The surface of the plate with clean and no oxide is the necessary condition to ensure the tightness. When the heat efficiency of plate heat exchanger is obviously reduced and the pressure drop is obviously changed, the scale is serious. The plate should be removed and the brush should be leveled and cleaned. The steam bubble tank and chemical cleaning method is an effective method to obtain high quality surface quality. During cleaning, the plate shall be first immersed in a alkaline solution tank with a temperature of 57-60oc (if the temperature is better than 70-80oc). The sealant and scaling pasted on the plate shall be softened by the high temperature of alkali solution. Then, the plate was soaked in the acid tank for 2 hours to make the scale react with the acid fully. After the plate is soaked, clean the plate with a soft brush on the platform, and it is forbidden to use steel brush. When cleaning the sealing groove, use a screwdriver to lift the washer, gently remove (or light bake with fire on the back, but avoid discoloration of metal), and then tear it off. Clean the sealing groove with acetone methyl solution or other ketone organic solvent. After cleaning, the plate shall be washed with clean water, then dried with clean cloth. Foreign particles and fibers shall not be left on the surface of the board. The chloride content of cleaning water is less than 25pp.