In composting plants, biowaste treatment facilities and recycling operations, technical equipment is exposed to demanding conditions: moisture, dust, ammonia and organic acids continuously attack materials and coatings. For this reason, corrosion protection class C5 is often specified.
However, C5 does not automatically mean that everything has to be made of stainless steel. What matters is a well-designed corrosion protection concept based on material selection, coating, construction details and system arrangement. A practical example from a composting plant in Kirchheim unter Teck shows how technical requirements and economic efficiency can be sensibly combined.
Caption: Composting facility in Kirchheim unter Teck, Germany. Moisture, organic acids, and ammonia create a corrosive atmosphere that places high demands on industrial equipment and corrosion protection.
Why is C5 corrosion protection often specified in composting plants?
Moisture, dust, ammonia and organic acids can place significant stress on materials and coatings. For this reason, C5 corrosion protection is often specified in tenders.
Many users immediately associate this requirement with stainless steel. In practice, however, the optimum solution is often much more differentiated.
Corrosion protection starts at the planning stage
In waste and biomass treatment applications, Airwall systems are often designed so that sensitive components are exposed to the aggressive hall atmosphere as little as possible.
In one biomethane plant, for example, the requirement was to minimise the system’s exposure to dust and ammonia-laden hall air. For this reason, the main components were installed outside the building. The required air is drawn directly from outside and supplied to the Airwall systems.
With this concept, the fans and air ducting systems come into contact with the aggressive hall atmosphere only to a limited extent.
This example shows that corrosion protection often starts as early as the system planning stage — not only when selecting materials or coatings.
At this biomethane facility, key airwall components were installed outside the building to reduce exposure to dust and ammonia-containing air.
C5 corrosion protection is not a material specification
C5 corrosion protection describes a requirement for the durability of components in a corrosive environment. However, it does not define which material must be used to achieve this requirement.
The decisive factor is not the individual material, but the long-term suitability of the combined concept: material, construction details and protection system.
Practical example from a composting plant
In a project for a waste treatment facility, C5 corrosion protection was explicitly specified. The tender documents described the hall atmosphere as highly aggressive and required resistance to organic acids and ammonia.
During the detailed planning phase, all components were evaluated with regard to corrosion resistance, availability and cost efficiency.
The final solution incorporated a combination of:
- Stainless steel
- Aluminum
- Engineered plastics
- C5 coating systems
Rather than applying a single approach throughout the installation, each component was assessed individually.
One example involved spiral ductwork and fittings. The engineering team evaluated both coated galvanized steel and stainless steel alternatives. In this case, stainless steel proved to be the more economical solution.
Numerous smaller components were also reviewed individually. Suitable stainless steel versions were available for most parts, while only a limited number of specialty components required integration into the coating system strategy.
Caption: Multiple materials and protection methods were combined within a comprehensive corrosion protection strategy. Depending on the application, stainless steel, coating systems, and other corrosion-resistant materials were used.
The fan housings were manufactured with internal and external protective coatings. Only the fan assemblies themselves were excluded from this treatment. Because these components are not directly exposed to the corrosive atmosphere, a more economical design could be selected.
The Most Economical Solution Is Rarely the Simplest
Experience from multiple projects shows that C5 corrosion protection does not automatically require a fully stainless-steel system.
Likewise, coating every component is not necessarily the most cost-effective approach.
The optimal solution is often achieved through a combination of:
- Intelligent system design
- Strategic placement of components
- Appropriate material selection
- Targeted use of coating systems
Caption: Installation of an airwall system at a composting facility. The operating environment illustrates the challenges associated with corrosion protection, material selection, and long-term durability.
Conclusion
C5 corrosion protection is a performance requirement, not a material specification.
The challenge is not to maximize the amount of stainless steel used but to identify the most technically and economically appropriate solution for each component.
In many cases, the best result comes from combining different materials, coating systems, and engineering measures within a comprehensive corrosion protection strategy.
Experience from composting facilities, organics recycling facilities, and waste treatment facilities demonstrates that the requirements of C5 environments can be met reliably with a well-designed system. The key is to address system layout, material selection, and corrosion protection at an early stage of the project.
