TM3D TRASAR Technology OptimizesUAN Corrosion Management Program

CASE STUDY – CHEMICALSCH-1198

BACKGROUND

THE FUNDAMENTALS OF UAN CORROSION MANAGEMENT

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 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 diameter of their tank bottom. This header pipe has this small amount of excess ammonia, UAN becomes several outlet spouts that point toward the floor at a extremely acidic and overwhelms protection from applied 45° angle. Recirculation of the UAN allows tank inhibitors. Measurement of pH is a good indication of how sludge to keep moving across the tank bottom. This much excess ammonia is contained in the UAN. Most helps to greatly reduce pitting corrosion.producers target a pH range of 6.5 to 8.0. A pH as low as

5. Maintain storage tanks temperature between 10-47°C 6.5 is acceptable, but much below that there is a risk of

(50-110°F). Elevated temperatures speed chemical stressing all the corrosion management systems.

reactions, including corrosion rates. 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 The aforementioned guidelines should be considered the program. Inhibitor treatment rates should be checked at bare minimum in mitigating UAN corrosion problems. least once per shift and by mass balance calculations Monitoring parameters like inhibitor levels, corrosion every week. rates, pH, and temperature on a periodic basis may not

detect deviations that can significantly impact corrosion There are also mechanical and operational parameters rates. To address this shortcoming, NALCO Water that should be followed. developed 3D TRASAR Technology for UAN corrosion

1. Storage tanks should be drained and cleaned at least management. It incorporates advanced software and

every two years. This will remove the surface specially designed monitoring devices to provide

corrosion sludge that leads to the more damaging instantaneous identification of parameters that are

“under deposit” or pitting corrosion. outside established limits for minimal corrosion rates and

2. Never leave small puddles or “heels” of UAN in communicates with system users via cell phone, pagers, storage tanks for long periods of time. The UAN and the web. As shown in Figure 1, the UAN Corrosion solution can easily be stripped of the excess ammonia Management Dashboard has gauges with a red, yellow resulting in acidic conditions and severe corrosion. and green color scheme providing users with a quick

interpretation of performance.3. Corrosion coupons should be installed in the storage tank at mid-level and at the tank bottom in sets of The result is a proactive approach to identifying and two; one for short term checks (quarterly) and the correcting upstream problems that could compromise other set for annual corrosion measurements. asset protection and UAN product quality.

4. Install a recirculation header in storage tanks. NALCO Water’s UAN corrosion inhibitors contain TRASAR, Deposition of corrosion sludge at the bottom of the an inert fluorescent compound. A slip stream of UAN tank builds up of pockets of corrosion cells. Many solution is illuminated by a special LED light source and a UAN producers now have adopted a best practice of photodiode measures the amount of fluorescence. The installing an inlet recirculation pipe across the entire amount of emitted light is proportional to the inhibitor

3D TRASAR TECHNOLOGY FOR UAN CORROSION MANAGEM,ENT

Figure 1 – 3D TRASAR Technology – UAN Corrosion Management Dashboard

concentration, thus providing 24/7 verification of If not identified in real time and quickly resolved, these treatment levels. acidic events could have significantly increased corrosion

in storage tanks and rail cars. One major stress event can 3D TRASAR Technology provides new insight into UAN

result in major corrosion damage. To illustrate, for UAN process dynamics and their effect on corrosion rates. As

solutions the mild steel corrosion rate at a pH of 7.0 is an example, two pH excursions with corresponding high

around 1 to 2 mpy. However, at a pH of 2.0, the corrosion corrosion rates were identified (as shown in Figure 2). In

rate is 60 mpy or higher; even worse still if localized the first excursion, after receiving the alarm, operators

pitting occurs. found a faulty nitric acid valve resulting in slugs of acidic UAN. In this instance, the valve was repaired and the pH 3D TRASAR Technology provides a step change in UAN swings in mix tank were ultimately buffered in the bulk corrosion management by monitoring your system 24 storage tank. The second excursion happened as the plant hours a day, 7 days a week, 365 days a year, and, was going into shutdown. Until 24/7 monitoring with 3D detecting variability that impacts product quality, asset TRASAR Technology, the plant did not know the adverse protection, and profits.effect of shutdown procedures and quickly amended future practices to minimize corrosion upsets.

Figure 2 – UAN Process Dynamics and pH Excursions

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 3-16 CH-1890

NALCO Water, an Ecolab Company