The CP potential protects only in a narrow band beyond which either anodic dissolution or metal stress erosion damage (hydrogen blistering) occurs. CP experts at home and abroad have proposed that the safety belt of polarization potential is from -850 to -1150mV /CSE through experiments and field testing, in which -755 to -788mV /CSE is the stress erosion sensitive section, and the latest test found in China is from -630mV to -730mV; -680mV to -730mV is also a metal stress erosion sensitive section. When the negative offset potential is greater than 1170mV /CSE, alkali will be added to the tube surface. Under the premise of water intervention, water is electrolyzed to natural hydrogen ions. Because there are a large number of microcracks and material defects on the tube surface, hydrogen ions are immersed first, and the stress result of the molecular process will make the crack increase in depth and width. The stress erosion cracking on the pipe is usually the result of the joint action of hydrogen stress and the tensile stress of the pipe load. Therefore, the potential on the pipeline should be controlled on the safety belt of the polarization potential. The -1200mV proposed on the national standard is obviously wrong. It is copied from foreign things. Therefore, the best protection potential should be -850-- 1100mV /CSE.