Cathodic Protection Potential of 9Ni Steel LNG Storage Tanks During Hydrostatic Test Using Seawater

9Ni steel is the main material for liquefied natural gas (LNG) storage tents. The corrosion behavior of 9Ni steel in simulated environment of hydrostatic test using seawater and under the condition of cathodic protection was investigated by means of electrochemical method, immersion method and slow strain rate test (SSRT) method. The results showed that when the cathodic protection potential decreased in the rage of -0.70 V (vs. SCE the same below) ~ -1.00 V, the corrosion rate of 9Ni steel decreased from 0.235 5 mm/a to 0.022 0 ~ 0.004 4 mm/a, and the protection degrees all reached above 90%. Also, -0.70 V was able to meet the requirements of crevice corrosion resistance of 9Ni steel during the period of hydrostatic test. When the potential decreased in the range of -0.85 V ~ -0.93 V, 9Ni steel was mainly subject to ductile fracture. A large number of microcracks appeared near the fracture surface. Quasi-cleavage feature was found on the fracture surface at -0.95 V and 9Ni steel entered dangerous zone of hydrogen embrittlement. So in order to ensure the service safety of 9Ni steel, the recommended cathodic protection potential range of 9Ni steel was -0.70 V ~ -0.90 V during hydrostatic test using seawater of LNG storage tanks.