Corrosion Failure Reason for X65 Pipeline and Weld

The failure of X65 oil pipe was analyzed by macro detection, chemical composition analysis, metallographic analysis, field emission scanning electron microscopy, energy spectrum analysis, X-ray detection and electrochemical method, the root cause of corrosion failure was found. The results showed that lots of carbon oxide of iron deposited on pipe, and localized corrosion formed due to the nonuniform deposition which resulted in the formation of under-scale CO2 acid corrosion; the corrosion products outside the pipe were mainly composed of oxides and carbon oxides of iron. After cleaning, the surface was smooth, the main form of corrosion was uniform corrosion. The base metal corrosion potential was more negative, so the near weld joint was easy to exhibit localized corrosion due to the corrosion potential difference.