Contents
Is DEF Corrosive to Metals?
Diesel Exhaust Fluid (DEF) is not inherently corrosive to metals. However, under certain conditions, DEF can decompose to produce ammonia, which is corrosive.
DEF is an aqueous urea solution comprising 67.5% deionized water and 32.5% urea. Urea is not corrosive to metals. However, when DEF is exposed to elevated temperatures, the urea breaks into ammonia through thermal decomposition.
The decomposition of urea to ammonia is accelerated by:
- High temperatures above 122°F (50°C)
- Low pH levels below 3
- Long exposure times
- Impurities in the DEF
So, while DEF in its stable form is not corrosive, the ammonia produced from its decomposition can be. However, ammonia corrosion will only occur if the metal is exposed to elevated temperatures and an aqueous solution.
DEF decomposition and ammonia corrosion will rarely occur under normal vehicle operating conditions. Corrosion requires prolonged exposure to high heat with poor DEF quality. Proper DEF handling, storage, and maintenance can prevent decomposition and corrosion issues.
DEF Corrosion Conditions
Diesel Exhaust Fluid (DEF) can be corrosive to certain metals under specific conditions. The three key factors that enable DEF corrosion are:
Presence of Copper and Zinc Alloys
DEF is most corrosive to copper—and zinc-containing metals, especially copper alloys such as brass and bronze.
High Temperatures Above 50°C
DEF’s corrosive effects accelerate above 50°C (122°F). The hotter the temperature, the faster corrosion occurs.
Concentration and Exposure Time
Higher DEF concentrations and longer exposure times increase corrosion rates. With more DEF and longer contact, more corrosion damage can occur.
DEF is generally only corrosive in this way when all three conditions are met simultaneously. Copper/zinc alloys heat over 50°C, and extended DEF contact enables the chemical reactions that lead to corrosion damage. Monitoring these factors can help prevent DEF’s corrosive effects.
How Does DEF Corrode?
Diesel Exhaust Fluid (DEF) is a liquid solution comprising 32.5% high-purity urea and 67.5% deionized water. At temperatures above 50°C, the urea in DEF decomposes into ammonia.
This ammonia can actively corrode certain metals by dissolving copper and zinc ions from their surface.
When ammonia comes into contact with copper alloys like brass or bronze, it forms soluble complexes with the copper ions, removing them from the alloy structure. The same reaction occurs with zinc galvanized steel. This leads to the degradation and weakening of metal components over time.
So, in summary, DEF corrosion occurs due to the release of ammonia at elevated temperatures. The ammonia then reacts with and dissolves certain metal ions, damaging alloys and coatings. Proper temperature control and compatible materials are key to preventing DEF corrosion.
Metals Prone to DEF Corrosion
Diesel exhaust fluid can corrode certain metals over time. The most susceptible metals include:
Copper and Brass Components
DEF readily corrodes copper and brass parts, especially at higher temperatures. This can lead to pinhole leaks, cracking, or complete failure of components like radiators, oil coolers, and heat exchangers made with copper or brass.
Zinc Coatings/Galvanization
DEF will attack and strip away zinc galvanization over time. This can expose the underlying steel to corrosion. Fuel tanks, fasteners, brackets, and other components commonly feature a zinc coating for corrosion protection. This coating is compromised by extended exposure to DEF.
Lead and Solder Joints
Lead and solder joints commonly used in cooling systems are incompatible with DEF. The DEF will corrode lead and dissolve soldered connections, leading to leaks and other issues.
Aluminum to a Lesser Degree
While less reactive than copper and brass, aluminum still exhibits corrosion when exposed to DEF long-term. This is especially true at higher temperatures. Heat exchangers, radiators, tanks, and other components made with aluminum can corrode. However, aluminum corrosion is slower compared to other metals when exposed to DEF.
Where Corrosion Occurs
Diesel exhaust fluid can cause corrosion in several components of a diesel vehicle’s exhaust system:
DEF Tank and Supply Lines
The DEF tank and supply lines that carry DEF from the tank to the injectors are prone to corrosion. Any spills, leaks, or condensation inside the tank or lines can cause the DEF to puddle and corrode the surrounding metal surfaces. Galvanized steel tanks and lines provide some corrosion resistance.
Injectors, Pumps, Sensors
The injectors that spray DEF into the exhaust, supply pump, and sensors are also vulnerable. Corrosion buildup around injectors can clog them, while pump and sensor failures can occur over time due to corrosion damage. Proper maintenance and occasional cleaning help avoid corrosion issues.
Downstream of Catalyst Converter
While less common, DEF sprayed into the hot exhaust can condense and collect downstream of the catalytic converter. If the condensed DEF is not drained or evaporated off regularly, it can potentially cause corrosion damage. Periodically running the exhaust system hotter helps avoid condensation buildup.
Preventing DEF Corrosion
Diesel exhaust fluid can corrode the engine and components without proper precautions.
Here are some ways to help prevent DEF corrosion:
- To avoid corrosion, choose metals and alloys compatible with DEF, such as stainless steel. Avoid aluminum, copper, and zinc alloys.
- Applying protective coatings or using corrosion inhibitors in DEF can help prevent corrosion of components. Epoxy or nitrite coatings are commonly used.
- Maintaining proper DEF temperature, between 10-30°C, will prevent conditions favorable for corrosion. Heating and cooling systems help regulate temperature.
- Regularly draining and flushing DEF systems removes contaminants and deposits that can lead to corrosion over time. Follow manufacturer recommendations for drain intervals.
Taking proactive steps to manage DEF exposure will minimize the corrosion risk to exhaust components. Proper materials selection, maintenance, and temperature control are key factors.
Detecting DEF Corrosion
Diesel exhaust fluid can cause corrosion in various parts of diesel engine systems.
Here are some signs that may indicate DEF corrosion is occurring:
Visible Pitting or Deposits
Corrosion damage from DEF will often first appear as pitting, etching, or unusual deposits on metal components. Visually inspecting parts, especially those prone to corrosion, can help detect issues early.
Decreased Performance
Over time, DEF causes corrosion and damage, which can lead to decreased performance in affected components and systems. Lower fuel economy, power loss, and problems with emissions control are possible symptoms.
Leaks and Blockages
Corroded components like tanks, lines, and injectors can leak or become blocked as small holes and cracks develop. Leaking DEF and issues with spray patterns, are signs corrosion may be present.
Diagnostic Trouble Codes
Engine computers detect and log faults through diagnostic trouble codes (DTCs). Corrosion damage can trigger DTCs related to the emissions system, fuel system, or engine performance. Scanning for codes can help identify corrosion-related problems.
Regularly inspecting components vulnerable to DEF corrosion, monitoring for performance issues, and scanning for diagnostic codes are key ways to detect corrosion before it leads to major repair costs or breakdowns. Addressing small problems early is critical to prevent extensive damage.
Repairing DEF Corrosion Damage
Once DEF corrosion has occurred, repairs will be needed to prevent further damage.
Some key steps for repairing DEF corrosion damage include:
Replace Affected Parts
Any components that show signs of corrosion damage will likely need to be replaced. This may include tanks, lines, sensors, valves, injectors, and other parts that have been degraded. Replacing corroded parts helps prevent leaks, clogs, and failures.
Flush the System
After removing corroded components, the entire DEF system should be thoroughly flushed. This removes any residual DEF fluid and contamination. Flushing may require specialized equipment and fluids. All tanks, lines, and components should be flushed.
Use Updated/Coated Components
When replacing corroded parts, opt for newer components that are DEF-compatible. Many manufacturers now use stainless steel or other alloys that resist DEF corrosion. Also, choose parts with protective coatings or treatments.
Improve Temperature Regulation
Fluctuating temperatures accelerate DEF corrosion. Repairs should address any temperature control issues. This may involve insulating tanks and lines, relocating components, or upgrading heating/cooling systems. Maintaining proper DEF temperatures helps prevent future corrosion.
These steps to repair, replace, flush, and upgrade the DEF system will help resolve corrosion damage and prevent further issues. Regular maintenance is also essential to minimize long-term corrosion risks.
FAQ
You asked, we answered.
Can DEF Damage My Diesel Engine If Misused?
Yes, if DEF is mistakenly added to the diesel fuel tank, it can cause significant damage to the fuel system and engine. DEF is designed to be used in a separate SCR system and not mixed with diesel. If DEF is introduced into the fuel system, it can lead to costly repairs and operational issues. In case of such a mishap, the vehicle should not be started and professional service assistance should be sought immediately.
How Should DEF Be Stored to Prevent Corrosion?
DEF should be stored in containers or tanks made from materials that are resistant to its mildly corrosive effects, such as HDPE or stainless steel. The storage area should be clean, dry, and well-ventilated, and should be kept at a temperature between 12°F (-11°C) and 86°F (30°C) to maintain its quality.
What Safety Precautions Should Be Taken When Handling DEF?
When handling DEF, wear gloves and eye protection to avoid irritation. In case of skin contact, wash the area with soap and water. If DEF gets in the eyes, rinse them with water for several minutes.
Can DEF Be Reused or Recycled?
DEF cannot be reused or reprocessed once it has been dispensed into a vehicle. However, DEF packaging and containers can often be recycled, depending on local recycling programs and the materials used in the packaging. Always check for recycling symbols on DEF containers and follow local guidelines for recycling or disposal.
Summary
Diesel Exhaust Fluid (DEF) can be corrosive to some metals under certain conditions, but corrosion is preventable with proper care and maintenance. DEF is made of urea and deionized water, which can be acidic and cause corrosion in the presence of heat, humidity, surface deposits, or galvanic reactions with dissimilar metals.
The most susceptible metals include aluminum, magnesium, zinc, steel, and copper alloys. Corrosion typically occurs when DEF residues collect and puddle around injector nozzles, supply modules, tanks, and lines. Regular cleaning and inspection can detect corrosion early before major damage occurs. Using compatible metals, proper sealing, and additives helps prevent corrosion.
If corrosion damage is found, options for repair include replacing affected parts, recoating or plating corroded surfaces, using corrosion-inhibiting additives with DEF, and addressing conditions causing corrosion. Overall, DEF corrosion is manageable through vigilant maintenance, detection, and mitigation practices. While DEF can be corrosive, following manufacturer guidelines, implementing preventive measures, and properly maintaining DEF systems keeps corrosion at bay.
Contact our experts at Azure Chemical for more information about DEF corrosion or to receive high-quality DEF products for your truck.
