Study On The Corrosion Behavior Of Coiled Tubing QT-900in H₂S And CO₂Environment

The corrosion behaviors of Coiled Tubing were studied in CO₂corrosion environment orCO₂and H₂S corrosion environment with high temperature and pressure，using SEM，EDS andXRD testing methods，and the galvanic corrosion and SCC resistance of Coiled Tubing wasalso investigated.what’s more，the rest corrosion life was predicted.The results showed that with increasing CO₂pressure，H₂S pressure and temperature，theuniform corrosion rate and the localized corrosion rate of Coiled Tubing increased first，thendecreased，and increased more in CO₂and H₂S coexistence corrosion environment.Themaximum variation appeared at60℃，CO₂pressure was1.1MPa，H₂S pressure was0.03MPa，the uniform corrosion rate was0.5699mm/a，according to NACE RP-0775-2005，the uniformcorrosion rate was very severe..In CO₂corrosion environment，with increasing CO₂pressure and temperature， theuniform corrosion rate of Coiled Tubing increased first，then decreased，the maximumvariation appeared at100℃，CO₂pressure was0.90MPa，the uniform corrosion rate was1.1722mm/a.In the galvanic corrosion test，the local corrosion of Coiled Tubing QT-900was veryserious in galvanic place，the uniform corrosion rate is up to2.6952mm/a，the depth of thelargest corrosion hole is63μm，the localized corrosion rate is up to2.2995mm/a.the SSC（Stress Corrosion Cracking） text results showed that the property of SSC resista nce of QT-900was very bad.According to SYT5724-2008，SY/T5322-2000and the Coiled Tubing data imformationsurported by oil company，the modulus of resistance to external pressure，internal pressure andtensile less than the standand data at3.38year，3.99year and5.95year，using the minimumdata as the corrosion life，the Coiled Tubing corrosion life was3.38year without any corrosionprotection.