Condenser Tube material Suitable for Ammonia gas?
For ammonia (R717) condenser tubes:
- Primary & Most Common Choice: Seamless Carbon Steel (e.g., ASTM A179)
- Premium/Corrosive Choice: Stainless Steel (e.g., AISI 304 or 316L)
Absolutely Avoid: Copper, brass, bronze, and any other copper alloys.
Detailed Breakdown
1. Carbon Steel (e.g., ASTM A179)
- Suitability: Excellent. This is the most common and standard material for ammonia condenser and evaporator tubes.
- Why it’s used:
- Compatibility: Ammonia does not corrode carbon steel at any significant rate. It is chemically compatible and highly reliable for this application.
- Cost-Effective: Carbon steel is significantly less expensive than stainless steel, making it the economical choice for most systems.
- Strength: It has high mechanical strength and can easily withstand the pressures of an ammonia refrigeration cycle.
- Consideration: Carbon steel is susceptible to rust from water/oxygen on the outside of the tubes (e.g., from the spray water in an evaporative condenser). This requires proper water treatment and occasional maintenance but does not affect the internal ammonia circuit.
2. Stainless Steel (e.g., AISI 304 / 316L)
- Suitability: Excellent.
- Why it’s used:
- Superior Corrosion Resistance: It is completely immune to corrosion from the ammonia on the inside and highly resistant to aggressive spray water (e.g., high chlorides, sulphates) on the outside. Type 316L is preferred for highly corrosive environments like coastal areas.
- Longevity: Offers the longest possible service life with minimal maintenance.
- Drawback: The primary drawback is higher cost, often 2-3 times that of carbon steel. It is also harder to machine and form.
Why Copper Alloys Are FORBIDDEN
This is the most important rule. Copper, brass, and bronze must never be used in the ammonia circuit.
- Cause: Ammonia, especially in the presence of water (which is always present as a trace moisture in the system), reacts with copper and zinc (found in brass).
- Effect: It causes Stress Corrosion Cracking (SCC) and formation of brittle compounds. This leads to rapid, catastrophic failure of the tubes, resulting in hazardous ammonia leaks.
- Rule of Thumb: If the refrigerant is ammonia, all wetted parts in the refrigerant circuit (tubes, valves, pipes, vessels) must be made of steel or stainless steel.
Summary Table
| Material | Suitability for Ammonia Gas | Key Advantages | Key Drawbacks | Typical Use |
| Carbon Steel (ASTM A179) | Excellent | Low cost, high strength, excellent ammonia compatibility. | Prone to external rust from water; requires water treatment. | The standard choice for most ammonia condensers. |
| Stainless Steel (304/316L) | Excellent | Superior corrosion resistance (inside & out), long life, no maintenance. | High initial cost. | Used for harsh environments (coastal, poor water quality) or for maximum longevity. |
| Copper / Brass | Unacceptable | N/A | Causes Stress Corrosion Cracking (SCC) and system failure. | Must never be used. |
Conclusion:
For condenser tubes in an ammonia system:
- Choose Carbon Steel for its proven reliability and cost-effectiveness in standard applications.
- Choose Stainless Steel if operating in a corrosive environment or if maximum longevity with minimal maintenance is the priority.
- Never, under any circumstances, use copper or its alloys.