Standard metal test sheet suspended in the test vessel, on-site inspection heat exchanger or test pipeline for corrosion determination. It is used to detect or evaluate the corrosion condition of cooling water system. Generally, the pre processed and weighed metal test pieces are placed in the test system for a period of time, and then taken out to observe the corrosion, clean and weigh. Determine the weight loss degree of metal corrosion, type of corrosion and pitting depth, etc. In addition to the influence of corrosive media, the data of metal hanging pieces are also related to the surface treatment, placement position, exposure time and metallurgical method of samples.