Failure Reasons of Three-phase Separator in an Offshore Oil-field

The reasons of bottom corrosion and weld-cracking of a three-phase separator tank were investigated via in situ investigation, X-ray diffraction analysis, hardness testing and cathodic protection simulation calculation. The results showed that the main causes of the separator tank bottom corrosion were CO2 corrosion, H2S corrosion and typical under-deposit corrosion while the coating and cathodic protection failed to protect the steel wall. The main reason of the cracking near the weld seam was induced by sulfide stress corrosion cracking under the combination effect of too-high local hardness and lack of suitable heat treatment after welding repair process.