unidas 17.891 • 6° andar • São Paulo • SP • Brazil • CEP 04795-100
nalco.ecolab.com
3D TRASAR, Ecolab, NALCO Water and the logo are Trademarks of Ecolab USA Inc.
©2016 Ecolab USA Inc. All Rights Reserved
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CH-1890