Study On Pitting Corrosion Of L360 Steel In H₂S/CO₂ Solution

The effects of Cl-,Ca2+ concentration and temperature on pitting corrosion of L360 steel in H2S/CO2 environment were studied using methods of weight loss testing, electrochemical testing, XRD, SEM, EDS and adhesion testing. In addition, distribution characteristic of pits was analyzed. The main results are as follows:1. XRD tests showed that in H2S/CO2 environment, the temperature, Cl- consentraion and Ca2+ consentraion had no significant effect on corrosion scales. It illustrates that H2S corrosion is the main corrosion.2. Pitting corrosion occurred in 15g/L Cl- solution at constant temperature, and uniform corrosion happened when the Cl- concentration is higher than 20 g/L. As the temperature increases, corrosion products on the surface become looser and the protective property decreases.3. The results showed that pitting corrosion tends to be more serious with the increase of temperature (from 40℃to 70℃) in 15 g/L Cl-solution. Serious pitting corrosion occoured at 70℃. At first uniform corrosion rate increased, then decreased with the increaseing temperature. And corrosion rate reached the maximum at 60℃. SEM photos showed that particle size of the corrosion scale decreases and becomes more density when the temperature reached to 70℃.4. As the Ca2+ concentration increased, uniform corrosion becamed more serious. When the Ca2+ concentration reached to 8.5g/L, not only pitting corrosion occoured but also local corrosion appeared and the corrosion scale falls off easily.5. The measured maximum depth of pits follows the Gumbel first approximating function at 40-70℃. Pit density was calculated by poisson distribution and the density is 1237-1791a/m2 and the depth of pits obeys the normal distribution at 70℃.