The Corrosion Study Of Two Kinds Of Oil Pipes In H₂S/CO₂ Solution

Pu-Guang reservoir belongs to acidic gas field. Corrosion is one of the key problems. But there is not exoteric mature experience of exploitation for this kind reservoir. Therefore, for the sake of secure exploitation of Pu-Guang gas field, corrosion study of oil pipes in H₂S/CO₂ solution is necessary.Corrosion behavior of oil pipe and sleeve in H₂S/CO₂ saturated 3% NaCl solution was investigated by galvanic corrosion, sulfide stress corrosion cracking, marinate weight loss test, potentiodynamic polarization curves, electro-chemical impedance spectrum, SEM, EDS, XRD and EIS. The disciplinarians of marinate corrosion and sulfide stress corrosion crack influenced by chemical composition were analyzed. The test also probed the relationship between pitting in H₂S/CO₂ solution and pH/Temp. The opinion of corrosion mechanism in H₂S/CO₂ solution was advanced. At last, galvanic corrosion was deeply discussed and the superiority of titanium in restraining galvanic corrosion was simply probed.The fact found in the test is that JSS sleeve is better than SRS oil pipe at high-temperature, contrarily at low-temperature. The analysis indicates that elements Mo, Cr and Ni from the steel could restrain the all-around corrosion. But the element of Mn , Ni and a bit of Cr are deleterious for SSCC. Polarization cure and EIS show corrosion of SRS oil pipe is firstly accelerated and is restrained in succession when the concentration of H₂S increasing, the inflexion at about 400mg/L. The experiment also proved that modes of iron sulfide formation in H₂S saturated brine are Surface Formation at fist and Mixed Surface/Solution Formation. Micrograph of steel surface revealed that pitting was accelerated when the temperature upgrades. And the pitting of JSS grows for the way of upright to surface at pH=4.0, but for around at pH=3.0.Galvanic corrosion experiment and SEM,EDS,XRD show: 1. The products formed in galvanic corrosion in H₂S/CO₂ saturated 3% NaCl solution is the same with that in marinate weight loss test. 2. Product film break induces the leap of galvanic corrosion rate straightway. 3. Galvanic corrosion rosen by product break wouldn't last out, but corrosion between SRS and G3 steel would be all along. The study results of Ti corrosion in brine (pH=3.2) indicates when solution resistance is big enough or Ti pipe is long enough, Ti pipe would reduce 85% of galvanic corrosion between G3 and SRS.