Seek help to analyze the causes of impeller corrosion
Thread Content
The circulating water pumps used by a pharmaceutical company use tap water that is heated to 80°C as the working medium; however, there is rust in the pipes. The pipeline pumps used by our company broke down after just one month of use – the cast-iron impellers and impeller nuts deteriorated. pH tests conducted on site showed that the pH level was neutral. We would appreciate it if experts could analyze the reasons behind this, determine whether corrosion actually occurred, and identify possible causes.
Circulating water contains agents such as scale inhibitors and disinfectants; since it’s not clear what exactly is in the water, it can’t be said that it is mainly tap water. I’ve seen that in some places, acids are used to clean the pipes during the commissioning phase. . .
Firstly, the purpose of tap water is for domestic use. It remains to be determined what the water analysis after the pump is like. Then, the process should be as clear as possible to facilitate discussion. Also, check whether the temperature and pressure specifications on the pump’s label match those of the medium, and whether the inlet pressure of the pump is suitable for the operating conditions. It seems to be chemical corrosion on the surface; for reference only.
The cause of rust is a redox reaction; whether it is pig iron or synthetic iron, it will react when exposed to oxygen as well as temperature and humidity. Of course, acidity and alkalinity accelerate this reaction by speeding up the movement of H ions and OH ions. The most terrifying aspect is also the effect of microorganisms; certain bacteriophages or iron-feeding organisms attach to the surface of iron objects and are also resistant to acids and alkalis. So the common practices include filtering out impurities, adjusting the pH, and selecting a material for the pump body that is resistant to acids and alkalis.
At 80°C, tap water is not cooled, and there are oxygen molecules between the water molecules or within the water; this results in an uneven compression ratio when it hits the impeller.
When the water pump is used at 80 degrees, what is its suction lift height? Is the diameter of the water inlet pipe matched to the flow rate? Can a hot water tank develop negative pressure? All these factors can cause cavitation in water pumps.
Cast iron is not recommended for use in hot water environments.