Corrosion Reason of P110 Tubing Used in LN206 Well

Severe corrosion occurred at thread joint between submersible pump and spill valve of P110 in LN206 well tubing after 43 days service. The reason of the corrosion failure was studied by metallographic examination, chemical composition analysis, and electrochemical test. The results indicated that to the tubing material, no abnormal phase was found according to micro-morphology observation chemical composition met the requirement of API Spec 5CT. The surface damage was observed on the thread, so the corrosive medium go into the crevice at the damage area. The electrochemical test results show that the potential difference between oil well tubing and spill valve is approximately 110 mV. It is concluded that the corrosion was mainly caused by crevice corrosion, galvanic corrosion, and the high concentration of Cl- accelerated the corrosion process. It is suggested to avoid thread damage during joining the oil well tubing and spill valve. It is necessary thread grease to fully fill the crevice between oil well tubing and spill valve avoid the direct contact of dissimilar metals with significant potential difference.