Water pressure test caused corrosion. The customer used a tank truck made of stainless steel to install phosphoric acid. The leak occurred during the first use. The customer believed that the stainless steel had a problem and caused leakage due to corrosion resistance. Therefore, he raised a quality objection. After inspection, the stainless steel material conforms to the standard, and there is no problem with the manufacturing process of the tank truck. The leak of the tank truck is located at the bottom of the tank body, which is in the form of pitting corrosion. After analysis, it turns out that the tank truck was tested by hydrostatic pressure before being put into use. The test used tap water. After the test, the water was not completely discharged. After standing for a period of time, the accumulated water evaporated and concentrated, and the chloride ion in it reached a very high content. After the phosphoric acid was installed, the chloride ion was greatly corrosive in an acidic environment, resulting in pores. The appearance of eclipse. There are many similar situations. For example, there is also a case where a 304L storage tank was made with river water for hydraulic test after it was made. After the pressure test, the water was not discharged, and corrosion occurred after 2 months. Leakage phenomenon. Stainless steel storage tanks must pay attention to drain the water and keep it clean after the hydraulic test. In addition, the chloride ion content in the pressure test water must also be controlled, and general companies have relevant regulations on this.