What Are The Anti-corrosion Measures for Ammonia Evaporators?

What are the anti-corrosion measures for ammonia evaporators?

Material selection

Selection of corrosion-resistant metal materials: In the key parts of the ammonia cooler that are easy to contact with ammonia, such as the evaporator, piping, etc., priority is given to the selection of corrosion-resistant metal materials. For example, copper pipe has good ammonia corrosion resistance, in some occasions of high corrosion resistance requirements can be preferred; for the need of higher strength and corrosion resistance of the parts, stainless steel can be used, such as 304 stainless steel or 316 stainless steel, of which 316 stainless steel because of molybdenum, in the anti-ammonia corrosion is more excellent performance.

The use of non-metallic materials: for some non-pressure-bearing or low-strength parts, non-metallic materials can be considered, such as polytetrafluoroethylene, polypropylene and so on. These materials have excellent chemical stability, almost no reaction with ammonia, can effectively prevent corrosion, can be used to make sealing gaskets, insulation materials.

Surface treatment

Passivation treatment: passivation treatment of metal parts can form a dense passivation film on its surface to improve corrosion resistance. Such as stainless steel parts for nitric acid passivation treatment, can enhance the surface of the antioxidant capacity, so that it is more difficult to be corroded in the ammonia environment.

Coating anti-corrosion coating: in the fan metal surface coating special anti-corrosion coating, such as epoxy zinc-rich paint, polyurethane coating, etc.. These coatings can isolate the metal from the ammonia medium and provide good protection. Before coating, the metal surface should be strictly descaled and degreased to ensure the adhesion and anti-corrosion effect of the coating.

Hot-dip galvanizing treatment: For some parts made of carbon steel, hot-dip galvanizing process can be used. The components will be immersed in molten zinc liquid, so that the surface of the formation of a layer of zinc, zinc layer can play a cathodic protection of carbon steel, even in the case of coating damage, but also the priority corrosion of the zinc layer to protect the base metal, and effectively extend the service life of the components.

Structural design optimization

Avoid fluid accumulation and dead zone: In the structural design of the ammonia chiller, it should be ensured that the fluid channel is smooth to avoid fluid accumulation and dead zone. Fluid accumulation will lead to localized high ammonia concentration, accelerating corrosion; dead zones are prone to accumulate impurities and moisture, triggering corrosive reactions. For example, in the pipeline arrangement, should ensure a certain slope, so that the liquid can be discharged smoothly; in the design of the evaporator, the reasonable setting of the guide plate and liquid discharge port, to ensure that the ammonia can be discharged in a timely manner.

Reduce dissimilar metal contact: different metals in the ammonia medium may occur between galvanic coupling corrosion, so should minimize the contact of dissimilar metals. If it can not be avoided, insulating gaskets or coatings can be used to isolate the different metals to prevent the occurrence of galvanic coupling corrosion. Such as in the copper evaporator and stainless steel piping connection, can be used in the connection of PTFE insulating gasket.

Operation and maintenance

Control of operating parameters: Strictly control the operating parameters of the ammonia chiller, such as temperature, pressure, ammonia concentration, etc., to avoid corrosion aggravation caused by abnormal parameters. Excessive water content of ammonia will increase the corrosiveness of the metal, so it is necessary to regularly test the water content in the ammonia liquid to ensure that it is within the prescribed range. Generally speaking, the water content in the ammonia liquid should be controlled below 0.2%.

Regular cleaning and inspection: Regularly clean the ammonia chiller to remove dust, oil and impurities on the surface to prevent it from reacting with ammonia or forming corrosion primary cells. At the same time, regularly check the corrosion of the equipment, timely detection and treatment of local corrosion problems, such as minor corrosion of the parts of the filler paint treatment, the corrosion of the serious parts of the timely replacement.

Dry maintenance: During the downtime of the ammonia chiller, dry maintenance should be carried out to prevent the accumulation of moist air in the equipment leading to corrosion. Dry nitrogen gas can be used to blow or place desiccant and other methods to keep the equipment dry inside.