Corrosion protection issues of heat exchangers

Zinc plates can be welded internally as sacrificial anodes to protect the equipment.

The galvanizing layer is probably not thick enough. Or it may be caused by improper handling during coating. Generally speaking, the anti-corrosion effect should be good

Graphite heat exchangers can be used when process conditions such as temperature and pressure permit it.

The anti-corrosion environment for the galvanized layer is primarily one in which the pH of the medium is neutral or slightly alkaline, with a typical range of 6.5 to 9. The function of this layer is to act as an active anode made of zinc, thereby protecting the base metal. If the thickness of the galvanized layer is insufficient, or if its adhesion and density are poor, the anti-corrosion effect will be reduced； If in an acidic medium, the zinc layer will be chemically corroded very quickly; no matter how thick it is, it will be ineffective ； Therefore, a film thickness gauge is usually used to measure the thickness of the galvanized layer; the zinc layer thickness on normal galvanized heat exchange tubes is generally greater than 80 microns ； In addition, the physicochemical properties of the medium should be regularly tested, and corrosion inhibitors, scale inhibitors, and other substances should be added periodically for maintenance.

I used to work with steel structures and was also involved in hot-dip galvanizing. The effectiveness of corrosion protection is highly dependent on the galvanizing process; if anything goes wrong at any stage, it’s not possible to ensure the quality of the product. I think it would be best for you to try working with a larger galvanizing factory! I remember that one year in Tianjin, someone demolished an electric power tower that had been installed during Japan’s invasion of China. So many years have passed since then, and the tower has rusted, yet the bolts on it could still be turned. But many of the towers we built more recently start to rust after just three or five years – what’s the problem? Japan is extremely strict when it comes to quality issues, while many of our private enterprises don’t care about quality – as long as the costs are low and profits can be made. Alas! ! ! This post was last edited by cwillow on 2009-3-8 09:20]

The heat exchanger tube bundles use surface treatment methods to address corrosion issues; aluminum infiltration, aluminum-zinc alloy infiltration, and Ni-P plating all yield good results in an environment without dielectrics. In a dielectric environment, manufacturing quality is crucial; a tiny pinhole (inevitable) can lead to a large cathode and a small anode, resulting in perforation. Using resin sealing is acceptable, depending on the temperature. In environments above 60°C, the potential of the sacrificial zinc anode shifts significantly to a more positive value, resulting in a reversal of the polarity in the cathodic protection system; this in turn accelerates the corrosion of the steel. Under these conditions, other methods must be used.

The corrosion resistance mechanisms of galvanizing and aluminizing are different. In galvanizing, zinc is consumed to form a protective layer, but this layer reacts with certain corrosive agents; as a result, more zinc is consumed until it is all used up, at which point corrosion of the base material begins； After aluminizing, an aluminum oxide layer is formed, which resists reactions; the aluminized layer is thick as it is processed at 700 degrees, while the galvanized layer is thin as it is processed at 400 degrees. wsdaixtt@163.com