System Corrosion Deep Diagnosis
Coolant turning black, copper corrosion, aluminum perforation, heat exchanger failure - 6 types of corrosion root cause analysis and solutions with real diagnostic cases and anti-corrosion best practices.
6 Corrosion Types
6 Real Cases
5 Anti-Corrosion Practices
System Corrosion Deep Diagnosis
Coolant turning black, copper corrosion, aluminum perforation, heat exchanger failure - 6 types of corrosion root cause analysis and solutions with real diagnostic cases and anti-corrosion best practices.
Why Corrosion Problems Are So Common
Coolant system corrosion is one of the most common failure types in industrial refrigeration. Corrosion not only causes coolant degradation (blackening, foaming) but also leads to serious consequences such as heat exchanger perforation, aluminum tube leakage, and copper tube damage. According to 2025 technical support case statistics, cases directly related to corrosion account for over 20% of 34 typical cases.
The root cause of corrosion is often not the coolant itself, but a combination of system residual impurities, water quality issues, material incompatibility, and oxygen ingress. Accurate diagnosis of the corrosion cause is essential for effective treatment.
Corrosion Types& Root Causes
Coolant Blackening and Foaming
Root cause: Residual impurities in the system (refrigeration oil, ammonia gas, etc.), poor make-up water quality, and inadequate system cleaning. Oxidation or contaminants cause coolant degradation. Solution: Sample and test to analyze corrosion causes. Minor cases can be treated with performance enhancers; severe cases require coolant replacement and thorough system cleaning.
Copper/Copper Alloy Corrosion
Root cause: Insufficient copper protection in the coolant inhibitor formulation, or abnormal system pH. Solution: Confirm pH. For severe copper corrosion, recommend LM-4D (nitrite-free, copper-friendly). Sample and test to confirm corrosion rate.
Frequent Heat Exchanger Corrosion
Root cause: Return liquid spray entraining large amounts of oxygen into the system, inhibitor depletion, and material incompatibility. Solution: Short-term: seal the tank to prevent oxygen ingress. Long-term: confirm operating temperature and replace with a suitable coolant. Check material compatibility.
Aluminum Tube Corrosion and Perforation
Root cause: Long-term contact between coolant and aluminum causing corrosion, or localized electrochemical corrosion. Crystalline substances found when cutting tubes. Solution: Sample and test coolant corrosion rate on aluminum. Cut corroded section for microscopic analysis to determine corrosion mechanism.
HCl/Ammonia Ingress
Root cause: Acidic/alkaline substances entering the system destroy the inhibitor system, lowering pH or altering chemical balance. Solution: HCl entry: add enhancers and alkali to adjust pH. Ammonia entry: organic acids lower pH but cannot resolve root cause; severe cases require coolant replacement.
Polymer Material Contamination
Root cause: Severe glycol system corrosion with PV polymer material entering the system. Solution: Sample and test enhancer effectiveness. New systems recommend LM-4; enhancer addition plans carry risk and require evaluation.
pHManagement Guide
Coolant pH is an important indicator for judging system corrosion status. Test pH regularly and maintain it in the 7-9 safe range.
| pH Range | Status | Recommended Actions |
|---|---|---|
| pH < 6 | Strongly acidic, extremely high corrosion risk | Shut down immediately, add alkali to adjust pH, sample and test corrosion extent |
| pH 6-7 | Weakly acidic, high corrosion risk | Add performance enhancers, monitor pH trend |
| pH 7-9 | Normal range | Regular monitoring, maintain in this range |
| pH 9-10 | Weakly alkaline, generally safe | Continue monitoring, watch copper corrosion |
| pH > 10 | Strongly alkaline, copper corrosion risk | Check copper material condition, replace coolant if necessary |
Corrosion inhibitors are the core of coolant anti-corrosion performance. Inhibitors are gradually consumed during long-term operation and require regular concentration testing and replenishment. For water-based coolants like LM-4, test pH and inhibitor concentration quarterly. When the coolant color darkens, unusual odors appear, or foaming increases, test immediately.
CorrosionFAQ
Solution: Sample and test to analyze corrosion cause. Minor cases: add performance enhancer; severe cases: replace coolant. Thoroughly clean system before replacement
Related Products: LM-4
Solution: Confirm system pH. For severe copper corrosion, recommend LM-4D (nitrite-free, copper-friendly). Sample and test to confirm corrosion rate
Related Products: LM-4D, LM-4
Solution: HCl entry: add enhancer and alkali to adjust pH, monitor continuously. Ammonia entry: organic acids can lower pH but cannot resolve root cause. Severe cases require coolant replacement and thorough system cleaning
Related Products: LM-4, LM-8
Solution: Short-term: seal water tank to prevent oxygen entry. Long-term: confirm operating temperature and recommend suitable replacement coolant. Check material compatibility
Related Products: LM-4, LM-8
Solution: Sample and test coolant corrosion rate on aluminum. Cut corroded section for microscopic analysis to determine corrosion mechanism. Decide whether to replace coolant or adjust formula based on results
Related Products: LM-4
Solution: pH can be lowered with organic acids, but root cause of corrosion cannot be resolved. Recommend long-term replacement with LM-4 system
Related Products: LM-4
CorrosionDiagnostic Cases
Anti-CorrosionBest Practices
System Cleaning Is Essential
New or converted systems must be thoroughly cleaned before filling to remove residual oil, impurities, and old coolant. Ammonia system conversions require special attention to refrigeration oil and ammonia gas residues.
Regular pH & Inhibitor Monitoring
Systems in long-term use require regular pH and inhibitor concentration testing. Adjust promptly when abnormalities are detected. Water-based coolants like LM-4 should be tested quarterly.
Seal System Against Oxygen
Return liquid spray entrains large amounts of oxygen causing corrosion. Seal the tank or use a closed-loop system. Add nitrogen blanketing protection when necessary.
Material-Matched Selection
Copper systems: prioritize LM-4D (nitrite-free). Aluminum systems: sample and test corrosion rate. Mixed-material systems: choose LM-4D-YE. LM-8 above 120C: use stainless steel.
Emergency Treatment for Contaminants
HCl ingress: add enhancers and alkali to adjust pH. Ammonia ingress: organic acids lower pH but cannot resolve root cause; replace coolant in severe cases. Increase monitoring frequency after any contaminant ingress.
When converting ammonia/brine systems to coolant systems, residual refrigeration oil and ammonia gas are the primary causes of corrosion. The system must be thoroughly cleaned before conversion, and pH changes must be closely monitored after filling. If coolant blackening or foaming is detected, sample and test immediately - do not wait until heat exchanger perforation occurs.
Related Topics
Complete Coolant Selection Guide
Select the right coolant to prevent corrosion from the source
Water Contamination & Ice Blockage
Chain reaction of water ingress leading to ice blockage and corrosion
LM-4D Low-Conductivity Coolant
Nitrite-free, copper-friendly
System Design Complete Manual
Anti-corrosion starts with system design
Post time: Aug-26-2026