What points should be noted when cleaning plate heat exchangers?

Cleaning agents : 
Currently, acid washing is used, which includes organic acids and inorganic acids. Organic acids mainly include oxalic acid and formic acid. Inorganic acids mainly include hydrochloric acid and nitric acid. According to the analysis of scaling, process, material and scale composition of plate heat exchangers: 
(1) Plate heat exchangers have a small flow area and complex internal structure, and it is not easy to discharge the cleaning fluid if precipitation occurs. 
(2) The plate heat exchanger is made of nickel-titanium alloy. Using hydrochloric acid as the cleaning fluid can easily cause strong corrosion to the plates and shorten the service life of the plate heat exchanger. Through repeated experiments, it was found that formic acid is the best choice as the cleaning fluid. Adding buffer and surfactant to the formic acid cleaning fluid can improve the cleaning effect and reduce the corrosion of the plates by the cleaning fluid.
2. Basic principles for removing scale 
from plate heat exchangers (1) Dissolution: Acid solutions readily react with calcium, magnesium, and carbonate scale to form easily soluble compounds, thus dissolving the scale. 
(2) Peeling: Acid solutions can dissolve oxides on the metal surface, breaking the bond with the scale. This causes the scale attached to the metal oxide surface to peel off and fall off. 
3. Process requirements for cleaning scale 
(1) Acid solution concentration: Based on repeated experiments, the acid solution should be prepared with a concentration of 81% formic acid, 17% water, 1.2 % buffer, and 0.8 % 
surfactant for excellent cleaning effect. (2) Acid washing temperature: Increasing the acid washing temperature is beneficial to improving the descaling effect. If the temperature is too high, it will aggravate the corrosion of the plate heat exchanger plates by the acid solution. Through repeated experiments, it was found that the acid washing temperature should be controlled at 60℃. 
(3) Passivation treatment: After pickling, most of the scale and metal oxides on the surface of the plate heat exchanger are dissolved and removed, exposing the new metal, which is very easy to corrode. Therefore, after pickling, the plate heat exchanger plates are passivated.