Cooling Coil Suitable for Ammonia Condenser?
The only suitable and standard choice for an ammonia (R717) condenser coil is Stainless Steel.
Copper or copper-based alloys must be absolutely avoided.
Why Stainless Steel is Mandatory for Ammonia
1. Chemical Incompatibility with Copper:
Ammonia (NH₃) is highly reactive with copper and most copper alloys (like brass). In the presence of moisture and ammonia, it forms a complex compound called tetra-ammonium copper sulphate, which causes Stress Corrosion Cracking (SCC). This leads to rapid, catastrophic failure of the copper tubes.
2. Superior Corrosion Resistance:
Stainless steel (typically Type 304 or 316) offers exceptional resistance to ammonia corrosion, ensuring long-term structural integrity and safety.
3. Mechanical Strength:
Stainless steel has higher tensile strength and better resistance to vibration and high operating pressures, which are common in ammonia systems.
Comparison: Why Not Other Materials?
| Material | Suitability for Ammonia | Reason |
| Stainless Steel (304/316) | Excellent (The Standard Choice) | Highly resistant to ammonia corrosion, strong, and durable. |
| Carbon Steel | Poor | Prone to rust and corrosion from the water side and requires extensive maintenance. |
| Copper / Brass | Unacceptable | Causes stress corrosion cracking, leading to rapid system failure and hazardous leaks. |
| Aluminum | Good (in certain applications) | Resistant to ammonia corrosion and sometimes used for internal components, but not typically used for condenser coils in evaporative condensers due to challenges in manufacturing and potential for galvanic corrosion. |
Key Considerations for the Stainless-Steel Coil:
- Grade Selection:
- Type 304 SS: The most common and cost-effective choice for general ammonia service with reasonable water quality.
- Type 316 SS: Contains molybdenum for increased resistance to pitting corrosion. It is the preferred choice for locations with poor water quality, high chloride levels (e.g., coastal areas), or aggressive chemical environments.
- Trade-off: The main disadvantage of stainless steel is its lower thermal conductivity compared to copper. This is compensated for by designing the coil with a larger surface area (e.g., more fins per inch, larger coil face area) to achieve the required heat transfer performance.
Conclusion:
For an ammonia condenser, specify a coil constructed from stainless steel (ASTM A249 TP304/TP316). This is a non-negotiable industry standard driven by safety and reliability requirements. Any use of copper in the ammonia circuit itself poses a severe risk of failure.